The bacterial biogenesis of isobutyraldoxime O-methyl ether, a novel volatile secondary metabolite

Production of the volatile metabolite, isobutyraldoxime O-methyl ether (IBME) by a Moraxella-like organism NCIB 11650 was investigated under a variety of environmental conditions using gas chromatography. Under aerobic conditions up to 10 micrograms IBME ml-1 was produced on mineral salts media containing 0.5% (w/v) glucose or succinate as sole C source with 0.1% (w/v) NH4Cl as sole N source. Exogenous L-valine further stimulated IBME formation up to 25 micrograms ml-1 but supplementation of the medium with D-isomer or other amino acids had little effect on IBME production and did not lead to the appearance of analogues of IBME. Trapping experiments using [14C]valine confirmed that IBME was derived from this amino acid. Several other bacterial species examined, e.g. Alcaligenes sp. NCIB 11652, another Moraxella-like organism NCIB 11651 and Pseudomonas sp. NCIB 11653 also produced IBME under similar conditions. The Alcaligenes strain synthesized up to 20 micrograms ml-1 in the absence of valine and up to 90 micrograms ml-1 in its presence. The product of IBME exhibited many features characteristic of the formation of a secondary metabolite. Thus biosynthesis was confined to a narrower range of temperature than cell division, was almost completely suppressed by 300 mM-phosphate and was inhibited by high concentrations of readily utilizable C sources. Although IBME synthesis in the Moraxella-like organism NCIB 11650 appeared to be growth-related, its formation by both the Alcaligenes sp. and the Moraxella-like organism NCIB 11651 was delayed until the late-exponential and early-stationary phases of growth. The biological significance of this novel class of secondary metabolite is discussed and a possible biosynthetic route proposed.