Introduction of ω-3 Desaturase Obviously Changed the Fatty Acid

Oct 23, 2015 - State Key Laboratory of Materials-Oriented Chemical Engineering, College of Biotechnology and Pharmaceutical Engineering, Nanjing Tech ...
0 downloads 11 Views 772KB Size
Subscriber access provided by NEW YORK MED COLL

Article

Introduction of #-3 desaturase obviously changed the fatty acid profile and sterol content of Schizochytrium sp. Lujing Re, Xiaoyan Zhuang, Sheglan Chen, Xiao-Jun Ji, and He Huang J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.5b04238 • Publication Date (Web): 23 Oct 2015 Downloaded from http://pubs.acs.org on October 26, 2015

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Journal of Agricultural and Food Chemistry is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 27

Journal of Agricultural and Food Chemistry

Introduction of ω-3 desaturase obviously changed the fatty acid profile and sterol content of Schizochytrium sp. Lu-jing Ren, Xiao-yan Zhuang, Sheng-lan Chen, Xiao-jun Ji, He Huang* State Key Laboratory of Materials-Oriented Chemical Engineering, College of Biotechnology and Pharmaceutical Engineering, Nanjing Tech University, No. 30 South Puzhu Road, Nanjing 211816, People’s Republic of China

*Corresponding author. Tel./fax: +86 25 58139942. E-mail: [email protected] (H. Huang)

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

1

Abstract:

2

ω-3 fatty acids play significant roles in brain development and cardiovascular

3

diseases prevention and have been widely used in food additives and pharmaceutical

4

industries. The aim of this study was to access the feasibility of ω-3 desaturase for

5

regulating fatty acid composition and sterol content in Schizochytrium sp. The

6

exogenous ω-3 desaturase gene driven by ubiqutin promoter was introduced by 18S

7

homologous sequence to the genome of Schizochytrium sp.. Genetically modified

8

strains had greater size and lower polar lipids than wild type strains. In addition, the

9

introduction of ω-3 desaturase improved ω-3/ω-6 ratio from 2.1 to 2.58 and converted

10

3% DPA to DHA. Furthermore, squalene and sterol contents in lipid of genetically

11

modified strain reduced by 37.19% and 22.31%. The present study provided an

12

advantageous genetically engineered Schizochytrium sp. for DHA production and

13

effective metabolic engineering strategy for fatty acid producing microbes.

14

Keywords: Schizochytrium sp., ω-3 desaturase gene, fatty acids, sterol, squalene

ACS Paragon Plus Environment

Page 2 of 27

Page 3 of 27

Journal of Agricultural and Food Chemistry

15

Introduction

16

Omega-3 polyunsaturated fatty acids (PUFAs), such as docosahexaenoic acid

17

(DHA, 22:6 ω-3) and eicosapentaenoic acid (EPA), are beneficial to the healthy

18

growth of human body and have been widely used in food additives and

19

pharmaceutical industries. They paly significant roles in preventing cardiovascular

20

diseases, malignant tumors, alzheimer's disease, as well as promoting the intellectual

21

development of infant 1. The recommended ω-6 /ω-3 PUFA ratio in diet is 1:1, but this

22

proportion in today’s diet is around 10–20:1 2. The human body cannot adjust the

23

proportion of ω-3 and ω-6 PUFAs, so improving the diet ω3 PUFAs have attracted

24

considerable interest.

25

Schizochytrium sp., a marine microalga, grow fast and could accumulate above

26

50% lipids in cell dry weight with 40% of DHA in total fatty acids 3, which is

27

noteworthy and often considered as a satisfactory strain for DHA industrialization.

28

Besides DHA, the lipid from Schizochytrium sp. also contains C14:0, C16:0, DPA and

29

a small amount of ARA and EPA 4. DPA, belongs to omega-6 polyunsaturated fatty

30

acids, lack one double bond in the C-19 position of carbon backbone comparing with

31

DHA. They were both synthesized by polyketide synthase pathway. Many previous

32

works 5 have concentrated on the regulation of fatty acid composition but is not very

33

effective. Interestingly, the proportion of DHA and DPA often increased and

34

decreased collectively as the environmental changes 6. It is very difficult to change the

35

ratio of DHA/DPA by traditional fermentation condition optimization and regulation.

36

ω-3 desaturase

7

can convert ω-6 PUFA into ω-3 PUFA effectively and this

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Page 4 of 27

37

enzyme have been widely used to change the fatty acid composition in animals, plants

38

and microorganism. Lai et al

39

expressing the fat-1 gene, encoding a kind of ω-3 fatty acid desaturase. Liu et al.

