Growth medium-dependent regulation of Myxococcus xanthus fatty acid content is controlled by the esg locus

We compared the cellular fatty acid profiles of Myxococcus xanthus cells grown in either a Casitone-based complex medium or a chemically defined medium. The cells grown in the complex medium had a much higher content of the abundant branched-chain fatty acid iso-15:0 and several other branched- chain species. The higher branched-chain fatty acid content of the cells grown in the complex medium was dependent on the esg locus, which encodes the E1α and E1β components of a branched-chain keto acid dehydrogenase (BCKAD) multienzyme complex involved in branched-chain fatty acid biosynthesis. Cells grown in the complex medium were also found to have a higher level of esg transcription and more BCKAD enzyme activity than cells from the chemically defined medium. The level of esg transcription appears to be an important factor in the growth medium-dependent regulation of the M. xanthus branched- chain fatty acid content.