Lithoautotrophic lifestyle of the widespread genus Roseovarius revealed by physiological and genomic characterization of Roseovarius autotrophicus sp. nov

Lithoautotrophy found in the new isolate expands the ecological role of the globally widespread genus Roseovarius. The genus Roseovarius, a member of the ecologically important Roseobacter-clade, is widespread throughout the world. A facultatively anaerobic lithoautotrophic bacterium (strain SHN287(T)), belonging to the genus Roseovarius, was isolated with molecular hydrogen as an electron donor and nitrate as an electron acceptor from a terrestrial mud volcano. Strain SHN287(T) possessed metabolic features not reported for Roseovarius such as chemolithoautotrophic growth with oxidation of molecular hydrogen or sulfur compounds, anaerobic growth and denitrification. Based on the phenotypic and phylogenetic characteristics, the new isolate is considered to represent a novel species of the genus Roseovarius, for which the name Roseovarius autotrophicus sp. nov. is proposed. The type strain is SHN287(T) (= KCTC 15916(T) = VKM B-3404(T)). An amended description of the genus Roseovarius is provided. Comparison of 46 Roseovarius genomes revealed that (i) a full set of genes for the Calvin-Benson cycle is present only in two strains: SHN287(T) and Roseovarius salinarum; (ii) respiratory H-2-uptake [NiFe] hydrogenases are specific for a phylogenetically distinct group, including SHN287(T)-related strains; (iii) the Sox enzymatic complex is encoded in most of the studied genomes; and (iv) denitrification genes are widespread and randomly distributed among the genus. The metabolic characteristics found in R. autotrophicus sp. nov. expand the ecological role of the genus Roseovarius.