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INTERNATIONAL JOURNAL OF SYSTEMATIC AND EVOLUTIONARY MICROBIOLOGY logo International Journal of Systematic and Evolutionary Microbiology

Volume 75, Issue 6

sp. nov., a novel rhizobial species isolated from nodules Open Access

Abstract

Three slow-growing rhizobial strains, designated as 1AS2L, 1AS20L and 1AS5L, were isolated from nodules of in Borj Cedria, northern Tunisia. These strains, which belong to the symbiovar cyanophyllae, were characterized using a polyphasic approach. Phylogenetic analysis of the 16S rRNA () gene placed these strains within the genus , specifically in the superclade associated with . Further phylogenetic analysis using concatenated sequences of the A, D, II and B genes (totalling 1,734 bp) positioned the strains in a distinct lineage, with identified as their closest related species, sharing a sequence identity of 95.2%. The type strain, 1AS2L, exhibited average nucleotide identity values of 89.10%, 89.08% and 89.00% with the type strains of the closest valid species: , and , respectively. Additionally, digital DNA–DNA hybridization values confirmed the novelty of strain 1AS2L, showing low similarity (38.0%–38.3%) with the type strains of the closest known species. Phylogenomic analyses based on up-to-date bacterial core genes, Type (Strain) Genome Server and the Genome Taxonomy Database (GTDB) pipelines further supported the uniqueness of the 1AS2L, 1AS20L and 1AS5L strains. The GTDB analysis also robustly clustered two strains (SZCCT0449 and NSD-1) with our strains, suggesting putative members of the proposed novel species. The differentiation of these novel strains from their closest phylogenetic neighbours was also corroborated by phenotypic, physiological and fatty acid content analyses. Based on genomic, phenotypic and biochemical data, we propose the establishment of a novel species, sp. nov., with strain 1AS2L (=LMG 33170=DSM 114401) as the type strain.

  • Received:
  • Accepted:
  • Published Online:
Keyword(s): Acacia saligna , Bradyrhizobium , phylogenomics , rhizobia and whole genomes
Funding
This study was supported by the:
  • Agriculture and Agri-Food Canada (Award J-002295)
    • Principal Award Recipient: JamesT. Tambong
  • Agriculture and Agri-Food Canada (Award J-002272)
    • Principal Award Recipient: JamesT. Tambong
  • PRIMA RESCHEDULE project (Award PRIMA/TN/20/06)
    • Principal Award Recipient: BacemMnasri
  • PHC Maghreb project (Award 34MAG21)
    • Principal Award Recipient: BacemMnasri
© 2025 Crown Copyright
  • This is an open-access article distributed under the terms of the Creative Commons Attribution License. This article was made open access via a Publish and Read agreement between the Microbiology Society and the corresponding author’s institution.
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2026-04-20

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Bradyrhizobium tunisiense sp. nov., a novel rhizobial species isolated from Acacia saligna nodules
Int J Syst Evol Microbiol 75, 006807 (2025); https://doi.org/10.1099/ijsem.0.006807
/content/journal/ijsem/10.1099/ijsem.0.006807
/content/journal/ijsem/10.1099/ijsem.0.006807
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