Role of flp pili during biofilm formation and swimming motility of Bradyrhizobium diazoefficiens USDA110

SERRANGELI, J.S.; FALDUTI, O.; MEDICI, I. ; SOLER BISTUE, A.; ABDIAN, P.; ALTHABEGOITI, M.J.; QUELAS, J. I.; PÉREZ GIMÉNEZ, JULIETA; MONGIARDINI, E.J.

Los Cocos

Congreso; XVII Congreso Argentino de Microbiología General; 2022

Sociedad Argentina de Microbiología General (SAMIGE)

Bradyrhizobium diazoefficiens is a soil bacterium with a dual lifestyle, capable of remaining in a free-living state forming a biofilm or establishing a symbiosis with soybeans invading their roots and residing in the nodules. In this situation, the bacteria transform the atmospheric nitrogen in a plant-assimilable form, which derived in its use in agriculture. In both states the bacteria are forced to interact with a surface, to recognize it and start the adhesion process. This process involves several components of the bacterial surface, including adhesins, polysaccharides and LPS, among others. Although the adhesion process of B. diazoefficiens has been studied in several aspects, few genetic studies were done to identify the mechanisms involved. We previously characterized a small cluster of genes related to flp pili, which played a role in root adhesion, but not in abiotic surfaces contact. In that same study, two other gene clusters were identified by bioinformatics methods, but no experimental characterization were performed. To continue this work, we carried out a function assignment of each of the genes present in these clusters by sequence similarity against of other known bacteria pili. Thus, we found out that the identified clusters encode all the necessary functions to synthesize a complete pilus. In addition, we identified a new small cluster that partially encodes some repeated functions, and other isolated genes on the chromosome that encode for putative pilins, the subunits that form the pilus filament. In order to test the functionality of these structures we obtained a mutant by a chromosomal deletion that include 6 out of the total of 10 genes that comprise one of the larger clusters. We initiated its phenotypic characterization. This mutant shows an alteration in biofilm formation capacity that depends on the culture medium and surface tested. In addition, its ability to move by swimming in a semisolid medium was altered. Further studies will be necessary to determine its putative role on root adhesion as well as its behavior during the establishment of a nitrogen-fixing symbiosis.