Achromobacter seleniivolatilans sp. nov. and Buttiauxella selenatireducens sp. nov., isolated from the rhizosphere of selenium hyperaccumulator Cardamine hupingshanesis

Two Gram-stain-negative bacterial strains, R39^T and R73^T, were isolated from the rhizosphere soil of the selenium hyperaccumulator Cardamine hupingshanesis in China. Strain R39^T transformed selenite into elemental and volatile selenium, whereas strain R73^T transformed both selenate and selenite into elemental selenium. Phylogenetic and phylogenomic analyses indicated that strain R39^T belonged to the genus Achromobacter, while strain R73^T belonged to the genus Buttiauxella. Strain R39^T (genome size, 6.68 Mb; G+C content, 61.6 mol%) showed the closest relationship to Achromobacter marplatensis LMG 26219^T and Achromobacter kerstersii LMG 3441^T, with average nucleotide identity (ANI) values of 83.6 and 83.4 %, respectively. Strain R73^T (genome size, 5.22 Mb; G+C content, 50.3 mol%) was most closely related to Buttiauxella ferragutiae ATCC 51602^T with an ANI value of 86.4 %. Furthermore, strain A111 from the GenBank database was found to cluster with strain R73^T within the genus Buttiauxella through phylogenomic analyses. The ANI and digital DNA–DNA hybridization values between strains R73^T and A111 were 97.5 and 80.0% respectively, indicating that they belong to the same species. Phenotypic characteristics also differentiated strain R39^T and strain R73^T from their closely related species. Based on the polyphasic analyses, strain R39^T and strain R73^T represent novel species of the genera Achromobacter and Buttiauxella, respectively, for which the names Achromobacter seleniivolatilans sp. nov. (type strain R39^T=GDMCC 1.3843^T=JCM 36009^T) and Buttiauxella selenatireducens sp. nov. (type strain R73^T=GDMCC 1.3636^T=JCM 35850^T) are proposed.