Abstract
The biosynthetic mechanism of 6-methyloctanoic and isooctanoic acids, which are present in the amide linkage with the α-amino group of the terminal α, γ-diaminobutyric acid residue of colistin A and B, respectively was investigated. From the isotopic experiments using isoleucine-U-14C, valine-U-14C and acetic acid-2-14C, it was concluded that 6-methyl-octanoic and isooctanoic acids were derived from isoleucine and valine, respectively.
Amino acids pooled in colistin-producing cells grown in the synthetic medium were abundant in isoleucine, valine and leucine, which were probable precursors of the above-described fatty acid components of colistin and cellular fatty acids. On the other hand, 6-methyloctanoic and isooctanoic acids were not found in the cellular fatty acids, while C-15 and C-16 branched chain fatty acids usually found in Bacillus sp. were abundantly contained in the cells, indifferently of an improved capacity of colistin formation.
