| Iron is the fourth most abundant active metal element in the Earth‘s curst. The constant redox cycle of iron, which contains the ferrous oxidation and ferric reduction, is an important link to the geochemical cycles of other elements. In the anoxic condition, ferrous iron oxidation is not chemically induced, but mediated by the microorganisms with biotic and abiotic processes. In particular, the nitrate dependent Fe(II) oxidation microorganisms were able to couple the cycles of iron and nitrogen at circumneutral p H in anoxic environments. The iron cycle couple to the reduction of nitrate by the type of microorganisms is an interesting scientific issue of the people who study in the field of biogeochemistry.Based on the ferrous oxidation, the function of nitrate reduction couple to ferrous oxidation in paddy soil was studied. Firstly, different paddy soils of parent materials were selected by adding the ferrous and nitrate repeatedly domesticated to verify the role of microbial communities of ferrous oxidation coupling to nitrate reduction. In addition, pure strain with the function of ferrous oxidation couple to the nitrate reduction was obtained to directly study the processes of kinetics and mineralizaion, in order to reveal the mechanisms of microbial mediated cycles of Fe and N. The main conclusions are as follows:1. Paddy soil of different soil parent materials(grantite, limestone and sediment) in the condition of Fe(II) oxidation couple to NO3- reduction by 4 cycles of repeated domestication under neutral anaerobic conditions showed the ferrous oxidation cannot proceed in the absence of nitrate. The processes of the oxidation of ferrous was similar among the three kinds of paddy soil. Using the high through-put technology to analyse the microbial community after domestion by Soil+Fe(II)+NO3-, revealed that in the level of phyla, Proteobacteria would become the dominant communities of all three paddy soils. In the level of genius, Geothrix, Zoogloea and Azospira would become the dominant communities of paddy soil of granite, when ferrous was difficult to become the crystal form minerals. Dechloromonas, Pseudomonas and Rhodocyclus would become the dominatnt communities of both paddy soil of limestone and sediment, when ferrous would become the crystal minerals like goethite after domestication with ferrous and nitrate, even lepidocrocite could be dectected in the paddy soil of limestone.2. A strain Rhodocyclaceae sp. Paddy-1 with the function of ferrous oxidation couple to nitrate reduction was isolated and confirmed to be a novel bacteria. To this strain, the ferrous oxidation would proceed in the presence of nitrate and the mineral produced was amorphous mineral. The addion of ferrous would decelerate the rate of nitrate reduction. To analyse the genome of the strain, we found that the key genes c1,c2,c553 å'Œ c556, which were similar to the key ferrous oxidation genes cyc1,cyc A-2,cyc A-1,were in the strain. In addition, the complete gene chain of nitrate reduction was in the strain. We build the metabolic pathway of ferrous oxidation couple to the nitrate reduction of strain Paddy-1. The information above can be for us to further understand the interaction mechanism of paddy fields Fe- N.3. A strain Cupriavidus metallidurans Paddy-2 was isolated from paddy soil. under neutral anaerobic conditions, the strain can reduce 97.7% nitrate(10 m M initial con.) and 89.7%(5 m M initial con.) ferrous in 6 days. The biological mineralization was confirmed to be the amorphous mineral after character with XRD, SEM and TEM. A metabolic pathway of ferrous oxidation couple to nitrate reduction was constructed based on the the genome information of 65553447 bp, in order to explain the mechanism of bio-mineralization of the strain in the angle of molecular biology. |
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