SUMMARY: When is grown on any one of a variety of defined culture media, an antibiotic metabolic product, alternaric acid, accumulates in the medium. The quantity of alternaric acid produced is directly related to the amount of mycelium formed; good yields of alternaric acid are obtained on any medium which supports good growth. Optimal media contain high concentrations (7·5% (w/v) or more) of sucrose, which is better than any other carbon source tested. Nitrogen may be supplied as nitrate or casein hydrolysate; ammonia as nitrogen source is equally good when supplied in conjunction with a suitable organic acid, 0·25% (w/v) acetic acid being particularly favourable.

The antibiotic is isolated from optimal media by extraction with chloroform after adjustment to pH 3·5; the solvent is then evaporated and the residue recrystallized from benzene. Yields of the order of 150 mg./l. are obtained.

Alternaric acid is not antibacterial. Germination of spores of some fungi (e.g. ) is prevented by 1 μg./ml. or less of alternaric acid. Germination of spores of other fungi (e.g. ) is unaffected by concentrations as high as 100 μg./ml., but extension of the germ-tubes is markedly retarded shortly after germination. This secondary retarding effect may be produced by very low concentrations; 0·01 μg./ml. produced an obvious effect with .


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