天然生物地球电池效应、形成机制及生态学意义

天然生物地球电池(biogeobattery)是一种发生在地球表层氧化-还原界面的自然现象,是微生物在厌氧区域氧化有机碳、硫化物等电子供体,产生的电子经胞外介体"长距离"传输至好氧区,从而与空间上隔离的氧气等电子受体发生还原反应的过程。由于生物电流的偶联,使得过去认为因空间隔离而难以发生的氧化-还原反应,可以快速、即时的进行。Biogeobattery的科学本质是:通过微生物驱动电子流动,偶联空间上隔离的生物地球化学过程。Biogeobattery可能容易发生在有机物丰富、具备氧化-还原界面的生境,如海底沉积物环境、有机物污染区域等;它对于有机物厌氧矿化、温室气体排放、C/N/S等元素地球化学循环、污染物自然恢复等关键生物地球化学过程有重要影响,具有重大生态学意义,正成为地球科学、微生物学及生态学共同关注的国际前沿和热点。从"人工"biogeobattery(沉积物微生物燃料电池)入手,阐述了biogeobattery效应及其形成机制,从电池的电势、阴极-阳极响应关系、传导介质等方面详细介绍其研究方法,论述了biogeobattery的生态学意义,展望了研究重点。

Biogeobattery effects: formation mechanism and ecological implications

The term "biogeobattery" describes a natural phenomenon in which biotic processes generate electrical currents within the surface of the earth. The biogeobattery phenomenon is caused by microbes driving electrons flow that is coupled to spatially separated biogeochemical processes. The biogeobattery phenomenon does not occur everywhere that microbially mediated redox interfaces occur because it requires specific geochemical and microbiological conditions. The phenomenon is much more apt to occur when a redox interface occurs at contaminated sites that are rich in organic material that is being biodegraded. The biogeobattery phenomenon was first identified when it was proposed to explain strong self-potential anomalies, which were believed to be associated with microbe-driven redox reactions, at the Entressen landfill in southern France. Subsequent laboratory experiments and field studies have provided evidence for the biogeobattery phenomenon. For instance, the biogeobattery phenomenon has been found in marine sediment, in which electrons generated by microbes (metabolizing sulfide) in anoxic zones were transferred over "long distances" to oxic zones where they were taken up by oxygen. Knowledge of the mechanisms involved in electron transfer is fundamental to understanding this natural phenomenon. A great deal of time and energy has therefore been put into identifying these mechanisms. However, the mechanisms involved in long distance electron transfer in the natural environment have not yet been determined. One possible mechanism involves long filamentous bacteria from the Desulfobulbaceae family, which were found to function as electrical cables, transporting electrons across centimeter-scale distances, in a marine-sediment-based biogeobattery. Electrochemically active species, such as conductive minerals and microbial nanowires, are also potential mediators for the long distance transfer of electrons in natural environments. The biogeobattery theory presents novel viewpoints in the field of microbial ecology that are different from some viewpoints that have been held for a long time. These novel viewpoints could have very significant effects on our understanding of the ways in which the geochemical cycles of elements such as C, N, and S are driven by microorganisms in the earth''s surface. The biogeobattery theory also provides new knowledge of the mechanisms involved in electron transport in subsurface environments. The biogeobattery phenomenon could have important effects on many vital biogeochemical processes, such as the anaerobic mineralization of organic matter, greenhouse gas emissions, and the degradation of contaminants. There can be no doubt that the biogeobattery phenomenon is becoming an important topic at the forefront of research in the earth science, microbiology, and ecology fields. A wide range of knowledge, including of geophysical, geochemical, and microbiological models and methods, needs to be combined to understand the biogeobattery concept. However, so far only a few technologies have been used to study the theory and effect of biogeobattery. Micro-targeting electrodes can be regarded as the most important and mature of these technologies. Low-frequency geoelectrical methods, such as self-potential, resistivity, and acoustic techniques, which provide geochemical signature data that are complementary to each other and to in situ measurements, may also be developed into powerful tools for the use of the biogeobattery phenomenon. In this review, we will redefine the concept and scope of the biogeobattery phenomenon to reflect recent research. In particular, we will summarize the regions where the biogeobattery effect occurs and the conditions under which the biogeobattery effect can take place. Some methods that may be useful for studying the battery potential, the response relationship between the anode and cathode, the conductive medium, and other parameters, will be introduced in detail. The ecological implications and future research needs will be discussed.