The Peculiar Structure of Acetobacter pasteurianus CIP103108 LPS Core Oligosaccharide.

Acetobacter pasteurianus, a member of the Alphaproteobacteria, is an acetic acid-producing bacterium present on sugar-rich substrates such as such as fruits, flowers and vegetables and traditionally used in the production of fermented food. The preferred living habitat associated with acid conditions makes the structure of the bacterial cell wall interesting to study, due to expected uncommon features. We have used a combination of chemical, analytical and NMR spectroscopy approaches to define the complete structure of the core oligosaccharide from A. pasteurianus CIP103108 LPS. Interestingly, the core oligosaccharide displays a high concentration of negatively charged groups, structural features that might contribute to reinforcing the bacterial membrane.

The Lipid†A Structure from the Marine Sponge Symbiont Endozoicomonas sp. HEX 311.

Endozoicomonas sp. HEX311 is a Gram-negative bacterium known to establish a commensal interaction with the marine demosponge Suberites domuncula. The molecular bases of the sponge-microbe interaction events are still poorly defined. Nevertheless, it has been proved that S. domuncula possesses an innate immune system with similarities to the mammalian one and is able to recognize the main component of the Gram-negative bacteria cell wall: the lipopolysaccharide. Whether this recognition occurs in a structure-dependent manner, which is typical for mammalian immune system receptors, is still under investigation. Herein, we report the Endozoicomonas sp. HEX311 lipid A structure obtained by a combination of data attained from chemical, MALDI MS, and MS2 approaches. The lipid A is a complex family of species decorated by pyrophosphate and phosphate units and carrying (R)-3-hydroxydodecanoic acid, (R)-3-hydroxytetradecanonic acid, iso-2-hydroxyundecanoic acid, iso-(R)-3-hydroxyundecanoic acid, and iso-nonanoic acid as acyl chains.

Zymomonas mobilis exopolysaccharide structure and role in high ethanol tolerance.

Bacterial cell surface exopolysaccharides (EPS) provide a protective barrier from the external milieu and participate in host-environment interactions. Zymomonas mobilis, an ethanologenic Gram negative bacterium, is used by the industry in bio-ethanol production process, due to its extraordinary resistance to a highly ethanolic environment. We found that Z. mobilis produces a mixture of two EPSs, an [α-(1→6)-D-Manp] mannose homopolymer and a galactose containing polysaccharide: [→2)-ß-D-Galf-(1→3)-ß-D-Galp-(1→]n. A physico-chemical study, conducted with diffusion-ordered spectroscopy (DOSY) and Dynamic Light Scattering (DLS), allowed to demonstrate that, differently from the majority of polysaccharides, ethanol is a good solvent for the galactose containing EPS, revealing that its chemical structure is specifically connected with the Zymomonas mobilis high ethanol tolerance.

Structure and inflammatory activity of the LPS isolated from Acetobacter pasteurianus CIP103108.

Acetobacter pasteurianus is an acetic acid-producing Gram-negative bacterium commonly found associated with plants and plant products and widely used in the production of fermented foods, such as kefir and vinegar. Due to the acid conditions of the bacterium living habitat, uncommon structural features composing its cell envelope are expected. In the present work we have investigated the A. pasteurianus CIP103108 lipopolysaccharide (LPS) structure and immunoactivity. The structure of the lipid A and of two different O-polysaccharides was assessed. Furthermore, immunological studies with human cells showed a low immunostimulant activity of the isolated LPS, in addition to a slight capability to lower the NF-kB activation upon stimulation by toxic LPS.

Bradyrhizobium Lipid A: Immunological Properties and Molecular Basis of Its Binding to the Myeloid Differentiation Protein-2/Toll-Like Receptor 4 Complex.

Lipopolysaccharides (LPS) are potent activator of the innate immune response through the binding to the myeloid differentiation protein-2 (MD-2)/toll-like receptor 4 (TLR4) receptor complexes. Although a variety of LPSs have been characterized so far, a detailed molecular description of the structure-activity relationship of the lipid A part has yet to be clarified. Photosynthetic Bradyrhizobium strains, symbiont of Aeschynomene legumes, express distinctive LPSs bearing very long-chain fatty acids with a hopanoid moiety covalently linked to the lipid A region. Here, we investigated the immunological properties of LPSs isolated from Bradyrhizobium strains on both murine and human immune systems. We found that they exhibit a weak agonistic activity and, more interestingly, a potent inhibitory effect on MD-2/TLR4 activation exerted by toxic enterobacterial LPSs. By applying computational modeling techniques, we also furnished a plausible explanation for the Bradyrhizobium LPS inhibitory activity at atomic level, revealing that its uncommon lipid A chemical features could impair the proper formation of the receptorial complex, and/or has a destabilizing effect on the pre-assembled complex itself.

Structure of the Lipopolysaccharide from the Bradyrhizobium sp. ORS285 rfaL Mutant Strain.

The importance of the outer membrane and of its main constituent, lipopolysaccharide, in the symbiosis between rhizobia and leguminous host plants has been well studied. Here, the first complete structural characterization of the entire lipopolysaccharide from an O-chain-deficient Bradyrhizobium ORS285 rfaL mutant is achieved by a combination of chemical analysis, NMR spectroscopy, MALDI MS and MS/MS. The lipid A structure is shown to be consistent with previously reported Bradyrhizobium lipid A, that is, a heterogeneous blend of penta- to hepta-acylated species carrying a nonstoichiometric hopanoid unit and possessing very-long-chain fatty acids ranging from 26:0(25-OH) to 32:0(31-OH). The structure of the core oligosaccharide region, fully characterized for the first time here, is revealed to be a nonphosphorylated linear chain with methylated sugar residues, with a heptose residue exclusively present in the outer core region, and with the presence of two singly substituted 3-deoxy-d-manno-oct-2-ulosonic acid (Kdo) residues, one of which is located in the outer core region. The lipid A moiety is linked to the core moiety through an uncommon 4-substituted Kdo unit.

The Deep-Sea Polyextremophile Halobacteroides lacunaris TB21 Rough-Type LPS: Structure and Inhibitory Activity towards Toxic LPS.

The structural characterization of the lipopolysaccharide (LPS) from extremophiles has important implications in several biomedical and therapeutic applications. The polyextremophile Gram-negative bacterium Halobacteroideslacunaris TB21, isolated from one of the most extreme habitats on our planet, the deep-sea hypersaline anoxic basin Thetis, represents a fascinating microorganism to investigate in terms of its LPS component. Here we report the elucidation of the full structure of the R-type LPS isolated from H. lacunaris TB21 that was attained through a multi-technique approach comprising chemical analyses, NMR spectroscopy, and Matrix-Assisted Laser Desorption Ionization (MALDI) mass spectrometry. Furthermore, cellular immunology studies were executed on the pure R-LPS revealing a very interesting effect on human innate immunity as an inhibitor of the toxic Escherichia coli LPS.