Title: Ecology of the hydrothermal candidate archaeal division, Korarchaeota
Description: There is an astounding amount of unexplored microbial diversity on our planet. The unique organisms within many divisions (i.e., kingdoms or phyla) have never been investigated, particularly in the domain Archaea . My thesis examines the Korarchaeota , a candidate archaeal division known only from their PCR-amplified, deeply-branching 16S rRNA genes. Korarchaeota -specific primers were designed based on previously published sequences and used to screen a variety of environments. Korarchaeota 16S rRNA genes were PCR-amplified exclusively from high temperature Yellowstone National Park hot springs and a 9°N East Pacific Rise deep-sea hydrothermal vent. A close match between the 16S rRNA gene-based phylogeny of all known Korarchaeota and the geographic locations where they were identified suggested that Korarchaeota groups are highly endemic. To examine this hypothesis, the Korarchaeota 16S rRNA genes present in hot springs of another region, Kamchatka, Russia, were PCR-amplified, cloned, and sequenced. Like previous Korarchaeota sequences identified from a given geographic area, these clustered together phylogenetically, and even by local regions within the peninsula. In addition to geographic isolation, water source (freshwater vs. seawater) and temperature also appear to have been important factors influencing the diversification of Korarchaeota .

The abundance of individual phylogenetic groups of Korarchaeota in Kamchatka and Yellowstone hot springs was determined using quantitative PCR. Despite examining a variety of microhabitats and conditions, Korarchaeota were present at relatively low numbers in all sites where found. Only the expected Korarchaeota groups were detected, suggesting that phylotypes identified by PCR and sequencing were representative of the indigenous populations. Little was known about the geochemical conditions present in hydrothermal springs that Korarchaeota inhabit. Therefore, the geochemical variables that most highly correlated with the presence and abundance of the Korarchaeota in Yellowstone were investigated. While their metabolic and physiological traits could not be directly inferred, the hot springs where Korarchaeota were found contained high levels of hydrogen sulfide and have properties typical of one class of hot springs, vapor-dominated systems. By examining the phylogeny, distribution, abundance, and geochemical environment of Korarchaeota , my thesis research has laid the foundation for understanding one of the most enigmatic archaeal divisions.