Doctor of Philosophy (PhD)


Biological Sciences

Document Type



Carbon monoxide (CO) has been exploited as a microbial energy source for much of life’s evolutionary history. A phylogenetically diverse array of microorganisms can oxidize CO using two distinct CO dehydrogenases, molybdenum-dependent (Mo-CODH) and nickel-dependent (Ni-CODH). Aerobes and facultative organisms contain Mo-CODHs which allow them to utilize oxygen as an electron acceptor in addition to alternatives such as nitrate and sulfate. Obligate anaerobic organisms contain Ni-CODHs, which oxidize CO at elevated concentrations, but cannot utilize oxygen. In systems where organic matter deposits are limited or absent, atmospheric trace gases such as CO are thought to assist in supporting the growth and survival of microbial communities. Extraterrestrially, the Martian atmosphere is dominated by CO2, however, CO also has also been documented at substantial levels. Martian regolith contains only trace levels of organic carbon, leaving CO as potentially the most abundant and available substrate capable of supporting near-surface microbial activity. However, Martian regolith also contains perchlorate, while potentially toxic it also serves an abundant potential oxidant. At locations such as the recurrent slope lineae, hypersaline perchlorate-based brines are thought to exist. Though previously unexplored for CO oxidation, chlorine oxyanions may act as suitable electron acceptors, expanding the current range of both Mo-CODH and Ni-CODH CO oxidizing microorganisms. This study used a variety of culture-dependent approaches, cultivating four novel haloarchaea from the Bonneville Salt Flats and surrounding saline soils capable of utilizing CO, ClO4-, or a metabolic coupling. Halovenus carboxidivorans was capable of CO oxidation, while Halobacterium bonnevillei and Halobaculum saliterrae, represent the first microbes capable of nitrate-dependent, perchlorate-coupled CO oxidation at concentrations up to 1 M ClO4-. All three isolates contained Mo-CODHs. The provisional species, Halanaeroarchaeum oxyrespirans, is capable of growth via perchlorate reduction, independently of nitrate, a first for haloarchaeal cryptic perchlorate reduction. Additionally, H. oxyrespirans, can respire oxygen, expanding the known capacities of the genus. Perchlorate-coupled CO oxidation was further expanded to include carboxidotrophic Ni-CODH containing microbes using the thermophilic Firmicute Moorella glycerini as a model organism. Collectively, the isolation of these haloarchaeal cultivars contributed to the expansion of haloarchaeal diversity through both physiological and genomic characterization.



Committee Chair

King, Gary