Interaction Between The Root Exudates Of Sedum Alfredii And The Quorum Sensing In Pseudomonas Aeruginosa

The extensive use of antibiotics caused the residual of antibiotics in soil and other environmental medium,which induce the antibiotic resistance genes.Nowadays,the pollution of the antibiotic resistance genes has been a new and global environmental issue.It is one of the few methods to prevent the pollution of the antibiotic resistance genes that regulating the quorum sensing to inhibit the producing and horizontal dissemination of antibiotic resistance genes.Most of the known quorum sensing inhibitors are synthetic products,which are too specific and expensive to be widely used in practical engineering.It is urgent to find a green,easy to get,cheap and natural quorum sensing inhibitor and root exudates of plant become one of the best available source.Based on Zn/Cd hyperaccumulator Sedum alfredii and Pseudomonas aeruginosa,a model bacterial for studying quorum sensing,we explored the interaction between the root exudates of S.alfredii and quorum sensing in P.aeruginosa.The present study can not only expand the species of quorum sensing inhibitor and the mechanism of quorum sensing inhibition,but also enrich the basic theory of the effect of microbial quorum sensing on plant growth,development and phytoremediation.The main conclusions of this study are follows:(1)Adding 25 ?mol/L C4 signal molecule,25 ?mol/L 3-oxo-C12 signal molecule and 25 ?mol/L C4 and 3-oxo-C12 signal molecule into the nutrition solution of S.alfredii.In all signal molecule treatements group,chlorophyll a,chlorophyll b and total chlorophyll content in leaves of S.alfredii were all significantly increased compared with the blank control group;In all signal molecule treatements groups,chlorophyll a occupy the dominant position in the total chlorophyll,and they had a same trend: 3-oxo-C12 signal molecular treatement group > C4 signal molecular treatement group > C4 and 3-oxo-C12 signal molecule treatement group.There is no significant influence on the content of the soluble sugar in the root exudates of S.alfredii in all signal molecule treatement groups.The oxalic acid content in the root exudates of S.alfredii were significantly increased with 25 ?mol/L 3-oxo-C12 signal molecule treatements.With 25 ?mol/L C4 signal molecular treatement,the MDA content in the leaves of S.alfredii were significantly increased.In all signal molecule treatement groups,the decrease of SOD activity were only appeared in roots and stems,SOD activity in leaves and CAT activity in roots and stems are significantly increased.(2)Under a gradient(the final concentration are 0,1×,2×,5×,10×)volume concentration of root exudates of S.alfredii,the growth of P.aeruginosa was no significant influence;The treatments of the root exudates of S.alfredii could significantly inhibit the activity of extracellular protease of P.aeruginosa with a concentration dependent coefficient,the inhibitory effect of extracellular protease activity rising with the rising of the concentration of root exudates of S.alfredii.Twelve substances of root exudates of S.alfredii were idetntified by GC-MS.As an inhibitor on the activity of protease of P.aeruginosa,thymol was identified from the twelf root exudates of S.alfredii with 50 ?mol/L.(3)With 50 ?mol/L thymol treatment,the activities of extracellular protease and elastase of P.aeruginosa were significantly decreased;Thymol is not directly as an enzyme inhibitor of elastase of P.aeruginosa,and its inhibition of elastase of P.aeruginosa is realized by affecting its quorum sensing system;The gene expression of lasB was significantly decrease by 50 ?mol/L thymol.However,the gene expression of lasI and lasR genes and the content of 3-oxo-c12 signal molecular were not significantly changed.Thymol could not as an agonist or antagonist of LasR transcriptional regulator of Pseudomonas aeruginosa to inhibit the activity of elastase.The 50 ?mol/L thymol can significantly promote the gene expression of rhl quorum sensing system genes(rhlI and rhlR)and the secretion of the downstream virulence factor,rhamnolipid;Similarly,thymol can also significantly promote the gene expression of pqs quorum sensing system genes(pqsH and pqsR)and the secretion of the downstream virulence factor,pyocyanin.