Sphingobacterium antarcticus sp. nov., a Psychrotrophic Bacterium from the Soils of Schirmacher Oasis, Antarctica

Researchers isolated two bacterial strains (designated 4BY and 6BY) from soil samples collected near Lake Zub in Schirmacher Oasis, Antarctica. Both isolates were gram-negative, nonmotile rods that produced yellow pigment and possessed characteristics typical of the genus Sphingobacterium, including sphingophospholipids in their cell membranes. The strains had DNA G+C contents of 39.3 and 40.3 mol%, respectively, with 100% DNA-DNA homology to each other but only ~7-10% homology to known Sphingobacterium species. Notably, both isolates were psychrotrophic, capable of growing between 2°C and 30°C with optimal growth at 25°C, distinguishing them from all previously described mesophilic Sphingobacterium species. The bacteria differed from S. multivorum primarily in fatty acid composition, with higher proportions of unsaturated fatty acids (c16:1 at 56% versus 13% in S. multivorum), consistent with adaptation to cold environments. Based on their distinct characteristics, genetic distance, and unique psychrotrophic properties, the authors propose these isolates represent a new species, Sphingobacterium antarcticus, with strain 4BY designated as the type strain.

Key findings

• Two psychrotrophic Sphingobacterium isolates from Antarctic soil grow at temperatures as low as 2°C and up to 30°C, distinguishing them from all known mesophilic Sphingobacterium species
• DNA-DNA hybridization studies showed only 7-10% homology with S. multivorum and S. spiritivorum despite sharing genus-level characteristics, supporting designation as a new species
• Fatty acid composition differs significantly from S. multivorum, with elevated unsaturated c16:1 content (56% versus 13%), likely an adaptation for membrane fluidity in cold environments
• This is the first report of Sphingobacterium species isolated from continental Antarctic soils, expanding the known geographic distribution of the genus