电子穿梭体及其介导的环境与地球化学过程研究进展

电子穿梭体是一类可通过自身氧化还原介导电子转移的化学物质的统称。在地球表层系统中,电子穿梭体可加速微生物向细胞外部进行的电子传递,参与矿物的微生物还原,驱动碳、氮、硫元素循环,并偶联有机污染物降解和重金属迁移转化。电子穿梭在自然界中存在广泛,对于元素循环、污染物环境行为以及微生物的生存行为影响深远,具有重要的环境地球化学意义。因此,该文以自然界存在的典型电子穿梭体为阐述对象,综述了以腐殖质、硫单质和生物炭为代表的三类典型穿梭体的反应特性。其中,腐殖质是土壤中天然存在的分布最广的穿梭体,硫单质是碱性环境下最典型的穿梭体,而生物炭则是稻田系统中人为输入的穿梭体。以上述三类穿梭体为核心,该文系统阐述了穿梭过程与碳氮循环、铁循环和污染物迁移转化的相互关系、以及穿梭体对微生物菌群变化产生的影响。在碳氮循环过程中,穿梭体主要参与有机碳的厌氧消耗、二氧化碳向甲烷的转化、氨氧化以及氧化亚氮向氮气的转化过程;在铁循环过程中,穿梭体主要影响氧化铁的还原溶解、含铁矿物的晶型转变以及氧化铁还原耦合的砷、铬污染物转化过程;而穿梭体作为电子受体,还可改变微生物的生长与竞争关系,调控微生物菌群。文章深入分析了穿梭过程在地球表层系统中产生的环境效应与生态效应,并提出了本领域今后需关注的重点,可为穿梭行为的进一步研究提供思考依据。

Electron Shuttle-Mediated Microbial Extracellular Electron Transfer:Mechanisms and Geochemical Implications

Electron shuttles,which play a key role in enhancing microbial anaerobic respiration by accelerating the extracellular electron transfer(EET)between microbes and minerals,are deeply involved in epigeosphere element cycling.As electron shuttles are widespread in nature,the shuttling process has a huge impact on the survival behavior of microorganisms and the environmental behavior of pollutants.Thus,electron shuttling has received extensive attention in recent decades.The aim of this review is to reveal the mechanism of electron shuttling between microbes and electron acceptors and clarify the implications of shuttling behavior on the environment.In this review,shuttles that widely distributed in nature,which contains humic substances,sulfur and biochar,are introduced.Their structural features,chemical properties,and typical characteristics are described,and the differences in the shuttling mechanism of different shuttles are discussed.These differentiating features make shuttling process complex and diverse.In addition,the implications of the shuttling behavior for environments and element biogeochemical cycling are discussed.Electron shuttling plays a critical role in the biogeochemical cycling of iron,which can influence the geochemical cycling of carbon and nitrogen.Additionally,the shuttling process has a direct effect on microbial pollutant reduction and degradation as several pollutants are extracellular electron acceptors.Meanwhile,the shuttling process also has a great indirect impact on pollutant toxicity by influencing microbial mineral reduction.Furthermore,the microbial community,which plays key role in pollutant transformation,can be affected by electron shuttles.Thus,understanding the mechanism and significance of the influence of electron shuttles on pollutants and the microbial community is analyzed in detail in this review,in order to provide deep insight into electron shuttling in nature.In summary,future studies in this field should encompass the following four aspects:(i)establish a method for evaluating the contribution of electronic shuttles in a complex environment;(ii)determine the environments in which the electron shuttle functions;(iii)determine the contribution of electron shuttling behavior in different biogeochemical processes;(iv)clarify the microbial ecological effects of electron shuttles;(v)explore the application of electron shuttles that regulate microbial community structure in environmental pollution control.This review is aimed at providing guidance for the further study of the microbial extracellular electron shuttling process.