1Department of Ecological Microbiology, University of Bayreuth
Charles Darwin was fascinated by the capacity of earthworms to alter terrestrial habitats. However, Darwin was not aware that the impact of earthworms is due in part to their effect on the activities of ingested microbes during gut passage. Anoxia and worm derived saccharides in the alimentary canal induce fermentation and denitrification, leading to the emission of hydrogen and nitrous oxide, respectively. The complex fermentation food web includes both facultative aerobes and obligate anaerobes. Certain earthworms emit methane. Hydrogen-producing fermentations in the gut drive methanogenesis, and Methanobacteriaceae and Methanoregulaceae are linked to the production of methane. Acetogens appear to participate in the methanogenic food web. These collective findings illustrate that the alimentary canal of the earthworm (a) constitutes a mobile and dynamic anoxic micro-compartment in soils and (b) augments diverse anaerobic microbial activities that impact on the production of greenhouse gases and the cycling of elements in the terrestrial biosphere.