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 μg 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 μg 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 μg ml−1 in the absence of valine and up to 90 μg ml−1 in its presence.
The production 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.
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