40

introduced ω-3 desaturase gene from soybean into rice and found that α-linolenic

41

acid content in the seeds increased from 0.36 mg g-1 to 8.57 mg g-1. ω-3 desaturases

42

isolated from different species have distinct substrate preferences. The ω-3 desaturase

43

derived from Saprolegnia diclina and Pythium irregular were proved to catalyze the

44

18-carbon, 20-carbon and 22-carbon fatty acids

45

convert 8.4 percentage of 22:4 n-6 to 22:5 n-3 11. The ω-3 desaturase from C. elegans

46

could also catalyze 22-carbon fatty acids and enable non-DHA producing Arabidopsis

47

generate 2.31% of DHA in its fatty acids 12.

8

generated cloned pigs rich in ω-3 fatty acids by 9

10

. Using this enzyme, yeast could

48

In this study, we established a transformation system for Schizochytrium sp. The

49

zeocin resistance gene (ble) driven with a CYC1II promoter-PEF1 terminator system,

50

and ω-3 desaturase gene from Saprolegnia diclina driven with an ubiquitin

51

promoter-terminator system were specifically incorporated into 18S ribosomal DNA

52

(rDNA) by homologous recombination. Then, cell growth, fatty acid composition and

53

sterol content were compared between the ω-3 desaturase transformants and the wild

54

type strains, aiming at accessing the feasibility of ω-3 desaturase for regulating the

55

fatty acid composition and sterol content in Schizochytrium sp.

ACS Paragon Plus Environment

Page 5 of 27

Journal of Agricultural and Food Chemistry

56

Materials and methods

57

Microorganism and medium

58

Schizochytrium sp. HX-308 (CCTCC M209059), stored in China Center for Type 13

59

Culture Collection (CCTCC)

, was used in the present study. This strain was

60

preserved in 20% (v/v) glycerol at -80oC. The seed culture medium and the conditions

61

were as same as our previous study 14. The culture preserved in the glycerine tube was

62

inoculated into a 250-ml flask with 50 ml medium and cultivated for 24 h. After three

63

generation cultivation, the seed culture was inoculated into a 5 L fermentor with the

64

fed-batch fermentation. The initial cell dry weight at the beginning of the

65

fermentation is about 1 g/L. The aeration rate and agitation speed in the preliminary

66

experiment were 1 vvm and 350 rpm, the initial glucose concentration was 40 g/L and

67

incubated at 30 °C. Glucose solution was fed into the bioreactor when the residual

68

glucose concentration was below 20 g/L to keep the residual glucose concentration at

69

40 g/L.

70

Construction of expression vector

71

As shown in Fig 1, the zeocin resistance gene expression cassette, which

72

contains the TEF1 promoter, zeocin resistance gene (ble) and CYC1 terminator, was

73

amplified from pGAPZaA and inserted into pBlueScript II SK by EcoRI and BamHI.

74

This resulting plasmid was designated pBS-Zeo. The 18S rDNA fragment of

75

Schizochytrium sp. HX-308 was amplified using universal primers and cloned into a

76

T-vector (Takara, Dalian, China), named PMD-18S. The 18S upper and downstream

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Page 6 of 27

77

segments were amplified using primers in Table 1. The segments for homologous

78

recombination were amplified from PMD-18S-up and PMD-18S-down and cloned

79

into pBS-Zeo, resulting in the targeting vector pBS-Zeo-18S. The ω-3 desaturase gene

80

from

81

promoter/terminator were respectively synthetized from the Genewiz, a company

82

providing the service of DNA synthesis and sequencing, and ligated into pUC57

83

Simple, generating pUC-ω-3, pUC-promoter, and pUC-terminator. After being

84

sequenced, the amplified fragments were further modified by PCR using primers P1

85

to P6 were list in Table 1, thus generating DNA fragments of ω-3 desaturase gene,

86

ubiquitin promoter, and ubiquitin terminator, respectively. Subsequently, overlap

87

extension PCR was applied once to splice the above three fragments in order, making

88

the full-length product promoter-ω-3-terminator. The spliced fragment was then

89

digested with BamHI, and the digested fragment was inserted into the multiple

90

cloning site (MCS) of PBZ-Zeo-18S, resulting in the plasmid PBZ-18S+omega3 (Fig

91

1).

92

Transformation of Schizochytrium sp.

