Genomic organization of Bradyrhizobium flagellar systems

ALTHABEGOITI M.J; MONGIARDINI, E. J; QUELAS J.I; LODEIRO, A. R.

Córdoba

Congreso; XI Congreso Argentino de Microbiología General; 2015

SAMIGE

Bacterial motility isan important trait for processes such as adherence to host cells, host cellinvasion, protein secretion, and biofilm formation. Bradyrhizobium diazoefficiens and B. japonicum can live into plant nodules as a symbiont, or in a planktonic,free-living state in the soil, where they can swim and swarm self-propelled bytheir flagellar systems. B.diazoefficiens USDA 110 and B.japonicum USDA 6 possess two flagellar systems: a subpolar flagellum andsome lateral flagella [1-3, Althabegoiti,unpublished]. This characteristicis shared with unrelated species such as Vibrioparahaemoliticus, Aeromonashydrophila, Chromobacterium violaceum,Rhodobacter shaeroides, Rhodopseudomonaspalustris and Azospirillum brasilensebut not with other rhizobial species, which instead have a single peritrichousflagellar system similar to the lateral one of Bradyrhizobium. The presence of two flagellar systems in the samecell is intriguing, since each one consumes a large amount of cell energy andmight interfere each other in motility and chemotaxis. Although in theabove-mentioned species the lateral flagella were described as only requiredfor motility on surfaces, in Bradyrhizobiumboth flagellar systems are expressed in liquid medium. Therefore, elucidation ofthe roles of these two flagellar systems in Bradyrhizobiumrequires more investigation. A possible approach is a comparative study of thegenomic organization of these systems. The most related species with thischaracteristic is R. palustris. In thiswork we compared the genome distribution and synteny of lateral and subpolar flagellargenes in B. diazoefficiens USDA 110, B. japonicum USDA 6 and R. palustris BisA53.Genesencoding lateral flagella are located in a single cluster in Bradyrhizobium and in R. palustris. The regions are syntenicand sequences are highly conserved: around 90 % of identity between B. diazoefficiens and B. japonicum and 75% identity betweeneach Bradyrhizobium sp. and R. palustris. An inversion of thiscluster was observed between B.diazoefficiens and B. japonicum. Inthe case of Sinorhizobium meliloti orRhizobium etli, they also have acluster enclosing all the genes for the synthesis of the flagellum. Thegenes that encode the subpolar flagellum of B.diazoefficiens are distributed among four regions in the genome. Thispattern of dispersed genes is similar also in B. japonicum and R. palustrisand they are more divergent than the lateral cluster. The aboveobservations are in agreement with the proposal that the lateral flagellum wasacquired by horizontal transfer [4]. In this way we can think that the highconservation of the lateral cluster is due to a recent insertion in thegenomes, while the subpolar (primary) system evolved together with theorganism. These results will aid us to pursue the study on the roles of eachflagellum in the life cycle of Bradyrhizobiumsp.