Microbial transformation rates of AZO and triphenylmethane dyes

Abstract

Abstract Using field-collected and laboratory cultures, bacterial transformation rates for one azo and two triphenylmethane dyes were studied as a means of assessing the potential degradation of these compounds in aquatic environments. Transformation was measured as loss of color by spectrophotometry, and first- and second-order transformation rate coefficients were determined. Second- order coefficients (kb) were based on total colony-forming units (CFU) of bacteria in batch cultures. Percentages of total bacteria that transformed the dyes were determined by isolating bacterial colonies from field-collected samples and testing the isolates for the capacity to transform the dyes in dilute nutrient medium. The azo dye, Acid Orange 6, was not transformed under the aerobic conditions of these studies. Basic Violet 1 was transformed and k1 values ranged from -0.003 to -0.023 h−1, with a mean (kb) of 3.5 × 10−14L CFU−1 h−1. Basic Violet 3 also was transformed and k1 values ranged from -0.002 to -0.012 h−1, with a mean kb of 2.8 × 10−14 L CFU−1 h−1. The percentage of transformer bacteria for Basic Violet 1 ranged from 6 to 28%, with a mean of 13.5%, and the range for Basic Violet 3 was 0 to 24%, with a mean of 8.32%. Therefore, the triphenylmethane dyes were transformed at similar rates, and similar fractions of the total bacterial populations were involved in the transformation.