A Transformative Technology

Bacterial Respiration

Bacterial respiration. Most bacteria can gain energy by transferring electrons from a low-potential substrate, such as glucose, to a high-potential electron acceptor, such as, for example, molecular oxygen (O2), a process commonly referred to as respiration. In humans, the mitochondria represent the metabolic “furnaces” that perform the same function, with both coupling oxidation and phosphorylation for the generation of ATP via the F1,F0 ATPase (Fig. 1). Essentially, our organism possesses nearly identical energetic properties of the human mitochondrion. In fact, many scientists believe that human mitochondria have evolved from bacteria. Our organisms utilize electrons from a myriad of carbon substrates to generate reducing power in the form of NAD(P)H/FADH2 within the cytoplasm, the bacterial equivalent of the mitochondrial matrix. These reduced pyridines supply a total of 8 electrons per revolution of the TCA cycle involving 8 enzymatic reactions that collectively generate 3 NADH, 1 FADH2, and 1 ATP equivalent (GTP), respectively. NADH, being a stronger reducing agent than FADH2, is a cofactor for Complex I (Fig. 1) while FADH2, a better oxidizing agent than NADH, is a substrate for the only TCA cycle enzyme that is embedded within the bacterial cytoplasmic membrane, succinate dehydrogenase. The NADH dehydrogenase complex (Complex I), menaquinone:cytochrome c oxidoreductase (Complex III) and the cytochrome oxidase (Complex IV) are the only coupling (H+ donating) sites during aerobic bacteria oxidative phosphorylation. However, during anaerobic growth, as will exist in the anode and cathode chambers of the Pilus Energy MFC, the coupling steps are at the nitrate reductase (NAR) and very weakly via the nitrite reductase (NIR), respectively (for review, see Hassett et al., 3 (, also Fig. 2). However, the energy gained via anaerobic respiration is still far greater than that of fermentation that is discussed below. The reason for this is that oxidation and phosphorylation during anaerobic respiration is still coupled, using the proton motive force, and unique cytochromes that operate independently of “aerobic” cytochromes.

Compared to Fermentation? Fermentation involves the anaerobic conversion of generally carbohydrates into acids and/or alcohols. In the case of another form of fermentation known as methanogenesis, it is a multi-step process that occurs in ruminants and humans that does not involve the respiratory chain. The components are enzymatically broken down without net oxidation. The pure energy yield in fermentation vs. respiration is paltry. For example, in the fermentation of glucose, only 2 ATP’s are generated. In contrast, during aerobic respiration, 36 ATP’s are generated.

Download the Pilus Mitochondrion Whitepaper

Reactor Prototype

Please click on a thumbnail below to view larger image.