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 cel ls grown in either a Casitone-based complex medium or a chemically def ined medium. The cells grown in the complex medium had a much higher c ontent of the abundant branched-chain fatty acid iso-15:0 and several other branched-chain species. The higher branched-chain fatty acid con tent of the cells grown in the complex medium was dependent on the esg locus, which encodes the E1 alpha and E1 beta components of a branche d-chain keto acid dehydrogenase (BCKAD) multienzyme complex involved i n branched-chain fatty acid biosynthesis. Cells grown in the complex m edium were also found to have a higher level of esg transcription and more BCKAD enzyme activity than cells from the chemically defined medi um. The level of esg transcription appears to be an important factor i n the growth medium-dependent regulation of the M. xanthus branched-ch ain fatty acid content.