Pseudomonas gelidaquae sp. nov., an Antarctic bacterium with a distinctive Type III Secretion System, isolated from Fildes Bay, King George Island

Pseudomonas gelidaquae IB20^T is a rod-shaped, motile bacterium distinguished by the presence of multiple polar flagella. The average nucleotide identity (ANIb) and average amino acid identity (AAI) values between P. gelidaquae IB20^T and its closest phylogenetic relatives were all below the 95–96% thresholds currently accepted for delineating a novel species. Pseudomonas antarctica CMS 35 ^T displayed the highest ANIb and AAI values, at 92.67% and 95.98%, respectively. A distinctive feature of the P. gelidaquae IB20^T genome is the presence of a Type III Secretion System (T3SS), which is absent in the genomes of all closely related strains, making it the first Pseudomonas species isolated from Antarctica to carry this virulence system. Notably, we identified a novel candidate effector protein encoded within the T3SS gene cluster of P. gelidaquae IB20^T, exhibiting similarity to VopS T3SS effector proteins, which are predominantly found in Vibrio species. A comprehensive search of publicly available databases confirmed that this candidate effector protein is not present in any other Pseudomonas genome. Additionally, chemotaxonomic analysis showed that the dominant cellular fatty acids include summed feature 3 (C16:1ω7c/C15:0 iso 2-OH), C16:0, and C18:1ω7c. Based on extensive phenotypic and genotypic evidence, we propose that strain IB20^T represents a novel species within the genus Pseudomonas, for which the name P. gelidaquae sp. nov. is proposed, with IB20 designated as the type strain.