Biochemical and genetic characterization of an auxotroph of Bacillus subtilis altered in the Acyl-CoA:acyl-carrier-protein transacylase.

We have analyzed a mutation of Bacillus subtilis (bfmB) that results in an acyl-CoA:acyl-carrier-protein transacylase with low affinity for branched acyl-CoA substrates; it maps in the acf-hisH region of the chromosome. The aceA mutation, present in the parent of the bfmB mutant, causes a deficiency in pyruvate dehydrogenase and maps in the pycA-pyrA region. Strains carrying the bfmB mutation synthesize branched-chain fatty acids at a rate sufficient for normal growth only if branched acyl-CoA precursors are present in the medium. They grow well if the medium is supplemented with 0.1 mM 2-methylbutyrate, isobutyrate or isovalerate, or with 1.0 mM isoleucine or valine; leucine does not support growth. Growth supported by valine and isoleucine is inhibited by butyrate and other straight short-chain fatty acids at concentrations (0.1 mM) which do not inhibit growth of the standard strain; the inhibition is prevented by short branched fatty acids which are converted to long-chain fatty acids appearing as activity of B. subtilis is controlled by separate enzymatic sites for the acyl-CoA precursors of branched and straight-chain fatty acids. Whether these sites are contained in one or two enzymes is not known.