Three bacterial strains producing blue-violet pigmented colonies on R2A agar were isolated from a wet rock wall and lakes in the deglaciated northern part of James Ross Island, Antarctica. The isolated strains inhibited phytopathogenic Gram-positive bacteria Clavibacter spp., Curtobacterium flacumfaciens, and Paenarthrobacter ilicis. Phylogenetic analysis based on the 16S rRNA gene indicated that the isolates belonged to the genus Massilia and the closest relatives were Massilia violaceinigra B2T, Massilia rubra CCM 8692T, Massilia frigida CCM 8695T, Massilia antarctica CCM 8941T, and Massilia aquatica CCM 8693T. A polyphasic taxonomic study based on lepA genes sequencing, automated ribotyping, MALDI-TOF MS, chemotaxonomy analyses, extensive biotyping, average nucleotide identity, and digital DNA-DNA hybridization calculations based on whole-genome sequences proved that the isolates represent a novel Massilia species for which the names Massilia pseudoviolaceinigra sp. nov. and Massilia scottii sp. nov. are suggested, with the type strains P3689T (= CCM 9206T = LMG 33568T) and P5043T (= CCM 9029T = LMG 32502T), respectively. These two bioactive metabolite-producing species may play an important role in shaping the composition of fresh-water Antarctic microbiomes due to the inhibition of various Gram-positive bacteria.

• Keywords
• Clavibacter, Curtobacterium, Massilia, Antarctica, Plant-pathogenic, Taxonomic description,
• MeSH
• Actinobacteria MeSH
• Biological Control Agents * isolation & purification   metabolism   MeSH
• Clavibacter * pathogenicity   MeSH
• DNA, Bacterial genetics   isolation & purification   MeSH
• Extremophiles * classification   genetics   isolation & purification   metabolism   MeSH
• Phylogeny MeSH
• Plant Diseases * microbiology   prevention & control   MeSH
• Oxalobacteraceae * classification   genetics   isolation & purification   metabolism   MeSH
• RNA, Ribosomal, 16S genetics   MeSH
• Whole Genome Sequencing MeSH
• Fresh Water microbiology   MeSH
• Publication type
• Journal Article MeSH
• Geographicals
• Antarctic Regions MeSH
• Names of Substances
• Biological Control Agents * MeSH
• DNA, Bacterial MeSH
• RNA, Ribosomal, 16S MeSH

The extreme conditions of the Antarctic environment have driven the evolution of highly specialized microbial communities with unique adaptations. In this study, we characterized five Pseudomonas isolates from James Ross Island, which displayed notable taxonomic and metabolite features. Phylogenomic analysis revealed that strain P2663T occupies a distinct phylogenetic position within the Pseudomonas genus, related to species Pseudomonas svalbardensis, Pseudomonas silesiensis, Pseudomonas mucoides, Pseudomonas prosekii, and Pseudomonas gregormendelii. The novelty of five Antarctic isolates was further confirmed through analyses of housekeeping genes, ribotyping, and REP-PCR profiling. MALDI-TOF MS analysis identified 11 unique mass spectrometry signals shared by the Antarctic isolates, which were not detected in other related species. Additionally, chemotaxonomic characterization, including fatty acid composition, demonstrated similarities with related Pseudomonas species. Phenotypic assessments revealed distinctive biochemical and physiological traits. In-depth genomic analysis of strain P2663T uncovered numerous genes which could be involved in survival in extreme Antarctic conditions, including those encoding cold-shock and heat-shock proteins, oxidative and osmotic stress response proteins, and carotenoid-like pigments. Genome mining further revealed several biosynthetic gene clusters, some of which are associated with antimicrobial activity. Functional assays supported the antimicrobial capabilities of this novel species, showing antagonistic effects against clinical isolates of Pseudomonas aeruginosa, possibly mediated by tailocins (phage tail-like particles). This comprehensive polyphasic study characterized a new cold-adapted species, for which we propose the name Pseudomonas rossensis sp. nov.

• Keywords
• Antarctica, Antibiotics, Antimicrobials, Cold adaptation, Inhibition, Novel species, Psychrotolerant bacteria,
• Publication type
• Journal Article MeSH