| Iron(Fe) is the fourth most abundant element, and the most abundant redox-active metal in Earth’s crust. The iron cycle is considered the main driving forces for most soil biogeochemical process such as pollutants degradation, removal and transformation of heavy metals and other cycles of biogenic elements. Of which the Fe(II) oxidation and nitrate reduction mediated by nitrate-dependent Fe(II)oxidation microorganism is one of the most important linkages to the biogeochemical cycles of Fe and nitrogen(N) in the environment. Briefly, under anoxic and dark condition, nitrate was utilized as electron acceptor coupled to oxidization of ferrous ions by nitrate-dependent Fe(II)-oxidizing microorganism,and then the Fe(III) produced from iron oxidation can be further used as electron acceptor by iron-reducing microorganism. Thus, it is of significant importance for accelerating the fixed nitrogen in nature environment back to the atmosphere and maintaining the global nitrogen balance by nitrate reduction coupled to iron oxidization. In the past, the nitrate-dependent Fe(II) oxidation was only known as a biotic process. But the thermomechanical analysis indicated that the abiotic nitrate and nitrite reduction coupled to Fe(II) oxidization could happen spontaneously.Therefore, it is urgent to distinguish the biotic and abiotic process in the nitrate-dependent Fe(II) oxidation system, but the detailed process is still less clear.In this study, a lithoautotrophic nitrate-dependent Fe(II) oxidation bacterium,Pseudogulbenkiania sp. strain 2002 was utilized. Furthermore, a combined methods of reaction kinetics, isotopic fractionation of N, mineral analysis were also used to investigate the biotic and abiotic processes in nitrate-dependent Fe(II) oxidation system. The main findings were as follows:(1) During the biotic process(nitrate-dependent Fe(II) oxidation with Pseudogulbenkiania sp. strain 2002), the Fe(II) and organic matter could be used as electron donor to reduction of nitrate and nitrite. In addition, the abiotic Fe(II)oxidization and nitrite reduction was also confirmed. Therefore, both biotic and abiotic processes occurred in the nitrate-dependent Fe(II) oxidation system.(2) The main product of biotic Fe(II) oxidation was lepidocrocite(>70%),which mainly wrapped around the cells and may influence the metabolism of microorganism. As a result, the rate of nitrate and nitrite reduction using Fe(II) aselectron donor was lower than that using the organic matter. By contrast, the product of abiotic Fe(II) oxidization and nitrite reduction was goethite, which mainly deposited rather not wrapped around the cells.This study analyzed the detailed processes of biotic and abiotic reactions in nitrate-dependent Fe(II) oxidation system with Strain 2002. The further study will focus on the distinguish and evaluation of the contribution of biotic and abiotic processes in nitrate-dependent Fe(II) oxidation system. |
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