Investigation of the indigenous bacterial communities in Vanadium (V) tailing and exploration of their metabolic potentials for V(V) reduction

Vanadium (V) is an important metal with critical industrial and medical applications. Elevated V contamination, however, can be a threat to environmental and human health. Microorganisms can reduce the more toxic and mobile VV to the less toxic and immobile VIV, which could be a detoxification and energy metabolism strategy adopted by V reducing bacteria (VRB). The limited understanding of microbial responses to V contamination and the mechanisms for V reduction, however, hampers our capability to attenuate V contamination. This study focused on determining the microbial responses to elevated V concentration and the mechanisms of VV reduction in a V tailing. The bacterial communities were characterized and compared between the V tailing and the less contaminated soils adjacent to the tailing. Further, VV-reducing anaerobic enrichment cultures indicated that bacteria associated with Polaromonas, a genus belonging to the family Burkholderiaceae, were potentially responsible for VV reduction. Metagenomic-binning, with a focus on the putative VRB Polaromonas, was performed to reveal the metabolic potentials of these key microorganisms. Retrieved metagenome assembled genomes (MAGs) suggested that the Polaromonas spp. encoded genes (cymA, omcA, and narG) were potentially responsible for VV reduction. Additionally, Polaromonas may be versatile in their ability to use both organic and inorganic electron donors. Collectively, it is proposed that the putative VRB Polaromonas spp. may use one of the two pathways for VV reduction: one catalyzed by OmcA and CymA; the other one catalyzed by NarG. In addition, their metabolic versatility in utilizing a wide variety of electron donors may be important for their ability to flourish in the V tailings.