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Metabolic engineering of Corynebacterium glutamicum for the high-level production of cadaverine that can be used for the synthesis of bio-polyamide 510 Hee Taek Kim, Kei-Anne Baritugo, Young Hoon Oh, Sung Min Hyun, Tae Uk Khang, Kyoung Hee Kang, Sol Hee Jung, Bong Keun Song, Kyungmoon Park, Il-Kwon Kim, Myung Ock Lee, Yeji Kam, Yong Taek Hwang, Si Jae Park, and Jeong Chan Joo ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b00009 • Publication Date (Web): 28 Feb 2018 Downloaded from http://pubs.acs.org on March 2, 2018
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ACS Sustainable Chemistry & Engineering
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Metabolic engineering of Corynebacterium glutamicum for the high-
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level production of cadaverine that can be used for the synthesis of
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bio-polyamide 510
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Hee Taek Kim1,8, Kei-Anne Baritugo2,8, Young Hoon Oh1,8, Sung Min Hyun1,3, Tae Uk
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Khang1,4, Kyoung Hee Kang1, Sol Hee Jung2, Bong Keun Song1, Kyungmoon Park3,
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Il-Kwon Kim5, Myung Ock Lee6,7, Yeji Kam6, Yong Taek Hwang6, Si Jae Park2,*,
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Jeong Chan Joo1,*
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1
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Institute of Chemical Technology, P.O. Box 107, 141 Gajeong-ro, Yuseong-gu,
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Daejeon 34114, Republic of Korea
Center for Bio-based Chemistry, Division of Convergence Chemistry, Korea Research
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52 Ewhayeodae-gil, Seodaemun-gu, Seoul 03760, Republic of Korea
Division of Chemical Engineering and Materials Science, Ewha Womans University,
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Sejong-ro, Jochiwon-eup, Sejong-si 30016, Republic of Korea
Department of Biological and Chemical Engineering, Hongik University, 2639
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Seongbuk-gu, Seoul 02841, Republic of Korea
Department of Chemical and Biological Engineering, Korea University, 145 Anam-ro,
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of Korea
Bioprocess R&D Center, DAESANG Corp., Icheon-si, Gyeonggi-do, 17384, Republic
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Lotte Chemical, 115 Gajeongbuk-ro, Yuseong-gu, Daejeon, 34110, Republic of Korea
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Department of Chemistry, KAIST, 291, Daehak-ro, Yuseong-gu, Daejeon 34141,
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Republic of Korea
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5 6
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work.
Hee Taek Kim, Kei-Anne Baritugo, and Young Hoon Oh contributed equally to this
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*Correspondence should be addressed to Si Jae Park (
[email protected]) and Jeong Chan Joo (
[email protected])
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Abstract
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Fermentative production of cadaverine from renewable resources may support a
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sustainable biorefinery process to produce carbon-neutral nylons such as bio-
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polyamide 510 (PA510). Cost-competitive production of cadaverine is a key factor in
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the successful commercialization of PA510. In this study, an integrated biological and
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chemical
7
polymerization with sebacic acid was developed to produce bio-PA510.
process
involving
cadaverine
biosynthesis,
purification,
and
its
8
To stably express ldcC from Escherichia coli in an engineered Corynebacterium
9
glutamicum PKC strain, an expired industrial L-lysine-producing strain, ldcC was
10
integrated into the chromosome of the C. glutamicum PKC strain by disrupting lysE
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and controlling its expression via a strong synthetic H30 promoter. Cadaverine was
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produced at a concentration of 103.78 g/L, the highest titer to date, from glucose by
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fed-batch culture of this engineered C. glutamicum PKC strain. Fermentation-derived
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cadaverine was purified to polymer-grade bio-cadaverine with high purity (99%) by
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solvent extraction with chloroform and two-step distillation. Finally, bio-based PA510
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with good thermal properties (Tm 216°C and Tc 165°C) was produced by
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polymerization of purified cadaverine with sebacic acid. The hybrid biorefinery
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process combining biological and chemical processes demonstrated in this study is a
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useful platform for producing bio-based chemicals and polymers.
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Keywords:
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Corynebacterium glutamicum, Lysine decarboxylase
Bio-polyamide,
PA510,
Cadaverine,
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L-lysine,
Recombinant
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Introduction
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Increasing concerns regarding global climate change and depletion of fossil resources
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have drawn much attention for the development of sustainable processes as promising
4
alternatives to conventional petroleum-based chemical processes.1-4 Biorefinery
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processes have been developed to promote sustainable chemical industries to produce
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several platform chemicals, polymers, and fuels from renewable resources.
