Gelidimonas denitrificans gen. nov., sp. nov., and Gelidimonas diazotrophica sp. nov. psychrophilic bacteria involved in the nitrogen cycle in tundra soils of South Spitsbergen

Two Gram-negative, psychrophilic, denitrifying bacterial strains, D2 and D11, were isolated from ornithogenic soil collected at a breeding colony of the marine bird Alle alle on Spitsbergen Island, Svalbard (Norway; High Arctic). Complete genome sequencing revealed that each strain possesses a single circular chromosome (3.83 Mbp and 3.63 Mbp, respectively) with similar GC content (55.3% and 55.5%), as well as plasmids – one shared by both strains (26.3 kb) and one unique to strain D11 (16.3 kb). Despite their striking genetic similarity, the two strains exhibit distinct physiological characteristics. Strain D2 is a facultative chemolithoautotroph capable of using hydrogen as an energy source and assimilating carbon dioxide and dinitrogen, whereas strain D11 displays a strictly heterotrophic lifestyle. Although the 16S rRNA genes of D2 and D11 share a high level of sequence identity (99.6%), whole-genome comparative analyses, including digital DNA–DNA hybridization (dDDH) and average nucleotide identity (ANI), indicated that they represent two distinct species within the family Oxalobacteraceae (class Betaproteobacteria). Core proteome-based phylogenetic analysis of Oxalobacteraceae unambiguously placed both strains within the family; however, neither clustered with any currently described genus. We therefore propose that these strains represent a novel genus, Gelidimonas gen. nov., with type species Gelidimonas denitrificans sp. nov. (type strain D11T) and a second species Gelidimonas diazotrophica sp. nov. (type strain D2T).