Isolation Of A Cd-resistant Bacterium And Its Effect On Cadmium Accumulation In Rice(Oryza Sativa L.)

Contamination of heavy metals has been increasing in recent years due to industrial activities.It is not only harmful to the ecological environment,but also to human health through the food chain.Microbial remediation of heavy metal polluted soils has received increasing interests.In the present study,a bacterial strain,B9,with high cadmium adsorption capacity was isolated from cadmium-polluted soils through a conventional method of bacterial isolation and cultivation,and the effects of the strain on soil Cd speciation were investigated by a pot experiment to evaluate the feasibility of using B9 in Cd bioremediation.The isolate was also evaluated for promoting plant growth and Cd uptakes of the different rice from heavy metal-contaminated soils.The main results are as follows:1.12 microorganisms resistant to Cd were screened from the Cd contaminated soil.No.B1 to No.B9 strains were bacteria,and No.F1 to No.F3 were fungi.The concentration of microorganisms resistant to Cd were 350 mg·L^-1.The results of 16S rRNA gene sequence analysis showed that B9 was 99%homologous to Delftia acidovorans,and was identified as Delftia sp.by morphological and biochemical analysis.The strain was also treated with scanning electron microscopy equipped with energy-dispersive spectroscopy?SEM-EDS?,transmission electron microscopy equipped with energy-dispersive spectroscopy?TEM-EDS?to understand the Cd²⁺biosorption behavior for the cells.It was found that the highest adsorption efficiency for Cd²⁺was achieved at pH 8,35?,and 48 h of incubation time.In these conditions,more than 60%of the Cd²⁺could be adsorbed from a concentration below 10mg·L^-1.And the Cd uptake for cells attributed to intracellular and surface biosorption.2.The experiment was conduced by three rice varieties with low Cd tolerance with different concentrations of Cd(0,0.01,0.1,1,10 mg·L^-1)and Delftia sp.B9 for 7 days.The germination rate?GR?,germination index?GI?,vigor index?VI?,tolerance index?TI?,stress index?SI?were emphatically analyzed,and the effects of the strain on soil Cd speciation were investigated by a pot experiment to evaluate the feasibility of using B9 in Cd bioremediation.The results showed that the effect of adding diluted 100 and 1000 times of B9significantly increased rice seed germination rate.When the Cd concentration was 0.01 and0.1 mg·L^-1,the effect of adding B9 on the germination and tolerance of rice seeds was not obvious.When the concentration of cadmium was 1,10 mg·L^-1,B9 bacterial fluid on rice seed germination and tolerance coefficient has a significant role in promoting.There were differences in the effects of cadmium stress and B9 on seed germination among different rice cultivars.When the concentration of cadmium was high,the stress index of rice seed germination was:Zhuliangyou 819>Huarun 2>Shenliangyou 5814.When adding B9 the stress index of the germination of rice seeds was:Shenliangyou 5814>Zhuliangyou819>Huarun 2.B9 could facilitate Cd transformation from weak acid-soluble to reducible and residual phases in soil.The addition of 3 mL and 10 mL bacterial suspensions into the soil resulted in 22.17%and 25.06%decreases in the content of weak acid-soluble Cd,9.66%and12.17%increases in the content of reduced Cd,and 13.55%and 13.61%increases in the content of residual Cd,respectively,whereas the content of oxidized Cd did not significantly change.3.The isolate was also evaluated for promoting plant growth and Cd uptakes of the different rice from heavy metal-contaminated soils and the effects of the strain on the Cd speciation in the soil in pot experiments.Added live cells to compared control were observed on early rice?Z39?,rice weight was increased 23.14%.For Z39 growing in soil with added suspension of dead cells,roots,stems,leaves,grains Cd concentrations were decreased 1.371,0.157,0.209,0.247 mg/kg compared to the control,respectively.The average content of F?I?with live and dead cells decreased by:0.076 and 0.056 mg/kg with the treatments of control,the average content of F?IV?with live and dead cells increased by:0.102 and 0.145 mg/kg with the treatments of control.Distribution fractions of Cd in soil followed the order of exchangeable?FI?>easily reducible?FII?>oxidizable?FIII?>residual?FIV?without treatment,while exchangeable?FI?>easily reducible?FII?>residual?FIV?>oxidizable?FIII?after treatment.