Production of indole-3-propanoic acid and 3-(p-hydroxyphenyl)propanoic acid by Clostridium sporogenes: a convenient thin-layer chromatography detection system

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Abstract
Indole-3-propanoic acid (IPA), 3-(p-hydroxyphenyl)propanoic acid (HPPA), and 3-phenylpropanoic acid (PPA) were present in the spent bacterial media of Clostridium sporogenes (20/20 strains) and C. cylindrosporum (1/1 strains), but absent in 32 other clostridial species (74 strains) tested. Both IPA and HPPA (but not PPA) could be readily detected by thin-layer chromatography and p-hydroxybenzaldehyde spray reagent. IPA forms a scarlet complex with p-hydroxybenzaldehyde which shifts to purple and remains stable for up to 6 weeks. IPA can be detected in acidified extracts of C. sporogenes by a simple spot test. The structures of IPA and HPPA were confirmed by nuclear magnetic resonance (nmr) and mass spectroscopy and their formation was detected by the absorbance at 280 nm. Addition of one of the precursor amino acids (L-tryptophan, L-tyrosine, or L-phenylalanine) to the medium greatly enhanced formation of the corresponding deaminated acid and depressed the formation of the other two acids. The products IPA, HPPA, and PPA, at 10−3M, and spent bacterial media were negative in the direct Ames's assay for mutagenicity and noncytotoxic towards MRC-S cells.