Structural characterization of two lipopolysaccharide O-antigens produced by the endofungal bacterium Burkholderia sp. HKI-402 (B4).

Two different polysaccharides were isolated and identified from the lipopolysaccharide fraction of endofungal bacterium Burkholderia sp. HKI-402 (B4). The complete structure was elucidated by chemical analysis and 2D NMR spectroscopy as the following:

A unique bicyclic monosaccharide from the Bradyrhizobium lipopolysaccharide and its role in the molecular interaction with plants.

Sugar coat: The nitrogen-fixing soil bacterium Bradyrhizobium sp. BTAi1 is coated with a unique lipopolysaccharide that does not induce innate immune responses in its host plant Aeschynomene indica or in different plant families. The chemical nature of the monosaccharide forming the polymer (see picture) is unprecedented in nature, which helps to avoid "harmful" recognition by its symbiotic host.

Deciphering the structural and biological properties of the lipid A moiety of lipopolysaccharides from Burkholderia cepacia strain ASP B 2D, in Arabidopsis thaliana.

Lipopolysaccharides (LPSs) are major, indispensable cell surface components of Gram-negative bacteria that have diverse roles in bacterial pathogenesis of plants. Environmental strains of Burkholderia cepacia have been described as phytopathogens, growth promotors, biocontrol agents and bioremediation agents. We have previously shown that LPSs from B. cepacia can be recognized as microbe-associated molecular pattern molecules, to elicit defense responses in plants. Recent findings suggest that the lipid A moiety might be partially responsible for LPSs perception. These studies were extended by analysis of the structure and biological activity of the lipid A moiety of LPSs of B. cepacia(.) The full structure was determined by a combination of negative/positive-ion matrix-assisted laser desorption ionization (MALDI) mass spectrometry (MS) on intact and partially degraded substrates. B. cepacia lipid A was found to contain a tetra- or penta-acylated, 1,4'-diphosphorylated, ß-(1-6)-linked D-GlcN disaccharide and further substituted by L-Ara4N in position 4'. As primary fatty acids, R-configurated 16:0(3-OH) (amide-linked in 2 and 2') and 14:0(3-OH) (ester-linked in 3 and 3', nonstoichiometric) were identified. A secondary 14:0 was located at position 2'. Its biological activity to elicit defense-related responses was subsequently investigated by monitoring the changes in the transcriptome of Arabidopsis thaliana seedlings. Genes found to be upregulated code for proteins involved in signal perception and transduction, transcriptional regulation, defense and stress responses. Furthermore, genes encoding proteins involved in chaperoning, protein interactions and protein degradation were differentially expressed as part of the metabolic reprogramming of cellular activities in support of immunity and defense.