Extremophiles in Built Environments

Author:

Wilpiszeski, Regina Leila

Graduate Program:

Geosciences

Degree:

Doctor of Philosophy

Document Type:

Dissertation

Date of Defense:

November 15, 2017

Committee Members:

Christopher Howard House, Dissertation Advisor/Co-Advisor
Christopher Howard House, Committee Chair/Co-Chair
Jennifer Macalady, Committee Member
Julie Genevieve Cosmidis, Committee Member
Istvan Albert, Outside Member

Keywords:

Extremophiles
Built environment
Subsurface
Astrobiology
Microbial ecology
Thermus scotoductus

Abstract:

A significant fraction of Earth’s microbial diversity derives from species living in extreme environments. On Earth life is generally found wherever liquid water exists, including extreme habitats built by humans. Understanding how communities function in such environments is critical for understanding the full extent of the biosphere and setting guidelines for the search for life on other planetary bodies. Extremophile communities have been known to inhabit the built environment since the 1970s, when Brock and Boylen discovered thermophiles in industrial water heaters similar to those growing in natural hot springs. There is public interest in understanding the ecology and functional diversity of those microorganisms which occupy the spaces that now serve as the primary human habitat in the developed world. In this dissertation I investigate microbial life in two human-impacted extreme environments: a deep subsurface mine, and domestic water heaters. I begin with a study of in situ growth of halophilic bacteria in boreholes 2.4 km deep inside a base metal mine in the Canadian Shield. Biosampler units were deployed into hydrogen-rich boreholes, recovering halophilic microbes growing in situ on geologically derived gases and ancient fracture water. Genetic and microscopic analyses reveal an ecosystem that supports microbial growth via lithoautotrophy despite being disturbed by human activity. The focus then moves away from the deep subsurface and into the extreme thermal environment of household water heaters. I present the results of a citizen scientist survey of thermophiles growing in domestic water heaters across the United States. Community level 16S sequencing, cell culture, and single species genome sequences are used to examine the distribution of thermophiles in domestic water heaters, particularly from the genus Thermus. Hot tap water is dominated by genetic signal from mesophilic organisms with a smaller but significant signal from thermophiles. Only one species, Thermus scotoductus, was recovered from cultures. This species was found in diverse water heaters across the United States and was by far the most prevalent member of the genus Thermus recovered from the water heater ecosystem. Finally, I explore the genetic makeup of these cultured strains in more detail, investigating the role of natural competence and phage transduction in shaping the pan-genome of Thermus scotoductus in the built environment.