Diversity and potential geochemical functions of prokaryotes in hot springs of the Uzon Caldera, Kamchatka
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Hot springs are modern analogs of ancient hydrothermal systems where life may have emerged and evolved. Autotrophic microorganisms play a key role in regulating the structure of microbial assemblage and associated biochemical processes in hot springs. This dissertation aims to elucidate the diversity, abundance and ecological functions of multiple groups of chemoautotrophs that use diverse energy sources including CO, NH3, and H2 in terrestrial hot springs of the Uzon Caldera, Kamchatka (Far East Russia). This dissertation consists of seven chapters. Chapter 1 reviews studies in geochemistry and microbiology of studied area. 13Chapter 2 reports H2, CO2, CH4 and CO contents and the /C values in vent gas samples. The gases were determined to be thermogenic with small temporal but large spatial variations among the springs investigated. Chemical and partial isotope equilibria between CO2 and CH4 may be attained in the subsurface at elevated temperature. Chapter 3 shows the distribution of bacteria was spatially heterogeneous whereas that of archaea was related to geographic features. Cluster analyses group bacterial and archaeal communities according to their similarities of lipid compositions. Hydrogen-utilizing Aquificales appeared to be dominant in two of the four bacterial groups, but was outnumbered by presumably Cyanobacteria-Thermotogae or Proteobacteria-Desulfurobacterium types in the other two groups. The lipid data also suggest the existence of possibly three types of archaea with each type producing one of GDGT-0, GDGT-1, and GDGT-4 as the main membrane lipids, respectively. Chapters 4 and 5 describe a novel aerobic, thermophilic and alkalitolerant bacterium Caldalkalibacillus uzonensis, which tolerated >90% headspace CO but cannot utilize CO as carbon and energy sources. Chapter 6 focuses on the study of carbon isotope fractionation associated with carbon fixation by an anaerobic CO oxidizing hydrogenogen Carboxydothermus hydrogenoformans. It reveals that a feedback 13system tends to hold the /C value constant among CO, CO2 and biomass. A steady state point and associated carbon isotope fractionations ( 0A-B = /A- /B) were hypothesized to be 18‰ for the CO2-CO system, 2‰ for the bulk biomass-CO2 system, and -20‰ for the CO-biomass system. Chapter 7 reports the diversity and distribution of ammonia-oxidizing archaea (AOA) in hot springs of the Uzon Caldera. A patchy presence of AOA and the absence of AOB (ammonia-oxidizing bacteria) were observed through PCR based surveys. AOA diversity correlated to abundances of archaea or crenarchaeota but was not directly correlated to temperature or chemical variables.