Physiological and Genomic Characterization of Two Novel Bacteroidota Strains Asinibacterium spp. OR43 and OR53

Abstract

Asinibacterium spp. (Family Chitinophagaceae, Phylum Bacteroidota) are abundant in environments contaminated with heavy metals. We characterized the physiology and genome of two Asinibacterium species to elucidate their ability to survive and grow at ambient conditions in the uranium-contaminated environments. Both strains were able to grow at pH 4.5 or 50 mM nitrate under aerobic conditions and did not grow with alternative electron acceptors under anaerobic conditions. Asinibacterium sp. OR53 grew in medium with uranium concentrations up to 300 µM uranium while Asinibacterium sp. OR43 could not grow at uranium concentrations > 200 µM. Elemental mapping using energy dispersive X-ray spectroscopy indicate that uranium co-localized with phosphorus-containing compounds on the cell surface. Genes potentially encoding resistance mechanisms to a variety of heavy metals were detected in the genomes of both strains. The localization of uranium and missing acidic and alkaline phosphatase genes in the genome suggest that biosorption of uranium to the lipopolysaccharide layer might be the mechanism of uranium resistance. In summary, Asinibacterium spp. OR43 and OR53 are physiologically similar to closely related strains within the Chitinophagaceae family but are uniquely acclimated to the presence of uranium and other heavy metals prevalent in the subsurface at Oak Ridge, Tennessee.