Abstract
Every year different industries generate numerous toxic environmental polluting agents throughout the world. Among the polluting agents, chromium (Cr) toxicity is a great concern nowadays. It is continuously released in soil and water, causing environmental and health problems thereby raising several public health issues in developing countries like Bangladesh. The primary goal of this study was to provide a bioremediation option to reduce toxic hexavalent chromium to a less toxic trivalent form by isolating chromium resistant bacteria from Cr contaminated environments. Bacterial isolates were obtained from seven tannery waste samples collected from Hazaribag and Hemayetpur, Savar, Dhaka. Twenty morphologically distinct colonies were screened, of which six showed the highest resistance. These were designated as A1, A2, B1, F1, K1, and P1. Their maximum tolerance to Cr (VI) was determined through growth assays in varying chromium concentrations up to 8000 mg/L on LB agar media. Strains A2 and B1 exhibited the highest resistances to chromium at 7700 mg/L and 7200 mg/L respectively. Bacterial strains A2 and B1 were identified through several biochemical tests and after PCR analysis finally identified as Bacillus sp. and Micrococcus sp. respectively. Their Cr (VI) reduction capabilities were assessed quantitatively using the diphenylcarbazide colorimetric assay. Both strains exhibit approximately 100% reduction of chromium from 100 mg/L concentration to non-toxic form within 48 h using accurate analytical methods. This study demonstrates the isolation of highly chromium-resistant bacteria from tannery waste that can efficiently bioremediate Cr (VI) pollution, thus providing an eco-friendly and cost-effective bioremediation approach.