Saprolegnia

diclina

encoding

ω-3

desaturase

and

the

ubiquitin

93

The Schizochytrium sp. cells in a logarithmic growth phase were harvested in

94

ice-cold polypropylene pipes by centrifugation (5000rpm, 4°C, 10 min) and washed

95

with ice-cold sterile water and 1M sorbitol twice respectively. Then suspend cell with

96

1M sorbitol. The targeting plasmid PBZ-18S+omega3 were digested with the

97

restriction enzyme BamHI for linearization before transformation. The competent

98

cells were mixed with linearized plasmid DNA and transferred to a 0.2-cm cuvette for

ACS Paragon Plus Environment

Page 7 of 27

Journal of Agricultural and Food Chemistry

99

electroporation. The parameters of cell electroporation were 0.75 KV, 200 Ω, 50 µF.

100

After electroporation, 1ml seed medium were added to incubate the cell at 200rpm,

101

30 °C for 1 h, then the putative transformants were selected by plating them on solid

102

media containing 1.5 ug/ml zeocin at 28 °C.

103

Analytical methods

104

Glucose was measured enzymatically using a bioanalyzer (SBA-40C, Institute of

105

Biology, Shandong Academy of Sciences, Jinan, China). Ten millilitres fermentation

106

broth was extracted by pipette and injected into a dried centrifuge tube. Then the

107

broth was centrifuged, and the supernatant was discarded. Then all the cells were

108

transferred to the filter paper which was dried and weighted, and the filter paper was

109

put into an oven at 60°C to dry until the drying did not reduce the weight. The

110

methods of lipid extraction and fatty acid methyl esters (FAMEs) preparation were the

111

same as those used in our previous study 15.

112

Analysis of lipid fractions was performed according to Fan et al.

16

with some

113

modifications. The total lipid (2.5 g) was fractionated to neutral lipids (NLs) and polar

114

lipids (PLs) by elution on a silica column, initially with petroleum ether/diethyl ether

115

(9:1) and then with methanol. After evaporation of the eluate, the amount of each lipid

116

fraction was determined gravimetrically. Unsaponifiable matters were isolated from

117

lipid by saponification and analyzed by GC-MS

118

three times to ensure the precision of data.

17

. Each experiment was conducted

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

119

Results and Discussion

120

Expression of ω-3 desaturase gene in Schizochytrium sp.

121

Our previous studies have verified the feasibility of ble gene transformation in

122

Schizochytrium sp. and proved that using 18SrDNA as the recombination site for

123

Schizochytrium has no obvious effect on cell growth and fatty acid composition. Then,

124

we expressed ω-3 desaturase gene using an omega-3 expression cassette driven by

125

ubiquitin promoter/terminator (Fig 2A). The omega-3 expression cassette, obtained by

126

the overlap extension PCR (Fig 2B), was inserted to the plasmid PBS-Zeo-18S to

127

generate the PBS-Zeo-omega 3 (Fig 2C). 2.6 kbp PCR products corresponding to the

128

size of omega-3 expression cassette were amplified from the genome DNA of the

129

transformates (Fig 3D), indicating that the exogenous gene has been incorporated into

130

the genome of Schizochytrium sp. As shown in Fig 3E, omega-3 transformate cells

131

were slightly greater than the original strain.

132

18SrDNA sequence is a suitable recombination site for genetic engineering.

133

Therefore, we chose the 18S sequence as the homologous recombination sites in this

134

study. Generally, the 18SrDNA sequence exists in multiple copies and locates at

135

transcriptional active regions in organisms. Thus, this homologous sequence provided

136

more integration chances and higher expression levels of exogenous gene.

137

Effect on cell growth and lipid accumulation

138

To further investigate the discrepancy between the wild-type strain and the

139

genetically modified strain, these two strains were further cultivated in a 5 L

140

fermentor respectively. The time courses of substrate consumption, cell growth and

ACS Paragon Plus Environment

Page 8 of 27

Page 9 of 27

Journal of Agricultural and Food Chemistry

141

lipid accumulation were shown in Fig. 3. During the fermentation, wild-type strains

142

consumed 209 g of glucose, while the genetically modified strain consumed 178 g of

143

glucose. Thence, cell dry weight and lipid yield of GM strain were all slightly lower

144

than that of wild type strain. But the conversion rate of glucose to cell dry weight and

145

lipid were approximately the same. These phenomena indicated that the genetically

146

modified strain has lower glucose consumption rate but the same substrate conversion

147

rate. As shown in Fig 3A, DO of genetically modified strain maintained at around 5%

148

while the value of wild type strain were always zero after 12h, indicating that

149

genetically modified strain consumed less oxygen than the original strains. Therefore,

150

the introduction of ω-3 desaturase genes reduced the glucose consumption rate and

151

cell oxygen demand. Yan et al

152

synthetase gene into Schizochytrium sp. TIO1101, and they found cell growth rate and

153

glucose consumption rate of the modified strain was also lower than the wild type

154

strain, which also indicated that the introduced exogenous gene might increase the

155

burden of the cell.

