Study On Exopolysaccharides Of Exor And Exod Genes In Sinorhizobium Fredii WGF03

Sinorhizobium fredii WGF03is a kind of producing exopolysaccharides (EPS) of gram-negative bacteria, it can form symbiotic interaction with root or stem of leguminous plants, it can make the gaseous nitrogen reduction into ammol/Lonia in the environment.With data reported exopolysaccharides (EPS) is one of the signaling molecule of Rhizobia invasion of leguminous plants.In this study,screening exoR, exoD two genes from genome mapping of S.fredii WGF03,through homologous double-crossover respectively buildΔexoR,AexoD mutants,found that two mutants production less exopolysaccharides (EPS) than wild type strain on YMA medium plate. Vaccinating soy seedlings, the number of root nodules is more than wild type, small and have different shape, profile mostly white or light yellow. Acetylene reduction method to determine mutant nitrogen fixation is smaller than the wild type strain.The nitrogenase of wild type strain WGF03,ΔexoR,ΔexoD is respectively23.61nmolg-1·h-1,8.24nmolg-1·h-1and7.14nmolg·h-1. Nodular time measurement:in the13d-16d, the number of noduling plants of mutant strains is more than wild type strain and the mutant strains reach50%of the plants of nodules in the13day,all plants complete the nodules about22days.Development research in sodium salt tolerance of mutant△exoR,△exoD,found that the low concentration of salt stimulates the growthing of wild strain WGF03,△exoR andAexoD mutant, OD600values of mutantAexoD rather than fell sharply with the increase of salt concentration, in contrast, less than50mmol/L-350mmol/L of salt concentration, bacteria can maintain relatively stable growth state, preliminary judgeAexoD for salt resistant strain. Comparing with motility of△exoR,△exoD mutant and wild type strain by0.3%of dilute agar plate, found that mutant motility decreased significantly. Phenotypic characterization and plant experiments result show that exoR, exoD gene effect exopolysaccharides synthesis in S. fredii WGF03, preliminary judge that they affect nodulation and nitrogenase activity at the same time. Although this study constructed the△exoR and△exoD mutants, but the mechanism of exopolysaccharides synthesis, nodulation and nitrogen fixation with host plants need for further experimental study.