Three novel Rothia species associated with Antarctic birds harbour novel biosynthetic gene clusters.

Antarctica's unique environment supports diverse avian populations, including penguins, skuas, and gulls. As climate-driven pressures on these populations intensify, their microbiota receives increased attention due to their relevance for host health. In this study, we investigated 11 bacterial isolates associated with Antarctic birds using a polyphasic taxonomic approach integrating genomic and phenotypic data. Phylogenetic analysis of 16S rRNA gene sequences and core-genome-based phylogenomics separated the strains into three groups and genome-relatedness indices confirmed that the three lineages represent novel species within the genus Rothia. Functional genomic analysis, combined with phenotypic testing, revealed broad metabolic capabilities with adaptations to host-associated environment. Further genome mining revealed the presence of several biosynthetic gene clusters, potentially encoding terpenes, siderophores, and other bioactive compounds. Some of these clusters likely encode variants of enterobactin, a nonribosomally synthesized siderophore. However, in vitro production of enterobactin was not confirmed, suggesting more complex expression regulation than iron depletion alone. Together, these findings broaden the known diversity of Rothia by three proposed novel species, Rothia ornithocola sp. nov., Rothia pygoscelis sp. nov., and Rothia antarctica sp. nov., and highlight genomic and phenotypic features that contribute to the ecology of Antarctic avian-associated bacteria.