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Fermentation processes employing metabolically engineered microbial host strains
8
have successfully been developed for production of platform chemicals such as organic
9
acids, alcohols, and amines, and polymers such as polyesters and polyamides from
10
biomass-derived sugars, including C6 glucose and C5 xylose.2-13
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Polyamides (nylons) are polymers of repeating monomers of diamines and
12
dicarboxylic acids. Because polyamides have high thermal and mechanical strength
13
and abrasion resistance, they have extensively been used in the manufacture of textiles
14
such as carpet and sportswear and in the automotive industry for engineering
15
plastics.14-17 Moreover, polyamides can be used in clinical medicine to produce sutures,
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catheters, and dental resin because of their high tensile strength and good elasticity and
17
flexibility.17,19 Global demands for representative petrochemical-based synthetic
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polyamides, polyamide 6 (nylon 6) and polyamide 66 (nylon 66), were 4.2 and 2.1
19
million metric tons in 2010, respectively.18 Polyamides form diverse material
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properties by employing monomers with different carbon atom numbers and functional
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groups. Particularly, bio-based polyamides such as nylon 4, nylon 510, and nylon 56
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have extensively been developed for their possible applications in the apparel, food
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packaging, automobiles, and electronics industries.14-25
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L-Lysine, one of the most successful commercial products produced by microbial
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fermentation processes, can be used as a versatile precursor to synthesize several
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building-block chemicals such as cadaverine, 5-aminovaleric acid, glutaric acid, 1,5-
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pentanediol, adipic acid, and carprolactam.9,10,15-21 The annual production of L-lysine
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by fermentation employing recombinant Escherichia coli and Corynebacterium
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glutamicum as host strains exceeds 1.5 million tons.9 Cadaverine, a C5 diamine
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biologically produced by decarboxylation of L-lysine using lysine decarboxylase as a
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biocatalyst, is a promising monomer for bio-based nylons such as nylon 56, nylon 510,
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and nylon 512. Microbial production of cadaverine has been examined in recombinant
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E. coli and C. glutamicum strains by plasmid- or genome-based heterologous
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expression of E. coli cadA and ldcC encoding inducible and constitutive lysine
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decarboxylase, respectively.18-27
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Plasmid-based heterologous expression of lysine decarboxylase gene has mainly been
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examined for cadaverine production in recombinant C. glutamicum strains.18-27
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Plasmid-based expression of E. coli cadA under a highly constitutive promoter in the
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engineered C. glutamicum strain with cell-surface expression of amylase enabled
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production of 2.34 g/L of cadaverine from 50 g/L of starch.26 However, plasmid-based
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expression of heterologous genes has serious limitations such as a gradual reduction of
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productivity and yield of target products in large-scale fermentation, as the metabolic
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burden of host strains may be increased by the maintenance of plasmids and
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segregational instability of plasmids, which may cause loss of plasmids during
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cultivation.4,28,29 Chromosomal integration of heterologous genes is a good alternative
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to plasmid-based expression of target genes.4 In a previous report, the highest
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cadaverine concentration of 88 g/L was achieved by fed-batch fermentation of C.
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glutamicum DAP-16. This strain was constructed by chromosome integration of a
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codon-optimized variant of E. coli ldcC at the bioD locus encoding diothiobiotin
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synthetase in an L-lysine hyper-producing strain C. glutamicum LYS-12, with
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replacement of the native promoter by the tuf promoter (PtufldcCopt).24
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The selection of suitable promoters for efficient expression of heterologous genes is a
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key factor for improving the production of target chemicals in host strains.30-33
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Previous studies showed that synthetic promoters have a favorable effect on tuning the
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expression levels of heterologous genes in recombinant C. glutamicum, ultimately
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supporting enhanced production of target products.31 For example, C. glutamicum
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strains can be engineered to produce gamma-aminobutyrate (GABA), cadav¬!erine,
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and 5-aminovaleric acid from renewable resources by expressing glutamate
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decarboxylase, lysine decarboxylase, and lysine 2-monooxygenase and delta-
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aminovaleramidase, respectively, under synthetic promoters with different promoter
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strengths.14-17,25,34,35 It was found that the final concentrations of GABA, cadaverine,
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and 5-aminovaleric acid were highly dependent on the promoter strength and
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metabolic capacity of host strains to provide precursor metabolites such as L-glutamate
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or L-lysine.14-17,25,34,35
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In this study, an integrated biological and chemical process for producing bio-PA510
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was developed by combining microbial fermentation for the production of cadaverine,
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purification of fermentation-derived cadaverine into polymer-grade cadaverine, and
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polymerization of bio-cadaverine with sebacic acid into PA510 (Figure 1). Plasmid-
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and genome-based expression of E. coli ldcC was examined under the control of
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synthetic promoters in a recombinant C. glutamicum PKC strain, an expired
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commercial L-lysine-producing strain. Fed-batch fermentation of the C. glutamicum
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PKC strain expressing E. coli ldcC under the optimal promoter PH30, which is
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integrated into lysE locus in the chromosome, resulted in the highest cadaverine
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production. Polymer-grade cadaverine was obtained by sequential solvent extraction
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and distillation of the fermentation broth. Finally, bio-based PA510 was produced by
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poly-condensation of purified cadaverine with sebacic acid.
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Methods
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Chemicals
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Chemicals used in this study were purchased from Sigma-Aldrich (St. Louis, MO,
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USA) and used without further purification unless otherwise specified. Sulfuric acid
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(Sigma-Aldrich, 95%) was employed as a dissolution solvent for the relative viscosity
6
analysis and m-cresol (Alfa Aesar, Haverhill, MA, USA, 99%) was used as a
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dissolution solvent for molecular weight analysis.
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Bacterial strains and plasmids
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All bacterial strains and plasmids used in this study are listed in Table 1. E. coli XL1-
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Blue (Stratagene, La Jolla, CA, USA) was used for general gene cloning studies and
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the C. glutamicum PKC strain was provided by DAESANG Corp (Gunsan, Korea).
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Plasmids for the expression of E. coli ldcC under different synthetic promoters were
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constructed as previously described.25 Recombinant C. glutamicum PKC strains
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harboring plasmids for the expression of E. coli ldcC were constructed as described
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previously.25
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Genetic modifications of the C. glutamicum PKC genome were carried out by
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homologous recombination and two-step colony selection using kanamycin resistance
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and the SacB system.24 The chromosome integration plasmid (pK19mobsacB)
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containing the SacB system was introduced into the C. glutamicum PKC strain for
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homologous recombination of the gene expression cassette containing synthetic
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promoter, E. coli ldcC, and terminator into the lysE locus encoding an L-lysine
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exporter.
