GENERAL MICROBIOLOGY - T.P. Pyrog - 2004

11. MAIN MECHANISMS OF METABOLISM AND ENERGY CONVERSION IN MICROORGANISMS

11.6. ELECTRON TRANSPORT CHAIN AND PHOSPHORYLATION (ATP SYNTHESIS) DURING ELECTRON TRANSFER

11.6.8. Electron transport processes in anaerobic bacteria

Under anaerobic conditions, chemoorganotrophs can generate energy (in the form of ATP) through two main pathways: Fermentation (substrate-level phosphorylation) and electron transport-coupled phosphorylation. However, in the latter case, oxygen cannot serve as the terminal electron acceptor (unlike in aerobes). Anaerobic Bacteria are capable of utilizing nitrate, sulfate, carbonate, fumarate ions, as well as elemental sulfur, as alternative electron acceptors. Consequently, these bacteria are grouped accordingly into: denitrifiers, sulfate-reducing bacteria, methanogens, and acetogenic bacteria. Since electron transport-linked phosphorylation was long considered a hallmark of aerobic Respiration, these energy-yielding processes during Oxidative Phosphorylation under anaerobic conditions are referred to as "Anaerobic respiration".

It should be noted that electron transport phosphorylation utilizing fumaric acid as an electron acceptor (fumarate respiration) occurs not only in bacteria, but also in helminths and even mammals. The reaction, catalyzed by fumarate reductase, can be identified by the accumulation or excretion of succinic acid (succinate).