1887

Abstract

Two Gram-negative, rod-shaped bacteria, H1 and H3, isolated from the digestive tract of entomopathogenic nematodes were biochemically and molecularly characterized to determine their taxonomic positions. The 16S rRNA gene sequences of these strains indicate that they belong to the Gammaproteobacteria, to the family , and to the genus. Deeper analyses using whole genome-based phylogenetic reconstructions show that strains H1 and H3 are closely related to DSM 15138, to DSM 22397, and to PB45.5. genomic comparisons confirm these observations and show that strain H1 shares 70.6, 66.8, and 63.5 % digital DNA–DNA hybridization (dDDH) with DSM 15138, DSM 22397, and PB45.5, respectively, and that strain H3 shares 76.6, 69.4, and 59.2 % dDDH with DSM 15138, DSM 22397, and PB45.5, respectively. Physiological and biochemical characterization reveals that these two strains differ from most of the validly described species and from their more closely related taxa. Given the clear phylogenetic separations, that the threshold to discriminate species and subspecies is 70 and 79% dDDH, respectively, and that strains H1 and H3 differ physiologically and biochemically from their more closely related taxa, we propose to classify H1 and H3 into new taxa as follows: H3 as a new subspecies within the species , and H1 as a new species within the genus, in spite that H1 shares 70.6 % dDDH with DSM 15138, score that is slightly higher than the 70 % threshold that delimits species boundaries. The reason for this is that H1 and DSM 15138 cluster apart in the phylogenetic trees and that dDDH scores between strain H1 and other strains are lower than 70 %. Hence, the following names are proposed: sp. nov. with the type strain H1 (=IARI-SGMG3,=KCTC 82683=CCM 9150=CCOS 1975) and subsp. subsp. nov. with the type strain H3 (=IARI-SGHR2=KCTC 82684=CCM 9149=CCOS 1976). These propositions automatically create subsp. subsp. nov. with DSM 15138 as the type strain (currently classified as ).

Funding
This study was supported by the:
  • science and engineering research board (Award SB/SO/AS/010/2014)
    • Principle Award Recipient: VishalS. Somvanshi
  • schweizerischer nationalfonds zur förderung der wissenschaftlichen forschung (Award 186094)
    • Principle Award Recipient: RicardoA. R. Machado
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2021-09-15
2024-03-28
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