18

introduced the Escherichia coli acetyl-CoA

156

The introduction of ω-3 desaturase gene also caused significant changes in lipid

157

fractions of Schizochytrium sp. HX-308. As shown in Table 2, the proportion of NLs

158

increased from 77.70% of wild-type strain to 89.77% of genetically modified strain.

159

Corresponding, the proportions of PLs decreased from 22.30% to 10.23%. As we

160

know, neutral lipids were the main storage lipids and polar lipids were the main

161

components of membrane structure

162

strain might be related to the change of cell morphology. The cell size of genetically

19

. The decrease of PLs in genetically modified

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

163

modified strain was greater than that of the wild-type strain (Fig 2). For a certain

164

weight of cells, larger ones requires less number of cells and need fewer membrane

165

structures to breeding, which means need less polar lipids.

166

Effect on ω-3/ω-6 ratio

167

In the genetically modified strain, the ratio of ω-3/ω-6 fatty acids and DHA/DPA

168

were all higher than that of wild-type strain at different stages of the fermentation (Fig

169

5). In particular, the ratio of ω-3/ω-6 at 24h in GM strain reached the maximum of

170

2.58, which was 25.85% higher than that of wild type strain, indicating that ω-3

171

desaturase had the highest expression at the beginning of the fermentation. At this

172

time, nitrogen did not exhaust and cell grew fast. The balanced nutrition conditions

173

might give good environment for the expression of exogenous genes. After 24h, the

174

ratio of ω-3/ω-6 decreased from 2.58 to 2.38 and then held constant until the end of

175

the fermentation, suggesting that the ω-3 desaturase expressed stable in lipid

176

accumulation stage. As we known, the reaction from DPA to DHA catalyzed by ω-3

177

desaturase need oxygen as an important substrate

178

dissolved oxygen during the fermentation was also an important reason for the

179

decrease of ω-3/ω-6 ratio. But the ω-3/ω-6 ration and DHA/DPA ratio of wide type

180

strain kept constant during fermentation, this might be related to the PKS pathway,

181

which does not need oxygen, so the values could keep constant during the

182

fermentation no matter the dissolve oxygen decrease or not. At the end of

183

fermentation, DPA and DHA percentage in total fatty acids in genetically modified

184

strain reached 18.67% and 49.23%. Compared with the value of 21.65% and 46.17%

20

, so we think the decrease of

ACS Paragon Plus Environment

Page 10 of 27

Page 11 of 27

Journal of Agricultural and Food Chemistry

185

of wild-type strain, 3% DPA was converted to DHA by the introduced ω-3 desaturase.

186

In fact, there are many other studies trying to modify the fatty acid compositions 17

187

by optimizing the culture conditions. We previously

investigated the differential

188

effects of nutrient limitations on biochemical constituents and docosahexaenoic acid

189

production of Schizochytrium sp. and found that the ratios of DHA/DPA at different

190

nutrient conditions were basically constant at 2.15, no big difference. Kavita P. Patil 21

191

studied the effect of different media supplements on DHA yields in Schizochytrium

192

limacinum SR21 and found that DHA yield and DPA yield mutually increased or

193

decreased. In addition, the DHA/DPA ratio could increase from 5.58 to 6.47 when

194

changing ammonium acetate to sodium acetate in the medium, but cell dry weight

195

decreased a half, which is very uneconomical. Song et al 22 found that DHA and DPA

196

percentage in total fatty acids could increase from 35.30% and 7.02% to 61.4 % and

197

12.32% respectively when adding pentanoic acid in the medium. The DHA/DPA

198

ratios in the two cultures were all around 5.0, which also indicated that DPA and DHA

199

percentages often increased and decreased collectively.

200

In addition, the ratio change in this study was also not too high, but it indeed

201

decreased the DPA percentage and increased the DHA percentage simultaneously,

202

which proved the introduction of ω-3 desaturase. The low conversion efficiency might

203

be ascribed to the pathway shift and enzyme catalysis efficiency. As we known, DPA

204

and DHA were synthesized by polyketide synthase pathway

205

but the mechanism of the double bond formation and chain elongation were still

206

unclear, especially how cell selectively synthesized DHA and DPA, the two molecules

ACS Paragon Plus Environment

23

in Schizochytrium sp,

Journal of Agricultural and Food Chemistry

207

with so similar structure but only differ with one double bond in the carbon chains. In

208

this study, the introduction of ω-3 desaturase gene integrated into the genome of

209

Schizochytrium sp. catalyzed parts of the intermediates of polyketide synthase

210

pathway, especially ω-6 fatty acids, to ω-3 fatty acids. Comparing with the conversion

211

efficiency

212

DPA was converted to DHA. This might be ascribed to the reason that polyketide

213

synthase pathway was independent of the elongation and saturation pathways, ω-6

214

fatty acids, such as DPA and ARA, obtained from polyketide synthase pathway might

215

need more time and space to complete the pathway transformation.

