Lipopolysaccharides
(LPS), the major components of the outer membrane of Gram-negative bacteria, are very important cell wall
glyco-conjugates and act as MAMPs (microbe-associated molecular patterns) in
plant/bacteria interactions; they possess a central role in the mechanisms of
bacterial invasion and adaptation to the host environment. LPSs are amphiphilic
macromolecules consisting of a hydrophilic hetero-polysaccharide covalently
linked to a lipophilic domain called Lipid A. Besides their general
architectural principle, a number of subtle chemical variations are at the
basis of the dynamic host-guest recognition that in case of pathogens is
followed by the innate response and in case of symbiosis is followed by its
suppression. Therefore, the structural determination of LPS is an important
step toward for the comprehension of its structure to function relationships,
either in the case of phytopatogenic bacteria or in endosymbiontic and
endophytic bacteria.
In the
present communication we show the structure and function of the novel lipopolysaccharide
isolated from Bradyrhizobium
sp. BTAi1, a symbiotic soil bacterium that
is able to fix atmospheric nitrogen into ammonia in specific organs called
nodules [1]. It is accepted that the formation of these nodules is dependent
by specific lipochitooligosaccharidic Nod factors,
encoded by the nodABC genes, and released from bacteria. Giraud et al [2] have recently demonostrated that
in two strains of Bradyrhizobium
(BTAi1 and ORS278) the canonical nodABC genes are absent. This finding suggests
an alternative strategy to establish the symbiosis in which (LPS) and
exopolysaccharides (EPS) are of particular interest, since they could play a
role as signaling compounds, presumably acting as suppressors of plant defense
reactions in initial colonization.
[1] Silipo
A, Leone MR, Erbs G, Lanzetta R, Parrilli M, Chang WS, Newman MA, Molinaro A. Angew Chem Int Ed Engl. 2011, Vol 50 Issue 52, 12610–12612
[2] Giraud, E. et all. Science 2007, 316, 1307.
