Lauric Acid Production in a Glycogen-Less Synechococcus sp. PCC 7002

Journal Article · Fri Apr 24 00:00:00 EDT 2015 · Frontiers in Bioengineering and Biotechnology

DOI:https://doi.org/10.3389/fbioe.2015.00048· OSTI ID:1578059

Work, Victoria H. ^[1]; Melnicki, Matthew R. ^[2]; Hill, Eric A. ^[2]; Davies, Fiona K. ^[3]; Kucek, Leo A. ^[2]; Beliaev, Alex S.  ^[2]; Posewitz, Matthew C. ^[4]

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1. Environmental Science and Engineering Division, Colorado School of Mines
2. BATTELLE (PACIFIC NW LAB)
3. Dept. of Chemistry & Geochemistry - Colorado School of Mines
4. Colorado School Of Mines

The cyanobacterium Synechococcus sp. PCC 7002 was genetically engineered to secrete biofuel compatible medium-chain fatty acids during photoautotrophic growth. By introducing a lauroyl-acyl carrier protein (C12:0-ACP) thioesterase to interrupt an endogenous putative acyl- ACP synthetase, secretion of 3-4 mg/L•d transesterifiable C12 was achieved in CO2-supplemented batch cultures. Grown at steady-state over a range of light intensities in an LED photobioreactor operated as a turbidostat, the secreting mutant exhibited a modest reduction in growth rate and increased O2 evolution relative to wildtype. Inhibition of i) glycogen synthesis by deletion of ADP-glucose pyrophosphorylase (AGPase, encoded by glgC) and ii) protein synthesis by nitrogen deprivation were investigated as strategies for metabolite redistribution to fatty acid synthesis. When the modification was introduced into a ?glgC (AGPase-deficient) background, the resulting strain secreted comparable amounts of C12 during nutrient replete growth and no C12 was generated in either background when nitrogen starved. The AGPase- disrupted strains accumulated ten-fold fewer reducing carbohydrates than wildtype during nitrogen deprivation and secreted several types of organic acids consistent with an energy spilling phenotype. At steady-state, the ?glgC modification caused growth rate saturation at a lower light intensity than wildtype backgrounds, but surprisingly, O2 evolution was not compromised on a cellular basis and continued to increase with irradiance. Photophysiological properties of the ?glgC mutant suggest energy dissipation from photosystem II and redox effects to the plastoquinone pool. Implications for further metabolic flux adjustments are discussed.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1578059
• Report Number(s): PNNL-SA-103691
• Journal Information: Frontiers in Bioengineering and Biotechnology, Vol. 3
• Country of Publication: United States
• Language: English

Related Subjects

synechococcus