216

Effect on squalene and sterol content

24

of ARA to EPA in Mortierella alpina 1S-4 by ω-3-desaturase, only 3%

217

Squalene and sterol were two main kinds of unsaponifiable matters in DHA-rich

218

oil of Schizochytrium sp. Squalene content of genetically modified strain decreased

219

from 22.09 mg/g at 48 h to 17.37 mg/g at 96 h during lipid accumulation stage, then

220

dropped to 27.86 mg/g. Wild type strains had similar change trends. In particular,

221

squalene contents of genetically modified strain were all lower than that of wild-type

222

strain during the whole fermentation process. The final squalene content of

223

genetically modified strain was 37.19% lower than 27.86 mg/g of wild type strains,

224

indicating that the introduction of ω-3 desaturase obviously decreased the squalene

225

content (Table 3). As we know, squalene has antioxidant activity and may thus

226

provide a cellular defense against active oxygen that damage DNA, protein amino

227

acids or polyunsaturated fatty acids

228

value of unsaponifiable matters, which was required to be below 4% in lipid

25

. But too much squalene would increase the

ACS Paragon Plus Environment

Page 12 of 27

Page 13 of 27

Journal of Agricultural and Food Chemistry

229

according to the GB 26400-2011. The introduction of ω-3 desaturase can improve the

230

quality of DHA-rich oil to a certain extent.

231

Sterols in Schizochytrium sp. were also identified and analyzed by GC–MS and

232

five main sterols, including cholesterol, stigmasterol, ergosterol, lanosterol and

233

cycloartenol, were detected and quantified throughout the fed-batch process (Table 3).

234

The sterol contents of genetically modified strain were all lower than the value of wild

235

type strain except ergosterol. The final lanosterol and cycloartenol content were only

236

0.492 mg/g and 0.152 mg/g respectively, which were 23.44% and 54.55% lower than

237

that of wild-type strain. Strangely, the ergosterol content of genetically modified strain

238

was three times of the value of wild type strains. The final value of ergosterol content

239

in modified strain reached 0.171 mg/g, while the value in wild type strain was only

240

0.052 mg/g. In wide type strain, the ergosterol content decreased during the

241

fermentation but the value in modified strain did not decrease. As we known, the

242

ergosterol belongs to the fungi sterol and is the common sterol in cell membrane. This

243

might indicate that the modified strain might need more ergosterol to maintain its

244

greater cell size.

245

Sterols and squalene were synthesized by the mevalonate pathway, in which

246

hydroxy-methylglutaryl CoA reductase (HMG CoA reductase) and fatty acyl-CoA

247

cholesterol acyltransferase (ACAT) were the main rate-limiting enzymes. Previous

248

studies

249

and increase the activity of ACAT. Therefore, the introduction of exogenous ω-3

250

desaturase gene improved the DHA content of Schizochytrium sp., and the increased

26

have found ω-3 PUFAs could reduce the activity of HMG CoA reductase

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

251

ω-3 polyunsaturated fatty acids might restrain the mevalonate pathway and thence

252

reduced the content of sterols and squalene 27.

253

In this study, the exogenous ω-3 desaturase gene was successfully incorporated

254

and expressed in Schizochytrium sp., and then the effect of ω-3 desaturase gene on

255

cell growth, lipid accumulation, and fatty acid synthesis were systematically

256

examined. The introduction of ω-3 desaturase not only improved the ratio of ω-3/ω-6

257

but also decreased the contents of unsaponifiable matters such as squalene and sterols.

258

This study proved the potential of ω-3 desaturase to improve the ratio of ω-3/ω-6 fatty

259

acids of oleaginous microorganism. In addition, this study provided an advantageous

260

genetically engineered Schizochytrium sp. for industrial DHA production and

261

effective metabolic engineering strategy for fatty acid producing microbes.

262

Author Information

263

Corresponding Authors

264

*He Huang Phone: +86 25 58139942. E-mail: [email protected] (H. Huang)

265

Funding

266

This work was financially supported by the National Science Foundation for

267

Distinguished Young Scholars of China (No. 21225626), the National Natural Science

268

Foundation of China (No. 21306085), the National High Technology Research and

269

Development Program of China (No. 2012AA021704 and No.2014AA021701) and

270

the Specialized Research Fund for the Doctoral Program of Higher Education (No.

