Hydrogenoxidizing

Hydrogenoxidizing refers to the oxidation of molecular hydrogen (H2) as an energy source or electron donor in chemical and biological processes. In microbiology, hydrogen-oxidizing organisms derive energy by oxidizing H2 and transferring electrons to an electron transport chain, where a terminal electron acceptor completes the reaction. This can occur under aerobic conditions with oxygen as the terminal acceptor, or under anaerobic conditions with alternatives such as nitrate, nitrite, sulfate, ferric iron, or carbon dioxide.

In biological systems, hydrogen oxidation is typically catalyzed by hydrogenase enzymes, which cleave the H–H bond and transfer electrons to carriers such as ferredoxin or NAD(P)+. The main classes of hydrogenases are [NiFe]-hydrogenases and [FeFe]-hydrogenases, and their cellular localization can be cytoplasmic or periplasmic. The energy generated by H2 oxidation can support chemolithotrophic growth and, in many autotrophs, CO2 fixation to biomass via pathways such as the Calvin cycle or other carbon fixation routes.

Hydrogen-oxidizing organisms are found in a wide range of environments, including soils, freshwater and marine systems, hydrothermal vents, and subsurface habitats. They play a role in global hydrogen cycles by serving as sinks for atmospheric and environmental hydrogen and by linking hydrogen oxidation to the reduction of various electron acceptors, thereby influencing nutrient cycling and energy flow in ecosystems. Some hydrogen-oxidizing archaea and bacteria also participate in hydrogenotrophic methanogenesis or heterotrophic lifestyles, illustrating the metabolic versatility of hydrogen as an electron donor.

Applications of hydrogen oxidation research include insights into bioenergy, microbial electrochemical systems, and biotechnological approaches to hydrogen production and uptake.