24
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Plasmid construction
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All DNA manipulations were performed following standard procedures.36 Polymerase
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chain reaction (PCR) was performed in the C1000 Thermal Cycler (Bio-Rad, Hercules,
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CA, USA). Primers used in this study (Table S1) were synthesized at Bioneer
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(Daejeon, Korea). Plasmid pK19mobsacB-lysEF was constructed by inserting the 5′-
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region of lysE amplified from C. glutamicum PKC gDNA into pK19mobsacB at the
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HindIII and PstI sites. Plasmid pK19mobsacB-lysEFB was constructed by inserting the
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3′-region of lysE amplified from C. glutamicum PKC gDNA into pK19mobsacB-lysEF
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at the BamHI and EcoRI sites. Plasmids pK19mobsacB-lysEFB-L10ECLdcC,
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pK19mobsacB-lysEFB-L26ECLdcC,
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pK19mobsacB-lysEFB-I64ECLdcC,
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pK19mobsacB-lysEFB-H36ECLdcC were constructed by inserting the gene expression
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cassette containing synthetic promoter, E. coli ldcC, and terminator, which was
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amplified
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pCES208I16ECLdcC,
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pCES208H36ECLdcC into plasmid pK19mobsacB-lysEFB at the PstI and BamHI
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sites, respectively (Table 1).
from
plasmids
pK19mobsacB-lysEFB-I16ECLdcC, pK19mobsacB-lysEFB-H30ECLdcC,
pCES208L10ECLdcC,
pCES208I64ECLdcC,
and
pCES208L26ECLdcC,
pCES208H30ECLdcC,
and
18 19
Culture condition
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E. coli XL1-Blue cells for gene cloning were cultured at 37°C in Luria-Bertani (LB)
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medium (10 g/L tryptone, 5 g/L yeast extract, and 5 g/L NaCl). Flask cultures of C.
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glutamicum were performed at 30°C and 250 rpm in a rotary shaker. The CG50
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medium for flask cultivation contained (per liter): 50 g glucose, 30 g yeast extract, 30 g
24
(NH4)2SO4·7H2O, 0.5 g KH2PO4, 0.5 g MgSO4·7H2O, 0.01 g MnSO4·H2O, 0.01 g
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FeSO4·7H2O, 0.5 mg biotin, and 0.3 mg thiamine-HCl. Kanamycin (Km) was added to
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the culture medium at 20 mg/L for recombinant C. glutamicum strains. For
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maintenance of pH around 7 during flask cultivation, 15 g/L of calcium carbonate was
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added in culture medium.
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Fermentation
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Batch fermentations were carried out at 30°C and 600 rpm in a 2.5-L jar fermenter
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(BioCNS, Daejeon, Korea) containing 500 mL of CG100 medium. CG100 medium
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contained (per liter): 100 g glucose, 30 g yeast extract, 30 g (NH4)2SO4·7H2O, 0.5 g
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KH2PO4, 0.5 g MgSO4·7H2O, 0.01 g MnSO4·H2O, 0.01 g FeSO4·7H2O, 0.5 mg biotin,
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and 0.3 mg thiamine-HCl.s
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Fed-batch fermentations were carried out at 30°C and 600 rpm in a 2.5-L jar
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fermenter (BioCNS) initially containing 500 mL of CG100 medium. Glucose feeding
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was started at a concentration of 10 g/L, and then the glucose concentration was
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maintained at 10–40 g/L by continuously adding glucose solution. The feeding solution
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contained (per liter): 700 g glucose, 270 g (NH4)2SO4·7H2O, 0.5 g MgSO4·7H2O, 0.01
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g MnSO4·H2O, and 0.01 g FeSO4·7H2O. The culture pHs of batch and fed-batch
17
fermentations were maintained at pH 6.9 by automatic addition of 28% (v/v) NH4OH.
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Foam formation was suppressed by adding Antifoam 204, and cell growth was
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monitored by measuring the OD600.
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Purification of cadaverine
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Solvent extraction was conducted to extract cadaverine in the fermentation broth as
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described by Kind et al. with some modifications.24 An appropriate amount of NaOH
24
was added to the supernatant in a glass reactor to adjust the pH to 14. The same
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volume of n-butanol or chloroform was added to the reactor and then mixed with the
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pH-adjusted supernatant using a magnetic heat stirrer at 300 rpm and 55°C for 2 h. The
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mixture was then transferred into separation funnels for phase separation. The organic
4
phase was collected in a round-bottom flask for further procedures and the aqueous
5
phase was treated again with the same extraction procedure as described above. The
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collected organic phase from the 1st and 2nd extractions was concentrated using a rotary
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evaporator at 60°C and 175 rpm. Fractional distillation was carried out using a
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laboratory distillation apparatus at 25–120 mbar and 120–135°C to yield cadaverine
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(diaminopentane) with a purity higher than 99.5%.
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Polymerization of purified cadaverine for the synthesis of bio-based PA510
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Purified cadaverine 65 g (636 mmol, 1.02 eq) and sebacic acid 126 g (623 mmol, 1.00
13
eq) were used as monomers for polymerization of bio-based PA510. Monomers and
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deionized water 170 g (47 wt%) as a solvent were added to a 1-L autoclave reactor.
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Next, the catalyst sodium hypophosphite monohydrate 13.2 mg (0.12 mmol, 79 ppm of
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final polymer) was added. After the reactor was closed tightly, the reactor was flushed
17
with nitrogen gas at room temperature to remove the oxygen gas present in the reactor.
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To obtain PA510 salt, the reaction temperature was raised to 140°C for 30 min. After
19
finishing salt formation, pre-polymerization was carried out. The reactor was heated
20
until 215°C, followed by increasing the pressure. After the pressure reached 17.2 bar,
21
the water vapor was slowly eliminated for 45 min to maintain a constant pressure.
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Subsequently, the pressure in the reactor was gradually reduced to an atmospheric
23
pressure of 45 min to complete pre-polymerization. To perform polymerization, the
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reaction temperature was increased to 270°C and the reactor was stirred for 80 min at 1
2
atm, followed by stirring for 10 min under full vacuum. PA510 polymerized in the
3
reactor was extruded under nitrogen pressure.
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Analysis
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The concentrations of organic acids and glucose were determined by high-
7
performance liquid chromatography using an Agilent Infinity 1260 System (Agilent
8
Technologies, Santa Clara, CA, USA) equipped with an Aminex HPX-76H column
9
(300 × 7.8 mm) (Bio-Rad). Concentrations of cadaverine and lysine were determined
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using an Agilent Infinity 1260 System equipped with an Optimapak C18 column (150
11
× 4.6 mm) (Restek, Bellefonte, PA, USA) as reported previously.25 The purity of the
12
distillation product was measured with an Agilent 7890A system equipped with an
13
RTX 5-Amine column (30 m × 0.25 mm × 0.5 µm; Restek). Helium (purity 99.999%)
14
was used as carrier gas at a flow rate of 1.7 mL min-1. The inlet temperature was 250°C
15
and temperature at the detector was 300°C.
