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Identification of quorum sensing signal molecule of Lactobacillus delbrueckii subsp. bulgaricus Xiaoyang Pang, Cuiping Liu, Pengcheng Lv, Shuwen Zhang, Lu Liu, Jing Lu, Changlu Ma, and Jiaping Lv J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.6b04016 • Publication Date (Web): 25 Nov 2016 Downloaded from http://pubs.acs.org on November 27, 2016
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Identification of quorum sensing signal molecule of Lactobacillus delbrueckii subsp. bulgaricus Xiaoyang Pang,†,‡,ǁ Cuiping Liu,†, ǁ Pengcheng Lv, ∆ Shuwen Zhang, ‡ Lu Liu, ‡ Jing Lu, ‡
†
Changlu Ma, # and Jiaping Lv‡,*
State Key Laboratory of Dairy Biotechnology, Shanghai Engineering Research
Center of Dairy Biotechnology, Dairy Research Institute, Bright Dairy Co. Ltd., Shanghai 200436, P.R. China. ‡Key Laboratory of Agro-Food Processing and Quality Control, Institute of Agro-Food Science and Technology, Chinese Academy of Agricultural Science, Beijing 100193, P.R. China.
∆
College of life science and
Bioengineering, Beijing University of Technology, Beijing 100124, P.R. China. #
Beijing Vocational College of Agriculture, Beijing 102442, P.R. China.
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Abstract: Many bacteria in nature use Quorum sensing (QS) to regulate gene expression. The quorum sensing system plays critical roles in the adaptation of bacteria to the surrounding environment. Previous studies have shown that during the high-density fermentation, the autolysis of lactic acid bacteria was regulated by the QS system, and the two-component system (TCS, LBUL_RS00115/LBUL_RS00110) is involved in the autolysis of Lactobacillus delbrueckii subsp. bulgaricus. However, the QS signal molecule which regulate this pathway have not been identified. In this study, we compared the genome of Lactobacillus bulgaricus ATCC BAA-365 with the locus of seven lactobacillus QS system, the position of QS signal molecule of Lactobacillus bulgaricus ATCC BAA-365 was predicted by bioinformatics tool. Its function was identified by in vitro experiments. Construction of TCS mutant by gene knockout of LBUL_RS00115 confirmed that the signal molecule regulates the density of the flora by the TCS (LBUL_RS00115/LBUL_RS00110). This study indicated that quorum quenching and inhibition based on the signal molecule might serve as an approach to reduce the rate of autolysis of LAB and increase the number of live bacteria in fermentation. Key words: Autolysis; quorum sensing; signal molecule; two-component system.
Introduction The lactic acid bacteria (LAB) is a kind of important food industry microorganism, which is widely used in the production of fermented food products such as dairy, meat, and vegetable products 1. Among the LAB, many Lactobacillus strains are considered
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to have excellent prebiotic effects in human 2. The genome sequences of a number of Lactobacillus species have been sequenced by Next Generation Sequencing(NGS) technology3, 4. This provides a basis for the analysis of the specific physiological characteristics of Lactobacillus using comparative genomics techniques
5-7
. During
the fermentation of dairy products, when the density of LAB exceeds a certain threshold, the phenomenon of cell lysis occurs in LAB, which is similar to the quorum sensing (QS) mechanism. In bacteria, the QS system is commonly composed of a two-component system (TCS) and a signal molecule
8, 9
. TCSs consist of a
membrane-located histidine protein kinase (HPK), which monitors one or more signal molecules, and a response regulator (RR), which modulates the expression of specific genes 10. Previous studies have shown that the autolysis rate of LAB is correlated with the
