Chromium tolerance and bioremediation potential of the novel Bacillus strains isolated from contaminated effluent water

This study explores the isolation and characterization of chromium-resistant bacterial strains from contaminated effluent water. Among 28 isolates, BHR1 and BHR5, identified as Bacillus thuringiensis and Bacillus pumilus, respectively, using 16S rRNA sequencing, exhibited high Cr (VI) tolerance (510 ppm and 550 ppm). BHR1 and BHR5 reduced Cr (VI) by 88.3% and 76.4% in culture media, and 63.2% and 56.7% in effluent water, respectively, after 120 hr. Chromate reductase assays demonstrated strain-specific detoxification strategies, converting toxic Cr(VI) into less mobile Cr(III) through membrane-bound and extracellular enzymatic pathways. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) analyses showed morphological changes and chromium accumulation in treated cells, indicating effective biosorption and biotransformation. These findings highlight BHR1 and BHR5 as promising agents for bioremediation of chromium-contaminated environments, utilizing biosorption and biotransformation to reduce chromium toxicity.