Exploring the microbe-mediated soil H2 sink: A lab-based study of the physiology and related H2 consumption of isolates from the Harvard Forest

Atmospheric hydrogen (H2) is a secondary greenhouse gas that attenuates the removal of methane (CH4) from the atmosphere. The largest and least understood term in the H2 biogeochemical cycle, microbe-mediated soil uptake, is responsible for about 80% of Earth's tropospheric H2 sink. A recent discovery of the first H2-oxidizing soil microorganism (Streptomyces sp. PCB7) containing a low-threshold, high-affinity NiFe-hydrogenase functional at ambient H2 levels (approx. 530 ppb) made it possible to identify a model organism to characterize microbial H2-uptake behavior. In the present research, several strains of Streptomyces containing the high-affinity NiFe-hydrogenase were isolated from the Harvard Forest LTER and used to characterize H2 uptake alongside analysis of their life cycles. It was found that containing the gene encoding for the specific hydrogenase predicted H2 uptake behavior in the wild Streptomyces strains and also in more distantly related organisms that contained the gene. The H2 uptake rates were correlated with the microorganisms' life cycles, reaching a maximal uptake corresponding with spore formation. Understanding how environmental conditions, organismal life cycle, and H2 uptake are connected can help reduce the uncertainty in atmospheric models. With the rise of H2-based energy sources and a potential change in the tropospheric concentration of H2, understanding the sources and sinks of this trace gas is important for the future.