Variovorax palleresanus sp. nov., a novel plant growth-promoting rhizobacterium isolated from sulphur-rich soil in Spain

Identifier:  imarina:9523796

Handle: https://hdl.handle.net/20.500.11797/imarina9523796

Authors:  Comas, Cristina; Peix, Alvaro; Garcsa-Seco, Daniel; Arola-Arnal, Anna; Brocal, Jonatan C Campillo-

Abstract:
During a screening of sulphur-oxidizing bacteria from different Spanish soils, a strain designated AFSI2.2T 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 AFSI2.2T 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 AFSI2.2T 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 AFSI2.2T were C16:0, Summed Feature 3 (C16: 1 omega 6c and/or C16: 1 omega 7c) and Summed Feature 8 (C18:1 omega 7c and/or C18:1 omega 6c). Apart from the ability of oxidizing inorganic sulphur compounds, AFSI2.2T 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 gammaaminobutyric acid biosynthesis, were identified in the AFSI2.2T 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 AFSI2.2T (=CECT 31217T=CIP 112526T).