Differentiating Bacillus subtilis incorporates valine and methionine carbon into the backbone of specific fatty acids

Sporulation in Bacillus subtilis has long been a model of cellular differentiation, many aspects of which are well understood. The early stage of this process is of particular interest, especially the interrelationship of regulatory processes with metabolism in response to environmental changes. We analyzed cellular fatty acids as their methyl esters using capillary gas chromatography coupled to mass spectrometry during the transition from vegetative growth to early sporulation phase. Measurement of changes in the content of heavy fatty acid analogs in cultures supplemented with deuterium-labeled valine or methionine, or 13C-labeld valine, showed that label was incorporated into the backbone of 12-methyltridecanoic and 14-methylpentadecanoic acid, in both sporulating and ∆spo0A cultures. These fatty acids were formed starting with isobutyryl-CoA apparently originating only from L-valine-d8 in cultures so supplemented. Our observations indicate that following vegetative growth a pathway exists from certain amino acids into fatty acid methylene groups, evidently passing through propionyl-CoA. This finding has the potential to deepen understanding of the metabolic basis of cellular differentiation and identify new targets for antibiotics. We also observed a significant, continuous increase in the proportion of 13-methyltetradecanoic acid in fatty acids during the same period in which the pre-spore membrane would be formed. ### Competing Interest Statement The authors have declared no competing interest.