Effect Of 1-aminocyclopropane-1-carboxylic Acid Metabolic Rate On The Chemotaxis Of Pseudomonas Putida UW4

Pseudomonas putida UW4 is a typical plant growth promoting bacterium(PGPR)with producing 1-aminocyclopropane-l-carboxylic acid(ACC)deaminase(ACC deaminase,AcdS).Our previous study found that UW4 can chemotaxis to ACC.ACC is a key chemoattractant for UW4 rhizocompetence and rhizosphere colonization through chemotaxis,consequently enhancing its chemotaxis response intensity to ACC should increase its rhizocompetence and rhizosphere colonization and lay a solid foundation for its promoting plant growth effect.In this study,we used the bacterial promoters with different expression intensity to express AcdS gene in UW4 AcdS deletion mutant,and investigated the effect of ACC metabolic rate on the chemotactic response intensity of UW4 to ACC.The brief results are as follows:1.Three bacterial promoters PB20,PB10 and PB1,rank ordered by expression levels from high to low,and UW4 AcdS gene promoter PA were selected to express the UW4 AcdS gene.The promoters and the downstream AcdS genes were ligated to the shuttle expression plasmid pBBR1MCS2,respectively,and four AcdS expression plasmids were constructed.2.Four AcdS expression plasmids were transferred into UW4 ?AcdS strain by three-parent transfer method,and four strains were successfully constructed,named UW4?AcdS+PB1-cdS,UW4?AcdS+PB10-AcdS,UW4?AcdS+PB20-AcdS,UW4?AcdS+PA-AcdS.3.In the liquid LB medium,the growth curves of UW4,UW4 ?AcdS,UW4?AcdS+PB1-AcdS,UW4 ?AcdS+PB10-AcdS,UW4 ?AcdS+PB20-AcdS,UW4?AcdS+PA-AcdS were determined.There was no difference in the growth rate of the five strains.4.The AcdS gene expression and enzyme activities of the five strains were determined.The expression levels of AcdS genes from high to low were UW4?AcdS+PB20-AcdS>UW4 ?AcdS+PA-AcdS>UW4 ?AcdS+PB10-AcdS>UW4,UW4?AcdS+PB1-cdS.The activities of AcdS enzymes of the five strains from high to low were UW4 ?AcdS+PB20-AcdS>UW4,UW4 AAcdS+PA-AcdS>UW4?AcdS+PB10-AcdS>UW4?AcdS+PB1-AcdS.5.Chemotaxis to ACC of the five strains was tested.The chemotaxis intensities of the strains from strong to weak were UW4 AAcdS+PB20-AcdS>UW4,UW4?AcdS+PA-AcdS>UW4 ?AcdS+PB10-AcdS>UW4 ?AcdS+PB1-AcdS.The diameters of the chemotactic rings in response to ACC of the five strains were significantly positively correlated with the AcdS enzyme activities.The above results indicated that using bacterial promoters with different expression levels to express UW4 AcdS gene,and the AcdS enzyme activities of the transformed strains were significantly positively correlated with the diameters of the chemotactic rings in response to ACC;therefor the chemotactic response intensities of the strains to ACC were depended to the metabolic rates of ACC.