Effect Of Iron On Population Stablity And Its Mechanism Of Pseudomonas Aeruginosa PAO1

Pseudomonas aeruginosa is a common opportunistic pathogen whose expression is regulated by quorum sensing.Laboratory studies have shown that ammonium as an environmental factor that may affect the stability of quorum sensing,which can lead to population collapse and also prevention of pathogenic infection.As an important environmental factor,iron is closely related with PQS system of quorum sensing,however,few studies have been reported about the effect of iron on population stability.With this basis,P.aeruginosa PAO1 was used as the experimental strain to study the effect of iron on the stability of quorum sensing,and to have an initial exploration about the molecular mechanism behind induction of population stability by iron.The main results are as follows:(1)Iron can affect the population stability of P.aeruginosa PAO1.There was no significant difference in the growth of P.aeruginosa PAO1 at the concentration of iron setting up;in the competing system,there was no group collapse at 0-12.5μM iron concentration;there was 40%groups collapse at 25-100μM iron concentration,the proportion of groups collapse was 60%under the iron concentration of 200μM.The higher the iron concentration,the more unstable the population was.In the long-term evolution system,exogenous iron also affected the population stability of P.aeruginosa.Under 25 μM iron concentration,the collapse of P.aeruginosa was 20%.In long-term evolution system,iron would influence the population less than the competition system,and further exploration is needed to understand it’s mechanism.(2)Iron had been shown different influences on the different quorum sensing systems of P.aeruginosa PAO1.In case of quorum-sensing signal secretion,exogenous iron had little effect on lasI and rhll,but would have been inhibited the expression of pqsH.Compared with non-added iron environment,the expression of pqsH in exogenous iron environment was only 68.01%lower than that of in non-added environment.Iron did not affect the activity of LasR receptors,but significantly inhibited the activity of RhlR and PqsR receptors.The expression of rhlR and pqsR were similar in the presence of iron environment,was only 40%lower than that of in the non-added iron environment.Iron could significantly inhibit the secretion of protease,pyocyanin and rhamnolipid.The secretion percentages of these three extracellular substances in the iron environment were 66.7-91.7%,89.3-93.8%and a range of 58.3-74.3%in non-added iron environment,respectively.Among the three quorum sensing systems,iron had a greater impact on Rh1IR and PQS than LasIR system.However,it’s ability to inhibit the public substance secretion might be one of the main factors to cause population instability.(3)Protease has significant effect on the stability of quorum sensing.Iron affects the secretion of protease by affecting mexT and ampR,then has an effect on the stability of P.aeruginosa population.Rhamnolipid has less effect on the stability of population than protease.Iron mainly influences pyocyanin and rhamnolipid through its influence on rhlR.However,further investigation is still needed to find out whether it also works on other genes.