Development of biofilm matrix and cell-cell cohesion in Rhizobium leguminosarum.

ABDIAN P.L.; RUSSO DM; VOZZA NF; ALONSO D; CARAMELO, J.; VON BILDERLING, C.; PIETRASANTA L, DOWNIE JA AND ZORREGUIETA, A

Maastrich

Congreso; FEMS 2015 Congress.6th Congress of European Microbiologists.; 2015

FEMS 2015-Kenes International

Formation of biofilms is important for rhizobia to colonize several environmental niches including plant roots. Within the microcolonies of the biofilm developed by Rhizobium leguminosarum, rhizobial cells interact tightly through lateral and polar connections forming compact aggregates. These microcolonies are surrounded by a biofilm matrix, whose main component is the acidic exopolysaccharide (EPS).In addition, the PrsDE secretion system has been implicated in biofilm formation. This system is responsible for the secretion of Rap (Rhizobium adhering-)proteins (including the PlyA and PlyB EPS-glycanases) that share one or two Ra/CHDL(cadherin-like-) domains. By biophysical and biochemical approaches we showed that one of these proteins (RapA), which consists of two Ra/CHDL domains, is a unipolar lectin that specifically binds the EPS. RapA overexpression enhanced biofilm formation and increased the distance between cells. In line with these observations we observed that RapA overexpression augments capsular polysaccharide (CPS) formation, which is structurally and genetically related with the EPS. We propose that RapA and the other Rap proteins, which are predicted to harbor one or two EPS/CPS-binding domains, play some role in the modulation or remodeling of the biofilm matrix structure. Finally, we showed that the O-chain core region of the lipopolysaccharide (LPS) is important for cell-cell cohesion. Mutants defective in the O-chain or O-chain core moiety developed premature microcolonies in which lateral bacterial contacts were greatly reduced, resulting in a biofilm with an altered three-dimensional structure. Further studies are required to give insight into the interplay between biofilm matrix components and Rap proteins.