A novel gene contributing to the initiation of fatty acid biosynthesis in Escherichia coli.

Abstract

Type-II fatty acid biosynthesis in bacteria can be broadly classified into the initiation and elongation phases. The biochemical function defining each step in the two phases have been studied in vitro Among the β-ketoacyl ACP synthases, FabH catalyzes the initiation reaction, while FabB and FabF which primarily catalyze the elongation reaction, can also drive initiation as side reactions. A role for FabB and FabF in the initiation of fatty acid biosynthesis would be supported by the viability of the ΔfabH mutant. In this study, we show, the ΔfabH and ΔyiiD mutations were synthetically lethal and the ΔfabH ΔrelA ΔspoT and ΔfabH ΔdksA synthetic lethality was rescued by the heterologous expression of yiiD In the ΔfabH mutant, the expression of yiiD was positively regulated by (p)ppGpp. The growth defect, reduced cell size, and altered fatty acid profile of the ΔfabH mutant and the growth defect of ΔfabH ΔfabF fabB15(ts) mutant in oleate and palmitate supplemented medium at 42°C were rescued by the expression of yiiD from multi-copy plasmid. Together, these results indicate, the yiiD encoded function supported initiation of fatty acid biosynthesis in the absence of FabH. We have renamed yiiD as fabY Importance Fatty acid biosynthesis is an essential process conserved across life forms. β-ketoacyl ACP synthases are essential for fatty acid biosynthesis. FabH is a β-ketoacyl ACP synthase that contributes to the initiation of fatty acid biosynthesis in E. coli In this study, we present genetic and biochemical evidence that the yiiD (renamed fabY) encoded function contributes to the biosynthesis of fatty acid in the absence of FabH activity and under this condition the expression of FabY was regulated by the stringent response factors (p)ppGpp and DksA. Combined inactivation of FabH and FabY resulted in growth arrest, possibly due to the loss of fatty acid biosynthesis. Molecule(s) that inhibit the two activities can be effective microbicides.