Isolation and Molecular Characterization of Chromium Reducing Bacterial Strains from Selected Chrome Contaminated Tannery Waste Sites in Nairobi, Kenya

Abstract

The leather industry a key agricultural sub-sectors in Kenya with a high potential towards contributing to economic growth, creation of wealth and employment. The Kenyan government is currently encouraging the setting up of tanneries to boost processing of leather. However, one cannot wish away the Cr6+ pollution that comes with tanneries. Hexavalent chromium is non-biodegradable and is listed as a Class A human carcinogen by the US Environmental Protection Agency (USEPA). Bioremediation is an evolving and promising technology for treatment of environmental wastes although the application of this technology is uncommon in Kenya and other developing countries. This study aims to isolate Cr6+ resistant bacteria and determine levels of parameters that encourage conversion of Cr3+ to Cr6+. Levels of hexavalent chromium were found to be below NEMA’s allowable limits while total Cr was found to be higher than NEMA’s allowable limits. The percentage of fats was found to be low as well as the pH in the tannery waste. Three isolates capable of reducing Cr6+ were obtained from tannery waste. Isolates CRB01, CRB02 and CRB03 showed the ability to reduce different concentrations of Cr6+ to different extents and exhibited Minimum Inhibitory Concentration levels of 60 mg/L, 80 mg/L and 80 mg/L respectively. Morphological, biochemical and molecular sequence analysis using amplified 16S rRNA genes of these isolates identified CRB01, CRB02 and CRB03 to be Lysinibacillus pakistanensis NCCP 54, Bacillus pumilus SAFR-032 and Bacillus safensis strain NBRC 100820 respectively. This study demonstrates the ability of microorganisms to biodegrade chrome polluted tannery waste. The isolates can be used in the biodegradation of chrome wastes by tanneries which will enable them meet the set maximum