Regulation Of AHL Quorum Sensing System On The Zn-resistant Behavior Of Aeromonas Veronii N8

In recent years,the pollution problem of heavy metal is increasingly serious.Heavy metal is difficult to be degraded and easy to be accumulated,and therefor restrict the sustainable development of environment.It is very important to find a way that can effectively remove heavy metals problem.Recently,widely used method is biosorption which has more advantages than traditional ways.Previous studies showed that,Quorum sensing(QS)system mediated by the acyl-homoserine lactone(AHL)can control the habits and a variety of physiological responses of bacterial cells such as bioluminescence,anti-stress reaction,biofilm formation,virulence factor expression antibiotic synthesis and spore formation etal.However,until now there is a little information about the regulation of QS system on the biosorption for heavy metal.In the study,the effects of Zn2+stress on growth behavior of N8/?LuxI and N8/?LuxR were analyzed,which is important to reveal the regulation effects of AHL system on the Zn-resistance behavior of Aeromonas veronii N8.The main research results were shown as follows:(1)The properties and Zn2+ adsorption characterizations of the loose extracellular polymer substances(LB-EPS)and the tight-binding extracellular polymeric substances(TB-EPS)from Aeromonas veronii N8,N8/?LuxI and N8/?LuxR were studied.The results showed that both EPS displayed the different composition proportion of protein and polysaccharide;The spectrums of1H NMR and XPS suggested that although TB-EPS and LB-EPS had the similar chemical structure and element composition,the composition ratio of various elements in both EPS was different.TB-EPS and LB-EPS also exhibited a similar Zn2+adsorption rule in which the adsorption balance of both EPS could be achieved for 90 minutes,but adsorption rate of LB-EPS was bigger than TB-EPS,N8 LB-EPS had the biggest adsorption rate in different extracellular polymeric substance.The adsorption rates of both EPS were increased with the EPS concentration and decreased with the Zn2+concentration.After adsorption,the FTIR spectrums of both EPS showed that some changes had taken place in the strength or position of some characteristic peaks originated from DNA,protein and polysaccharide,which implied that those functional groups acted the different function roles for the Zn2+adsorption.The Zn2+adsorption process of N8 LB-EPS and N8 TB-EPS might be described by Freundlich and Temkin models,EPS mutant strains of Zn2+adsorption processes can be described using the Freundlich and Sips model.(2)The properties and Zn2+ adsorption characterizations of bacterial cells of Aeromonas veronii N8,N8/?LuxI and N8/?LuxR were studied.The results showed that Aeromonas veronii N8 growth cycle was about 66h,and a minimum concentration for Zn2+was 150mg/L.Under the same conditions,the growth speed of N8/?LuxI strains was slowest and Zn2+adsorption capacity of N8/?LuxR was weak.During the adsorption process,the adsorption rate of original strain was larger than other strains,which means that the Zn2+ adsorption rates are related with the AHL quorum sensing system.After Zn2+adsorption,all the bacteria was analyzed by SEM+EDX.The results proved that the Zn2+adsorbed on the surface of bacterial cell wall.Moreover,the Zn2+ adsorption process of original strain and mutants might be described by Toth models.(3)The production and Zn2+ adsorption characterizations of biofilm of Aeromonas veronii N8,N8/?LuxI and N8/?LuxR were studied.The results showed that biofilm production of all bacteria were increased first with the time and then decreased.Biofilm production of the original strain of the largest and LuxI deleted strain was minimum.The minimum biofilm eradication concentration(MBIC)of Aeromonas veronii N8,N8/?LuxI and N8/?LuxR were different,original strain's maximum,while N8/LuxI's was weakest.Biofilm of original strain and mutants also exhibited a similar Zn2+ adsorption rule in which the adsorption balance could be achieved for 90 minutes,biofilm adsorption rate of original strain larger than the strains.The adsorption rates of biofilm were increased with the biofilm concentration and decreased with the Zn2+ concentration.The Zn2+ adsorption process of original strain and deletion mutant might be described by Radke-Prausnitz models.