During a screening of sulphur-oxidizing bacteria from different Spanish soils, a strain designated AFSI2.2 T was isolated from the rhizosphere soil of a mulberry plant thriving in a sulphur-rich environment. Cells of this strain were Gram-stain-negative motile rods with flagella. Its taxonomic classification was determined through a polyphasic approach. Phylogenetic analysis of the 16S rRNA gene revealed that strain AFSI2.2 T shares high similarity (99.64%) with certain Variovorax species, suggesting that the isolate belongs to this genus. Whole-genome phylogeny showed that the novel strain forms a distinct lineage within the genus Variovorax . Whole-genome analysis of AFSI2.2 T exhibited average nucleotide identity values of 78.37–89.63% and digital DNA–DNA hybridization values of 21.90–38.90% with closely related Variovorax species, both below the established thresholds for species delineation. The predominant cellular fatty acids of strain AFSI2.2 T were C 16 : 0 , Summed Feature 3 (C 16 : 1 ω 6 c and/or C 16 : 1 ω 7 c ) and Summed Feature 8 (C 18 : 1 ω 7 c and/or C 18 : 1 ω 6 c ). Apart from the ability of oxidizing inorganic sulphur compounds, AFSI2.2 T presented further in vitro plant growth-promoting (PGP) activities such as production of indole-3-acetic acid and siderophores and 1-aminocyclopropane-1-carboxylate deaminase activity. Genes associated with these PGP traits, as well as with cytokinin and gamma-aminobutyric acid biosynthesis, were identified in the AFSI2.2 T genome, supporting its potential as a PGP bacterium. In conclusion, phylogenetic, genomic, phenotypic and chemotaxonomic analyses support the classification of the isolate as a novel species within the genus Variovorax , for which the name Variovorax palleresanus sp. nov. is proposed. The type strain is AFSI2.2 T (=CECT 31217 T =CIP 112526 T ).
Comas et al. (Mon,) studied this question.