Sarah Piché-Choquette

INRS-Institut Armand-Frappier
Ph.D. candidate

Supervisor: Philippe Constant
Start: 2014-09-01
End: 2018-08-31

Project

Molecular hydrogen as an ecological stress to soil microbial communities
A single hectare of legume plants can evolve up to 5,000 L H2 per day via nitrogen fixation in nodules, most of which is quickly oxidized by surrounding H2-oxidizing bacteria. The fertilization effect of these short-lived H2 emissions has been known for decades. This is especially intriguing considering that while Hup+ nodules exist, which possess hydrogenase enzymes enabling them to recycle H2 evolved through nitrogen fixation and thus being more energy-efficient, they are much less widespread than their Hup- counterpart, without hydrogenase enzymes. Recent findings in the field have suggested that this H2 fertilization effect cannot be merely explained by the stimulation of a few H2-oxidizing plant growth-promoting rhizobacteria. Nevertheless, our understanding of the actual impact of these diffuse H2 gradients on soil ecosystems is still in its infancy. Our current working hypothesis on the matter is that as a potent energy source, H2 has the potential to alter soil microbe-microbe interactions and consequently microbial diversity and biogeochemical processes on a dose-response basis, thus more concretely, driving microbial successions. The goal of my research project is therefore to confirm or infirm this hypothesis by measuring the impact of H2 on soil microbial communities. A dynamic microcosm chambers system was developed in order to incubate soil microcosms to precise H2 stoechiometric ratios representative of natural gradients and then measure the response of soil microbial communities to these varying H2 fluxes. Microbial community structure is routinely analyzed by a combination of molecular biology techniques targeting taxonomic and functional marker genes surveyed mostly through qPCR and PCR-amplicons sequencing. Biogeochemical processes are, on the other hand, analyzed by first measuring potential trace gases production and oxidation rates, and then computing these into oxidation/production kinetics. Those datasets are then used as input for the parameterization of theoretical frameworks modeling microbial feedback to H2 point sources such as Hup- N2-fixing nodules. Such analyses give us insight into the potential impact of diffusive H2 fluxes onto microbial diversity and biogeochemical processes. Results from this specific project have led to a few interesting papers so far, with more to come out soon. While current models isolated the impact of H2 on soil microbial communities, the next step is to challenge those models’ predictions in situ in order to determine how additional variables present within natural soil ecosystems, such as root exudates, will alter microbial feedback when compared to laboratory experiments.

Keywords

hydrogen, soil microorganisms, microbial processes, microbial ecology

Publications

1- Survey of High-Affinity H2-Oxidizing Bacteria in Soil Reveals Their Vast Diversity Yet Underrepresentation in Genomic Databases
Piché-Choquette, Sarah, Mondher Khdhiri, Philippe Constant
2017 Microbial Ecology

2- The Tale of a Neglected Energy Source: Elevated Hydrogen Exposure Affects both Microbial Diversity and Function in Soil
Khdhiri, Mondher, Sarah Piché-Choquette, Julien Tremblay, Susannah G. Tringe, Philippe Constant,
2017 Applied and Environmental Microbiology

3- H2-saturation of high affinity H2-oxidizing bacteria alters the ecological niche of soil microorganisms unevenly among taxonomic groups
Piché-Choquette, Sarah, Julien Tremblay, Susannah G. Tringe, Philippe Constant
2016 PeerJ