The Mediation Of Chemotaxis And Biofilm Formation Of Bacillus Atrophicus QHZ3 By Potato Root Exudates And Its Components

The premise of plant growth-promoting and biocontrol of growth-promoting rhizobacteria is to colonize in the rhizosphere,which is mainly mediated by the root exudates of host plants.A plant growth-promoting rhizobacterium strain,Bacillus atrophicus QHZ3,with both growth-promoting and biocontrol effects,was isolated in our laboratory.The strain could colonize on the root surface and multiple parts of potato plants successfully,but the signal substances mediating its colonization were not clear.In this study,hydroponic experiment and GC-MS were used to collect and identify the root exudates of potato seedlings,and the effects of phenolic acids and organic acids in root exudates on the chemotaxis,biofilm-forming and colonization of strain QHZ3 were investigated.The main results are as follows:1.Root secretion mediated the chemotaxis of strain QHZ3,which was closely related to the concentration(1)Thirty compounds were identified from potato seedlings root exudates by GC-MS,including organic acids,carbohydrates,phenolic acids,alcohols,amines,esters,amino acids,fatty acids and amides.Among them,acids and carbohydrates were the most abundant compounds in potato root exudates,but the relative content of organic acids and amines were relatively large,accounting for 29.79% and 29.86% of the total content,respectively.(2)Compared with the control,the root exudates had positive chemotaxis to strain QHZ3 and promoted the growth of strain QHZ3 significantly,and the chemotaxis and growth-promoting effects of root exudates on strain QHZ3 increased significantly with the increase of root exudates concentration.(3)Root exudates could promote the biofilm formation of strain QHZ3,and different concentrations had different effects.The effect of 120-240 ?g/m L root exudates on biofilm formation was the most significant.2.Phenolic acids and organic acids had significant chemotactic effect on strain QHZ3(1)The chemotaxis of phenolic acids and organic acids to strain QHZ3 was qualitatively analyzed by semi-solid plate method.The results showed that all phenolic acids and organic acids except methylmalonic acid had chemotaxis to strain QHZ3,but the degree of chemotaxis was different.Fumaric acid had the strongest effect on phenolic acids,and succinic acid had the strongest effect on organic acids.(2)The chemotactic effects of phenolic acids and organic acids with different concentrations on strain QHZ3 were quantitatively analyzed by capillary-like test,and the results showed that some concentrations of phenolic acids and organic acids had significant chemotactic effect on strain QHZ3.Among the phenolic acids,50 ?mol/L fumaric acid had the most significant chemotactic effect on strain QHZ3,and the number of bacteria in the capillary was 2.8 times higher than that of the control.Among the organic acids,75 ?mol/L succinic acid had the most significant chemotaxis on the strain,and the number of bacteria in the capillary was 4.8 times higher than that of the control.3.Phenolic acids and organic acids could promote biofilm formation of strain QHZ3The effects of phenolic acids and organic acids on biofilm formation of strain QHZ3 were determined by Crystal violet staining method.The results showed that fumaric acid and p-hydroxybenzoic acid in phenolic acids could significantly promote the biofilm formation of strain QHZ3,while ferulic acid and cinnamic acid had no significant effect on the biofilms formation.Organic acids such as succinic acid,azelaic acid and 2,3-dihydroxypropionic acid could significantly promote biofilm formation of strain QHZ3,while 4-aminoacetic acid,glycolic acid,3-hydroxybutyric acid and methylmalonic acid had no effect on biofilm formation.4.Phenolic acids and organic acids could improve the colonization of strain QHZ3 on potato root surfacesThe effects of exogenous phenolic acids and organic acids on the colonization of strain QHZ3 on potato root surface were studied by in situ experiment,and the mediating effect of phenolic acids and organic acids on the chemotaxis and film formation of strain QHZ3 was further verified.The results showed that fumaric acid,succinic acid,azelaic acid and 2,3-dihydroxypropionic acid could significantly promote the colonization of strain qhz3 on potato root surface,The colonization number of strain QHZ3 was 1.31,1.65,1.46 and 1.39 times of the control,respectively.Other phenolic acids and organic acids had no significant effect on the colonization of strain QHZ3 on potato root surfaces.