Abstract
Lipid A is a major constituent of the lipopolysaccharides (or endotoxins), which are complex amphiphilic macromolecules anchored in the outer membrane of Gram-negative bacteria. The glycolipid lipid A is known to possess the minimal chemical structure for LPSs endotoxic activity, able to cause septic shock. Lipid A isolated from extremophiles is interesting, since very few cases of pathogenic bacteria have been found among these microorganisms. In some cases their lipid A has shown to have an antagonist activity, i.e., it is able to interact with the immune system of the host without triggering a proinflammatory response by blocking binding of substances that could elicit such a response. However, the relationship between the structure and the activity of these molecules is far from being completely clear. A deeper knowledge of the lipid A chemical structure can help the understanding of these mechanisms. In this manuscript, we present our work on the complete structural characterization of the lipid A obtained from the lipopolysaccharides (LPS) of the haloalkaliphilic bacterium Salinivibrio sharmensis. Lipid A was obtained from the purified LPS by mild acid hydrolysis. The lipid A, which contains different number of fatty acids residues, and its partially deacylated derivatives were completely characterized by means of electrospray ionization Fourier transform ion cyclotron (ESI FT-ICR) mass spectrometry and chemical analysis.
Highlights
Saline environments, for example deep sea or saline lakes, are the perfect habitat for extremophilic microorganisms such as haloalkaliphiles
Lipid A was analyzed by ESI FT-ICR mass spectrometry
In the organization of the microbial membrane, lipopolysaccharides occupy the outer leaflet, and they are the first to come in contact with the external habitat. This is the reason why they are thought to play a key role in the adaptation mechanisms of extremophilic microorganisms
Summary
For example deep sea or saline lakes, are the perfect habitat for extremophilic microorganisms such as haloalkaliphiles. LPS amphiphilic nature is defined by their three different covalently linked regions These are: The hydrophilic polysaccharide portion composed of the O-specific antigen, which glycosylates the core oligosaccharide. The lipid A is an immunomodulatory molecule and is recognized by different classes of receptors on both mammalian and plant cells [6] It has a conserved architecture consisting of a β-D-GlcN′-(1′→6)-D-GlcN disaccharide (GlcpN is 2-amino-2-deoxy-D-glucopyranose) carrying an α-glycosidic-bound phosphate group at position C-1 of the proximal reducing glucosamine residue (GlcpN I) and an ester-bound one at position 4′ of the distal, non-reducing end glucosamine residue (GlcpN II). From the saline lake in Ras Mohammed Park (Egypt), a novel haloalkaliphilic, facultative anaerobic and Gram-negative microorganism (designated strain BAGT) has recently been recovered It was identified as a novel species of the Salinivibrio genus, and named Salinivibrio sharmensis [13]. Fourier transform ion cyclotron (ESI FT-ICR) mass spectrometry and chemical analysis in order to reveal the nature and the distribution of fatty acids linked to the disaccharidic glucosamine backbone
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