Ecological traits of high-affinity hydrogen-oxidizing soil bacteria involved in the hydrogen cycle

Every year, soil microbial-mediated hydrogen (H 2 ) oxidation removes about 80 % of the global atmospheric H 2 , an indirect greenhouse gas. Soil-dwelling high-affinity H 2 oxidizing bacteria use this trace gas as an energy source to persist when other substrates are limited or to meet their maintenance energy requirements during dormancy. However, there is limited knowledge of the distribution, composition, diversity, and functions of this group of bacteria, particularly their ecological traits (i.e., characteristics that influence their interactions with the environment and other organisms). This is because the high-affinity H 2 -oxidizing bacteria are not phylogenetically conserved, potentially due to the horizontal transfer of their functional gene, which still needs to be demonstrated. This makes it difficult to answer ecological questions related to the distribution, functional role, and ecological contribution of H 2 -oxidizing bacteria in the soil H 2 cycle, as well as their responses to environmental factors. Such information is needed to estimate the contribution of the H 2 -oxidizing bacteria to the global H 2 cycle. Although many H 2 -oxidizing bacteria are not culturable, they may share similar ecological traits when responding to environmental changes, such as pH, moisture content, and H 2 concentrations. Therefore, a community or guild-level trait-based approach (defined as the analysis of functional traits shared by groups of bacteria (guilds) that perform similar ecological roles) could be useful to synthesize complex genomic and phylogenetic information. This review discusses the impact of soil environmental factors on soil H 2 uptake (by oxidation), and identifies ecological response traits under controlled conditions. Our approach connects the biological activity of the H 2 -oxidizing bacteria to their resident environment, for scaling up and estimating the capacity of soil microbial communities to mitigate global warming linked to increased atmospheric H 2 . • Atmospheric hydrogen cycling in soil involves hydrogen-oxidizing bacteria. • High-affinity hydrogen oxidation genes may not be conserved phylogenetically. • Method was proposed for identifying ecological traits of bacteria with hhy genes. • Ecological traits explain hydrogen-oxidizing bacteria responses to soil factors.