Enrichment and characterization of an effective hexavalent chromium-reducing microbial community YEM001.

Chromium (Cr) is one of the most widely used heavy metals in industrial processes, resulting in water and soil pollution that seriously threaten environmental safety. In this paper, we have directionally enriched a Cr(VI)-reducing bacterial community YEM001 from no-Cr(VI) polluted pond sedimental sludge by selectively growing it in Cr(VI)-containing media. This community could effectively reduce Cr(VI) in laboratory rich media containing different concentrations of Cr(VI), such as 61% reduction at 435 mg/L Cr(VI), 85% reduction at 355 mg/L Cr(VI), and complete reduction at 269 mg/L Cr(VI) in 93.5 h. It was also able to completely reduce 100 mg/L and 300 mg/L Cr(VI) in landfill leachate and natural sludge in 48 h, respectively. Optimal pH for Cr(VI) reduction of the YEM001 is between 7 and 8 and the best efficiency for Cr(VI) reduction occurs at 30 °C. Metagenomic data demonstrated that the YEM001 community was composed of multiple bacteria, including well-known Cr(VI)-reducing bacteria and non-Cr(VI)-reducing bacteria. Delftia, Comamonas, Alicycliphilus, Acidovorax, Bacillus, and Clostridioides account for 83% of total community abundance. The stability of the composition of the YEM001 community and its Cr(VI)-reducing activity allows for its application in bioremediation of environmental Cr(VI) pollution.