Nutrition of Myxococcus xanthus FBa and some of its auxotrophic mutants.

A defined medium containing 15 amino acids plus salts was used to study the nutrition of Myxococcus xanthus FBa. The amino acids phenylalanine, leucine, isoleucine, valine, and methionine were essential for growth, whereas glycine, proline, asparagine, alanine, lysine, and threonine stimulated growth. An unusual pattern of requirement was found in the aromatic amino acids. Phenylalanine was essential and served as the precursor of tyrosine. Growth in the absence of tryptophan was adaptive, with cells reaching a growth rate equal to that of controls after a lag of about a week. (14)C-labeled ribose and glucose were not appreciably metabolized. Auxotrophs requiring purines and pyrimidines were isolated and were used to study the fate of externally supplied nucleic acid derivatives. Appropriate mutants could satisfy their requirements with free bases, nucleosides, and nucleotides, and could hydrolyze nucleic acids and use the products. However, studies using (14)C-ribose-labeled uridine (isolated from a Salmonella typhimurium pyrimidine auxotroph) showed that externally supplied nucleic acid derivatives were incorporated almost solely into the nucleic acids of the myxobacters, with little used either for energy-yielding oxidations or other cell anabolism.