Role of Wax Ester Synthase/Acyl Coenzyme A:Diacylglycerol Acyltransferase in Oleaginous Streptomyces sp. Strain G25

Abstract

Recently, we isolated a novel Streptomyces strain which can accumulate extraordinarily large amounts of triacylglycerol (TAG) and consists of 64% fatty acids (dry weight) when cultivated with glucose and 50% fatty acids (dry weight) when cultivated with cellobiose. To identify putative gene products responsible for lipid storage and cellobiose utilization, we analyzed its draft genome sequence. A single gene encoding a wax ester synthase/acyl coenzyme A (CoA): diacylglycerol acyltransferase (WS/DGAT) was identified and heterologously expressed in Escherichia coli. The purified enzyme Atf(G25) showed acyltransferase activity with C-12-orC(16)-acyl-CoA, C-12 to C-18 alcohols, or dipalmitoyl glycerol. This acyltransferase exhibits 24% amino acid identity to the model enzyme AtfA from Acinetobacter baylyi but has high sequence similarities to WS/DGATs from other Streptomyces species. To investigate the impact of Atf(G25) on lipid accumulation, the respective gene, atf(G25), was inactivated in Streptomyces sp. strain G25. However, cells of the insertion mutant still exhibited DGAT activity and were able to store TAG, albeit in lower quantities and at lower rates than the wild-type strain. These findings clearly indicate that Atf(G25) has an important, but not exclusive, role in TAG biosynthesis in the novel Streptomyces isolate and suggest the presence of alternative metabolic pathways for lipid accumulation which are discussed in the present study.