271

20133221120008).

272

ACS Paragon Plus Environment

Page 14 of 27

Page 15 of 27

Journal of Agricultural and Food Chemistry

273

References

274

(1) LLOYD, A.H.; Yeo, Y. K.. Health benefits of docosahexaenoic acid (DHA).

275

Pharmacol. Res., 1999, 40, 211-225.

276

(2) Simopoulos A.P. Human requirement for n-3 polyunsaturated fatty acids. Poultry

277

Sci. 2000, 79, 961-970.

278

(3) Sijtsma, L.; Swaaf, M. E.. Biotechnological production and applications of the

279

omega-3 polyunsaturated fatty acid docosahexaenoic acid. Appl. Microbial.Biot. 2004,

280

64, 146-53.

281

(4) Ren, L. J.; Ji, X. J.; Huang, H.; Qu, L.; Feng, Y.; Tong, Q. Q.; Ouyang, P. K..

282

Development of a stepwise aeration control strategy for efficient docosahexaenoic

283

acid production by Schizochytrium sp. Appl. Microbial.Biot. 2010, 87, 1649-56.

284

(5) Zhu, L.; Zhang, X.; Ji, L.; Song, X.; Kuang, C., Changes of lipid content and fatty

285

acid composition of Schizochytrium limacinum in response to different temperatures

286

and salinities. Process Biochem. 2007, 42, 210-214.

287

(6) Huang, T. Y.; Lu, W. C.; Chu, I. M. A fermentation strategy for producing

288

docosahexaenoic acid in Aurantiochytrium limacinum SR21 and increasing C22:6

289

proportions in total fatty acid. Bioresource Technol. 2012, 123, 8-14.

290

(7) Wang, M.; Chen, H.; Gu, Z.; Zhang, H.; Chen, W.; Chen, Y. Q. Omega3 fatty acid

291

desaturases from microorganisms: structure, function, evolution, and biotechnological

292

use. Appl. Microbial.Biot.2013, 97, 10255-62.

293

(8) Lai, L.; Kang, J. X.; Li, R.; Wang, J.; Witt, W. T.; Yong, H. Y.; Hao, Y.; Wax, D.

294

M.; Murphy, C. N.; Rieke, A.; Samuel, M.; Linville, M. L.; Korte, S. W.; Evans, R.

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

295

W.; Starzl, T. E.; Prather, R. S.; Dai, Y. Generation of cloned transgenic pigs rich in

296

omega-3 fatty acids. Nat. biotechnol. 2006, 24, 435-6.

297

(9) Liu, H. L.; Yin, Z. J.; Xiao, L.; Xu, Y. N.; Qu le, Q. Identification and evaluation

298

of omega-3 fatty acid desaturase genes for hyperfortifying alpha-linolenic acid in

299

transgenic rice seed. J Exp. Bot. 2012, 63, 3279-87.

300

(10) J, B., Pythium omega 3 desaturase with specificity to all omega 6 fatty acids

301

longer than 18 carbon chains. EP 2 500 420 A1 2007.

302

(11) Petra C, J. B., Thorsten Z, Ernst H, Method for producing unsaturated ω-3-fatty

303

acids in transgenic organisms. US 7,777,098 B2 2010.

304

(12) John AB, J. P., Omega-3 fatty acid desaturase. US 2002/0170090 A1 2002.

305

(13) Ren, L. J.; Huang, H.; Xiao, A. H.; Lian, M.; Jin, L. J.; Ji, X. J., Enhanced

306

docosahexaenoic acid production by reinforcing acetyl-CoA and NADPH supply in

307

Schizochytrium sp. HX-308. Biopro. Biosyst. Eng. 2009, 32, 837-43.

308

(14) Ren, L. J.; Sun, L. N.; Zhuang, X. Y.; Qu, L.; Ji, X. J.; Huang, H., Regulation of

309

docosahexaenoic acid production by Schizochytrium sp.: effect of nitrogen addition.

310

Biopro. Biosyst. Eng. 2014, 37, 865-72.

311

(15) Ren, L. J.; Sun, G. N.; Ji, X. J.; Hu, X. C.; Huang, H., Compositional shift in

312

lipid fractions during lipid accumulation and turnover in Schizochytrium sp.

313

Bioresource Technol. 2014, 157, 107-13.

314

(16) Fan, K. W.; Jiang, Y.; Faan, Y. W.; Chen, F., Lipid characterization of mangrove

315

thraustochytrid--Schizochytrium mangrovei. J. Agric. Food Chem..2007, 55, 2906-10.