QS system
11
, and
one
of the
two-component regulatory systems
LBUL_RS00115/LBUL_RS00110 is involved in the autolysis of Lactobacillus delbrueckii subsp. bulgaricus ATCC BAA-365. However, the QS signaling molecule (Autoinducing Peptide, AIP) of L. bulgaricus has not been reported. In this study, the QS signal molecule of L. bulgaricus ATCC BAA-365 was found by bioinformatics analysis, and its function was identified by in vitro experiments. The aim of the present study was to increase the number of live LAB in fermentation by quorum quenching and inhibition based on the signal molecule. Materials and methods Bacterial culture and growth. L. bulgaricus ATCC BAA-365 was routinely grown at 37ºC in the Man–Rogosa–Sharpe (MRS) medium (Beijing Land Bridge
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Technology Co., Ltd. CM187) under static conditions. The polypeptides were synthesized by GL Biochem (Shanghai) Ltd. Genome sequence source and sequence analysis tools. The genome sequences of Lactobacillus acidophilus NCFM, Lactobacillus salivarius UCC118, Lactobacillus sakei subsp. sakei 23K, Lactobacillus plantarum WCFS1, Lactobacillus johnsonii NCC533 and Lactobacillus bulgaricus ATCC BAA-365 were downloaded from NCBI (http://www.ncbi.nlm.nih.gov/genome/). The Simple Modular Architecture Research Tool (SMART, http://smart.embl.de/) was used to analyze the main domain. The TMHMM Server (http://www.cbs.dtu.dk/services/TMHMM/) was used to analyze the transmembrane domain of proteins. Candidate QS-AIPs were examined according to their amino acid composition, residue position, motifs, and physicochemical properties using prediction algorithm “QSPpred”
12
. The Artemis
tool (http://www.sanger.ac.uk/science/tools/artemis) was used to browse and annotate the genomes. Functional verification of candidate QS-AIPs. The liquid (1 mL) containing bacteria in the logarithmic growth phase was added to a 1.5-mL centrifuge tube and centrifuged at room temperature at 5000 rpm for 5 mins. The supernatant was discarded, and the bacterial cells were collected. The cells were washed three times with 50 mL of sterile MRS culture media. After washing, the bacterial cells were inoculated into 50 mL of MRS culture medium. Candidate QS-AIP (2µM) was added to the bacterial suspension, and the change in the bacterial autolysis rate was detected. The autolysis rates were determined using the propidium iodide (PI)-flow cytometry
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method, as previously described 11. Briefly, about 1 × 107cells were stained with PI– phosphate-buffered saline away from light (30 min, 4ºC). Flow cytometry was used for analysis, with 100,000 cells collected per specimen, using the CellQuest software. The cells stained with PI were considered autolyzed. The groups were compared using one-way analysis of variance and least significant difference test. Construction of TCS Mutant. In order to verify the relationship between the two-component system (LBUL_RS00115/LBUL_RS00110) and the signal molecule, the LBUL_RS00115 mutant strain was constructed. A 819bp fragment intermediate region of the LBUL_RS00115 gene was first amplified by PCR with the HPK0115-SphI-F (5’- ACGCGCATGCCGCGGGCAGGCAAAAAG -3’) [SphI site underlined]
and
HPK0115-EcoRI-R
(5’-ACATGAATTCAACGCAGCGGATGATGCTTA-3’) [EcoR I site underlined] primers, and inserted into pUC19 to generate pUC19-HPK0115. The erythromycin resistance gene was amplified by PCR from pMG76e with the EryB-BstEII-F (5’CGGGTAACCATGACCACCGACGCCGCGACG -3’) and EryB-BstYI-R (5’CGAGATCCTCACTGCAACCAGGCTTCCGG -3’) primers, and inserted into pUC19-HPK0115
to
create
the
pUC19-HPK0115::EryBII
plasmid.
