Diversity of hexavalent chromium-reducing bacteria and physicochemical properties of the Kanpur tannery wastewater

The tannery effluent sample was collected from a tannery located in Jajmau area of Kanpur, India and subjected to physicochemical analysis. The tannery effluent was brownish in color with a foul odor. It was alkaline in nature and characterized by high biological oxygen demand (BOD), chemical oxygen demand (COD), total solids (TS), total dissolved solids (TDS) and high amounts of chromium. Total eighteen chromium resistant bacteria were isolated from the tannery effluent sample. Based on the 16S rRNA gene sequencing and phylogenetic analysis, these eighteen bacteria belong to seven different genera including Bacillus, Pseudomonas, Kocuria, Cellulosimicrbium, Klebsiella, Microbacterium, Brucella. The members of genus Bacillus constitute 28% of total chromium transforming isolates; followed by members of genus Microbacterium (17%) Brucella (17%), Pseudomonas (11%), Cellulosimicrobium (11%), Kocuria (11%) and Klebsiella (5%). Furthermore, all eighteen bacteria were screened for their ability to reduce hexavalent chromium with increasing concentrations (600–1200 ppm) of potassium dichromate. Results showed that one bacterium, Bacillus licheniformis strain KNP exhibited hexavalent chromium reduction up to concentrations of 1000 ppm. This bacterium was selected for further study.