Overexpression of genes involved in fatty acid biosynthesis increases lipid content in the NaHCO3-tolerant Chlorella sp. JB6

ABSTRACT Microalgae are a potential source of biodiesel owing to their simple structure and high biomass and lipid production rates. Here, we demonstrate that fatty acid (FA) contents can be altered in Chlorella sp. JB6 in the presence of sodium bicarbonate (NaHCO3). We cloned the key genes necessary for FA de novo synthesis conserved in JB6, including biotin carboxyl carrier protein (BCCP), β-carboxyltransferase (β-CT), malonyl CoA-ACP malonyl transferase (MCMT), 3-ketoacyl-ACP reductase (KAR), β-ketoacyl-[acyl carrier protein] synthase I (KASI), and KASII, and successfully transferred plasmids carrying these genes into JB6 cells. We found that overexpression of BCCP, MCMT, KASI, and KASII inhibited the growth of JB6 cells and decreased their resistance to NaHCO3. Notably, ectopic expression of these genes promoted very long-chain saturated FA (>20 C) accumulation. Taken together, we demonstrate that these genes are critical for JB6 growth and resistance to NaHCO3 and can be used for metabolic engineering. IMPORTANCE Fatty acid (FA) contents can be altered in Chlorella JB6 in the presence of sodium bicarbonate (NaHCO3). Overexpression of the FA de novo synthesis genes inhibited the growth of JB6 cells and decreased their resistance to NaHCO3, but these transgenic JB6 strains could grow in a medium containing as high as 300 mM NaHCO3. In JB6, ectopic expression of the FA de novo synthesis genes increased the synthesis of very long-chain saturated FA (> 20C).