Bactericidal photoproducts in medium containing riboflavin plus aromatic compounds and MnCl2.

Exposure to visible light of growth medium containing riboflavin and indole at low concentrations created photoproducts highly toxic to Salmonella typhimurium and other bacteria. No toxicity was detected in the dark or when either of these two components was present singly. Other aromatic compounds (serotonin, indole-3-acetic acid, indole-3-propionic acid, tryptophan, tyrosine, phenylalanine, and p-aminobenzoic acid) tested in place of indole produced various degrees of toxicity. The presence of MnCl2 significantly enhanced the toxicity. Addition of catalase eliminated the toxicity, indicating an important role for hydrogen peroxide.