| Dissimilatory Iron Reduction （DIR）, a process of microbial metabolism, and in this processthe microorganism use the insoluble iron oxides which extracellular microorganisms asterminal electron acceptor to oxidated the electron donor, by coupled with Fe （Ⅲ） forreduction, in paddy soil, DIR can reduce the toxicity of toxic heavy metal, aromatichydrocarbons, some organic pollutants halogenated aromatics and some dye compounds,inhibit the production of methane. The tannic acid and pyrogallic aicd can increase thesolubility of iron oxide by generated complex compound with Fe（Ⅲ）, thus promotingFe（Ⅲ） reduction. The strains of S.oneidensis MR-1can grow both in the aerobicenvironment and the anaerobic conditions, not only can bioremediate the halogenatedorganic pollutants, but also can restore and dissolve some insoluble metal oxides. Thispaper selects the strain as the research object, studied the effects of different factors on theFe（Ⅲ） reduction rate of S. oneidensis MR-1by adding the complexing agent in paddy soil.The main research contents and results are as follows:1. Characteristics of iron reducetion of Shewanclla oneidensis MR-1: the iron reductionrates were39.12%,50.89%and44.98%using the acetate, lactate and pyruvate as the soleelectronic donor of strain MR-1, respectively. The forms of Fe（Ⅲ） could influence theirreduction, and iron reduction rates were44.72%,51.54%and10.45%using ferrictrichloride, ferric hydroxide and ferric citrate as the sole electronic receptor of strain MR-1,respectively. Dissolved oxygen inhibited the dissimilatory iron reduction. Strain MR-1could reduce Fe（Ⅲ） in the range of pH5.0to9.0. The effects of protein denatumts SDSand OGP suggested that Fe（Ⅲ） reduction function proteins of the strains were mainlylocalized to the soluble outer membrane fraction.2. Effects of dissimilatory iron reduction on the S. oneidensis MR-1by complexing agent.The results showed that: in the conditions of sufficient electron donor, the Fe （Ⅲ）reduction rate of the strains increased with the increase of concentration of complexingagent.When the concentration of tannic acid and pyrogallic aicd is5mmol L-1and10mmol L-1, the maximum iron reduction rate is57.07%,64.30%and44.60%,48.35%, thepH decline in the system caused the decline of iron reduction in later period.3. Effects of Fe（Ⅲ） reduction by adding different complexing agents in the paddy soil. Theresults showed that: the iron reduction rate improved by increasing the concentration of complexing agent, the Fe（Ⅱ） accumulation is the alfisol>vertisol>red soil; in the co-cultureincubation, the iron reduction rate of red soil reach the hightest in the three days, becauseof the conditions of the pH increased later but the iron reduction rate has dropped becauseof the decline of pH value in the late; vertisol in response to the initial iron reduction rate ismore stable, acquired a significant increase in later period; the reduction rate of alfisol isthe most effective; in the soil slurry, the complexing agent in the paddy soils haveaccelerated Fe（Ⅲ） reduction rate initially, and the Fe（Ⅱ） accumulation improvedsignificantly compared to the control.4. Effecs of Fe（Ⅲ） reduction by adding complexing agents on S.oneidensis MR-1insterilized paddy soil. The results show that: there is not effective electron donor to reduceFe（Ⅲ） in the sterilized co-culture incubation for the strains, by adding the electron donor,the iron reduction rate in these three kinds of soil is5.14%,8.95%and9.18%, by addingtannic acid, the iron reduction rate increased to8.59%,24.05%and37.99%; in thesterilized paddy soil, the accumulation of Fe（Ⅱ） is almost no change in red soil,but in theand alfisol and vertisol, the Fe（Ⅱ） accumulation has been significantly improved by addingthe strains and complexing agents, and vertisol>alfisol. |
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