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Bio-based PA510 was dissolved in hexafluoro-2-propanol (HFIP) and CDCl3 solvent
17
for proton nuclear magnetic resonance (1H-NMR, DD2 (500 MHz), Agilent) analysis.
18
Chemical shifts were expressed in parts per million (ppm) scale. Melting temperature
19
(Tm) and crystallization temperature (Tc) were measured by differential scanning
20
calorimetry (DSC, Q200, TA Instruments, New Castle, DE, USA). The PA510 sample
21
was melted gradually at 10°C/min and then cooled, and then reheated at the same rate
22
from 30 to 250°C. The degradation temperature (Td) was determined by Thermo-
23
Gravimetric Analysis (TGA, Q2950, TA Instruments). The PA510 sample was heated
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from 40°C to 900°C at 20°C/min under N2. Relative viscosity was measured with an
2
Ubbelohde viscometer at 25°C. To determine the viscosity, 0.3 g of prepared polymer
3
was dissolved in 30 mL 95% H2SO4 solvent. The RV value was calculated using a
4
formula. The RV value was dimensionless because the units of the numerator and
5
denominator canceled each other. RV = η/η0 (η: viscosity of the polymer solution, η0:
6
viscosity of the solvent). Molecular weight was determined by gel permeation
7
chromatography (PL220C, Agilent) with a Jordi column for polyamide analysis. The
8
gel permeation chromatography analysis solvent was m-cresol, and the sampling and
9
analysis temperature was 100°C with the PS standard. To validate the physical
10
properties as plastics, tensile strength was measured with a Universal testing machine
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(5566, Instron, Norwood, MA, USA) following the ASTM D634 with test specimen
12
type1.
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Results and discussion
2
Examination of the L-lysine production capacity of expired industrial C.
3
glutamicum strains
4
C. glutamicum has extensively been used for industrial production of L-amino acids,
5
particularly L-lysine, a direct precursor of cadaverine. Therefore, a cadaverine-
6
producing C. glutamicum strain can be relatively easily developed by heterologous
7
expression of lysine decarboxylase in C. glutamicum (Figure 1).9 However, it is
8
important to screen C. glutamicum strains with high L-lysine production capacity as
9
the host strain for the expression of lysine decarboxylase to achieve enhanced
10
production of cadaverine. Previously, we examined the L-lysine production ability of
11
expired industrial C. glutamicum strains to select an optimal host for 5-aminovalerate
12
production.35 C. glutamicum KCTC 1857 strain produced the largest amount of lysine
13
compared to other expired industrial strains that were mutated by ultraviolet light (UV)
14
or chemical analogues to attenuate feedback inhibition.35 The C. glutamicum KCTC
15
1857 strain showed the highest lysine production of 4.32 ± 0.45 g/L from 50 g/L of
16
glucose in shaking flask cultivation for 120 h, but also produced 1.17 ± 0.19 g/L of
17
lactic acid.35 A low concentration of dissolved oxygen in culture media frequently led
18
to the formation of by-products by the C. glutamicum strain, such as lactic acid and
19
acetic acid. This result indicates that metabolic flux of the C. glutamicum KCTC 1857
20
strain does not mainly use the tricarboxylic acid cycle, which maintains cell growth
21
and produces oxaloacetate, a precursor of lysine in this cycle.37 Thus, in this study, C.
22
glutamicum PKC strain, another expired industrial L-lysine producer kindly provided
14
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by Daesang Corp., was further examined to compare its L-lysine production capacity
2
with that of other strains examined previously.
3
C. glutamicum PKC strain produced 10.4 ± 1.56 g/L of L-lysine from 50 g/L of
4
glucose, which is more than two-fold higher than that produced by C. glutamicum
5
KCTC 1857 (Figure 2). Furthermore, no accumulation of lactic acid and acetic acid
6
was observed in flask cultivation of C. glutamicum PKC, suggesting that this strain can
7
be used as a practical biorefinery biocatalyst for L-lysine-derived products. Therefore,
8
the C. glutamicum PKC strain was examined as a host strain for enhanced production
9
of cadaverine by constructing an efficient expression cassette for the lysine
10
decarboxylase gene.
11 12
Plasmid-based expression of E. coli ldcC in recombinant C. glutamicum PKC
13
strain for cadaverine production
14
Synthetic promoter-based expression cassettes previously developed for the
15
heterologous expression of E. coli ldcC in recombinant C. glutamicum KCTC 185725
16
were transformed into the C. glutamicum PKC strain to investigate the effect of
17
promoter strength on cadaverine production (Table 1). The expression level of E. coli
18
ldcC in recombinant C. glutamicum PKC strains was controlled by three constitutive
19
promoter groups: high (H), intermediate (I), and low (L) strength (Figure 1). All
20
recombinant C. glutamicum PKC strains showed higher cadaverine production (8.50–
21
12.5 g/L) compared to previous results in recombinant C. glutamicum KCTC 1857
22
strains (0.64–1.01 g/L) (Figure 3).22 The highest cadaverine concentration of 12.5 ±
23
0.67 g/L was produced by recombinant C. glutamicum P-H30. In contrast, a relatively
24
lower amount of cadaverine (9.7 ± 0.71 g/L) was produced by the recombinant C.
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glutamicum P-H36. Interestingly, C. glutamicum P-L10 (10.9 ± 0.93 g/L) and C.
2
glutamicum P-L26 (11.2 ± 2.61 g/L) strains with low strength promoters produced
3
higher concentration of cadaverine compared to the recombinant strains with
4
intermediate strength promoters, C. glutamicum P-I16 (8.50 ± 3.24 g/L) and C.
