Serpentinimonas gen. nov., Serpentinimonas raichei sp. nov., Serpentinimonas barnesii sp. nov. and Serpentinimonas maccroryi sp. nov., hyperalkaliphilic and facultative autotrophic bacteria isolated from terrestrial serpentinizing springs

Three highly alkaliphilic bacterial strains designated as A1(T), H1(T) and B1(T) were isolated from two highly alkaline springs at The Cedars, a terrestrial serpentinizing site. Cells from all strains were motile, Gram-negative and rod-shaped. Strains A1(T), H1(T) and B1(T) were mesophilic (optimum, 30 °C), highly alkaliphilic (optimum, pH 11) and facultatively autotrophic. Major cellular fatty acids were saturated and monounsaturated hexadecenoic and octadecanoic acids. The genome size of strains A1(T), H1(T) and B1(T) was 2 574 013, 2 475 906 and 2 623 236 bp, and the G+C content was 66.0, 66.2 and 66.1 mol%, respectively. Analysis of the 16S rRNA genes showed the highest similarity to the genera Malikia (95.1–96.4 %), Macromonas (93.0–93.6 %) and Hydrogenophaga (93.0–96.6 %) in the family Comamonadaceae . Phylogenetic analysis based on 16S rRNA gene and phylogenomic analysis based on core gene sequences revealed that the isolated strains diverged from the related species, forming a distinct branch. Average amino acid identity values of strains A1(T), H1(T) and B1(T) against the genomes of related members in this family were below 67 %, which is below the suggested threshold for genera boundaries. Average nucleotide identity by blast values and digital DNA–DNA hybridization among the three strains were below 92.0 and 46.6 % respectively, which are below the suggested thresholds for species boundaries. Based on phylogenetic, genomic and phenotypic characterization, we propose Serpentinimonas gen. nov., Serpentinimonas raichei sp. nov. (type strain A1(T)=NBRC 111848(T)=DSM 103917(T)), Serpentinimonas barnesii sp. nov. (type strain H1(T)= NBRC 111849(T)=DSM 103920(T)) and Serpentinimonas maccroryi sp. nov. (type strain B1(T)=NBRC 111850(T)=DSM 103919(T)) belonging to the family Comamonadaceae . We have designated Serpentinimonas raichei the type species for the genus because it is the dominant species in The Cedars springs.