Reduction of sulphonated water-soluble azo dyes by micro-organisms from human faeces

Abstract

The anaerobic reduction of four currently used sulphonated azo dyes, amaranth, sunset yellow, new coccine and tartrazine, has been studied by incubating bacterial suspensions isolated from human faeces and from the intestinal contents of rats with 50 μ m concentrations of the dyes in phosphate buffer, pH 7·4, using nitrogen as the gaseous phase. Human faecal flora from five male volunteers reduced the four dyes at mean rates of 38·4, 25·1, 18·2 and 6·5 nmol/mg protein/hr, respectively. For each dye, there was little difference in the reduction rates effected by the bacterial suspensions from the different individuals in spite of a considerable divergence in age, daily diets and living circumstances. These reductions proceeded at an approximately constant rate until the colours had faded almost completely. The rates of amaranth and sunset yellow reduction by rat-gut flora were four to five times higher than those by human faecal flora, but there was no significant difference between the two types of bacterial suspension in the reduction rates for new coccine and tartrazine.