316

(17) Sun, L.; Ren, L.; Zhuang, X.; Ji, X.; Yan, J.; Huang, H., Differential effects of

ACS Paragon Plus Environment

Page 16 of 27

Page 17 of 27

Journal of Agricultural and Food Chemistry

317

nutrient limitations on biochemical constituents and docosahexaenoic acid production

318

of Schizochytrium sp. Bioresource Technol. 2014, 159, 199-206.

319

(18) Matsuda, T.; Sakaguchi, K.; Hamaguchi, R.; Kobayashi, T.; Abe, E.; Hama, Y.;

320

Hayashi, M.; Honda, D.; Okita, Y.; Sugimoto, S.; Okino, N.; Ito, M., Analysis of

321

Delta12-fatty acid desaturase function revealed that two distinct pathways are active

322

for the synthesis of PUFAs in T. aureum ATCC 34304. J Lipid Res. 2012, 53,

323

1210-22.

324

(18) Yan, J.F., Cheng R. B., Lin, X.Z., You, S., Li, K., Rong, H., Ma, Y.

325

Overexpression of acetyl-CoA synthetase increased the biomass and fatty acid

326

proportion in microalga Schizochytrium. App.l Microbio.l Biotechnol. 2013, 97,

327

1933-1939

328

(19) Suzumura, M., Phospholipids in marine environments: a review. Talanta 2005,

329

66, 422-34.

330

(20) Behrouzian, B., Buist, P.H., Mechanism of fatty acid desaturation: a bioorganic

331

perspective. Prostag. Leukotr. Ess. 2003, 68: 107-112

332

(21) Patil, K.P.; Gogate, P.R., Improved synthesis of docosahexaenoic acid (DHA)

333

using Schizochytrium limacinum SR21 and sustainable media. Chem Eng J. 2015, 268:

334

187-196

335

(22) Song, X.J., Tan, Y.Z., Liu, Y.J., Zhang, J.T., Liu, G.L., Feng, Y.G., Cui, Q.

336

Different impacts of short-chain fatty acid on saturated and polyunsaturated fatty acid

337

biosynthesis in Aurantiochytrium sp. SD116. J. Agric. Food Chem. 2013, 61,

338

9876-9881.

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

339

(23) James GM, P. R., Daniel F, Charlene L, Franziska D, Michael L, Ray V, Kathryn

340

L, Frederic D,; Akiko Y, K. Y., Vic K, John B, Production of polyunsaturated fatty

341

acids by polyketide synthases in both prokaryotes and eukaryotes. Science 2001, 293,

342

290-293.

343

(24) Sakuradani, E.; Abe, T.; Iguchi, K.; Shimizu, S., A novel fungal

344

omega3-desaturase with wide substrate specificity from arachidonic acid-producing

345

Mortierella alpina 1S-4. Appl. Microbial.Biot. 2005, 66, 648-54.

346

(25) Gupta, A.; Singh, D.; Barrow, C. J.; Puri, M., Exploring potential use of

347

Australian thraustochytrids for the bioconversion of glycerol to omega-3 and

348

carotenoids production. Biochem. Eng. J 2013, 78, 11-17.

349

(26) DU CY, S. A., Watanaba S, Wu CZ, Ikemoto A, Ando K, Kikugawa K, Fujii Y,

350

Ikuyama H, Cholesterol synthesis in mice is suppressed but lipofuscin formation is

351

not affected by long-term feeding of n-3 fatty acid-enriched oils compared with lard

352

and n-6 fatty acid-enriched oils. Biol Pharm Bull 2003, 26, 766-770.

353

(27) Conquer JA, H. B., Effect of supplementation with different doses of DHA on. J

354

Lipid Res 1998, 39, 286-292.

ACS Paragon Plus Environment

Page 18 of 27

Page 19 of 27

Journal of Agricultural and Food Chemistry

Figure Captions Fig. 1 Structure of the targeting vector recombinant plasmid PBZ-18S+omega-3 Fig 2 Argarose gel of different fragements. (A) ω-3 desaturase gene, ubiqutin promoter and termenter; (B) the products of the overlap extension PCR; (C) PBZ-18S-omega-3 gene vector; (D) PCR product amplified from the genome DNA of the transformates; (E) Cell morphology of wild type strain and genetically modified strain in electron microscope. Fig.3 (A) Time course of cell dry weight and DO of two strains (B) Time course of glucose consumption and lipid accumulation of two strains. (W is wild-type strain, G is genetically modified strain). Fig.4 (A) Comparison of ω-3/ω-6 fatty acid ratio between W and G. (B) Comparison of DHA/DPA ratio between the W and G. (W is wild-type strain, G is genetically modified strain)

