Extracellular factors that alter the structure of the Rhizobium leguminosarum biofilm matrix

ABDIAN, P.L.; TARSITANO, J.; ZORREGUIETA, A.; RUSSO, DANIELA M.

San Miguel de Tucuman

Congreso; XXII Congreso Argentino de Microbiologia General SAMIGE 2017; 2017

Asociacion Civil de Microbiologia General SAMIGE

EXTRACELLULAR FACTORS THAT ALTER THE STRUCTURE OF THE Rhizobium leguminosarum BIOFILM MATRIX.The ability to form biofilms confers bacteria several advantages to survive in unfavourableenvironments. One of the key steps in the formation of a biofilm is the production of an extracellularmatrix. Gram negative bacteria called rhizobia are able to form symbiotic atmospheric nitrogen fixing nodules with legumes thus contributing to sustainable farming practices. Rhizobia rely on biofilms to inhabit either the soil or the competitive nutrient - rich rhizosphere. Understanding of the process of a proper biofilm formation is crucial to further expand the knowledge of this symbont and its interaction with plants.Formation of the capsular (CPS) and extracellular polysaccharide (EPS) is a key process in the formation of a mature biofilm in Rhizobium leguminosarum. Besides, mutants lacking the PrsDE secretion system were found to be defective in the formation of a mature biofilm. This system secretes an unusually high number of substrates, including the Ply glycanases, which cleave the polysaccharide chains shortening their length, and the Rap proteins such as RapA. Rap proteins share at least one EPS/CPS-binding domain (Ra: Rhizobium adhering) and, in general, harbour another specific domain. In particular, RapA is only made of two Ra domains and has been shown to be involved in adhesion to the legume?s roots, infection competitivity alteration of the EPS/CPS balance and biofilm formation. Interestingly, RapA was found strongly associated with the bacterial cell surface. In the current study we aimed to further understand the role of PrsDE-dependent extracellular proteins in biofilm formation. Firstly, to identify all PrsDE substrates, we performed a proteomic analysis by comparing the secretome of the reference strain R.l.v. 3841 with the prsD::Tn5 isogenic mutant. We confirmed all substrates that were previously described; besides, we found a new set of PrsDE-dependent extracellular proteins, including a new Rap protein, which we called RapD. This protein harbours a N-terminal Ra domain and another C-terminal domain of unknown function. Using polyclonal antibodies generated against RapD, we found that, unlike RapA, RapD was solely detected in the extracellular medium. This observation suggests that RapA and RapD might play different roles in the modulation of the extracellular matrix structure. Ongoing studies are focused on determining the effect of the absence or the overproduction of RapD on biofilm formation and the interaction with the legume roots.