Diversity and Adaptive Responses of Microorganisms in Extreme Environments

An extreme environment is one in which the physical and chemical properties tend toward unfavorable and may impose temporary or chronic stress on cells, or where the energy supply of the environment is close to the energy demand of any life form. In this thesis, I have investigated three distinct environments to uncover facets of microbial diversity and adaptations in extreme subsurface environments. The first investigation focuses on landfills, which are unique and underexplored engineered subsurface environments. A time series study was conducted on waste microcosms to assess changes to the microbiome using 16S rRNA sequencing in response to 1) Fe(OH)3 and 2) Na2SO4 to represent redox active components of construction and demolition waste and 3) antibiotics. These results suggest that the microbial community composition in fresh waste may be significantly impacted by influxes of iron waste and a single application of antibiotics. In the second investigation, samples from Yellowstone National Park hydrothermal features were subjected to various temperature and pressure conditions to determine whether microorganisms in these environments were also adapted to high-pressure conditions expected in the continental subsurface. Hydrothermal features deliver subsurface material to the surface, which may include microorganisms that seed the surface hot springs and pools. Metagenomic sequencing was conducted to understand changes to the microbial community in response to high-pressure stress. I find that both thermophiles and acidophiles are tolerant to high pressures. In the third investigation, I focus on a single microbial isolate rather than a mixed community to ascertain the adaptions required to withstand the high-pressure conditions of Titan's subsurface ocean. I conducted high-pressure incubations of an extremotolerant bacterial isolate, Shewanella oneidensis MR-1, and sequenced RNA from this isolate to determine patterns of gene expression under Titan-like pressure conditions. I find that the genes regulated by S. oneidensis under Titan-like pressure are common adaptation mechanisms that have been previously found to be expressed by piezophiles and non-piezophiles alike, so there is reason to believe potential life in Titan's high-pressure environments may utilize similar adaptations.