Phenotypic and genotypic characterization of a novel multi-antibiotic-resistant, alginate hyperproducing strain of Pseudomonas mandelii isolated in Antarctica

Until recently, it was thought that Antarctica was a sterile continent due to extreme environmental conditions. In fact, this cold continent is one of the most diverse in terms of microorganisms. In the present study, the bacterial isolate Pseudomonas sp. 6A1 was obtained from marine sediments originating from the Fildes Peninsula Bay, King George Island, Antarctica. Subsequently, this isolate was identified as Pseudomonas mandelii. To arrive at this conclusion, molecular studies were performed using the 16S rRNA and multilocus sequence analysis. Both techniques were used to construct phylogenetic trees, revealing 99.99% similarity between the 6A1 strain and P. mandelii. To provide phenotypic support for this finding, BIOLOG GN2 and API20 NE tests, as well as assimilation assays with different carbon sources, were performed. These tests revealed 87% similarity with P. mandelii. This result was primarily due to an inability of the 6A1 strain to reduce nitrates, as well as to variations in the assimilation of different carbon sources. Another important phenotypic difference was alginate hyperproduction by 6A1, a trait never before described in a P. mandelii strain. Finally, the 6A1 strain was found to present multiple antibiotic resistances. Altogether, these results confirm the first case of P. mandelii isolation from the Antarctic.