rRNA operon copy-number correlates to growth rate of Bradyrizobia.

LEILA BARTROLÍ; DIEGO COMERCI; ALFONSO SOLER BISTUE

Paraná

Congreso; LIV Congreso Anual de SAIB; 2018

Growth rate(GR) varies widely among bacterial species. Comparative genomics suggest thatthe structure of the chromosome contributes to determine GR. In particular,bacteria bearing a high number of ribosomal operons (rrn) display faster GRs. Bradyrhizobiaare capable of interacting symbiotically with soy, enabling the biologicalfixation of nitrogen by the plant increasing crop productivity.Bradyrhizobiaceae shows a particularly slow GR which makes its study difficultand impacts on its biotechnological utility. Close examination of completegenomes within this group shows that this clade bears 1 or 2 rrn. We hypothesize that species with 2 rrn should grow faster. To test this, weused as model, the completely sequenced strains B. diazoeficiens USDA110 and B.diazoefficiens USDA122, with one rrnand B. japonicum E109 and B. japonicum USDA6T that have 2 rrns. Growth curves of this four strainsallowed obtaining their generation time (GT) in YEM broth. B. diazoefficiens USDA110 and USDA122 displayed median GT of 17 and20 hours respectively. Meanwhile, B.japonicum E109 and U6T displayed a significantly lower GTs of 15h and 9 hsrespectively. These differences in GR remained across all media tested. In sum,we observed that strains bearing 2 rrngrow faster than those bearing a single operon. Our results suggest that theaddition of additional rrn couldallow the increase of the GR of Bradyrhizobia. We are cloning rrn to introduceadditional copies in the strains to try to artificially modify the GR of theseslow-growing microorganisms.