地杆菌：驱动厌氧生物地球化学循环的“多面手”

Geoabcter: the “generalist” driving anaerobic biogeochemical cycles

摘要:

地杆菌属隶属于δ变形菌纲、地杆菌科，为革兰氏阴性严格厌氧微生物，是一类广泛分布于水体沉积物、土壤和多种地下厌氧环境中的异化铁还原菌。地杆菌可通过多种途径参与厌氧环境中碳、氮、铁等元素生物地球化学循环，具有“多面手”特性，如通过碳分解代谢分解乙酸等小分子有机酸或芳香族化合物、或碳固定利用甲酸、一氧化碳等一碳化合物以及通过胞外电子传递驱动产甲烷菌产甲烷参与碳循环过程；通过硝酸盐异化还原成氨(DNRA)、固氮作用以及与反硝化菌建立互营关系参与氮循环过程；表达多种内膜醌脱氢酶ImcH、CbcL和CbcAB、外膜细胞色素C及导电纳米线，通过直接接触或在电子穿梭体和螯合剂的协助下实现胞外多种Fe (Ⅲ)氧化物的还原而参与铁循环过程。地杆菌的“多面手”特性，使其在多种环境中生存并占据着厌氧环境中重要的生态位，并成为驱动厌氧环境中生物地球化学循环的引擎。本文介绍了地杆菌的代谢特征及分布情况，揭示其在碳、氮、铁元素生物地球化学循环中的作用，并系统分析了地杆菌“多面手”的特性。本文有利于加深对地杆菌驱动的关键元素生物地球化学循环的认识，为理解地杆菌在自然环境中产生的环境效应提供夯实的理论基础，将推动地杆菌在维持生态平衡以及污染治理中的实际工程应用。

Abstract:

The strictly anaerobic Gram-negative Geobacter (Geobacteraceae, Deltaproteobacteria) members, the dissimilatory iron-reducing bacteria, are ubiquitous in aquatic sediment, soil, and various underground anaerobic environments. Geobacter is versatile as it participates in the biogeochemical cycles of carbon, nitrogen, iron, and other elements in anaerobic environments through a variety of pathways. To be specific, in the biogeochemical cycle of carbon, it decomposes small organic acids such as acetic acid or aromatic compounds through carbon catabolism, utilizes one-carbon compounds such as formic acid and carbon monoxide by carbon fixation, and drives methane production of methanogens through extracellular electron transfer. It contributes to nitrogen cycle by dissimilatory reduction of nitrate to ammonia (DNRA), nitrogen fixation, and establishing direct interspecies electron interaction with denitrifying bacteria. It expresses quinone dehydrogenases (ImcH, CbcL and CbcAB) in inner membrane and cytochrome C and conductive nanowires in outer membrane to reduce various extracellular Fe(Ⅲ) oxides by direct contact or with the assistance of electron shuttles and chelators, thereby facilitating iron cycle. As a result, the versatile Geobacter survives in a variety of environments and occupies an important niche in anaerobic environments by driving the biogeochemical cycles. This paper introduces the metabolic characteristics and distribution of Geobacter, elucidates the roles in biogeochemical cycles of carbon, nitrogen, and iron, and summarizes the versatile feature of this genus. The result is expected to deepen the understanding of the biogeochemical cycles of key elements driven by Geobacter, lay a solid theoretical basis for understanding the environmental effect of Geobacter in the natural environment, and pave the way for application of Geobacter in maintaining ecological balance and pollution control.