Pleiotropic Effects of a mutation in lpsB Gene of Sinorhizobium meliloti Rm 8530 strain

NIEVAS F.L; SORROCHE, F.G; NOCELLI N; GIORDANO W.F; BOGINO P.C

San Luis

Congreso; XIII congreso argentino de microbiologia general; 2018

Asociación Civil de Microbiología General

Bacterial surface molecules such as exopolysaccharides (EPSs), lipopolysaccharides (LPSs) andcapsular polysaccharides (KPSs), are crucial for adherence properties, colonization of surfaces, and asa barrier for defense against stressful environmental factors. For rhizobial bacteria those molecules arealso relevant for the development of a successful rhizobia-legume symbiosis. Lipopolysaccharides(LPSs) are the most important structural components of the outer membrane of Gram-negative bacteriacontributing to their structural properties and acting as a permeability barrier. Because of their positionat the contact zone with the external environment, the LPSs of many bacterial species are the maindeterminants of interaction with biotic or abiotic surfaces. LPSs contribute to the establishment of thesymbiotic relationship through suppressing host defenses and facilitating rhizobial entry into roothairs, infection thread formation, and eventually bacteroid differentiation. The Medicago symbiontSinorhizobium meliloti produces a heterogeneous population of LPSs: LPS-1 which includes the Oantigen (S-LPS) and LPS-2 which lacks the O-antigen (R-LPS). The lpsB gene codes for a type Iglycosyltransferase involved in the synthesis of the LPS core.In the present study, we evaluated the pleiotropic effects of a mutated lpsB gene in S. meliloti Rm 8530strain. This mutation was examined alone and combined to deficiency of EPS II (exopolysaccharideII). We studied the mutated LPSB strain in cell-cell and cell-surface interactions, motility andsymbiotic parameters with the host plant Medicago sativa. The LPSB mutant, which has a defectivecore portion of LPS, exhibited a reduction in biofilm formation on abiotic surfaces compared to thewild type strain. However, this ability in the in the LPSB mutant was not so reduced when comparedto EPS II-defective mutant strains. Cell aggregation studies clearly showed that the LPSB mutantstrain formed a greater number of higher cell aggregates compared to wild type strain. Moreover,autoaggregation experiments carried out with LPS and EPS mutant strains showed that bothpolysaccharides had an impact on the cell-cell adhesive interactions of planktonic bacteria. The lpsBmutation had also a marked effect in reducing the motility of strains carrying the mutation. In spite ofthe effects on several important physiological mechanisms caused by the lpsB mutation in thisbacterium, the symbiotic process was not altered. In this sense the number and efficiency of nodules aswell as the biomass parameters were not reduced because of the lpsB mutation. On the other hand,symbiosis was negatively affected in a LPS and EPS II double mutant. Taken into account the resultsobtained, this work shows that S. meliloti interactions with biotic and abiotic surfaces as well as thedevelopment of a successful symbiosis could depend on the interplay between LPS and EPS II.