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

分子氢（H2）是一种间接的温室气体，调节羟基自由基的丰度，清洁分子从大气中去除甲烷。目前，约80%的H2排放总量通过生物土壤对大气H2的吸收而减轻，从而解释了过去几十年来其全球大气负担的稳定性。基于H2的经济模拟情景引起了人们对大气H2水平可能增加、改变大气氧化能力和增加大气甲烷寿命的担忧。这一增长归因于H2生产、运输和储存过程中不可避免的损失，以及土壤对大气H2的吸收无法补偿这些额外的排放。这些预测引起了一些争议，因为燃料技术和H2排放的未来趋势是非常难以预测的，此外，大气H2的土壤汇是否容易受到气候演变和其他人为干扰的问题仍然没有得到解决。该研究计划的总体目标是确定环境如何塑造H2氧化细菌的多样性，分布和活性，这些细菌具有一种新型的高亲和力[NiFe]-氢化酶，负责土壤吸收大气中的H2。这一挑战将通过微生物和分子分析的独特组合以及细菌培养物和土壤的H2周转监测来解决。本文将阐明高亲和性H2酶的生理作用、高亲和性H2氧化细菌的多样性及其分布和活性的环境控制。定位和量化土壤中的活性H2氧化细菌，并将其分布和活动与环境变量和生物地球化学网络联系起来，对于认识生态系统消耗大气H2的能力易受全球变化和土地管理做法的影响至关重要，从而有利于实施战略，确保加拿大和世界范围内大气H2目前质量平衡的持续稳定。

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.