Structural characterization of the core region of the lipopolysaccharide from the haloalkaliphilic Halomonas pantelleriensis:: Identification of the biological O-antigen repeating unit

Halomonas pantelleriensis is an extremophile, haloalkaliphilic microorganism that requires strictly aerobic conditions for growth. It is able to optimally grow in media containing 3-15% (w/v) total salt at a pH value between 9 and 10. To survive in these harsh conditions the extremophiles have developed several strategies that allow the microorganism to thrive. These adaptative strategies probably concern the bacteria outer membrane, which is a barrier regulating the exchange with the environment. In such a context, the lipopolysaccharides (LPSs), which are among the major constituent of the Gram-negative outer membrane, are thought to contribute to restrictive membrane permeability properties. Previous studies concerning the structure of the O-chain repeating unit of the lipopolysaccharide from this bacterium showed that it is constituted of a tetrasaccharidic repeating unit containing a high number of acidic monosaccharides. It was hypothesized that the carboxylate groups might serve as a protective buffer for bacterium under the extreme life conditions. To provide insight into the relationship and interactions between the environmental factors and microbial life, the core structure was also characterized. The LPS was hydrolyzed under both mild acid and strong alkaline conditions. This last treatment was the best one to obtain the whole core backbone and to gain information about the phosphates position. Moreover, the strong alkaline treatment product allowed us to identify the linkage between the O-chain and the core structure. Two core oligosaccharides were found and their structures were determined by FTICR MS and NMR spectroscopy. To the best of our knowledge, this represents the first description of the core structure of a lipopolysaccharide of an extremophile bacterium. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008.