细菌胞外多聚物介导的土壤铁呼吸过程及电子转移机制研究

Iron respiration (i.e. dissimilatory iron reduction) is an important soil process, has significant implications in ecology and environment: including the gleying process of soils, in situ anaerobic decomposition of organic pollutants, heavy metal detoxication through reduction, and inhibition of methane emission. Internationally, many studies have been carried out on iron respiration, but how electrons are transferred from the outer membrane to the insoluble Fe(III) minerals remains to be answered. Recent studies showed that extracellular polymeric substances (EPS), which are important in mediation of environmental interactions, might play an important role in extracellular electron transfer (EET) during iron respiration. This project aims to quantify the electron transfer capacity (ETC) of EPS from dissimilatory iron-reducing bacteria (DIB) using electrochemical methods, investigate how different Fe(III) (hydr)oxides and oxygen conditions influence the formation and composition of EPS, and reveal how EPS of DIB works in EET during iron respiration by investigating the correlation between EPS's ETC and its components. After that, laboratory studies with soil-Fe(III) (hydr)oxides-DIB incubation systems will be carried out to investigate the relationship between the ETC of EPS and the iron-reducing process in soils to reveal how the EPS of DIB works in mediating dissimilatory iron reduction in soils.

土壤铁呼吸（即异化铁还原）是厌氧环境中最为重要的电子转移途径，它直接参与并驱动有机碳周转、养分矿化利用与温室气体排放等关键土壤生态过程。胞外电子转移过程（即微生物如何将胞内电子传递至土壤中的氧化铁）是土壤铁呼吸的关键科学问题。胞外多聚物（EPS）是微生物与土壤铁氧化物相互作用的"屏障与媒介"，但前期研究主要关注两者的表面吸附或络合反应，而对于EPS的氧化还原活性及电子转移功能少有关注。本项目将铁还原菌EPS电子转移能力与土壤铁还原过程联系起来研究，提出EPS介导的土壤铁呼吸电子转移机制假说，采用生物电化学方法定量表征EPS电子转移能力，研究不同氧化铁种类、好氧/厌氧条件对铁还原菌EPS产生动态、结构特征及电子转移容量的影响，探讨有机碳-铁还原菌-氧化铁体系中EPS电子转移容量与铁还原动力学的关系，揭示EPS介导的土壤铁呼吸过程及胞外电子转移机制，为深入理解土壤铁循环及环境效应提供科学依据。

本项目以铁还原菌为对象，研究铁还原菌胞外多聚物的分离及其电化学性质的表征，探索铁还原菌胞外多聚物介导土壤铁呼吸过程及铁还原菌胞外多聚物的电子转移机制。主要成果包括：（1）分离并鉴定1株铁还原新种GSS02，为研究铁还原菌胞外多聚物介导土壤铁呼吸过程及其电子转移机制提供基础；（2）研究了常用胞外多聚物分离方法对铁还原菌胞外多聚物的分离效率，及对所分离得到的胞外多聚物进行了电化学等性质的表征；（3）研究了铁还原菌胞外多聚物介导土壤铁呼吸过程，初步阐明了铁还原菌胞外多聚物的电子转移机制。本项目初步揭示了铁还原菌胞外多聚物的电子转移机制，为深入理解铁呼吸胞外电子转移机制提供了科学依据，为利用铁还原菌进行污染环境的生物修复提供了技术支撑。项目发现并命名铁还原新种1株，发表SCI论文6篇及核心期刊论文1篇。