Role of Sinorhizobium meliloti and Escherichia coli Long-Chain Acyl-CoA Synthetase FadD in Long-Term Survival

Abstract

FadD is an acyl-coenzyme A (CoA) synthetase specific for long-chain fatty acids (LCFA). Strains mutated in <i>fadD</i> cannot produce acyl-CoA and thus cannot grow on exogenous LCFA as the sole carbon source. Mutants in the <i>fadD</i> (<i>smc02162</i>) of <i>Sinorhizobium meliloti</i> are unable to grow on oleate as the sole carbon source and present an increased surface motility and accumulation of free fatty acids at the entry of the stationary phase of growth. In this study, we found that constitutive expression of the closest FadD homologues of <i>S. meliloti</i>, encoded by <i>sma0150</i> and <i>smb20650</i>, could not revert any of the mutant phenotypes. In contrast, the expression of <i>Escherichia coli fadD</i> could restore the same functions as <i>S. meliloti fadD</i>. Previously, we demonstrated that FadD is required for the degradation of endogenous fatty acids released from membrane lipids. Here, we show that absence of a functional <i>fadD</i> provokes a significant loss of viability in cultures of <i>E. coli</i> and of <i>S. meliloti</i> in the stationary phase, demonstrating a crucial role of fatty acid degradation in survival capacity.