Segnochrobactrum spirostomi gen. nov., sp. nov., isolated from the ciliate Spirostomum yagiui and description of a novel family, Segnochrobactraceae fam. nov. within the order Rhizobiales of the class Alphaproteobacteria

Int J Syst Evol Microbiol. 2020 Feb;70(2):1250-1258. doi: 10.1099/ijsem.0.003907.


A bacterial strain, designated Sp-1T, was isolated from the heterotrich ciliate Spirostomum yagiui collected from a reservoir located in Ulsan, Republic of Korea. Cells of Sp-1T were Gram stain-negative, rod-shaped, non-spore-forming, non-motile and contained poly-β-hydroxybutyrate granules. Phylogenetic analyses based on 16S rRNA gene sequences indicated that Sp-1T constituted a distinct phylogenetic lineage within different families in the order Rhizobiales with a pairwise sequence similarity of 95 % to the species of the genus Ochrobactrum: Ochrobactrum anthropi ATCC 49188T and Ochrobactrum cytisi ESC1T (family Brucellaceae). The major cellular fatty acids were C19 : 0 cyclo ω8c (44.4 %) and C16 : 0 (32.1 %). The identified sole isoprenoid quinone was ubiquinone-10 (Q-10). The major polar lipids produced were phosphatidylcholine, phosphatidylglycerol, phosphatidylethanolamine, an unidentified aminolipid, two unidentified phospholipids and three unidentified lipids. The genome size was about 5.4 Mbp and the DNA G+C content was 68.2 mol%. Sp-1T exhibited the highest average nucleotide identity value of 76.6 % and in silico DNA-DNA hybridization value of 22.1 % with Pseudoxanthobacter soli DSM 19599T (family Xanthobacteraeae). This strain is distinguishable from closely related members of the order Rhizobiales by its differential phenotypic, chemotaxonomic, genomic and phylogenetic characteristics. On the basis of evidence from polyphasic taxonomic analysis, we concluded that Sp-1T represents a novel species in a novel genus within the order Rhizobiales, for which the name Segnochrobactrum spirostomi gen. nov., sp. nov. is proposed. The type strain is Sp-1T (=KCTC 62036T=JCM 32162T). We also describe a novel family, Segnochrobactraceae fam. nov., to encompass the proposed novel genus and species.

Keywords: Segnochrobactrum; Spirostomum yagiui; ciliate-host; novel family; novel genus; novel species.

MeSH terms

  • Alphaproteobacteria / classification*
  • Alphaproteobacteria / isolation & purification
  • Bacterial Typing Techniques
  • Base Composition
  • Ciliophora / microbiology*
  • DNA, Bacterial / genetics
  • Fatty Acids / chemistry
  • Nucleic Acid Hybridization
  • Phospholipids / chemistry
  • Phylogeny*
  • RNA, Ribosomal, 16S / genetics
  • Republic of Korea
  • Sequence Analysis, DNA
  • Ubiquinone / analogs & derivatives
  • Ubiquinone / chemistry


  • DNA, Bacterial
  • Fatty Acids
  • Phospholipids
  • RNA, Ribosomal, 16S
  • Ubiquinone
  • coenzyme Q10