The Carbon Resource Utilization Characteristic Of Fe(Ⅲ) Reduction Microbe In Paddy Soil

Dissimilatory iron reduction in nature plays an important role to physical geochemistry cycle. Reduction of Fe(III) oxide which occurred in kinds of anaerobic conditions, such as sediments, aquifer and inundational paddy soil, is a rather important geochemistry process, which Fe(III)-Fe(II) cycle is to some extent controlled by bio-transform and enzyme reaction. Under anaerobic condition, metal could not only been reduced from high value, but also its transform, toxicity and radioactivity in the environment could be changed with the microbial iron reduction. Meantime, dissimilatory iron reduction could oxide organic compound and promote organic carbon metabolism. Dissimilatory metal reduction has been gradually applied in bio-metallurgy (such as biology immersion of Mn, Co, Ni and Au), bioremediation of heavy metal ions (such as Cr, V, Co, Ni, U, Cu and Cu) and bio-decomposing of permanent organic contaminated water. Using dissimilatory Fe(III) reductive microorganism (DIRM) could also be used to develop bio-cell to produce clean energy, which DIRM use organic compound, such as acetate, as electron donor to transform electron to graphite anode and produce persistent electricity. Therefore, dissilmilatory Fe(III) reduction not only has important geochemistry significance, but has displayed prominent environment applied foreground.In this paper, the typical paddy soils in our country were selected, and soil extractions and pure microbes were incubated under anoxic conditions. The effect of organic acid (formate, acetate, propionate, pyruate, citrate and succinate), glucose, fructose, inositol, starch and cellulose as sole electron donors on dissimilatory iron reduction were studied, and the influences of different concentrations of carbon source and different temperatures on dissimilatory iron reduction were compared. The change rule of pH and reductive glycose concentration had been analyzed. Through mix and pure culture, the reductive extents using same carbon source were compared, and the potential of using different carbon sources by microorganism from various places. Some conclusive results were obtained as following.(1) It was clearly different of Fe(II) accumulation in microbial communities from different paddy soils. Microbes from Sichuan paddy soil could use well all of carbon materials in our study, and the relevant Fe(II) accumulation was the most. The rate of iron reduction of Jiangxi microbes using organic acid, Tianjin microbes using monosaccharide and Guangxi microbes using cellulose were notable lower than other microbes treatments, which reflected their low bioactivities. The diversity of carbon utilization extents on Fe(OH)₃ process in various microbial communities reflected the dissimilarity of microbial communities'composition, metabolism and functions.(2) In mix culture model, pyruvate, glucose and fructose could rapidly be used by different microbes, showing that some common characteristics of bacterial dissimilatory Fe(III) reducing in paddy soil. In the whole incubation process, the Fe(II) accumulation was lowest when sorbitol as electron donor, which illuminated sorbitol was not the dominant carbon source for Fe(III) reductive microorganisms. Sorbitol and inositol of high concentration inhibited Sichuan and Jilin microbial communities, which caused the fall of Fe(II) accumulation and reaction rate. The relation between iron reduction extent and initiation concentration of starch was direct ratio, Fe(II) final accumulation was: 15 g/L>10 g/L>5 g/L.(3) There was significant effect of temperature on Fe(III) reduction. The iron reductive rate under 50℃was notable lower under 30℃treatment in iron reductive process from Tianjin microbial coummunity. The Fe(II) accumulation in 30℃was:10 g/L>20 g/L>5 g/l, the most Fe(II) accumulation was 595.6 g/L, which was almost closed to Fe(OH)₃ concentration at the beginning. It demonstrated that C/N maybe played an important role in iron reductive process.(4) In pure culture, the strain 813, 818 and 819 which were isolated from Sichuan paddy soil all could use glucose, fructose and starch, and the final Fe(II) accumulation was: fructose treatment>glucose treatment>starch treatment. The reductive glycose of glucose and fructose gradually dropped off till steadily, and starch treatment first rose, then fell down. Inositol and cellulose could not be decomposed by the three strains, so there were little reductive glycose, which demonstrated reductive glycose played important role in iron reductive process.(5) pH was gradually dropped off in Fe(OH)₃ reductive process in mix culture model, which used monosaccharide, starch and cellulose as carbon source, and pH descended from 6.8⁷.5 to 3.6⁴.5. Under pure culture condition, pH fell down in early days of reaction when three strains used glucose, fructose and starch. For cellulose and inositol could not be used by these three strains, their pH did not change in the whole culture period, which maintained about pH6.5.(6) In the extract and isolate process, colony-forming units (CFU) obtained from extracted from soils with 2 mmol/L pyrophosphate was more than that with high concentration pyrophosphate and 0.9 % NaCl solution. However, because there may be a negative effect of pyrophosphate on cell metabolism, stilled water was more appropriate to be used in extracting the dissmilatory iron reductive microorganic from paddy soils in sequent experiments.(7) Because of the diversity of clime, temperature, parent material and organic matter, CFU extracted by same method from different paddy soils varied. In this experiment, CFU from Hunan paddy soil was the most, whose magnitude was 107; there was no significant differences of CFU from Zhejiang, Sichuan, Tianjin and Jilin treatments, which was 7.03×10⁵～4.28×10⁶;CFU in Guangdong and Guangxi treatment were the lowest, whose magnitude was just 10⁵.