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A new mutant of Bacillus subtilis is described lacking the activity of branched chain α-keto acid dehydrogenase. The mutant requires short branched chain fatty acids biosynthetically related to leucine, isoleucine, and valine for growth. Long branched chain fatty acids derived from these short molecules can also serve as growth factors. One type of branched chain fatty acid, however, is sufficient to support growth of the mutant at 37°, although wild type cells of B. subtilis normally contain three different pairs of long branched chain fatty acids. Therefore, this mutant allows extensive alterations of the fatty acid composition in membranes of B. subtilis. Straight chain fatty acids do not support growth. Out of a series of tested analogues, 2-methylvalerate, 2-ethyl butyrate, and trimethylacetate were found to be active in vivo as primer molecules of branched chain fatty acid biosynthesis. The chain-lengthened products derived from these primer substrates were characterized by mass spectrometry.
Willecke et al. (Wed,) studied this question.