Impact of malic enzymes on antibiotic and triacylglycerol production in Streptomyces coelicolor.

In this paper, we have characterized two malic enzymes (ME), SCO2951 and SCO5261, from Streptomyces coelicolor and analyzed their role in antibiotic and triacylglycerol (TAG) production. Biochemical studies have demonstrated that Sco2951 and Sco5261 genes encode NAD(+)- and NADP(+)-dependent malic enzymes, respectively. Single or double mutants in the ME-encoding genes show no effect on growth rate compared to the parental M145 strain. However, the single Sco2951 and the double Sco2951 Sco5261 mutants display a strong reduction in the production of the polyketide antibiotic actinorhodin; additionally, the Sco2951 Sco5261 mutant shows a decrease in stored TAGs during exponential growth. The lower production of actinorhodin in the double mutant occurs as a consequence of a decrease in the expression of actII-ORF4, the transcriptional activator of the actinorhodin gene cluster. On the other hand, the reduced TAG accumulation is not due to reduced transcript levels of fatty acid biosynthetic genes nor to changes in the amount of the precursor acetyl coenzyme A (acetyl-CoA). This mutant accumulates intermediates of the tricarboxylic acid (TCA) cycle that could alter the regulation of the actinorhodin biosynthetic pathway, suggesting that MEs are important anaplerotic enzymes that redirect C4 intermediates from the TCA cycle to maintain secondary metabolism and TAG production in Streptomyces.