The decolorisation capacity and mechanism of Shewanella oneidensis MR-1 for Methyl Orange and Acid Yellow 199 under microaerophilic conditions

Shewanella oneidensis MR-1 was found to reach 99.36% and 78.25% decolorisation for Methyl Orange and Acid Yellow 199 in solutions, respectively. The suitable pH range for decolorisation of Methyl Orange and Acid Yellow 199 by S. oneidensis MR-1 was 4.0–7.0 and 6.0–8.0, respectively, The azo dyes' removal by S. oneidensis MR-1 was slightly enhanced by addition of Mg²⁺, but inhibited by Pb²⁺, Cd²⁺, Cu²⁺, Fe³⁺ and Fe²⁺. The enzyme activities of NADH-DCIP reductase and azoreductase were 2.67 and 3.0 times higher, and 1.92 and 2.48 times higher, respectively, in the Methyl Orange treatment and in the Acid Yellow 199 treatment as compared to the control treatment. These findings indicated that the azo dyes' decolorisation by S. oneidensis MR-1 was via reduction mechanism.