James Holden

Primary producers are organisms that convert CO 2 into the organic matter that forms the base of the foodweb. While most primary production occurs by photosynthesis, there is increasing evidence that a significant portion of global primary production occurs by chemosynthesis in the absence of light within geothermal regions of the earth's crust. Geothermal fluids are predicted to circulate through vast portions of the earth's crust and it was estimated that 20% of the earth's total biomass may be found within this environment in the form of microorganisms. Some of these organisms, called hyperthermophiles, grow optimally at temperatures between 80 and 105°C without sunlight or O 2 and can grow on volcanically-derived H 2 and CO 2 as well as on iron and sulfur compounds from the surrounding minerals. The current need is to better understand the growth and physiology of these subsurface hyperthermophiles and to further develop biogeochemical models that predict the significance of their activity in subsurface environments based on predicted levels of energy sources (especially H 2 , CO 2 , Fe, and S) and fluid chemistry (pH, redox).

My research focuses on the physiology and genomics of hyperthermophilic archaea that grow near 100°C and the geomicrobiology of the geothermal environments where these organisms are found. The physiology studies within my laboratory can be separated into two sets of projects: characterization of dissimilatory Fe(III) reduction and characterization of CO 2 fixation. My genome analysis projects involve the genome sequencing of one hyperthermophile and the bioinformatic analysis of it and another hyperthermophile genome. My geomicrobiology projects include the study of hyperthermophiles from deep-sea hydrothermal vents collected from the northeastern Pacific Ocean using the deep-sea submarine Alvin. These projects will have a broader societal impact by providing tools to better understand the nature of the geothermally-heated regions of the subsurface, which represents a vast and largely unknown ecosystem and natural resource. Likewise, many of our physiology findings are likely to be new to biology and will significantly enhance our understanding of Archaea.