Geoabcter: the “generalist” driving anaerobic biogeochemical cycles

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.