Defining the Enterococcus faecalis Fatty Acid Kinase System of Exogeneous Fatty Acid Utilization.

Phospholipid synthesis in Firmicute bacteria differs markedly from that of the paradigm Escherichia coli pathway in that acyl phosphates are a key intermediate. Acyl phosphates are required for the first acylation step of the phospholipid synthesis pathway catalyzed by the PlsY acyltransferase and are synthesized by two different pathways. In the absence of exogenous fatty acids, de novo synthesized acyl-acyl carrier protein (ACP) species are converted to acyl phosphates by the PlsX acyl-ACP: phosphate acyltransferase, which transfers the acyl chain from ACP to inorganic phosphate. When exogenous fatty acids are present, these acids are converted to acyl phosphates by the FakAB fatty acid kinase and can be converted to acyl-ACPs via PlsX. The active kinase is composed of the ATP-requiring FakA subunit and a FakB fatty acid binding protein, which acts to present the fatty acid carboxyl group to the FakA kinase active site. In all Firmicutes examined to date, multiple FakB species are present. Staphylococcus aureus has two, whereas Streptococcus pneumoniae has three, whereas Enterococcus faecalis encodes four FakB proteins. We report the fatty acid preferences of these proteins obtained by use of mutant strains lacking each FakB or all possible combinations of three FakB deletions, plus a strain lacking all four FakB proteins. We also report the phenotype of a ∆fakA strain and of a ∆fakA bypass suppressor mutant, plus the first indication of a role of the FakAB pathway in recycling of acyl chains.