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, KW56T and 2063T, isolated from root nodules of Chamaecytisus albus (Spanish broom), was investigated using a polyphasic approach. Both isolates belong to the genus Phyllobacterium, yet exhibit significant genotypic and phenotypic differences from all currently described species. Whole-genome comparisons revealed that strain KW56T is most closely related to Phyllobacterium trifolii PETP 02T, while strain 2063T is related to Phyllobacterium brassicacearum strains STM 196T 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 Phyllobacterium, 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 KW56T, and 3-OH 14:0, 3-OH 17:0, and 3-OH 18:0 for strain 2063T. Based on the genomic, phenotypic, and chemotaxonomic data, we propose that strains KW56T and 2063T represent two novel species, for which the names Phyllobacterium chamaecytisi sp. nov. (DSM 113831) and Phyllobacterium lublinensis sp. nov. (DSM 113830) are proposed.