Azo dye decolorization by Shewanella aquimarina under saline conditions

Decolorization of azo dyes under saline conditions was studied with Shewanella aquimarina, which demonstrated good growth at up to 7% NaCl. No inhibition on acid red 27 (AR27) decolorization was caused by 1–3% NaCl. Additionally, 14.5% AR27 (0.2 mM) could still be removed in 12 h in the presence of 10% NaCl. The relationship between specific decolorization rate and AR27 concentration followed Michaelis–Menten kinetics (Km = 0.34 mM, Vmax = 6.44 μmol mg cell−1 h−1). Lactate and formate were efficient electron donors for AR27 decolorization. The initial decolorization rate was in direct proportion to biomass concentration (0.18–0.72 g l−1). Compared to NaCl, slighter inhibitive effects were found with Na2SO4 whereas more severe inhibition was caused by NaNO3. Lower NaCl concentration stimulated azoreductase, laccase and NADH–DCIP reductase activities of cell extracts. AR27 decolorization products were found to be aromatic amines, which were less phytotoxic than the untreated dye.