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Page 20 of 27

Table 1 Primers used in this study Gene

Primer

Primer sequence(5’-3’)

name Ubiquitin

P-S

TCGGATCCCGTTAGAACGCGTAATAC

promoter

P-A

TTCGTCTTATCCTCAGTCATGTTGGCTAGTGTTGCTTAGGTCGCT

ω-3 desaturase

ω-3-S

CCTAAGCAACACTAGCCAACATGACTGAGGATAAGACGAAGGT

gene

ω-3-A

ATACTACAGATAGCTTAGTTTTAGTCCGACTTGGCCTTGG

Ubiquitin

T-S

CCAAGGCCAAGTCGGACTAAAACTAAGCTATCTGTAGTATGTGC

terminator

T-A

TCGGATCCACCGCGTAATACGACTCACTATAGGGAGACTGCAGTT

18SupS

5’- GGGTACCCGTAGTCATATGCTTGTCTC -3’

18SupA

5’- CCTCGAGGATTTCACCTCTAGCGAC -3’

18SdownS

5’- CGGATCCGATGCCGACTAGAGATT-3’

18SdownA

5’- GAGCTCTCCGCAGGTTCACCTACGGA-3’

18Sup

18Sdown

ACS Paragon Plus Environment

Page 21 of 27

Journal of Agricultural and Food Chemistry

Table 2 Comparison of kinetic parameters and lipid fractions of wild type and modified strains

Wild-type strain

Genetically modified strain

Yx/s

0.360±0.002

0.390±0.002

Yp/s

0.230±0.002

0.275±0.002

YDHA/s

0.116±0.001

0.141±0.001

NLs (%)

77.700±0.541

89.770±0.690

PLs (%)

22.301±0.130

10.230±0.342

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Page 22 of 27

Table 3 . Differences of unsaponifiable matters during fed-batch cultivation of Schizochytrium sp.

Time

(W is wild-type strain, G is genetically modified strain)

Squalene

Ergosterol

Cholesterol

Stigmasterol

Lanosterol

Cycloartenol

(mg/g)

(mg/g)

(mg/g)

(mg/g)

(mg/g)

(mg/g)

W

33.21±0.841

0.170±0.002

0.091±0.002

0.231±0.012

0.541±0.025

0.291±0.014

G

22.09±0.293

0.120±0.004

0.052±0.003

0.192±0.013

0.373±0.021

0.052±0.024

W

24.19±0.682

0.090±0.004

0.071±0.002

0.141±0.011

0.382±0.014

0.154±0.017

G

17.37±0.514

0.141±0.004

0.053±0.002

0.091±0.009

0.344±0.015

0.071±0.022

W

38.22±0.782

0.052±0.006

0.081±0.003

0.111±0.008

0.641±0.017

0.330±0.022

G

27.86±0.864

0.171±0.003

0.052±0.004

0.082±0.012

0.492±0.020

0.152±0.017

Strain

48h

72h

108h

ACS Paragon Plus Environment

Page 23 of 27

Journal of Agricultural and Food Chemistry

Fig. 1 Structure of the targeting vector recombinant plasmid PBZ-18S+omega-3

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Ubi pro

A

Omega-3 desaturase Ubi ter

B

2000

Omega-3 desaturase cassette

C

PBZ-18S-omega3

D

Page 24 of 27

desaturase M( bp) expression cassette

10000 7000

1000

5000

750

3000

500

2000

5000 3000 2000 1000

2600

E

Modified strain

Wild type

Fig 2 Argarose gel of different fragements. (A) ω-3 desaturase gene, ubiqutin promoter and termenter; (B) the products of the overlap extension PCR; (C) PBZ-18S-omega-3 gene vector; (D) PCR product amplified from the genome DNA of the transformates; (E) Cell morphology of wild type strain and genetically modified strain in electron microscope.

ACS Paragon Plus Environment

Page 25 of 27

Journal of Agricultural and Food Chemistry

Fig.3 (A) Time course of cell dry weight and DO of two strains (B) Time course of glucose consumption and lipid accumulation of two strains. (W is wild-type strain, G is genetically modified strain).

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Fig.4 (A) Comparison of ω-3/ω-6 fatty acid ratio between W and G. (B) Comparison of DHA/DPA ratio between the W and G. (W is wild-type strain, G is genetically modified strain)

ACS Paragon Plus Environment

Page 26 of 27

Page 27 of 27

Journal of Agricultural and Food Chemistry

Graphic for table of contents

ACS Paragon Plus Environment