A Mutation in the Gene Alters the Physicochemical Properties of the Bacterial Cell Wall and Reduces Survival inside .

In our previous report, we had shown that the free-living amoeba influenced the abundance, competiveness, and virulence of NZP2213, the microsymbiont of agriculturally important plants of the genus . The molecular basis of this phenomenon; however, had not been explored. In the present study, we demonstrated that , the -acetyltransferase encoding gene located in the lipopolysaccharide (LPS) synthesis cluster of , was responsible for maintaining the protective capacity of the bacterial cell envelope, necessary for the bacteria to fight environmental stress and survive inside amoeba cells. Using co-culture assays combined with fluorescence and electron microscopy, we showed that an mutant, unlike the parental strain, was efficiently destroyed after rapid internalization by amoebae. Sensitivity and permeability studies of the mutant, together with topography and nanomechanical investigations with the use of atomic force microscopy (AFM), indicated that the incomplete substitution of lipid A-core moieties with O-polysaccharide (O-PS) residues rendered the mutant more sensitive to hydrophobic compounds. Likewise, the truncated LPS moieties, rather than the lack of -acetyl groups, made the mutant susceptible to the bactericidal mechanisms (nitrosative stress and the action of lytic enzymes) of .