The Effect Of Carbon Sources On Microial Iron Reduction And Microbial Hydrogen Production In Paddy Soils

Cometabolism of iron reduction was highly valued among the mechanism of Fe(III)reduction by microorganism. Currently, the relationship between iron reduction and differentelectron donors and the study on the variation of microbial community composition in soilenvironment were widely studied. While little attention was paid to the mechanism of H2served as electron donors for iron reduction. The study on the relationship of Fe(III) reductionand microbial hydrogen production was significant for explaining the mechanism of reducingFe(III) by hydrogen and discussing the contribution of microbial iron reduction to anaerobicelectron transmission, thereby, it is important for understanding the importance of microbialiron reduction in anaerobic electron transmission. The paddy soils, the soil microbialcommunity and the typical iron reducing bacteria were incubated anaerobically. Theconcentration of Fe(II), pH and the partial pressure of hydrogen was measured, and therelationship among them was discussed. The mainly conclusions are as follows:(1) The ability of reducing iron by four types of paddy soil was that Jilin and Tianjin wasbetter, and then followed Guizhou, and the Ningxia paddy soil was weaker. Different carbonsource promoted the process of iron reducing process by the order: pyruvate and glucose>lactate>acetate. Microorganisms from different paddy soil have a certain selective to carbonsources. The main factor that influences the potential capacity of reducing Fe(III) in paddysoil is the content of amorphous iron. High content of soil total phosphorus also inhibited theprocess of iron reduction. Besides, there was a negative correlation between pH and theconcentration of Fe(II) in the incubation system with carbon sources.(2) The influence of the concentration of carbon sources related to the pH of the system.The result of microbes incubation showed that the lowest concentration had the fast Vmaxand the largest accumulation amount of Fe(II). The utilization rate of electron by the processof iron reduction decreased with the increase of the concentrations of carbon sources. The ironreducing process was the main electron accepting pathway under lower concentration ofglucose, whose utilization of electrons was80%. (3) Microbial production of hydrogen by paddy soil was influenced by different kinds ofcarbon sources and the partial pressure of hydrogen decreased by the following order,glucose> pyruvate>lactate. While when adding different concentrations of glucose andpyruvate to the incubation of different microbial communities, the partial pressure of H2increased with the increase of concentration of carbon sources. The accumulation andconsumption of hydrogen was decided by the microbial community composition. Besides, thepartial pressure of H2was significantly negative correlated with the pH of the system.(4) Besides the strain SC-a18, the other three trains can better reduce ferric rion whenglucose served as electron donors, and the maximum iron reducing amount was increasedwith the increase of the glucose concentrations. Although the utilization rate of carbon sourcesdiffers from different strains, but all the rates were less than5%. In pure culture, ironreduction was a minor pathway for electron transport. While when the concentration ofglucose were less than4mmol/L, little amount of ferric iron were reduced.