Phenotypic, Chemotaxonomic, and Genome-Based Classification of Phyllobacterium Strains: Two Proposed Novel Species, Phyllobacterium chamaecytisi sp. nov. and Phyllobacterium lublinensis sp. nov

The taxonomic status of two bacterial strains, KW56^T and 2063^T, isolated from root nodules of <i>Chamaecytisus albus</i> (Spanish broom), was investigated using a polyphasic approach. Both isolates belong to the genus <i>Phyllobacterium</i>, yet exhibit significant genotypic and phenotypic differences from all currently described species. Whole-genome comparisons revealed that strain KW56^T is most closely related to <i>Phyllobacterium trifolii</i> PETP 02^T, while strain 2063^T is related to <i>Phyllobacterium brassicacearum</i> strains STM 196^T and 29-15. However, digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) values between the new isolates and their closest relatives were below established species delineation thresholds, supporting their recognition as novel species. Phenotypic analyses confirmed morphological and growth characteristics typical for <i>Phyllobacterium</i>, while also revealing several discriminatory physiological traits. Fatty acid profiling showed that cyclopropyl 19:0 was the major fatty acid in both strains, though each exhibited a unique fatty acid composition. Chemotaxonomic markers included 3-OH 14:0, a19:1, and 21:0 for strain KW56^T, and 3-OH 14:0, 3-OH 17:0, and 3-OH 18:0 for strain 2063^T. Based on the genomic, phenotypic, and chemotaxonomic data, we propose that strains KW56^T and 2063^T represent two novel species, for which the names <i>Phyllobacterium chamaecytisi</i> sp. nov. (DSM 113831) and <i>Phyllobacterium lublinensis</i> sp. nov. (DSM 113830) are proposed.