Life history strategies to study the succession of H2-oxidizing bacteria and their ecological role along H2 concentration gradients in upland soils

The recent discovery of atmospheric chemosynthesis has caused a paradigm shift in the way H2-oxidizing bacteria (HOB) are examined. The field has transitioned from the consideration of HOB as a specialized functional group benefiting from the energy potential of H2 for mixotrophic growth or persistence to a versatile group of bacteria using multiple trace gases. We discuss four life history strategies supported by H2, namely chemolithoautotrophic growth, mixotrophic growth, persistence, and atmospheric chemosynthesis. There is experimental evidence supporting the role of HOB in various ecosystem services beyond the uptake of H2 including, for instance, carbon cycling, plant growth promotion, and primary production. Decoupling between the intensity of HOB activation in soil and compositional change of microbial communities remains puzzling, highlighting our poor understanding of the ecological role of HOB. We call for new experimental approaches to delineate the interactions between HOB and the other members of the community. We propose a dedicated framework integrating life history strategies of HOB for mechanistic assessment of microbial interactions and processes supported by H2 in soil.