PNNL

Abstract

Members of the genus Exiguobacterium are found in diverse environments from marine and fresh waters to permafrost and hot springs. As such, they can grow at a wide range of temperature, pH, salinity, and heavy-metal concentrations. Here we propose Exiguobacterium pavilionensis sp. nov. strain RW2 using phylogenetic, biochemical, and genome analyses. Isolated from a cold freshwater microbialite in Pavilion Lake, British Columbia, E. pavilionensis can grow between 4 and 50 °C, the broadest temperature range reported for the genus. The three Mbp circular genome includes a large set of core genes associated with stress responses to temperature, salinity and heavy metals that are conserved among all sequenced strains of Exiguobacterium spp., and which may explain their distribution across such a wide range of ecosystems. We also nominate potential pathways involved in carbonate precipitation (and therefore microbialite formation), as well as carotenoid biosynthesis that could lend the characteristic orange color to members of the genus. The unexpectedly high thermal tolerance of this cold-water bacterium, as well as its latent flagellum synthesis operons, suggest that this species may have had its evolutionary origins in a much warmer environment in which motility was important. These results provide further insight into the potential of Exiguobacterium to exploit a wide range of environmental conditions.