EPS II FROM Sinorhizobium meliloti AS AN ADHESIVE MOLECULE IN MULTI-SPECIES BACTERIAL AGGREGATES

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

San Miguel de Tucuman

Congreso; XIII congreso argentino de microbiologia general; 2018

Asociación Civil de Microbiología General

Sinorhizobium meliloti is a rhizobium able to establish a nitrogen fixing symbiosis with the Medicagolegume. This bacterium produces a mix of exopolysaccharides (EPSs) identified as succinoglycan orEPS I and galactoglucan or EPS II. EPSs play a major role in the bacterial processes of cellaggregation, flocculation, and biofilm formation. Those physiological events are critical for the initialsteps of the interaction mechanism between bacteria and eukaryotic hosts.Bacterial aggregation is a highly specific process which involves interaction between molecules frombacterial surfaces that act as adhesins and complementary receptors, which are carbohydrates andproteins respectively. The bacterial aggregative mechanism can occur between bacteria belonging tothe same species (autoaggregation) or between bacteria of different genus (co-aggregation). Since theprocess requires protein-saccharide interactions on the surfaces of both partners, aggregation can bemodulated by the regulation of EPSs synthesis. Co-aggregation interactions contribute to the initialdevelopment of biofilms through specific recognition and adhesion of single, genetically differentbacteria in suspension and the subsequent adhesion of previously co-aggregated cells.The aim of the present work was to study co-aggregation between S. meliloti strains and differentrhizospheric bacteria. The co-aggregative phenotype was analyzed in the wild type S. meliloti Rm8530 strain (complete EPS producer) and in their derivative mutants in the EPS synthesis: exoY strain(EPS I defective), expA strain (EPS II defective) and exoY-expA double mutant strain (DM, EPSdefective). Each S. meliloti strain was tested for co-aggregation with microorganisms that share thesame ecological niche, including Pseudomonas fluorescens, Azospirillum brasilense and Burkholderiasp. In general, the strains producing EPS II (wt, exoY) were shown to produce more co-aggregationcompared to those strains incapable of producing EPS II (expA, DM). Co-aggregation assays were alsocarried out by adding to washed cells different sources of EPSs, i.e. either from supernatants of singlecultures or purified EPS. It was always detected that the co-aggregative percentage was increased byproviding a source of EPS II. Accordingly, it is concluded that EPS II from S. meliloti play animportant role in the co-aggregation process with different rhizospheric bacteria. Thisexopolysaccharide may be a key factor for microorganisms to start the development of biofilms innature. Moreover, this molecule could be considered as a possible universal connector with severalrelevant properties at ecological, biotechnological and agro-productive levels