Award Date


Degree Type


Degree Name

Master of Science in Biological Sciences


Life Sciences

Advisor 1

Brian Hedlund, Committee Chair

First Committee Member

Eduardo Robleto

Second Committee Member

Helen Wing

Graduate Faculty Representative

Linda Stetzenbach

Number of Pages



Despite a wide diversity of possible electron donors available to fuel chemolithotrophy, it has been proposed that hydrogen is the single most important electron donor in geothermal ecosystems. To directly test this hypothesis, a simple system was devised to determine whether microorganisms in hot spring water and sediment are capable of using hydrogen and other electron donors for aerobic respiration using microrespirometry. The protocol for these experiments was developed using pure cultures of Thermocrinis ruber to determine the effect of growth conditions on the rate of oxygen consumption following the addition of electron donors. For field experiments, samples were collected without introduction of oxygen or change in temperature and measurements of oxygen consumption were initiated within ten minutes of collection. After a baseline oxygen consumption rate was established, possible electron donors were added and oxygen consumption was measured over a twenty-minute window. This system was used to evaluate the impact of electron donor addition (1 mM each of S 2 O 3 2- , formate/lactate/acetate/propionate mixture, yeast extract/peptone, NH 3 and 10 μM each H 2 and CH 4 ) on oxygen consumption in source water and surface sediment of two near-neutral pH hot springs in the Great Basin, Great Boiling Spring (GBS, 80°C, pH 7) and Sandy's Spring West (SSW, 83°C, pH 7). The composition of the microbial community in the corresponding environments was also evaluated using a combination of terminal restriction fragment length polymorphism (T-RFLP) and fluorescent in situ hybridization (FISH). The resulting data showed that both the simple water-borne microbial communities (~2-4 species) and the more complex sediment microbial communities (~20-35 species) have diversified to take advantage of a variety of electron donors. These data do not support the hypothesis that hydrogen is the most important electron donor in the source water and sediments of the springs that were examined because hydrogen only stimulated an increased rate of oxygen consumption in two of the four environments tested. This study provides an important step in providing a more complete understanding of the energy budgets of high-temperature ecosystems and provides a template to study other habitats.


Aerobic respiration; Chemolithotrophy; Ecology; Extremophiles; Great basin; Great Boiling Spring; Hot springs; Hydrogen usage; Microbial communities; Microrespirometry; Oxygen consumption; Sandy’s Spring West; Thermocrinis ruber; Thermophiles


Environmental Microbiology and Microbial Ecology | Microbiology

File Format


Degree Grantor

University of Nevada, Las Vegas




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