The
pUC19-HPK0115::EryBII plasmids was transformed into L. bulgaricus ATCC BAA-365 with minor modifications described in a previous study
13, 14
. The
transformed bacteria were transferred on solid MRS medium with 0.5M sucrose and erythromycin (200 µg/mL) for selection. Statistical Analysis. Statistical analysis was performed with one way ANOVA in
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Origin 6.5 software. Results were accepted as statistically significant at a 0.05 significance level. Results Analysis of QS-TCS of Lactobacillus. Based on the published literature15-19 and the Quorumpeps database (http://quorumpeps.ugent.be), eight QS-TCS from six bacteria (L. acidophilus NCFM, L. johnsonii NCC533, L. sakei subsp. sakei 23K, L. salivarius UCC118, L. plantarum WCFS1, and L. bulgaricus ATCC BAA-365) were collected (Table 1) and analyzed. The results are shown in Figure 1. The eight QS-TCSs had similar domains of HPK and RR. Seven QS-HPKs have a typical transmembrane domain and histidine kinase-like ATPase domain (HATPase_c), but the HPK from L. sakei 23K lacked the transmembrane region. It might sense the intracellular signal (such as changes in the redox potential) through the unique signal transduction protein to obtain external environmental signals. The HPK generally has a conserved C-terminal ATP-binding domain in which a phosphoryl-accepted histidine residue is located and have highly conserved clusters of residues called homology boxes
20, 21
. Grebe & Stock classifies HPK proteins
according to the variable structure of homology boxes
22
. According to this
classification system, quorum sensing-related HPKs belonging to the subfamily called HPK10. In this study, a multiple comparison of different sources of HPK was conducted, and the phylogenetic tree was built using MEGA 6.0. The results are shown in Figure 2. WP_011677872.1 (which is encoded by LBUL_RS00115) from L. bulgaricus ATCC BAA-365 belongs to the HPK10 subfamily. All the eight QS-RR
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have LytTr DNA-binding domain (LytTR) and cheY-homologous receiver domain. The LytTR domain is extensively distributed in the low GC content of Gram-positive bacteria and involved in virulence
23, 24
, synthesis of bacteriocin
26
and extracellular
polysaccharides 25, and metabolic regulation. Sturme
26
summarized the characteristics of different kinds of QS-related proteins.
These characteristics included the following: (1) The HPK protein has an HPK10 subfamily domain and 5-7 N-terminal transmembrane segments and (2) The HPK protein have LytTr DNA-binding domains or RD/ComE subfamily domains. For L. bulgaricus ATCC BAA-365, one of the TCS (LBUL_RS00115/LBUL_RS00110) was in accordance with the aforementioned (1) and (2), but its QS-AIP has not been reported. Prediction QS-AIP of L. bulgaricus ATCC BAA-365. In many cases, the genes encoding the QS-AIP precursor, the histidine kinase receptor, and the RR form an operon, and its expression is auto-induced by QS 27. Figure 1 shows that the location of QS gene locus in Lactobacillus is AIP-HPK-RR, which gives a direction to analyze and predict the QS signal molecule (QS-AIP) of L. bulgaricus ATCC BAA-365. The whole genome of L. bulgaricus ATCC BAA-365 was analyzed, and it was found that a 372bp region (gene position 25031–25403) located upstream of the gene LBUL_RS00115 (HPK) was not annotated. All the possible coding peptides in this region were analyzed according to the three different reading frames, and 13 candidate QS-AIP precursor sequences were obtained (Table 2). The “QSPepPred” tool (http://crdd.osdd.net/servers/qsppred/) was used to predict and
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analyze the QS-AIP from the 13 candidate peptides. QSPepPred is the first web server for predicting and designing QS peptides (QSPs). The tool can examine peptides whether they are QSPs according to their amino acid composition, residue position, motifs, and physicochemical properties. The QSPepPred tool was used in this study to predict QSPs from 13 candidate precursor sequences. The results are shown in Supplementary Table 1. Eleven candidate mature AIP sequences were selected according to the scores (Table 3). The length of the 11 AIP sequences ranged from 7 aa to 14 aa, and they were mainly distributed in three regions. Candidate AIPs in the same region had a very high degree of sequence overlap, and were considered as different fragments of the same polypeptide. One polypeptide was selected from each region, and the three peptides (I: LLSFFFY; II: MLDYFLFEN; III: FNINNNYS) were synthesized by