Physiological characterization of lipid accumulation and in vivo ester formation in Gordonia sp. KTR9

Previous work has demonstrated the feasibility of in vivo biodiesel synthesis in Escherichia coli, however, ethyl ester formation was dependent on an external fatty acid feedstock. In contrast to E. coli, actinomycetes may be ideal organisms for direct biodiesel synthesis because of their capacity to synthesize high levels of triacylglcerides (TAGs). In this study, we investigated the physiology and associated TAG accumulation along with the in vivo ability to catalyze ester formation from exogenous short chain alcohol sources in Gordonia sp. KTR9, a strain that possesses a large number of genes dedicated to fatty acid and lipid biosynthesis. Total lipid fatty acids content increased by 75 % and TAG content increased by 50 % under nitrogen starvation conditions in strain KTR9. Strain KTR9 tolerated the exogenous addition of up to 4 % methanol, 4 % ethanol and 2 % propanol in the media. Increasing alcohol concentrations resulted in a decrease in the degree of saturation of recovered fatty acid alcohol esters and a slight increase in the fatty acid chain length. A linear dose dependency in fatty alcohol ester synthesis was observed in the presence of 0.5-2 % methanol and ethanol compared to control KTR9 strains grown in the absence of alcohols. An inspection of the KTR9 genome revealed the presence of several putative wax ester synthase/acyl-coenzyme A : diacylglycerol acyltransferase (WS/DGAT) enzymes, encoded by atf gene homologs, that may catalyze the in vivo synthesis of fatty acid esters from short chain alcohols. Collectively, these results indicate that Gordonia sp. KTR9 may be a suitable actinomycete host strain for in vivo biodiesel synthesis.