Multiple pathways for triacylglycerol biosynthesis in Streptomyces coelicolor

The terminal reaction in triacylglyceride (TAG) biosynthesis is the esterification of diacylglycerol (DAG) with a fatty acid molecule. To study this reaction in Streptomyces coelicolor, we analyzed three candidate genes (sco0958, sco1280, and sco0123) whose products significantly resemble the recently identified wax ester synthase/acyl-coenzyme A (CoA):DAG acyltransferase (DGAT) from Acinetobacter baylyi. The deletion of either sco0123 or sco1280 resulted in no detectable decrease in TAG accumulation. In contrast, the deletion of sco0958 produced a dramatic reduction in neutral lipid production, whereas the overexpression of this gene yielded a significant increase in de novo TAG biosynthesis. In vitro activity assays showed that Sco0958 mediates the esterification of DAG using long-chain acyl-CoAs (C-14 to C-18) as acyl donors. The K-m and V-max values of this enzyme for myristoyl-CoA were 45 mu M and 822 nmol mg(-1) min(-1), respectively. Significantly, the triple mutant strain was not completely devoid of storage lipids, indicating the existence of alternative TAG-biosynthetic routes. We present strong evidence demonstrating that the residual production of TAG in this mutant strain is mediated, at least in part, by an acyl-CoA-dependent pathway, since the triple mutant still exhibited DGAT activity. More importantly, there was substantial phospholipid:DGAT (PDAT) activity in the wild type and in the triple mutant. This is the first time that a PDAT activity has been reported for bacteria, highlighting the extreme metabolic diversity of this industrially important soil microorganism.