5
glutamicum P-I64 (11.0 ± 1.83 g/L). No significant correlation between promoter
6
strength and cadaverine production was observed in six recombinant C. glutamicum
7
PKC strains. However, it was found that L-lysine accumulated up to 0.47 ± 0.07 and
8
0.88 ± 0.16 g/L in the culture medium during flask cultures of recombinant C.
9
glutamicum P-L12 and C. glutamicum P-L26. In contrast, C. glutamicum P-H30 and C.
10
glutamicum P-H36 resulted in lower accumulation of L-lysine of approximately 0.05–
11
0.09 g/L in the culture medium. It was demonstrated that the deletion of L-lysine
12
exporter protein (LysE), which is mainly responsible for L-lysine secretion in C.
13
glutamicum, enhanced the production of L-lysine-derived platform chemical, 5-
14
aminovaleric acid by reducing much secretion of L-lysine into culture medium without
15
any deleterious effects on cell growth.
16
of cadaverine in C. glutamicum PKC strains may be enhanced if secretion of L-lysine
17
into cultivation medium is eliminated, which makes more L-lysine in the cells
18
available for cadaverine production.
34.,38
Therefore, it was reasoned that production
19 20
Examination of recombinant C. glutamicum PKC strains with genomic
21
integration of expression cassette for E. coli ldcC at lysE site for cadaverine
22
production
23
Because L-lysine accumulation in the culture medium may have resulted from
24
unstable expression of E. coli ldcC or metabolic burden caused by the plasmid-based
16
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expression system, the expression cassettes comprised of different combinations of six
2
synthetic promoters (L10, L26, I16, I24, H30, and H36) and E. coli ldcC were
3
integrated into the chromosome of a C. glutamicum PKC strain at the lysE locus via
4
homologous recombination (Table 1).21,39,40 Because the lysine exporter protein LysE
5
secretes L-lysine independently of cadaverine secretion, we predicted that
6
chromosomal integration of E. coli ldcC into the lysE locus of the C. glutamicum PKC
7
strain will lead to increased production of cadaverine by stable expression of lysine
8
decarboxylase and reduction of L-lysine secretion. The concentrations and yield of
9
cadaverine produced by recombinant C. glutamicum PKC strains expressing E. coli
10
ldcC integrated into the chromosome were 1.30–12.0 g/L and 0.05-0.42 mol
11
cadaverine/mol glucose. As shown in Figure 3, these were lower than those produced
12
by recombinant C. glutamicum PKC strains with plasmid-based expression of E. coli
13
ldcC (8.50–12.5 g/L, 0.30-0.44 mol cadaverine/mol glucose). Among the lysE deletion
14
mutants, only C. glutamicum G-H36 was able to produce relatively higher
15
concentrations of cadaverine (12.0 ± 0.76 g/L) compared to C. glutamicum P-H36
16
(9.70 ± 0.71g/L). Notably, the highest production and yield of cadaverine were
17
observed in C. glutamicum G-H36 (12.0 ± 0.76 g/L; 0.42 mol cadaverine/mol glucose)
18
and C. glutamicum P-H30 (12.5 ± 0.67 g/L; 0.44 mol cadaverine/mol glucose).
19
Interestingly, the C. glutamicum G-I64 strain showed significant reduction of
20
cadaverine production (1.30 ± 0.36 g/L) compared to C. glutamicum P-I64 (11.0 ± 1.83
21
g/L). Among all the lysE deletion mutants, only C. glutamicum G-L26 (2.36 ± 0.25
22
g/L) showed accumulation of L-lysine, suggesting that integration of E. coli ldcC into
23
the lysE locus successfully repressed secretion of L-lysine into the culture medium.
24
Because recombinant C. glutamcium PKC strains with genome-based expression of E.
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coli ldcC can support stable expression of the lysine decarboxylase gene without
2
antibiotics along with low accumulation of L-lysine in the culture medium, these
3
strains can be examined for fermentative production of cadaverine to confirm their
4
production efficiency of cadaverine at a lower cost.24,28,29
5 6
Enhanced production of cadaverine in batch fermentations by recombinant C.
7
glutamicum PKC strains with chromosome-based E. coli ldcC expression
8
C. glutamicum is an obligate aerobic microorganism, wherein oxygen transfer is
9
known to be a crucial factor for balancing lysine production and cell growth.37,41-43 We
10
predicted that low production of cadaverine by recombinant C. glutamicum PKC
11
strains with chromosome-based E. coli ldcC expression in flask cultures was attributed
12
to the limited availability of oxygen in flask cultures. Thus, the cadaverine production
13
capability of six lysE deletion mutants with chromosome-based E. coli ldcC expression
14
was investigated in batch fermentations to support oxygen rich conditions. The time
15
profiles of cell growth, glucose consumption, extracellular L-lysine concentration, and
16
cadaverine concentration during batch fermentations of recombinant C. glutamicum
17
PKC strains are shown in Figure 4. The highest cadaverine concentration of 23.8 g/L
18
was produced by the C. glutamicum G-H30 strain, which was the second highest
19
producer in flask cultivation (5.26 ± 0.56 g/L) (Figure 3,4d). Recombinant C.
20
glutamicum G-L10 and C. glutamicum G-L26 produced larger amounts of cadaverine
21
(10.2 g/L and 8.83 g/L) than recombinant C. glutamicum G-I64 (8.40 g/L). Although
22
efficient glucose consumption was observed in C. glutamicum G-L10 and C.
23
glutamicum G-I64, relatively lower production of cadaverine (10.2 g/L and 8.40 g/L,
24
respectively) was observed compared to the other C. glutamicum strains. In contrast, C.