GL Biochem (Shanghai) Ltd. Functional verification of candidate QS-AIPs. Previous studies have shown that during high-density fermentation, the autolysis rate of LAB is correlated with the QS system11, and the TCS (LBUL_RS00115/LBUL_RS00110) is involved in the autolysis of L. bulgaricus ATCC BAA-365. To verify the function of the candidate QS-AIPs predicted by the present study, three candidate QS-AIPs were added to the suspension of L. bulgaricus ATCC BAA-365. The change in autolysis rate was detected after adding QS-AIPs. Flow cytometry revealed no significant differences between BAA-365 with 2µM peptide I and BAA-365 with no peptide, indicating that peptide I was not associated with cell autolysis. Peptides I and III had similar experimental results. However, the autolysis rate of BAA-365 with 2µM peptide II
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sharply increased compared with the rate for BAA-365 with no peptide at the early cultivation. In addition, a markedly reduced maximum optical density value was obtained in BAA-365 with 2µM peptide II compared with BAA-365 with no peptide indicating that the density of L. bulgaricus population significantly decreased when peptide II was added (Fig3 a-d). The relationship of the TCS and the peptide II. In order to verify the relationship of
the
TCS
(LBUL_RS00115/LBUL_RS00110)
and
the
peptide
II,
the
LBUL_RS00115 mutant strain was constructed. The peptide II was added to the suspension of LBUL_RS00115 mutant according to the above method, and the growth curve of the mutant was observed and compared with the wild-type bacteria (Fig3 e-f). From the figure, it can be seen that the mutant with the peptide II reached its maximum growth density at 22 h, and the OD600 value at this time was significantly higher than that of wild-type BAA-365, the mutant without peptide II showed no significant difference in growth curve and autolysis rate with the mutant with 2 uM peptide II. By comparing Figures 3a, 3c and 3e, it can be seen that the peptide II has a function of regulating the growth density of Lactobacillus bulgaricus, and this regulatory process is involved by LBUL_RS00115. These findings indicated a significant role of peptide II in L. bulgaricus QS. Discussion Bacteria use the cell density–dependent quorum sensing system to regulate the expression of related genes to make themselves more adaptable to the surrounding environment
28
. In food industry, quorum sensing is related to many cases, for
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example (foodborne) pathogenicity29, food spoilage30, and biofilm formation31, 32. The bacterial QS system consists of a two-component system (TCS) and a signal molecule33. TCSs consist of a membrane-located histidine protein kinase and a cytoplasmic response regulator, the former is responsible for sensing signal molecules, the latter is responsible for regulating specific genes expression34. Previous studies have shown that during the high-density fermentation, the autolysis rate of LAB is correlated with the QS system, and the TCS (LBUL_RS00115/LBUL_RS00110) is involved in the autolysis of Lactobacillus delbrueckii subsp. bulgaricus. However, the QS signaling molecule of L. bulgaricus has not been reported. The signal molecule play an important role in QS system of lactic acid bacteria, fermented milk producer can increase the number of live bacteria in fermentation by quorum quenching and inhibition based on the signal molecule. Acyl-homoserine lactones (AHLs) are a major QS signal molecules used by Gram-negative bacteria35. At present, many methods are used to detect AHL signal molecules, for example, high-performance liquid chromatography mass spectrometry, lysogeny broth plate method, agar strip method, beta-gal assay, and so on. But for Gram-positive bacteria, it primarily use autoinducing peptide as the signal molecule in the QS system to control gene expression. At present, there are few studies on the detection methods of autoinducing peptide. In this study, the QS intraspecies signal molecule of the L. bulgaricus ATCC BAA-365 was identified by bioinformatics analysis, and its function was identified by in vitro experiments. Construction of TCS mutant by gene knockout of
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LBUL_RS00115 confirmed that the signal molecule regulates the density of the flora by the TCS (LBUL_RS00115/LBUL_RS00110). This study indicated that quorum quenching and inhibition based the signal molecule might serve as an approach to reduce the rate of autolysis of LAB and promote the number of live bacteria in fermentation.
