A possible cross-talk between the two Bradyrhizobium diazoefficiens flagellar systems by fliL gene

CAROLINA DARDIS; MICHIO HOMMA; FLORENCIA MENGUCCI; SEIJI KOJIMA; ELIAS JAVIER MONGIARDINI; JUAN IGNACIO QUELAS

Gifu

Congreso; 82.a reunion de la sociedad japonesa bioquimica; 2018

Bradyrhizobium diazoefficiens is a motile soil α-proteobacterium used as commercial inoculants for soybean crops due to its capability to fix atmospheric nitrogen. This species has two different flagellar systems that contribute to swimming motility: a subpolar system (with FliC flagellins) constitutively expressed and an inducible lateral system (with LafA flagellins). The lateral system induction depends on the carbon source, viscosity, pH and oxygen level. We focused our experiments in FliL protein whose specific role remains unclear, despite it has been studied in several bacterial species. It seems to be associated to the flagellar basal body and would contribute to the stability of the flagellar structure when torque increases. B. diazoefficiens USDA 110 have two putative fliL genes, each one related to the subpolar or lateral flagellar gene clusters (fliLsub and fliLlat, respectively). In order to study their roles, we obtained deletion mutants for each gene and evaluated flagellins production and swimming behavior in semi-solid media. Here, we report experiments with ΔfliLsub strain. In semi-solid medium, the swimming halo of ΔfliLsub was higher than the wild-type, a difference that declines when viscosity increase. As judged by SDS-PAGE and electron microscopy, the subpolar and lateral flagellin filaments are intact and expressed normally. We also evaluated a ΔlafA/ΔfliLsub double mutant expressing only the subpolar flagellum. In this mutant, we observed a reduction of the swimming halo compared to the wild type strain. This results and previous work with ΔfliLlat lead us to conclude that both FliL proteins possess similar functions in B. diazoefficiens flagella, despite its low amino acid identity (22%) and the apparent dissimilar topology. Furthermore, we hypothesized that the absence of FliLsub in subpolar flagellar system induces overexpression of the lateral flagellar system. This hypothesis is supported on three observations in ΔfliLsub strain: 1-An increased swimming motility, 2-Superior levels of mRNA of the lateral flagella master regulator (lafR) and 3-Higher content of lateral flagellins.