BACKGROUNDEffluents discharged from tannery industry contain significant amount of chromium and synthetic dyes. Both chromium and dyes can be transformed individually into less toxic forms, but very little is known about their simultaneous treatment. The present study was aimed at isolating bacteria capable of removing toxic hexavalent chromium (CrVI) and reactive black-5 azo dye simultaneously in liquid mineral salt medium (MSM). RESULTSAbout 150 bacterial isolates were collected from tannery wastewater and sludge through enrichment of the MSM with CrVI (2mgL(-1)) and reactive black-5 dye (100mgL(-1)) under static (batch) condition. Bacterial strains KI (Pseudomonas putida ) and SL14 (Serratia proteamaculans) were able to reduce simultaneously 93% CrVI and 100% color of reactive black-5 azo dye in 24h at pH 7.2 and 35 degrees C in a batch culture. Individually, 100% reduction of CrVI and reactive black-5 dye was achieved in 12h by strain KI and SL14. CONCLUSIONThese bacterial strains are one of the most efficient bacteria capable of reducing toxic CrVI and synthetic reactive dye simultaneously and could be used for developing bioreactors to treat tannery effluent prior to its discharge into the environment. (c) 2012 Society of Chemical Industry