Molecular Mechanisms Of Bacillus Strain Colonization On Tomato Root Surface

In the interaction progress between plant growth-promoting bacteria(PGPR)and plants,PGPR must colonize on the plant root surface and subsequently can play an important role for plants.As is well known,colonization is an important prerequisite for growth promoting and biocontrol of Bacillus subtilis.In addition,biofilm formation is one of colonization-related phenotype.However,the mechanism of colonization and biofilm formation under adversity stress are poorly understood at the molecular level.So this study is very important for agricultural development.The main results obtained in this study were summarized as below:(1)At the early stage,we have obtained 4 genes involved in colonization.The 4 colonization relative genes are bltR?lysC?yjbQ and minJ.However,the way that 4 genes effect colonization of Bacillus subtilis is little known until now.In this research,we construct single-point mutants of the 4 genes by DNA homologous recombination,and find all the mutants are colonization-defective on tomato roots.In another way,compared with wild type,yjbQ mutant produces less exopolysaccharides(EPS),which is an important component of biofilm.In addition,minJmutant is defective in swarming motility.(2)Studies have suggested that biofilm formation by B.subtilis plays an important role in its colonization on plant root.However,research about bacillus under abiotic stress is little reported.In this study,we chose different salts ions and found Zn2+ ion can suppress biofilm formation of Bacillus amyloliquefaciens.The mechanism remains to be further explored.(3)In this study,four histidine kinases kinA,kinB,kinC,kinD mutants were constructed by homologous recombination double exchange in Bacillus amyloliquefaciens FZB42.Their biofilm formation were tested for quantification and their production of exopolysaccharides(EPS)for qualitative analysis.Compared with wild FZB42,the kinC,kinD mutants formed thinner and flatter biofilm;the deeper colour of kinA mutant solution means it produced more cytochromes.However,there was no obvious difference in the production of exopolysaccharides.This study suggested four histidine kinase genes are one-to-one correspondence in the biofilm network.They cannot replace each other and should work together,rather than a single one to regulate the expression of downstream gene.