The importance and impact that microbial activity has on the geology, geochemistry and ecology of hydrothermal vent ecosystems is now well-recognized. One aspect that has until recently been a puzzle, is --why with the low vent fluid pH had no acidophiles been isolated from these ecosystems? Given the recent discovery that the first cultured member of the deep-sea endemic archeael lineage, DHVE2, is a thermoacidophile, growing best at pH 4.5 and unable to grow above pH 6, the investigators in this project are poised to use this organism as a model organism to explore the ecology of thermoacidophiles at deep-sea vents. Furthermore, this is the most abundant archaeal lineage detected in many molecular taxonomy studies, representing up to 15% of the archaeal community, and its genome is currently being sequenced by the Venter Institute. Therefore, the proposed study will further our understanding of the molecular physiological ecology and biogeography of this important archaeal lineage at hydrothermal vents. The long-term objective of this project is to provide insights into the role that thermoacidophiles play in deep-sea hydrothermal vent ecosystems. Specific objectives include understanding the spatial distribution, relative abundance and co-occurrence patterns of thermoacidophilic archaea in chimneys from the Eastern Lau Spreading Center, Guaymas Basin and Mid-Atlanic Ridge vent sites, and to examine the vent chemistries at these sites as they could have dramatic effects on the occurrence of thermoacidophiles and affect the competition for overlapping niches with other vent microbes. The investigators in this project are predicting that thermoacidophiles will be more abundant at deep-sea vent sites of intermediate pH (pH 3-5), whereas they will be less abundant in sites with extreme vent fluid pH (pH <3, >5). To accomplish this work the investigators will collect chimney samples from the three contrasting deep-sea hydrothermal vent systems named above. A variety of cultivation and molecular techniques will be conducted on samples collected at these locations to look at the diversity of thermoacidophiles between vent sites, their ability to compete with other vent bacteria, and their metabolic activity. Additionally, new thermoacidophiles from deep-sea vents will be isolated and characterized. The unique biology of thermoacidophiles is being used in bioleaching/biomining applications and the discovery of new thermoacidophiles from deep-sea vents has the potential to provide tools for bioremediation and biotechnological applications by these organisms. The investigators are also involved in the training of minority graduate students and high school science teachers.