Lab-based study of the physiology and related H² consumption of isolates from the Harvard Forest Long Term Ecological Research.

Thesis: Ph.D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (pages 91-92).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.by Deepa Rao.S.B