New PCBs-degrading and hexavalent chromium-resistant bacteria isolated from Lake Mariout, Egypt

Polychlorinated biphenyls (PCBs) are persistent organic pollutants. They were widely used and distributed in the environment causing endocrine disruption, carcinogenicity, and immunotoxicity. The toxic heavy metal, Hexavalent chromium Cr(VI), co-exists with PCBs leading to ecological deterioration and health problems. Thus, bioremediation of the coexisting PCBs and Cr(VI) is essential for the environment and public health. In this study, three bacterial strains identified as Bacillus safensis, Bacillus cereus, and Bacillus vietnamenesis, were isolated. As revealed, various strains belonging to the genus Bacillus degraded PCBs. However, this study can be considered the first report on isolated strains as PCB-degraders that resist Cr(VI) as co-contaminants. All strains had the biphenyl dioxygenase (bphA) gene and grew on PCBs as the sole carbon and energy source and completely remediated 5 mg/l Cr(VI) individually within 24 h. The three isolates showed different response mechanisms to Cr(VI) that enabled Bacillus safensis and Bacillus cereus to grow on PCBs and Cr(VI) as co-contaminants. Bacillus vietnamensis recorded the highest growth on PCBs, but could not grow on PCBs with Cr(VI). Therefore, Bacillus safensis and Bacillus cereus are concluded to be good candidates for bioremediation of PCBs and Cr(VI) as cocontaminants, while Bacillus vietnamensis is more suitable for bioremediation of either PCBs or Cr(VI) individually.