Aerobic hydrogen-oxidizing bacteria in soil: from cells to ecosystems

Aerobic hydrogen-oxidizing bacteria (HOB) is a group of active, abundant, and diverse microorganisms with representatives in nearly all phyla, distributed in soil exposed to atmospheric or elevated hydrogen. In this review, first, we discuss the fundamental physiology, isolation, and identification techniques for HOB. On this basis, the hydrogenase genetic organization and metabolic strategy of Cupriavidus necator, Mycobacterium smegmatis as representative HOB are summarized. Availability of hydrogen, oxygen, nutrients, and environmental variables such as temperature and moisture are key ecological factors influencing H-2 oxidation activity, hydrogenase groups, and microbial composition. Finally, we systematically illustrate the ecological roles of HOB and the interactions between HOB and other soil microbiota, particularly rhizobia in agricultural soils and Cyanobacteria in deserts. Intensive studies should focus on the cell functioning regulated by hydrogenases and on the full play of ecological roles by competitive HOB consortiums in soil niches, which is expected to facilitate the biogeochemical process of carbon dioxide fixation and energy utilization. [GRAPHICS] .