ASSOCIATED CONTENT Supporting Information Signal peptide prediction results by the “QSPepPred” tool. (Supplementary Table 1) AUTHOR INFORMATION Corresponding Author *
(J.L.) Mail: Institute of Agro-Food Science and Technology, Chinese Academy of
Agricultural Science, No. 1 Nongda South Rd., Xi Beiwang, Haidian District, Beijing 100193, China. Phone: (86) 10-62815542. E-mail:
[email protected]. Author Contributions ǁ
Xiaoyang Pang and Cuiping Liu contributed equally to this work.
Funding This work was financially supported by National Natural Science Foundation of China (No.31471603), National Science-technology Support Plan Projects of China (No.2013BAD18B01),
Science
and
Technology
Commission
Municipality, China (No.16DZ2280600). Notes The authors declare no competing financial interest.
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Figure 1. Analysis results of six species of the Lactobacillus quorum sensing system. a, Lactobacillus salivarius UCC118; b, Lactobacillus johnsonii NCC533; c, Lactobacillus sakei subsp. sakei 23K; d, Lactobacillus acidophilus NCFM; e–g, Lactobacillus plantarum WCFS1; h,Lacbobacillus bulgaricus BAA-365. Figure 2. Evolutionary relationships of different histidine protein kinases. The evolutionary history was inferred using the Neighbor-Joining method36. The optimal tree with the sum of branch length = 16.51471714 is shown. The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (1000 replicates) are shown next to the branches. The tree is drawn to scale, with branch lengths in the same units as those of the evolutionary distances used to infer the phylogenetic tree. The evolutionary distances were computed using the Poisson correction method and are in the units of the number of amino acid substitutions per site. The analysis involved 36 amino acid sequences. Evolutionary analyses were conducted in MEGA637. Figure 3. Change in autolysis rate and OD600 of L. bulgaricus BAA-365 with 2µM candidate peptide.
Table 1 General features of HPKs and RRs of candidate QS-TCSs in different lactobacilli Gene/
Size
HPK10 Gene/
Locus Accession No.
Size
LytTR
Gene/
(aa)
domains
Accession No.
Locus (aa)
subfamily Accession No.
Locus
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HPK
RR
AIP
L. salivarius UCC118: abpK
LSL_1913
429
+
abpR
LSL_1912
264
+
abpIP
LSL_1914
435
+
NP_964619
LJ0766
265
+
NP_964616
LJ0763b
183
+
sppR
LSA0563
248
+
sppIP
440
+
YP_194633
LBA1798
274
+
L. johnsonii NCC533: NP_964617
LJ0764
L. sakei subsp. sakei 23K: sppKC
LSA0562
LSA0560b
L. acidophilus NCFM: LBA1799
YP_194634
YP_194635 LBA1800
L. plantarum WCFS1: plnB
lp_0416
442
+
plnC
lp_0417
247
+
plnA
lp_0415
pltK
lp_1355
420
+
pltR
lp_1356
255
+
pltA
lp_1354a
lamC
lp_3581
419
+
lamA
lp_3580
247
+
lamD
lp_3581a
LBUL_RS00115 434
+
RR
LBUL_RS00110 260
+
Unknown
Unknown
L. bulgaricus BAA-365: HPK
Table 2 Candidate QS-AIP sequences No.
