Reduction of seven azo dyes (amaranth, Ponceau SX, Allura Red, Sunset Yellow, tartrazine, Orange II, and methyl orange) was carried out by cell suspensions of predominant intestinal anaerobes. It was optimal at pH 7.4 in 0.4 M phosphate buffer and inhibited by glucose. Flavin mononucleotide caused a marked enhancement of azo reduction by Bacteroides thetaiotaomicron. Other electron carriers, e.g., methyl viologen, benzyl viologen, phenosafranin, neutral red, crystal violet, flavin adenine dinucleotide, menadione, and Janus Green B can replace flavin mononucleotide. These data suggest that an extracellular shuttle is required for azo reduction. Azo dyes are widely used as colorants in foods such as soft drinks, candy, hot dogs, ice cream, and cereals and in drugs, cosmetics, etc. The extent of such use is related to the degree of industrialization of the society. For example, approximately 1.5 x 106 pounds (0.68 x 106 kg) of the dye amaranth were used each year in over 60 countries (9). It has been calculated that the annual American per capita consumption of these compounds is close to 5 pounds, which is twice the intake of 20 years ago (22).

Seventeen commonly used dyes and 16 of their metabolites or derivatives were tested in the Salmonella-mammalian microsome mutagenicity test. Mutagens active with and without added Aroclor-induced rat liver microsome preparations (S9) were 3-aminopyrene, lithol red, methylene blue (USP), methyl yellow, neutral red, and phenol red. Those mutagenic only with S9 activation were 4-aminopyrazolone, 2,4-dimethylaniline, N,N-dirnethyl-p-phenylenediamine, methyl red, and 4-phenyl-azo-1-naphthylamine. Orange II was mutagenic only without added S9. Nonmutagenic azo dyes were allura red, amaranth, ponceau R, ponceau SX, sunset yellow, and tartrazine. Miscellaneous dyes not mutagenic were methyl green, methyl violet 2B, and nigrosin. Metabolites of the azo dyes that were not mutagenic were 1-amino-2-naphthol hydrochloride, aniline, anthranilic acid, cresidine salt, pyrazolone T, R-amino salt (1-amino-2-naphthol-3,6disulfonic disodium salt), R-salt, Schaeffer's salt (2-naphthol-6-sulfonic acid, sodium salt), sodium naphthionate, sulfanilamide, and sulfanilic acid. 4-Amino-inaphthalenesulfonic acid sodium salt was also not mutagenic. Fusobacterium sp. 2 could reductively cleave methyl yellow to N,N-dimethyl-p-phenylenediamine which was then activated to a mutagen.

No abstract

Twenty-three strains of intestinal anaerobes obtained from two laboratories were examined for indole production from tryptophan. Among the 23 isolates tested, three of Bacteroides fragilis thetaiotaomicron and one Citrobacter sp. were indole positive. The tryptophanase of the indole-positive strains of intestinal anaerobes was inducible by tryptophan and was susceptible to glucose repression. The products of tryptophanase activity were formed in stoichiometric amounts by dialyzed, freshly prepared extracts. The tryptophan concentration and tryptophanase activity in feces from rats on an all-meat diet were significantly higher than those in feces from rats on a normal diet. The results indicated that the higher tryptophanase activity in the feces of rats fed an all-meat diet is due to the inducibility of this enzyme by tryptophan and is not due to any inhibitor in the feces of rats on a normal diet. The results also suggested that a population with a diet rich in meat has a greater chance for exposure to possible carcinogens such as indole and other tryptophan metabolites. This agrees with the hypothesis, based on epidemiologic data, that a high intake of meat may be related to the development of colon cancer in man.

Indoleacetic acid was produced from tryptophan by only three of 23 intestinal anaerobes studied. Evidence is presented to show that the formation of indoleacetic acid proceeds through the intermediate, indolepyruvic acid, via transamination with alpha-ketoglutarate rather than by tryptamine pathway.