Fig. 2

Broad variety of microbial metabolomics. a) Different modes of electron transport; I using artificial electron transporters such as neutral red; II electron transport by means of bacterial cellular components such as outer membrane cytochromes; III direct electron transport by using external appendages such as flagella and nanowires. b) Schematic illustration of complex organic matter degradation. Planktonic microbial community (for example, Rhodopseudomonas, Pseudomonas, Paracoccus denitrificans) degrades the hydrolysates of the complex organic matter in to short-chain acids such as acetate with the production of H₂, with a trivial exogenic electron transport. Electrogenic bacteria (Pelobacter propionicus, Desulfotomaculum, Shewanella, Geobacter) then can mediate complete degradation of these organic compounds. Bacterial communities such as Paracoccus denitrificans and Geobacter further mediate the oxidation of hydrogen with the help of hydrogenases