Candidate QS-AIP sequences
ORF
Position
Peptide 1
YCCCLLSFFFYAF
–3
25293–25331
Peptide 2
QFLVSSMLDYFLFENFEYLYS
–3
25212–25274
Peptide 3
LFPPLRSMLPVICLSSLPRKNNF
–3
25140–25208
Peptide 4
ALLALHFAGHCFNINNNYSVARVFSRK
–3
25035–25115
Peptide 5
EIASLKELAQNVKVDVIAQNADIAVAYSRFSSMLFSPETCSNSL
–2
25265–25396
Peptide 6
VRCWIIFCLKILSICIHSYFLP
–2
25196–25261
Peptide 7
DLCFLLYAFPASREKIIFER
–2
25133–25192
Peptide 8
ISGLERCWRCTLPGTALT
–2
25076–25129
Peptide 9
HVYFQGNKK
–2
25028–25054
Peptide 10
LHRMLILLLLTLVFLLCFLARRLVAIPCKFDAGLFSV
–1
25237–25347
Peptide 11
VSVFIVISSLKIYASCYMPFQPPAKK
–1
25147–25224
Peptide 12
FLNVEFLALSVAGVALCRALL
–1
25081–25143
Peptide 13
QLFCSTCIFKEIKK
-1
25027–25068
Table 3 QS PepMap protein scan and mapping of peptides on proteins Peptide
SVM
SVM
SVM
SVM
Sequence
Comp Binary Physico Hybrid
KNN
KNN
KNN
Binary
Physico Hybrid
RF
RF
RF
Region Comp Physico
Hybrid
I
LLSFFFY
0.97
0.72
0.85
0.99
1
1
1
0.7
1
0.5
I
LLSFFFYA
0.94
0.68
0.89
0.95
0.8
1
1
0.9
1
0.5
II
DYFLFEN
1.26
1
1.27
1.3
1
1
1
1
0.9
1
II
DYFLFENF
1.17
0.3
1.04
1.16
1
1
1
1
0.9
0.8
II
MLDYFLFEN
1.14
0.29
0.75
1.14
1
1
1
1
0.9
0.8
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II
SMLDYFLFEN
1.04
0.85
0.57
1.03
1
1
1
1
0.9
0.7
II
SSMLDYFLFEN
1
1.17
0.27
0.96
1
1
1
1
0.9
0.9
II
SSMLDYFLFENFEY 0.87
0.84
-0.41
0.9
1
1
1
0.9
0.8
0.9
III
FNINNNY
1.04
0.07
0.94
1
1
1
1
1
1
0.9
III
FNINNNYS
1.08
0.22
0.84
1.03
1
1
1
1
0.9
0.9
III
CFNINNNYS
0.93
0.11
0.8
0.84
1
1
1
0.8
1
0.8
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Journal of Agricultural and Food Chemistry
Figure 1. Analysis results of six species of the Lactobacillus quorum sensing system. a, Lactobacillus salivarius UCC118; b, Lactobacillus johnsonii NCC533; c, Lactobacillus sakei subsp. sakei 23K; d, Lactobacillus acidophilus NCFM; e–g, Lactobacillus plantarum WCFS1; h,Lacbobacillus bulgaricus BAA-365. 194x499mm (72 x 72 DPI)
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II
4
70
3.5
3
60
3
2.5
50
2
40
1.5
30
1
20
1
0.5
10
0.5
2
4
6
8
10
12
14
16
18
20
22
24
60 50
2.5
40
2 30
1.5
0
20 10
0
0
2
4
6
8
10
Time/h
0.4 0.2
10
12
14
16
18
20
22
24
80
60
2.5
50
2
40
1.5
30
20
1
20
10
0.5
10
0
0
0
2
4
6
8
10
autolysis rate
12
14
16
18
70
20
22
24
growth curve
d: BAA-365 + peptide III (2uM) 80
autolysis rate
6
70
5
growth curve
80
autolysis rate
70
5
60
40
3
30
2
4
OD600nm
50
60
Autolysis rate/%
OD600nm
4
50
3
40 30
2
20 1
10 0
2
4
6
8
10
12
0
Time/h
c: BAA-365 + peptide II (2uM)
0
0
3
growth curve
Time/h
6
24
60
30
8
22
3.5
40 0.6
6
20
70
50
0.8
4
18
4
OD600nm
OD600nm
1
2
16
80
Autolysis rate/%
autolysis rate
1.2
0
14
b: BAA-365 + peptide I (2uM)
growth curve
0
12
Time/h
a: BAA-365 1.4
70
autolysis rate
Autolysis rate/%
0
growth curve
14
16
Time/h
ΔH0115++peptide peptideIIII(2uM) (2uM) c:e:BAA-365
18
20
22
24
0
20 1 0
10 0
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4
6
8
10
12
14
Time/h
f: ΔH0115
16
18
20
22
24
0
Autolysis rate/%
0
OD600nm
OD600nm
3.5
Journal of Agricultural and Food Chemistry
autolysis rate
Autolysis rate/%
growth curve
Autolysis rate/%
80
4
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