Peteryoungia limnocola sp. nov., a Novel Rhizobiaceae Species Isolated from the Surface Water of Lake Chaohu, with the Reclassification of Rhizobium mayense as Martinezella mayensis comb. nov.

The family Rhizobiaceae comprises multiple genera that are ecologically significant in the environment, and are one of the most challenging groups for taxonomic classification. Strain G187T, obtained from the surface water of Lake Chaohu, China, was characterized using a polyphasic taxonomic approach. Both 16S rRNA gene-based and genome-scale phylogenetic analyses placed the strain within the genus Peteryoungia. However, its genomic relatedness to Peteryoungia type strains was low, with ANI values of 82.2–82.8% and dDDH values of 22.0–22.8%, both below the species-level thresholds. In addition, differences in phenotypic and chemotaxonomic characteristics distinguished G187T from its closest phylogenetic relatives. A genome-based reassessment of related Rhizobium type strains further showed that Rhizobium mayense was phylogenetically affiliated with Martinezella, supporting a new combination with the name Martinezella mayensis comb. nov. proposed. Comparative genomic analysis of representative strains of Rhizobium, Martinezella, Paenirhizobium, and Peteryoungia further revealed distinct patterns of genome-wide gene content among these genera. Evidence from phylogenetic reconstruction, genome-based comparisons, phenotypic characterization, and chemotaxonomic analysis collectively supports the proposal of strain G187T as a new species of the genus Peteryoungia, for which the name Peteryoungia limnocola sp. nov. is proposed. The type strain is G187T (=CCTCC AB 2026024T=NBRC 117770T=MCCC 1K10184T). This study proposes a novel species in the genus Peteryoungia and a new combination for Rhizobium mayense, and contribute to the ongoing genome-based refinement of Rhizobiaceae taxonomy.