Quorum sensing inhibitors in legume-associated bacteria.

NIEVAS, F.L., VILCHEZ, L., BOGINO, P.C., GIORDANO, W

San Miguel de Tucumán

Congreso; XII Congreso Argentino de Microbiología General (SAMIGE); 2017

Quorum sensing (QS) systems use N-acyl-homoserine lactones (AHLs) as signaling molecules, commonly found in Gram-negative bacteria that live in association with plants. QS system allows bacteria to function as multicellular organisms, because the extracellular concentration of autoinducer increases with bacteria population growth, after attaining a determinate number. Presently, QS mechanisms are considered as a potential novel target for the study of bacteria-plant interactions. Arachis hypogaea L. (peanut) constitutes an important legume crop with high relevance at different agroecological areas worldwide. Peanut establishes a nitrogen-fixing symbiosis with genetically diverse rhizobia grouped as Bradyrhizobium sp.. In this work, we analyzed the QS mechanisms used by rhizobia with special emphasis on the advances related to QS inhibitors produced by legume and bacteria. For that purpose, the bacterial biosensor strains, were employed for the different assays. In order to determine QS inhibitors molecules in bacteria and peanuts materials, inverse assays were carried out. Inhibition test of short and long acyl chain were performed by adding C6-HSL or C12-AHL, respectively. QS inhibition assay with biosensor strains demonstrated that legume and bacteria inhibited the expression of short and long homoserine lactones mediated phenotypes, suggesting a possible degradative activity for AHL in these extracts. In addition, Bradyrhizobium sp. P8A, a native strain isolated from peanut nodules, in contact with the biosensor strain and in absence of the plant was capable of producing AHLs with long acyl chains. Since that the synthesis of these AHLs by the P8A strain is only reached at the interface medium-air and not in the entire medium, we were able to demonstrate the production of inhibitors of QS molecules in strains capable of moving to the air interface would be linked to the aerobic behavior of this bacteria. We are currently in the process of identifying of AHL-lactonase activity. So far, our results indicate that in our experimental work model, legume and rhizobacteria are capable of communicating among themselves to coordinate group responses in order to adapt their physiology to environmental factors.