Deciphering microbial mechanisms for hexavalent chromium reduction in contaminated sediment and paddy soil

Hexavalent chromium [Cr(VI)] is a heavy metal that poses serious environmental risk. Microbial Cr(VI) reduction is a potential remediation approach to reduce the mobility and toxicity of this metal in the environment. However, the diversity and metabolic mechanisms of Cr(VI)-reducing bacteria (CrRBs) remain unknown. In this study, a combination of enrichment incubation and high-throughput sequencing was used to elucidate CrRBs and their associated metabolic pathways for Cr(VI) reduction. Enrichment incubation identified bacterial populations belonging to Cellulomonas, Enterobacter, Rikenellaceae , and Citrifermentans as putative CrRBs in the two Cr(VI)-contaminated sediments and paddy soils as they gradually dominated the microbial community. High-quality metagenome-assembled genomes (MAGs) associated with putative CrRBs were reconstructed, and functional genes responsible for Cr(VI) reduction were detected, suggesting that they are putative CrRBs. This study advances our understanding of CrRBs diversity and their underlying metabolic mechanisms.