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glutamicum G-L26 showed retarded growth, slow glucose uptake capability, and
2
inefficient cadaverine production, although the culture condition in batch fermentation
3
was more favorable for maintaining cellular function compared to flask cultures
4
(Figure. 4). Interestingly, although C. glutamicum P-I16 resulted in the production of
5
8.50 ± 3.24 g/L cadaverine in flask culture, C. glutamicum G-I16 did not grow in batch
6
culture cultivation for unknown reasons (data not shown). Although six E. coli ldcC
7
expression cassettes under different synthetic promoters were integrated in the
8
chromosome of the C. glutamicum PKC strain by disrupting lysE, respectively, only
9
one strain, C. glutamicum G-I16, failed to grow in batch culture. The disruption of lysE
10
may result in the accumulation of L-lysine in the cytosol. Because toxic to the host
11
strain leading to cell rupture or death,44 this may have been caused by intracellular
12
accumulation of L-lysine which could not be rapidly converted into cadaverine in C.
13
glutamicum G-I16. Based on this observation in batch fermentation, prevention of
14
precursor secretion into the medium is not an ideal solution for maximizing the
15
production of target chemicals, although only a single enzyme reaction is involved in
16
the synthesis pathway of the target chemicals.45,46 Thus, metabolic engineering
17
strategies should be designed by carefully considering possible changes in metabolism
18
at the system level.47
19 20
High-level production of cadaverine by C. glutamicum G-H30 strain in fed-batch
21
culture
22
Because the C. glutamicum G-H30 strain produced the highest concentration of
23
cadaverine among the five recombinant C. glutamicum strains expressing E. coli ldcC
24
integrated into the chromosome examined in batch fermentations, C. glutamicum G-
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H30 strain was selected as the host strain for high-level production of cadaverine by
2
fed-batch culture. Although the C. glutamicum G-H36 strain produced cadaverine in
3
batch culture at high concentrations for up to 18 h compared to the C. glutamicum G-
4
H30 strain (Figure 4), the cadaverine concentration with C. glutamicum G-H36 strain
5
reached a peak at 18 h and then decreased. Additionally, the final concentration of
6
cadaverine produced by the C. glutamicum G-H36 strain was lower than that of the C.
7
glutamicum G-H30 strain, and thus the C. glutamicum G-H30 was selected for fed-
8
batch fermentation.
9
The parental C. glutamicum PKC strain was also examined for its ability to provide
10
L-lysine as a direct precursor for cadaverine in fed-batch fermentation. As shown in
11
Figure S1, 140 g/L of L-lysine was produced in fed-batch culture of the C. glutamicum
12
PKC strain at 67 h. Based on this value, the efficiency of cadaverine production by the
13
C. glutamicum G-H30 strain developed was evaluated in this study. During fed-batch
14
fermentation of the C. glutamicum G-H30 strain, the highest L-lysine accumulation in
15
the culture medium up to 3.4 g/L was observed at 18 h accompanied by the production
16
of 10.6 g/L of cadaverine. The low concentration of L-lysine in the fermentation broth
17
indicates that disruption of the lysE locus was effective and L-lysine secretion was
18
successfully reduced. Through fed-batch fermentation of the C. glutamicum G-H30
19
strain, 103.8 g/L of cadaverine, the highest concentration to date to our knowledge,
20
was produced with a cadaverine productivity of 1.47 g/L/h at 65 h cultivation without
21
accumulation of L-lysine and by-products in the culture medium (Figure 5). The
22
cadaverine production achieved in fed-batch fermentation was 4.4-fold higher than that
23
of batch fermentation and conversion yield based on glucose was 53.5% (mol/mol).
24
Notably, deleterious effects such as growth inhibition and L-lysine accumulation by
20
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expression of E. coli ldcC integrated in the chromosome was not observed. Based on
2
these results, C. glutamicum G-H30 strain developed in this study is a good candidate
3
for high-level production of cadaverine from renewable resources.
4 5
Cadaverine purification from fermentation broth
6
Cadaverine was purified from fermentation broth by liquid-liquid extraction and
7
distillation. For efficient purification of cadaverine, the selection of appropriate
8
extraction solvent was conducted and the potential impurities that may impede
9
purification during concentration and distillation were analyzed. In a previous study, n-
10
butanol, 2-butanol, 2-octanol, and cyclohexanol were examined for cadaverine
11
extraction from the aqueous fermentation broth, and n-butanol was selected as
12
extraction solvent because of its low water solubility and high polarity to allow for
13
high solubility of cadaverine.24 In contrast, chloroform is non-reactive, immiscible
14
with, and denser than water and thus is a good extraction solvent for cadaverine
15
purification. Thus, in this study, the efficiency of chloroform and n-butanol as an
16
extraction solvent for cadaverine was compared. As shown in Figure 6a, the extraction
17
yields of both solvents were improved as extraction temperature increased. Chloroform
18
exhibited a slightly higher extraction yield (73.9% (w/w)) than n-butanol (70.6%
19
(w/w)) at 60°C (Figure 6a). Less water was present in the chloroform phase and more
20
than 90% of the chloroform remained after 10 cadaverine extractions (data not shown).
21
The boiling point of chloroform (61.2°C) is much lower than that of n-butanol
22
(117.7°C) and cadaverine (179°C), suggesting that chloroform can be easily removed
23
during the distillation process. Chloroform used in the extraction step was recovered
24
easily during the concentration and distillation steps, and the purity of the recovered
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chloroform was higher than 99.5% (GC analysis), which is similar to that of unused
2
chloroform (data not shown). Considering the general characteristics of n-butanol as a
3
potential fuel, which may cause explosions during the distillation process and higher
4
yield of chloroform in the extraction of cadaverine, chloroform was selected as a
5
solvent to extract cadaverine from the fermentation broth. To improve the recovery
6
yield, cadaverine extraction using chloroform was conducted twice, and then the
7
extracted cadaverine solution was concentrated using a rotary evaporator at 60°C and
8
175 rpm. Finally, the concentrated cadaverine solution was further purified by
9
distillation at 25 mbar and 120°C. As a result, cadaverine recovery yields of 87.9%
10
(w/w) and 68.4% (w/w) were obtained after concentration and distillation with purities
11
of 72.0% and 99.7%, respectively (Figure 6b).
