TY - JOUR
T1 - Modulation of the balance of fatty acid production and secretion is crucial for enhancement of growth and productivity of the engineered mutant of the cyanobacterium Synechococcus elongatus
AU - Kato, Akihiro
AU - Use, Kazuhide
AU - Takatani, Nobuyuki
AU - Ikeda, Kazutaka
AU - Matsuura, Miyuki
AU - Kojima, Kouji
AU - Aichi, Makiko
AU - Maeda, Shin Ichi
AU - Omata, Tatsuo
N1 - Funding Information:
This study was supported by the Japan Science and Technology Agency CREST funding program in the area of ‘Creation of Basic Technology for Improved Bioenergy Production through Functional Analysis and Regulation of Algae and Other Aquatic Microorganisms’.
Publisher Copyright:
© 2016 Kato et al.
PY - 2016
Y1 - 2016
N2 - Background: Among the three model cyanobacterial species that have been used for engineering a system for photosynthetic production of free fatty acids (FFAs), Synechococcus elongatus PCC7942 has been the least successful; the FFA-excreting mutants constructed from this strain could attain lower rates of FFA excretion and lower final FFA concentrations than the mutants constructed from Synechocystis sp. PCC6803 and Synechococcus sp. PCC7002. It has been suggested that S. elongatus PCC7942 cells suffer from toxicity of FFA, but the cause of the low productivity has remained to be determined. Results: By modulating the expression level of the acyl-acyl carrier protein thioesterase and raising the light intensity during cultivation, FFA secretion rates comparable to those obtained with the other cyanobacterial species were attained with an engineered Synechococcus elongatus mutant (dAS1T). The final FFA concentration in the external medium was also higher than previously reported for other S. elongatus mutants. However, about 85 % of the total FFA in the culture was found to remain in the cells, causing severe photoinhibition. Targeted inactivation of the wzt gene in dAS1T, which gene manipulation was previously shown to result in loss of the hydrophilic O-antigen layer on the cell surface, increased FFA secretion, alleviated photoinhibition, and lead to 50 and 45 % increase in the final cell density and the total amount of FFA in the culture (i.e., the sum of the cellular and extracellular FFA), respectively. The average rate of production of total FFA by the culture of the Δwzt strain was 2.7 mg L-1 h-1, being five times higher than those reported for Synechocystis sp. PCC 6803 and comparable to the rates of triacylglycerol production in green algae. Conclusion: Synechococcus elongatus PCC7942 has larger capacity of FFA production than Synechocystis sp. PCC6803 but accumulates most of the product in the cell because of the imbalance of the rates of FFA production and secretion. This causes severe photoinhibition and exerts adverse effects on cell growth and FFA productivity. Enhancement of FFA secretion would be required to fully exploiting the capacity of FFA production for the purpose of biofuel production.
AB - Background: Among the three model cyanobacterial species that have been used for engineering a system for photosynthetic production of free fatty acids (FFAs), Synechococcus elongatus PCC7942 has been the least successful; the FFA-excreting mutants constructed from this strain could attain lower rates of FFA excretion and lower final FFA concentrations than the mutants constructed from Synechocystis sp. PCC6803 and Synechococcus sp. PCC7002. It has been suggested that S. elongatus PCC7942 cells suffer from toxicity of FFA, but the cause of the low productivity has remained to be determined. Results: By modulating the expression level of the acyl-acyl carrier protein thioesterase and raising the light intensity during cultivation, FFA secretion rates comparable to those obtained with the other cyanobacterial species were attained with an engineered Synechococcus elongatus mutant (dAS1T). The final FFA concentration in the external medium was also higher than previously reported for other S. elongatus mutants. However, about 85 % of the total FFA in the culture was found to remain in the cells, causing severe photoinhibition. Targeted inactivation of the wzt gene in dAS1T, which gene manipulation was previously shown to result in loss of the hydrophilic O-antigen layer on the cell surface, increased FFA secretion, alleviated photoinhibition, and lead to 50 and 45 % increase in the final cell density and the total amount of FFA in the culture (i.e., the sum of the cellular and extracellular FFA), respectively. The average rate of production of total FFA by the culture of the Δwzt strain was 2.7 mg L-1 h-1, being five times higher than those reported for Synechocystis sp. PCC 6803 and comparable to the rates of triacylglycerol production in green algae. Conclusion: Synechococcus elongatus PCC7942 has larger capacity of FFA production than Synechocystis sp. PCC6803 but accumulates most of the product in the cell because of the imbalance of the rates of FFA production and secretion. This causes severe photoinhibition and exerts adverse effects on cell growth and FFA productivity. Enhancement of FFA secretion would be required to fully exploiting the capacity of FFA production for the purpose of biofuel production.
KW - Biofuel production
KW - Cyanobacteria
KW - Free fatty acids
KW - O-antigen
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U2 - 10.1186/s13068-016-0506-1
DO - 10.1186/s13068-016-0506-1
M3 - Article
AN - SCOPUS:85007574318
VL - 9
JO - Biotechnology for Biofuels
JF - Biotechnology for Biofuels
SN - 1754-6834
IS - 1
M1 - 91
ER -