Diversity and Ecophysiology of High Affinity H2-Oxidizing Bacteria Scavenging Atmospheric H2

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Molecular hydrogen (H2) is an indirect greenhouse gas regulating the abundance of hydroxyl radicals, the cleansing molecules removing methane from the atmosphere. About 80% of total H2 emissions are currently mitigated by the biological soil uptake of atmospheric H2, thus explaining the stability of its global atmospheric burden over the last decades. H2-based economy modeling scenarios raised concerns about a potential increase of atmospheric H2 levels, altering the oxidative capacity of the atmosphere and enhancing atmospheric methane lifetime. This rise was attributed to inevitable losses during H2 production, transport and storage and, the inability of the soil uptake of atmospheric H2 to compensate for these additional emissions. These projections have caused some controversy because future trends in fuel technologies and H2 emissions are very difficult to predict and moreover, the question whether the soil sink of atmospheric H2 is vulnerable to climate evolution and other anthropogenic disturbances remains unresolved. The overall objective of this research program is to define «how» the environment is shaping the diversity, distribution and activity of H2-oxidizing bacteria possessing a novel high affinity [NiFe]-hydrogenase responsible for the soil uptake of atmospheric H2. This challenge will be addressed by a unique combination of microbiological and molecular analyses and the monitoring of H2 turnover of bacterial cultures and soil. We will elucidate the physiological role of high affinity H2ase, the diversity of high affinity H2 oxidizing-bacteria and reveal the environmental control of their distribution and activity. Localizing and quantifying active H2-oxidizing bacteria in soil and relating their distribution and activity to environmental variables and biogeochemical networks is essential to recognize ecosystems for which the ability to consume atmospheric H2 is susceptible to global change and land-management practices - thus favouring the implementation of strategies to ensure a continued stability of the current mass balance of atmospheric H2 in Canada and worldwide.