12 13
Investigation of potential impurities that impede purification yield of cadaverine
14
After solvent extraction, concentration, and distillation, bio-based cadaverine with
15
high purity was obtained, but a considerable amount of impurities was also detected
16
during purification. To identify potential impurities that may reduce purification yield,
17
GC analyses were conducted using the concentrated sample after liquid-liquid
18
extraction and distillated sample. As shown in Figure 7, three major peaks
19
corresponding to chloroform, cadaverine, and an unknown compound in the
20
concentrated sample were detected by GC analysis. All peaks except for cadaverine
21
were eliminated after distillation. However, a significant amount of the unknown
22
compound remained in the reservoir until the end of distillation, and the unknown
23
compound and cadaverine were distilled together above 135°C, reducing purification
24
yield (data not shown). Therefore, GC/MS analysis was conducted to identify the
22
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unknown compound (Figure S2). Unfortunately, the mass spectrum of this unknown
2
compound did not match to any compounds in the mass spectral database tested; 3-
3
amino-2-cyclohexene was the closest candidate with 0.43 similarity (Figure S2). The
4
unknown impurity in the concentrated sample could not be fully eliminated by
5
increasing the temperature and remained in the final distillation fraction, indicating that
6
the boiling point of the unknown compound is higher than that of cadaverine. Based on
7
this observation, the unknown impurity concentrated during the liquid-liquid extraction
8
process was likely because of its structural similarity to cadaverine. However, this
9
impurity has no deleterious effect on the polymerization of purified cadaverine and
10
sebacic acid as shown below, but further optimization of the purification process is
11
required to improve the yield and purity of cadaverine.
12 13
Polymerization of PA510 and its chemical properties
14
PA510 was synthesized from the purified cadaverine and sebacic acid. As shown in
15
Figure 8a, the following chemical shift values were detected as representatives; 4.56–
16
4.22 (multiplet, HFIP) and 7.27 (singlet, CDCl3) as a solvent peak used in analysis and
17
6.15 (2H, t), 3.27 (4H, q), 2.27 (4H, t), 1.62–1.55 (8H, m), 1.41–1.37 (10H, B) as
18
corresponding peaks to the backbone of PA510. Based on this result, the synthesized
19
polymer was identified as PA510. To characterize the chemical properties of the
20
synthesized PA510, DSC and TGA were conducted (Figure 8b, 8c). Melting
21
temperature (Tm) and crystallization temperature (Tc) were measured at 216°C and
22
165°C, respectively. The Tm value is similar to that of nylon 510 synthesized from
23
petroleum-based raw materials.24, 49 Degradation temperature (Td) was determined to
24
be 443°C by TGA, indicating that the synthsesized PA510 can be used as a heat-
23
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resistant material. Based on thermal characteristic analyses, cadaverine is suitable for
2
use in the electronics and automobile industries, which demand high-performance
3
materials that are durable in harsh thermal environments. As shown in Table 2, the
4
relative viscosity was 4.6, average molecular weight (Mw) was 253,000 g/mol, and
5
number average molecular weight (Mn) was approximately 174,000 g/mol. The degree
6
of polymerization was much higher than that of chemical-based PA510. Thus, bio-
7
based cadaverine can be used as raw material for synthesizing nylon. The polymeric
8
characteristics of bio-based PA510 make it useful for extrusion applications, such as
9
films and filaments, which require comparatively high viscosity, while for injection
10
molding application such as electrical/electronic devices and automotive parts,
11
viscosity must be controlled to increase process ability by using a terminator such as
12
acetic acid.49 In addition, the tensile stress value at break was 39 MPa, which is
13
comparable to the value of chemical-based PA510.24,
14
based PA510 can be applied as a high-strength polyamide. Based on these results, the
15
polymerization product in this supports its application in diverse industrial areas
16
requiring polymers with high thermal and mechanical properties.
48
Therefore, synthesized bio-
17 18
Conclusion
19
In this study, the C. glutamicum PKC strain, an expired commercial L-lysine
20
producing host strain, was metabolically engineered for high-level production of
21
cadaverine from glucose by optimizing the expression of the E. coli lysine
22
decarboxylase gene. Fed-batch fermentation of the recombinant C. glutamicum G-H30,
23
expressing E. coli lysine decarboxylase integrated at the lysE locus of the chromosome
24
produced 103.78 g/L of cadaverine from glucose, which is the highest titer of
24
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cadaverine reported to date to our knowledge. The purification yield of cadaverine was
2
enhanced by using chloroform as an extraction solvent, which resulted in the
3
production of polymer-grade bio-based cadaverine. Finally, polymerization of purified
4
cadaverine with sebacic acid resulted in bio-based PA510. Recombinant C. glutamicum
5
strains and fermentation and purification strategies of these strains, all of which were
6
developed to enhance the production of bio-based cadaverine in this study, are useful
7
for the development of a more economically feasible process for the sustainable
8
production of bio-based PA510.
9
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Supporting Information
2
Supporting information for this study includes: table for list of primers, figure for
3
lysine production by C.glutamicum PKC and mass spectroscopy analysis of purified
4
cadaverine from fermentation broth. The related table and figures can be found via the
5
internet at https://pubs.acs.org.
6 7
Acknowledgements
8
This work was supported by the R& D Program of MOTIE/KEIT (10049674), Mid-
9
career Researcher Program from the Ministry of Science and ICT (MSIT) through the
10
National Research Foundation (NRF) of Korea (NRF-2016R1A2B4008707), and Ligin
11
Biorefinery from MSIT through the NRF of Korea (NRF-2017M1A2A2087135).
12 13 14
Competing interests The authors declare that they have no competing interests.
15 16 17
Availability of data and materials All data generated or analyzed during this study are included in this published article.
18 19 20
Consent for publication All authors consent for publication.
21 22 23
Funding Funding sources are declared in acknowledgement section.
