Isolation And Characterization Of Arsenic-resistant Endophytic Bacteria From Hyperaccumulators Pteris Vittata And Pteris Multifida

Environmental contamination by arsenic has been a serious problem worldwide.Natural sources including paroxysmal eruption,rock weathering resulted in high As background level in enviroment.While anthropogenic sources including arsenical pesticides,food additives and coal burning have intensified arsenic contamination in environment.Pollution of food chain is the main pathway of As exposion,presenting a serious threat to human health.As not only can induce acute,subacute or chronic toxic effect on human,but also is one of the most dangerous carcinogens well know.Thus it is an urgent problem to remove As accumulated in water and soil systems so that can prevent people from arsenic poisoning.Phytoremediation is a effective technology which can be used in As contamination remediation.Compared with traditional approachs,it has the advantages of being low cost,high efficiency and easy manage.However,there are several limiting factors like low plant biomass and limited metal uptake affecting its effectiveness.To enhance phytoremediation,more and more researches have focused on the roles of plant-associated microbes,which impact the efficiency of metal extraction by plants.Some studies proved that combining endophytic bacteria with plants is benefit to alleviation of metal toxicity and enhancement of phytoremediation.However,there is little information available on endophytes associated with P.vittata and P.multifida and their roles in As tolerance and transformation.In this study,74 As-resistant endophytic bacteria(AEB)were isolated from two arsenic hyperaccumulators:P.vittata and.multifida and identified based on 16S rRNA.Then their plant growth promoting traits,As tolerance and transformation capacities as well as the relation between As tolerance and transformation were evaluated.The main results are as follows:1.A total of 41 and 33 AEB were isolated from Pteris vittata(PV)and Pteris multifida(PM)respectively.PV AEB represented 2 genera while PM AEB comprised of 12 genera,with Bacillus sp.being the most dominant bacteria from both plants.2.Except PVR 12 and PVR20,other AEB from both plants all could product IAA,with the ones from roots had higher IAA production ability than those from shoots.But all AEB had limited ability in solubilizing P and producing siderophore.3.All isolates showed 10 mM AsV tolerance while only some tolerated 10 mM As?.PV endophytes were more tolerant to AsV while PM endophytes were more tolerant to As?.4.6 selected bacteria were verified to have the dual capacity of AsV reduction and AsIII oxidation.The bacteria from PM shoots had better ability in reducing AsV than oxidizing As? while those of PV shoots were better in oxidizing As?.The ability of PV endophytes to reduce AsV and oxidize AsIII was related to their As tolerance while those of PM endophytes was not.Bacterial arsenic tolerance was also related to their ability to retain As in the biomass to a varying extent.