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.

• Klíčová slova
• Clavibacter, Curtobacterium, Massilia, Antarctica, Plant-pathogenic, Taxonomic description,
• MeSH
• biologická ochrana * izolace a purifikace   metabolismus   MeSH
• Clavibacter * patogenita   MeSH
• DNA bakterií genetika   izolace a purifikace   MeSH
• extremofilové * klasifikace   genetika   izolace a purifikace   metabolismus   MeSH
• fylogeneze MeSH
• nemoci rostlin * mikrobiologie   prevence a kontrola   MeSH
• Oxalobacteraceae * klasifikace   genetika   izolace a purifikace   metabolismus   MeSH
• RNA ribozomální 16S genetika   MeSH
• sekvenování celého genomu MeSH
• sladká voda mikrobiologie   MeSH
• Publikační typ
• časopisecké články MeSH
• Geografické názvy
• Antarktida MeSH
• Názvy látek
• biologická ochrana * MeSH
• DNA bakterií MeSH
• RNA ribozomální 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.

• Klíčová slova
• Antarctica, Antibiotics, Antimicrobials, Cold adaptation, Inhibition, Novel species, Psychrotolerant bacteria,
• Publikační typ
• časopisecké články MeSH

A group of seven bacterial strains producing blue-purple pigmented colonies on R2A agar was isolated from freshwater samples collected in a deglaciated part of James Ross Island and Eagle Island, Antarctica, from 2017-2019. The isolates were psychrophilic, oligotrophic, resistant to chloramphenicol, and exhibited strong hydrolytic activities. To clarify the taxonomic position of these isolates, a polyphasic taxonomic approach was applied based on sequencing of the 16S rRNA, gyrB and lepA genes, whole-genome sequencing, rep-PCR, MALDI-TOF MS, chemotaxonomy analyses and biotyping. Phylogenetic analysis of the 16S rRNA gene sequences revealed that the entire group are representatives of the genus Massilia. The closest relatives of the reference strain P8398T were Massilia atriviolacea, Massilia violaceinigra, Massilia rubra, Massilia mucilaginosa, Massilia aquatica, Massilia frigida, Massilia glaciei and Massilia eurypsychrophila with a pairwise similarity of 98.6-100% in the 16S rRNA. The subsequent gyrB and lepA sequencing results showed the novelty of the analysed group, and the average nucleotide identity and digital DNA-DNA hybridisation values clearly proved that P8398T represents a distinct Massilia species. After all these results, we nominate a new species with the proposed name Massilia antarctica sp. nov. The type strain is P8398T (= CCM 8941T = LMG 32108T).

• Klíčová slova
• Antarctica, Massilia, description, psychrophilic, violacein, whole-genome sequencing,
• Publikační typ
• časopisecké články MeSH