The Two Acyl Carrier Proteins of Enterococcus faecalis Have Nonredundant Functions.

Enterococcus faecalis encodes two proteins, AcpA and AcpB, having the characteristics of acyl carrier proteins (ACPs). We report that the <i>acpA</i> gene located in the fatty acid synthesis operon is essential for fatty acid synthesis and the Δ<i>acpA</i> strain requires unsaturated fatty acids for growth. The Δ<i>acpA</i> strain could be complemented by a plasmid carrying a wild-type <i>acpA</i> gene, but not by a plasmid carrying a wild-type <i>acpB</i> gene. Substitution of four AcpA residues for those of AcpB resulted in a protein that modestly complemented the Δ<i>acpA</i> strain and restored fatty acid synthesis, although the acyl chains synthesized were unusually short. <b>IMPORTANCE</b> Enterococcus faecalis, as well as related species, has two genes-<i>acpA</i> and <i>acpB</i>-encoding putative acyl carrier proteins (ACPs). It has been assumed that AcpA is essential for fatty acid synthesis whereas AcpB is involved utilization of environmental fatty acids. We report here the first experimental test of the essentiality of <i>acpA</i> and show that it is indeed an essential gene that cannot be replaced by <i>acpB</i>.