Two putative Enterococcus faecalis fabG genes do not encode β-ketoacyl-acyl carrier protein reductases

Enterococcus faecalis encodes three putative Escherichia coli β-ketoacyl-acyl carrier protein (ACP) reductases (FabG). The fabG1 gene is located within the operon that encodes most of the fatty acid synthesis genes, while the putative fabG2 and fabG3 genes are located elsewhere on the chromosome. The genes were tested for the ability to complement the growth of an E. coli fabG(Ts) strain at the non-permissive temperature. Of the three genes, only E. faecalis FabG1 restored growth at high temperature. Moreover, deletion of the E. faecalis fabG1 gene resulted in an auxotrophic strain that required oleic acid for growth, arguing that it encodes the only functional β-ketoacyl-ACP reductase. Growth of this strain in the absence of fatty acid was restored by plasmid-borne fabG1, but not by plasmids encoding either fabG2 or fabG3. Although E. faecalis fabG2 has a putative binding site for the FabT transcription factor at the 5' end of the coding region, expression of a transcriptional fusion with β-galactosidase was unaffected by deletion of fabT or by fatty acid supplementation.