The Isolation Of Antimony Resistant Bacteria And The Effect On Antimony Uptake And Accumulation In Paddy Rice

As a typical toxic metalloid,Antimony?Sb?has sharply increased and been the ninth most mined metal worldwide,due to its commercial importance in industrial applications.With the Sb related applications and mining/smelting activities,uncontrolled Sb often releases into the environment,resulting in elevated concentrations of Sb in the soils,sediments,waters and biota.China has the world's most abundant Sb mineral resource,and the majority of all the 114 antimony mines in China are located in the south/southeast of this country.These Sb mine areas face serious Sb contamination in soils,water systems and plants.Likewise,in the Sb mine areas,people live on rice grain as the staple food.Rice plants were reported to accumulate high concentrations of Sb.Hence,more attention should be paid to the uptake and accumulation of Sb in rice,with perspective of a better understanding of its health risk to human beings.Further,heavy metal resistant bacteria on the rhizosphere can alleviate heavy metal accumulation in rice plants.However,Sb resistant bacteria and their effects on Sb uptake,accumulation and transport in rice plants have been poorly documented.Therefore,the present study started with the investigation of Sb and other heavy metal contamination in soils of typical Sb mine area-Xikuangshan,as well as the microbial community in the soil of this area.Sb resistant bacteria in this Sb contaminated soils were also isolated,screened and identified.Among,one of three strains of identified Sb resistant bacteria?named B1 in this study?,which can colonize on the rice rhizosphere was used to alleviate the Sb contamination in rice plant.With the present study,we could better understand the interaction between iron plaque and Sb resistant bacteria on rice root;furthermore,we could develop the efficient bioremediation of Sb contamination in soils or rice plant with Sb resistant bacteria,which in return promote the safe production of grain crops in the Sb mine area.Through this study,we found that:1.The average concentration of Sb in the typical Sb mine area-Xikuangshan was356.58 mg kg^-1,and it was 119 times of the background values in Hunan province.Further,the average concentrations of cadmium?Cd?,zinc?Zn?and copper?Cu?were 9.98 mg kg^-1,486.42 mg kg^-11 and 53.13 mg kg^-1,being 117,5.17 and 3.79 times of their corresponding local background values,respectively.Using Pearson and PCA analysis,it indicated that Sb mining and/or smelting activities cause co-pollution of Sb and arsenic?As?,and Zn mining and/or smelting were relating to Cd pollution in this mine area.Considering the multiple heavy metal pollution,the comprehensive pollution index were far more than 5,which indicting the extremely serious pollution level in the soil of the studied area.2.Although the extremely serious pollution level,the OTUs in the soils?per 2 g?were955-1925,and the Shannon induces were 4.79-6.04.It indicated that a large number of bacteria survive in the Sb and other heavy metal contaminated soils.According to the unclassified DNA sequencing based on the phylogenetic classification of species,it implied that a large quantity of Sb resistant bacteria have not yet be discovered,and it also indicated that the study area is an important bio-resource for heavy metal bioremediation with bacteria.3.The present study isolated three strains of Sb resistant bacteria using Sb contaminated soils.With phylogenetic identification,B1strains was of Ochrobactrum.sp,B2 and B3 were of Bacillus.sp.Among these three strains,B1and B2 were showed antimonite resistant ability,and both of their MICs for antimonite were>20 mM,however,the MIC of B3 for antimonite was<1 mM.Furthermore,this study found that strain B1 could perform the antimonite detoxification through the production of Sb2O3 precipitation.The antimonite detoxification of strain B2 remains unclear in the present study.4.When Sb(both Sb^III and Sb^V)enters the waterlogged paddy soils,they can be adsorbed immediately by soil phase.However,it showed that there were still a proportion of Sb remained in the soil solutions after Sb equilibration in soil-solution system.5.In the entire growth period of rice plant,Sb accumulation in the rice tissues were in the order of:IPs?roots?straws>husks?ears>rice grains.In the Sb^III treatments,the IP formations and rice root uptaken Sb sharply increased from tillering to jointing stages,and slightly declined in the following growth stages.However,in the Sb^V treatments,IP formation and rice root uptaken Sb continuously increased in the whole rice growth period.Further,Sb concentration changes in rice straws,ears and grains on growth stages were similar in both Sb^IIIII and Sb^V treatments.6.Compared with Sb^V,Sb^III is more easily uptaken by rice roots.However,since rice straws,ears and husks in The Sb^III treatments also accumulated more Sb than that in Sb^V treatments,Sb concentrations in rice grains in Sb^III treatments were comparable with that in Sb^V treatments.Further,the TF_soil-grainoil-grain decreased with increasing Sb treatment level,but when Sb concentrations in soils were more than 50 mg kg^-1,there were substantial potential human health risk through rice grain consumption.Under this circumstance,certain efficient managements on Sb in paddy soils should be taken into consideration.7.With the alleviation of Sb resistant bacterium?B1?,the EC50 of both antimonate and antimonite for rice seedlings?Zhongjiazao-17?increased.In Sb^IIIII treatments,the inoculum of Sb resistant bacterium increased the siderite fraction in iron plaque;however,the formation of iron plaque was not promoted.By contrast,the Sb resistant bacterium enhanced the iron plaque formation in Sb^v treatments.The Sb resistant bacterium inhibited the oxidation of Sb^IIIII into Sb^V,which was adsorbed on the iron plaque.Apparently,Sb resistant bacterium decreased the uptake of both Sb^III and Sb^V concentrations in rice roots,and it decreased the transport of Sb from root to shoot both in Sb^III and Sb^V treatments.