ISOLATION AND MOLECULAR CHARACTERIZATION OF CHROMIUM-REDUCING BACTERIAL STRAINS FROM CHROME-CONTAMINATED TANNERY WASTE SITES IN KARACHI, PAKISTAN

Abstract

The leather industry represents a key agricultural sub-sector in Pakistan with significant potential to contribute to economic growth, wealth creation, and employment. The Pakistani government actively encourages tannery establishment to boost leather processing, though this comes with unavoidable environmental challenges from Cr⁶⁺ pollution. Hexavalent chromium is non-biodegradable and classified as a Class A human carcinogen by the US Environmental Protection Agency (USEPA). While bioremediation offers promise for treating such hazardous waste, this technology remains underutilized in Pakistan and other developing nations. This study isolated Cr⁶⁺-resistant bacteria from tannery waste in Karachi and evaluated parameters influencing chromium reduction. Analytical results revealed hexavalent chromium levels below Pakistan EPA's allowable limits, while total chromium exceeded regulatory thresholds. The tannery waste exhibited low fat content and acidic pH. Three bacterial isolates (CRB01, CRB02, CRB03) demonstrating Cr⁶⁺ reduction capability were obtained, showing varying reduction efficiencies across different chromium concentrations with minimum inhibitory concentrations of 60 mg/L, 80 mg/L, and 80 mg/L respectively. Through morphological, biochemical, and molecular characterization via 16S rRNA gene sequencing, the isolates were identified as Lysinibacillus pakistanensis NCCP-54 (CRB01), Bacillus pumilus SAFR-032 (CRB02), and Bacillus safensis NBRC 100820 (CRB03). This research confirms the capacity of native Pakistani microorganisms to bioremediate chromium-contaminated tannery waste, providing sustainable solutions to help tanneries meet environmental compliance standards through biodegradation of hazardous chrome wastes.