Study On Induced Mineralization And Adsorption Of Cd²⁺ By A Cd Tolerant Bacteria

The process of Karst mountain carbonate weathering and soil formation is closely related to the vital activities of microorganisms.The growth and metabolism of the microorganisms and the induced biomineralization process have a certain important impact on the migration and transformation of heavy metal ions.The exploration of the bio-induced mineralization of calcium carbonate minerals for the retention of heavy metals is thus of great significance for understanding the unique ecological function of rock-forming microorganisms in the Karst area.In this study,a predominant cadmium-tolerant bacterium-Pseudomonas nitroreducens DH-1 was selected and isolated from cadmium-rich farmlands in the Karst area.The adsorption characteristics to Cd²⁺ of both this bacterium and the inducting substance were studied.The adsorption characteristics of calcium carbonate to Cd²⁺,the mechanism of adsorption of Cd²⁺ via the bacteria and its induced calcium carbonate were preliminarily discussed.The main research results are as follows:1.A strain of cadmium-tolerant bacteria named DH-1 was selected from cadmium-rich farmland in Luodian County,Guizhou Province.It was found that the bacteria can grow in LB solid medium with a Cd²⁺ concentration of 800 mg·L-1,which showed that it has a strong tolerance to cadmium;2.The cultivation and growth curve of DH-1 strain showed that the strain has a logarithmic growth period from 2 to 16 h first,a stable period from 16 to 44 h afterwards,and ends up to a recession period.The bacteria is rod-shaped,gram-negative,motile,oxidase positive,hydrolyzed starch negative,nitrate reducing,gelatin not liquefying.Compared to the sequencing results of its 16 S r DNA sequence,a highest homology was obtained with Pseudomonas nitroreducens bacteria?similarity reached 99.02%?;3.The growth curves of Pseudomonas nitroreducens DH-1 under different concentrations of Cd²⁺ showed that: when the concentration of Cd²⁺ is lower than 30mg·L-1,the effect on the growth of bacterial is less,and the growth of strain will not be inhibited;when the concentration of Cd²⁺ treatment increases above 50 mg·L-1,the growth of bacterial will be significantly inhibited;and when the concentration reaches150 mg·L-1,the strain cannot grow;4.The results of the adsorption test for this strain showed that in 100 m L ofsterilized LB liquid medium(Cd²⁺ 10 mg·L-1,p H=7.0),2% of the seed solution is inserted.Under the conditions of 30?,180 r·min-1 shaking culture for 96 h,the adsorption effect is the best,and the removal rate of Cd²⁺ reaches 63.40%;5.The experimental results of bacteria-induced mineralization showed that with the increase of Ca?NO₃?₂?1?10 g·L-1?,the calcium carbonate induced could be gradually transformed from bio-sourced amorphous calcium carbonate?ACC?to biological source vaterite?BV?,and the effect is best with a dosage of 5 g·L-1;6.The adsorption of Cd²⁺ on calcium carbonate induced via Pseudomonas DH-1was studied.The results showed the best effect of mineralization induction and adsorption of the LB liquid medium could be reached when it is inserted into the LB liquid medium of 2% seed liquid at 30? and 180 r·min-1 shaking culture for 7 d with10 mg·L-1 of Cd²⁺ and 5 g·L-1 of Ca?NO₃?₂,and the mineralized calcium carbonate induced by DH-1 has the best adsorption effect,and the removal rate of cadmium in the medium can reach 98.99%.The results showed that DH-1 is a dominant bacterium which can resist cadmium,and the mineralized calcium carbonate induced has a good adsorption and retention capacity for cadmium.It can be used to repair cadmium pollution in the environment.This study provides a scientific basis and a new idea for the development of new technologies for the prevention and control of heavy metal pollution.