The Strengthen Effect Of Endophytic Bacteria From Ramie On The Remediation Of Cadmium Polluted Soil

The rapid developments of industry and agriculture have caused serious Cd polluted soils.Traditional physical and chemical ways to deal with Cd polluted soil were accompany with large amount of work and high cost,but small area can be repaired.The application of new chemical reagents caused secondary pollution.Single phytoremediation or microbial remediation would be low efficiency.It would be a hot method which makes use of microorganisms to enhance the phytoremediation of Cd contaminated soils.Two strains with Cd tolerance were isolated from ramie,and their capacity of secreting indole-3-acetic acid?IAA?,producing siderophores and dissolving CdCO₃ were studied.Meanwhile,the effect of two strains on the geo-speciation of Cd was analyzed.The pot experiments were carried out to investigate the strengthen effect of endophytic bacteria on the growth and phytoextraction of Cd from contaminated soils.The main researche contents are as follows:1.Isolation and identification of cadmium-resistant endophytic bacteria from ramie.Two strains WG-1 and WJ-3 isolated from ramie around the smelter beside Qingshuitang Industrial Park in Zhuzhou are tolerant to Cd with the concentrations of 60 mg/L and 80 mg/L,respectively.They were identified as Bacillus sp.by scanning electron microscope,physiological and biochemical characteristics and 16S rDNA gene sequence.2.Studies on biological characteristics of cadmium-resistant endophytic bacteria from ramie and the optimum conditions.The growth curves of WG-1 and WJ-3 were studied and the optimal pH and NaCl concentration were also determined.The effects of carbon source,nitrogen source,temperature,shaking speed,and pH on strain WJ-3growth and the production of IAA and siderophore were studied,respectively.It was found that the time of entering the exponential growth phase of two strains were 8 hours and the optimal pH and NaCl concentration were 7.0 and 0.5%,respectively.The optimal carbon and nitrogen source were glucose and yeast extract.The optimal cultivation conditions were with temperature at 30?,180 r/min for shaking speed,and pH 7.0 in the initial medium.The WJ-3 biomass increased and the microbial siderophore could increase from 52.31%to 64.12%after shaking culture for 48 h.Differently,the microbial IAA could increase from 4.28 mg/L to 5.51 mg/L when the optimal carbon was tryptone.In addition,strain WJ-3 had the ability of dissolving CdCO₃ and the cadmium concentration in culture supernatants increased from 0.029?g/L to 4.978?g/L.3.The effects of cadmium-resistant endophytic bacteria from ramie on the ramie growth and the Cd accumulation.The effects of strains WG-1 and WJ-3 on pH and the geo-speciation of Cd contaminated soil were evaluated.It could be concluded that strain WJ-3 can decrease soil pH and the WJ-3 can convert bound to organic and Fe-Mn oxides to exchangeable Cd in contaminated soil.The pot experiments were carried out to investigate the strengthen effect of endophytic bacteria on ramie growth?plant height,fresh weight,dry weight?and the Cd accumulation contaminated soils.Compared with the control,the height,resh weight,and dry weight increased by 33.1%,39.8%and 66.7%,respectively.It should be noted that the Cd accumulation in ramie increased by 53.1%eventually.