3-Methylindole production is regulated in Clostridium scatologenes ATCC 25775

3-Methylindole (3-MI) is a degradation product of l-tryptophan and is both an animal waste malodorant and threat to ruminant health. Culture conditions influencing 3-MI production in Clostridium scatologenes ATCC 25775 were investigated. Extracellular 3-MI levels in cells cultured in brain heart infusion (BHI) medium (pH 7.0) at 33 degrees C and 37 degrees C for 72 h were 907 +/- 38 and 834 +/- 121 mu mol l(-1), respectively. Cells cultured in tryptone-yeast (TY) extract medium at 37 degrees C for 48 h produced 104 +/- 86 mu mol l(-1) 3-MI; however, addition of 1 mmol l(-1) l-tryptophan failed to increase extracellular levels (113 +/- 50 mu mol l(-1) 3-MI). Specific activity of indole acetic acid decarboxylase measured in BHI, TY and TY plus 1 mmol l(-1) tryptophan-grown cells displayed 35-, 33- and 76-fold higher levels than in semi-defined medium-grown cells. When cultured in rich medium, at 33 degrees C or 37 degrees C and pH 7.0, Cl. scatologenes ATCC 25775 optimally produced 3-MI. Addition of l-tryptophan to medium did not lead to significant increases in extracellular 3-MI levels. Whole cell assays indicate growth in rich medium significantly up-regulated 3-MI production. Information presented here may prove useful in understanding what factors influence 3-MI production in malodorous animal wastes.