Research On The Bioaccesibility Of HgS By Shewanella Oneidensis MR-1

Mercury as a special heavy metal has paied more and more attention by peoplebecause of its easily global pollution. In the natur, mercuric sulfide which has a very lowsolubility widely exists in the ore，sediment and soil. And any form of mercury cantransform into methylmercury under the action of microbes. Sulfate reducing bacteriawhich is a mercury methylation microorganism was mainly studied, while the ironreducing bacteria Shewanella oneidensis MR-1has been little researched, speciallymercuric sulfide under the action of S.oneidensis MR-1has been rarely researched if it willcause mercury pollution in the environment. The biological dissolution and methylation ofsolid HgS by S.oneidensis MR-1and influenced factors under laboratory conditions wasresearched. The research provided direct evidence to biological solubility and biologicalmethylation on solid HgS by iron-reducing bacteria in the natural aquatic ecosystem, andproved that the solid mercuric sulfide was also one of the major sources of environmentalmercury pollution. The main research contents and results were as follows：1. Through the pure culture microbial experiment, the iron reducing bacteria S.oneidensisMR-1has a certain tolerance of sulfide concentration.But S.oneidensis MR-1could notsurvive When the sulfide concentration was exceeds3.4mg L^-1. S.oneidensis MR-1couldgrow, but its growth was inhibited when the concentration of Na2S less than3mg L^-1,which mainly expressed in the prolonged lag phase but had no significant effect for thetime of logarithmic growth period.2. The different influencing factors of dissolution of solid HgS without S.oneidensis MR-1was researched. The results showed that the dissolution of solid HgS would slightlyincrease under different influencing factors, but the maximum concentration was no morethan30μg L^-1. In addition, the solubility of HgS was enhanced with the increasingconcentration of Na2S, and neutral or alkaline environment was more beneficial todissolution of HgS than acidic and weakly acidic conditions; the solubility of HgS wasenhanced with the increasing concentration of humic acid, but different concentrations ofcysteine had no effect to the dissolved quantity of mercuric sulfide.3. The biological dissolution of solid HgS by S.oneidensis MR-1were studied underlaboratory conditions with different influencing factors such as different concentrations ofNa2S, humic acid, cysteine and pH values. The results showed that the biological solubilityof HgS was enhanced with the increasing concentration of Na2S and humic acid, and weakly acidic environment was more beneficial to biological dissolution of HgS thanacidic, neutral or alkaline conditions, but the concertration of cystein had little effect by S.oneidensis MR-1. In addition, from the perspective of quantity of dissolved solid mercuricsulfide,iron reducing bacteria S.oneidensis MR-1greatly promoted the dissolution of thesolid mercuric sulfide.4. The study found that in the process growth of iron reducing bacteria S.oneidensis MR-1could convert the dissolved mercuric sulfide into methyl mercury. The results show thatunder the condition of mercuric sulfide1mg,30℃, pH6.0, the concentration of sodiumsulfide1mg L^-1, total volume20mL, the methylation rate of mercuric sulfide by S.oneidensis MR-1reached30%; When other conditions were the same, humic acidconcentration of5mg L^-1, the maximum biological methylation rate of mercuric sulfidereached10.55%by S. oneidensis MR-1; When adding300mg L^-1cysteine could increasethe methylation rate up to19.16%.5. The biological methylation of solid HgS by Shewanella oneidensis MR-1were studiedunder laboratory conditions with different influencing factors.The results show that theiron reducing bacteria S.oneidensis MR-1under the appropriate concentration of sodiumsulfide, could rapidly promote the biological methylation of HgS. But when the sodiumsulphide concentration range of2.0mg L^-1～3.0mg L^-1would have an inhibition ofmethylation of HgS, and weakly acidic environment was more beneficial to biologicalmethylation of HgS than acidic, neutral or alkaline conditions; and the quantity ofbiological methylation of mercuric sulfide increased with the increasing concentration ofhumic acid when the concentration range of humic acid to1.0mg L^-1～5.0mg L^-1, while itwould have an inhibition when humic acid concentration was5.0mg L^-1～10.0mg L^-1byS.oneidensis MR-1; Different concentrations of cysteine could increase biologicalmethylation of mercuric sulfide by S. oneidensis MR-1, and accelerate the process ofreaction.