Indoleacetic Acid and Growth of Bacteria with Varying Requirements for Nicotinic Acid and Tryptophane

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Abstract
A number of organisms whose tryptophane and nicotinic acid requirements are known were tested for possible inhibition by indoleacetic acid and reversal by nicotinic acid and tryptophane in chemically defined media. Escherichia coli, Lacto-bacillus arabinosus 17-5, L. casei, Streptococcus faecalis R, and Aerobacter aerogenes were inhibited by concs. of indoleacetic acid of 1 mg./ml. Occasionally slight inhibitions were noted at 0.1 mg./ml. levels. No significant relief of inhibition was obtained with either nicotinic acid or tryptophane. Staphylo-coccus aureus and Mycobacterium tuberculosis (607) were not inhibited by indoleacetic acid at the concs. studied. Fairly consistent stimulation at 0.1 mg./ml. levels of indoleacetic acid was obtained with L. arabinosus and L. casei in the presence of limiting concs. of tryptophane. It is concluded that the indoleacetic acid-nicotinic acid antagonism which has been observed in rats is not an invariably occurring biological phenomenon.

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