INSTITUTO DE BIOTECNOLOGIA Y BIOLOGIA MOLECULAR
Unidad Ejecutora - UE
congresos y reuniones científicas
REGULATION OF THE SUBPOLAR FLAGELLUM SYNTHESIS IN Bradyrhizobium diazoefficiens
C. DARDIS, F. MENGUCCI, M.J. ALTHABEGOITI, A. LODEIRO, J.I. QUELAS , E.J. MONGIARDINI; G. PARISI
Congreso; XI Congreso Argentino de Microbiología General; 2015
Bradyrhizobium diazoefficiens is an α-proteobacterium with high agronomic importance due to its ability to fix atmosphericnitrogen in symbiosis with soybean. Our previous studies showed that a hyper-motile strain of B. diazoefficiens is able tocompete for nodulation and produce higher soybean grain yields than the wild type in certain conditions. This observation led usto study different aspects of bacterial motility, including the regulation of the synthesis of its dual flagellar systems. The flagellarsynthesis is an energy-expensive process, which occurs in several steps that are tightly controlled by master regulators. Theseproteins trigger an ordered transcription cascade which means that the expression of one gene at a given level requires thetranscription of another gene at a higher level. Applying bioinformatic tools, we identified putative regulators of B. diazoefficiensUSDA 110 involved in the synthesis of the subpolar flagellum using Caulobacter crescentus as a model. We found the followingcandidates: ctrA (master regulator), flbD (class II regulator), fliX (trans-activation factor of flbD), flbT (class III regulator) and flaF(trans-activation factor of flbT). To confirm the role of these genes, mutations by insertion or deletions of each one were raised.However, initial attempts to obtain ctrA mutants were unsuccessful probably because the absence of CtrA causes deleteriousphenotype. In this work, we constructed and partially characterized flbD and fliX mutants in B. diazoefficiens USDA 110. Bothmutants were obtained by double-crossing over. For the flbD, we used the counter selection method in order to avoid polareffects, while the fliX mutant was obtained by insertion of an antibiotic cassette inside the ORF. All these mutants were checkedby PCR and sequencing. When we began the mutant characterization, we noticed that none of these were able to produceextracellular subpolar flagellins, although the lateral flagellins were present in both of them. In addition, we observed thatswimming in soft-agar plates was reduced in each mutant compared to the wild-type. These new findings suggest that bothgenes are involved in the regulation of the subpolar flagellum synthesis in B. diazoefficiens independently of the regulation oflateral flagella. In this sense, the model of regulation seems to be similar to C. crescentus but not to Salmonella, as was thoughton the first studies. From now on, we will continue working to determine which genes are under the control of these two proteinsin order to construct a hierarchy model for the regulation of the synthesis of this flagellum.