Effect Of The Electron Transter On The Microbial Iron(Ⅲ) Reduction In Paddy Soils

The reduction of iron oxide in paddy soil is the alienation of microbial-mediated reduction, and the process of microbial Fe (III) used as the final electron acceptor by the anaerobic respiration. There are mainly various oxides of the Fe (III) in paddy soil. Goethite and hematite iron oxide crystal structure is difficult to use by the micro-organisms, because iron oxide contacted with microbial cell membrane difficultly. However, people have a new recognition on Fe (III) reduction of iron oxide after Lovley proposed the concept of electronic shuttle, and electron could be transfered from the cell membrane of microbial protein to the iron oxide through the intermediate, what is known as electron shuutle that promoted Fe (III) reduction. There are something known as the organisms with electronic transmission, such as anthraquinone 2 ,6 - sulfonate (AQDS), humic acid, riboflavin (VB2) and vitamin B12 (VB12), they were involved in the reduction of carbon fragments and the transfer of functions in the nature. It was the matter of great theoretical significance to explore the effect of these electron transter on the process of microbial iron reduction, with deepening understanding of the mechanism of microbial iron reduction, strengthening and controlling the process of alienation iron reduction in paddy soil. Through co-culture incubation, soil slurry anaerobic incubation and pure culture method, it was used to study the effect on the microbial iron reduction, to verificat the potential function of these electron shuttles, and compare the use level of these electron shuttles as carbon. Following main findings were known.1. In the microbial co-culture incubation, compared to the control the rate of reduction has increased significantly in the add of AQDS, and the use of AQDS in Fe(OH)3 reduction was promoted obviously with the increase of the AQDS concentration. It was confirmed that AQDS as electron shuttle played a role of transporting elector and promote the process of microbial iron reduction in the system. The microbes from different paddy soils had different capacity of Fe (III) reduction. Microbes from SC have greater capacity of Fe (III) reduction than microbes from ZJ, but Microbes from ZJ was more sensitive in response to AQDS.2. In the microbial co-culture incubation, adding FA accelerated the Fe(OH)3 reduction, and the role of FA in Fe(OH)3 reduction was promoted more obviously with the increase of FA concentration, especially in the microbial co-culture incubation of SC, the role of FA in Fe(OH)3 reduction was promoted most obviously. It was confirmed that FA as electron shuttle has played a role of transporting elector and promote the process of microbial iron reduction.3. In pure culture incubation with strains that can reduct Fe (III), the rate of Fe(OH)3 reduction was promoted obviously in the add of AQDS. Different strains such as SC-a09, SC-a24, JX-a03 and JX-a12 have different ability of Fe (III) reduction, and also have different response to AQDS. Adding AQDS to the strain SC-a24 and JX-a03, Fe(OH)3 reduction was promoted more obviously. It could be further confirmed that AQDS as electron shuttle accelerate transporting elector in the process of Fe (III) reduction. Adding FA to the strains SC-a09, SC-a24and JX-a03, Fe(OH)3 reduction was promoted more obviously, but JX-a12 have less sensitive response to AQDS.4. In soil slurry anaerobic incubation, adding AQDS of different concentrations to the paddy soil, not only Fe (III) reduction rate was affected, also the Fe (II) output has increased. In the early training, AQDS speed up the Fe (III) reduction rate, and Fe (III) reduction was as more as the add of AQDS. In the latter training, Fe (II) output compared to the control have a significant increase, so AQDS play an important role of the reduction of iron oxide in paddy soil. Adding FA of different concentrations has no apparent role of Fe (III) reduction in paddy soil, and only the Fe (II) generation has slightly increase.5. Through comparing different electron transters as carbon source used by iron microbes, it was found that VB12 only could promot a few Fe (OH)3 reduction without carbon, and the total volume of Fe (II) has little increased. VB12 may be used as carbon source by iron microbes. And compared to the control in add of carbon, VB12 could inhibit the Fe (OH)3 reduction in the latter part of training (20 d later). It was confirmed that VB12 does not played a role of electron shuttle. In the conditions of no carbon, iron microbes could used VB2 as carbon source to reduct Fe(OH)3, and Fe (II) output has increase with increasing of VB2 concentration. Compared with adding carbon, VB2 has promoted Fe(OH)3 reduction, and also with the increasing concentration of VB2 Fe (II) output has increase. It was confirmed that VB2 can be used as an electron transter to speed up Fe (OH)3 reduction, and have a certain electronic characteristics of the electron shuttle. In the condition of no carbon, FA has almost no impact on the Fe (OH)3 reduction, it was known that FA could not be used as carbon source. In the add of FA, FA could promote Fe (OH)3 reduction, and the maximum aggregate amount (a)of Fe (II), the largest response rate (Vmax) and the rate of Fe (III) reduction with the increasing concentration of FA. It was confirmed that FA could transfer elector, and could be used as electron shuttle to speed up Fe (OH)3 reduction.