HEXAVALENT CHROMIUM REDUCTION POTENTIAL OF CHROMIUM RESISTANT TANNERY EFFLUENT BACTERIA AND THEIR CONSORTIA

Abstract

Seventeen bacterial isolates from tannery effluent was tested for their ability to resist chromium (Cr) and reduce hexavalent chromium (Cr (VI)). Reduction study was carried out by individual isolates and also by their consortia. All the isolates could resist 25 mg L^-1 chromium. Some isolate was found to resist >90 mg L^-1 chromium. It was evident that isolates those were more resistant to chromium were not necessarily reduce more chromium. Some of these isolates were identified by their 16S rRNA gene sequencing. In general tested isolates showed more reduction potential when Cr added at the starting point of culture propagation than Cr addition after passing exponential phase. Micrococcus sp. showed maximum Cr (VI) reduction ability in both condition. For construction of consortia bacteria were chosen according to their antagonistic and synergistic property. Those isolates exhibiting antagonistic activity to other isolates were excluded from consortia preparation. Two types of consortia were prepared by mixing well grown isolates in equal proportion. Type 1 consortia that was prepared by mixing six most chromium reducing bacteria showed lesser chromium reduction ability than type 2 consortia which was prepared by mixing isolates able to reduce >1500 μg Cr(VI) g^-1 dry cell biomass. It has been observed that, although isolate Micrococcus sp. individually reduce more chromium, consortia including this isolate did not performed well. Other combination of isolates including Micrococcus sp. might be able to reduce more chromium and could be studied further.