Atosan, a new exopolysaccharide secreted by a Vibrioalginolyticus strain isolated from a deep-sea hydrothermal vent...

Bacteria are able to colonize various environments, even the most hostile ones, due to their ability to synthesize an extracellular protective matrix. Bacteria isolated from deep-sea hydrothermal vent environments have been identified as very effective producers of polysaccharide-rich matrix. In particular, exopolysaccharides (EPS) synthesized by Vibrio marine species have shown to be composed of uronic acid and hexosamine residues, similarly to glycosaminoglycans, components of mammalian tissues. In the present study, the fine structure of a new high-molecular weight EPS, named atosan, secreted by the deep-sea hydrothermal vent bacterium Vibrio alginolyticus AT1219 strain, was determined. A complementary analytical approach, including Nuclear Magnetic Resonance spectroscopy and mass spectrometry was applied to elucidate the repeating unit of the polysaccharide. A linear pentasaccharide with a unique monosaccharide sequence: [→3)-α-d-Galp-(1 → 3)-β-d-GalpA-(1 → 3)-β-d-GlcpNAc-(1 → 4)-α-d-GalpNAc-(1 → 4)-β-d-GlcpA-(1→] was described. In parallel, the genome sequence was investigated to get insight into the genetic mechanisms of atosan biosynthesis. Amongst eight clusters assigned to carbohydrate biosynthesis, three of them were closely related to the biosynthesis of the extracellular polysaccharide. Determination of the fine structure of atosan is a prerequisite step to better understand the relationship between its structure and resulting functional properties.