[Isolation, identification and characterization of a broad-spectrum azo-reducing Citrobacter strain AzoR-2]

A broad-spectrum azo-reducing bacterial strain, AzoR-2, was isolated from a active-sludge of textile-printing wastewater treatment plant and the strain was identified and characterized. This strain was identified as Citrobacter sp. according to its morphological, physiobiochemical characteristics and analysis of its 16S rDNA and beta-lactamase gene sequence. Studies showed that strain AzoR-2 was able to reduce various azo dyes with several organic substances and H2 as electron donor and the electrons for azoreduction came from primary electron donor. The azoreduction by strain AzoR-2 was inhibited strongly by O2. The enzyme system for azoreduction of strain AzoR-2 was located on cellular membrane, suggesting that the microbial azoreduction is linked to electron transport chain. Azoreduction by strain AzoR-2 was occurred in the range of alkaline pH at the temperature range 20 - 40 degrees C with optimum pH 7.5 and 35 degrees C. Azo-reducing Citrobacter bacterium may play important roles in bioremediation of the environment contaminated by azo dyes and in the decolorization of textile-printing wastewater.