24
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Table 1. Lists of bacterial strains and plasmids used in this study Plasmid
Relevant characteristics
Reference
Strain
E. coli XL1-Blue
recA1 endA1 gyrA96 thi-1 hsdR17 supE44 relA1 lac Stratgene [Fe proAB lacIq Z∆M15 Tn10 (TetR)
C. glutamicum PKC
An expired industrial L-lysine-producing strain
C. glutamicum P-L10
C. glutamicum PKC with pCES208L10LdcC
This study
C. glutamicum P-L26
C. glutamicum PKC with pCES208L26LdcC
This study
C. glutamicum P-I16
C. glutamicum PKC with pCES208I16LdcC
This study
C. glutamicum P-I64
C. glutamicum PKC with pCES208I64LdcC
This study
C. glutamicum P-H30
C. glutamicum PKC with pCES208H30LdcC
This study
C. glutamicum P-H36
C. glutamicum PKC with pCES208H36LdcC
This study
C. glutamicum G-L10
C. glutamicum PKC derivative: LysE replaced with This study E. coli ldcC under L10 synthetic promoter.
C. glutamicum G-L26
C. glutamicum PKC derivative: LysE replaced with This study E. coli ldcC under L26 synthetic promoter
C. glutamicum G-I16
C. glutamicum PKC derivative: LysE replaced with This study E. coli ldcC under I16 synthetic promoter
C. glutamicum G-I64
C. glutamicum PKC derivative: LysE replaced with This study E. coli ldcC under I64 synthetic promoter
C. glutamicum G-H30
C. glutamicum PKC derivative: LysE replaced with This study E. coli ldcC under H30 synthetic promoter
C. glutamicum G-H36
C. glutamicum PKC derivative: LysE replaced with This study
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E. coli ldcC under H36 synthetic promoter Plasmids pCES208L10LdcC
pCES208 derivative; PL10, E. coli ldcC, Kmr
(25)
pCES208L26LdcC
pCES208 derivative; PL26, E. coli ldcC, Kmr
(25)
pCES208I16LdcC
pCES208 derivative; PI16, E. coli ldcC, Kmr
(25)
pCES208I64LdcC
pCES208 derivative; PI64, E. coli ldcC, Kmr
(25)
pCES208H30LdcC
pCES208 derivative; PH30, E. coli ldcC, Kmr
(25)
pCES208H36LdcC
pCES208 derivative; PH36, E. coli ldcC, Kmr
(25)
1
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Table 2 Comparison of material properties of synthesized bio-based polyamide
2
and commercially available polyamide.
Mechanical Property
Chemical-based
Biobased
Polyamide
Polyamide PA510
Melting temperature 214
215
167
158
Degradation temperature (Td, °C)
436
449 (Td5% 428)
Relative viscosity (g/mol)
3.6
4.6
128,655
174,294
199,477
25,000
48
39
(Tm, °C) Crystallization temperature (Tc, °C)
Number average molecular weight (Mn, g/mol) Weight average molecular weight (Mw, g/mol) Tensile test (stress at break) (Mpa) 3 4
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1
Figure legends
2
Figure 1. Schematic diagram of proposed production of bio-polyamide using
3
recombinant C. glutamicum strains containing chromosomal and plasmid expression
4
of E. coli LdcC using synthetic-promoter-expression cassettes used in this study.
5
Enzymes: LdcC, Lysine decarboxylase; LysE, lysine exporter. Abbreviations:
6
Glucose-6P, glucose 6-phosphate; PEP, phosphoenolpyruvate; CO2, carbon dioxide;
7
OAA, oxaloacetate; TCA cycle, tricarboxylic cycle; ASP, L-aspartate; ASP-P, L-
8
aspartyl-phosphate;
9
tetrahydrodipicolinate; DAP, D,L-Diaminopimelate.
DHDP,
L-2,3-dihydrodipicolinate;
THDP,
L-
10
Figure 2. Lysine production by different strains of C. glutamicum
11
Figure 3. Cadaverine production and lysine consumption of recombinant C.
12
glutamicum strains expressing either plasmid-based expression or chromosomal
13
integration of expression cassettes in shake-flask experiments
14
Figure 4. Comparison of cell growth (A), glucose consumption (B), lysine
15
concentration (C), and cadaverine production (D) of batch fermentation of
16
recombinant C. glutamicum strains with chromosomal integration of expression
17
cassettes with different strengths of promoters. Legends: H36-open circle, H30-
18
filled circle, L10-filled square, L26-open square, I64-open triangle
19
Figure 5. Lysine production of commercial L-lysine overproducing strain, C.
20
glutamicum PKC, used as a host strain (A) and cadaverine production and glucose
21
and lysine substrate consumption of recombinant strain C. glutamicum G-H30 with
22
chromosomal integration of lysine decarboxylase at the LysE site from fed-batch
23
fermentation from fed-batch experiments (B). Legends: cell growth – filled triangle,
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cadaverine concentration – open circle, glucose consumption – open triangle and
2
lysine concentration – filled circle
3
Figure 6. Cadaverine extraction yields obtained by n-butanol or chloroform extraction
4
of fermentation supernatant (a) and schematic illustration and mass balance of
5
cadaverine production process (b). All cadaverine concentrations were measured by
6
high-performance liquid chromatography, except that of the distillation product
7
measured by GC. Cadaverine amounts were calculated. (Symbols are: filled bar, n-
8
butanol extraction yield; open bar, chloroform extraction yield)
9
Figure 7. Gas chromatography analysis of purified cadaverine from fermentation broth
10
Figure 8. Results of nuclear magnetic resonance spectroscopy (1H NMR spectra) (a),
11
differential scanning calorimetry (DSC) (b), and thermogravimetric (TGA) analysis
12
(c) of biobased polyamide PA510
13
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For Table of Contents Use Only.
2
3 4 5
Schematic diagram of sustainable production of bio-polyamide 510 from high level
6
production cadaverine using recombinant C. glutamicum PKC strains. Bio-polyamide
7
510 was produced by polymerization of sebacic acid with purified cadaverine.
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