Biochemical and Genetic Characterization of an Auxotroph of Bacillus subtilis Altered in the Acyl-CoA:Acyl-Carrier-Protein Transacylase

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Abstract
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 Jaline; 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 major constituents in membrane lipids. Other results suggest that the acyl‐CoA:acyl‐carrier‐protein transacylase 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.