ABSTRACT

Microorganisms from the Kingdom Archaea produce novel membrane lipids of the class isoprenoidal diethers and glycerol dialkyl glycerol tetraethers (GDGTs). In particular, crenarchaeol was recognized to be the key biomarker for low temperature crenarchaeota and known to be associated with ammonia-oxidizing archaea (AOA). AOA and crenarchaeol have recently been found in Great Basin hot springs and in a thermophilic culture ("Candidatus N. yellowstonii") enriched from springs in Yellowstone National Park. "Candidatus N. yellowstonii"-like species were also present in some of the Great Basin hot springs. The goal of this research is 1) to seek the linkage between crenarchaeol production and distribution of "Candidatus N. yellowstonii"-like species and 2) to determine the factors controlling the distribution of crenarchaeol and other archaeal lipid biomarkers in Great Basin hot springs. The PIs hypothesize that crenarchaeol is actively produced in situ by these microbes and can serve as a proxy for archaeal ammonia oxidation. This hypothesis will be tested by quantifying of archaeal biomarkers (particularly crenarchaeol) and "Candidatus N. yellowstonii"-like archaea in hot springs of different temperatures and chemical compositions and evaluation of soil contamination to the hot spring environment. The production of crenarchaeol will be linked to specific archaeal populations from natural environments using stable isotope probing (SIP) of RNA/DNA and lipids. Finally, the PI will evaluate the role of ammonia-oxidizing archaea in carbon fixation using in situ CO2 fixation experiments. These objectives will be achieved by using advanced molecular approaches and innovative chemical tracer studies (hydrogen isotopes of archaeal biomarkers and 13C-labeling of carbon substrates). The major phylogenetic and functional groups of archaea will be characterized using standard protocols for DNA/RNA extraction, amplification, cloning, and sequencing. Statistical analysis will be employed to link differences in aqueous geochemistry, lipid biomarkers, and predominant 16S rRNA or functional gene phylogenies among springs with diverse lipid profiles.

The crenarchaeol isomer is an important part of a paleothermometer (TEX86) based on tetraether lipids. Thus, understanding the source and distribution of crenarchaeol and its isomers has evolutionary implications and contributes to a better understanding of how this molecule's distribution relates to paleotemperature. This project will be closely linked to studies of geothermal features in China and will coordinate efforts with colleagues who are actively doing archaeal research in Yellowstone National Park and other countries to promote the establishment of an archaeal research network on phylogeny, biogeography and ecological functions of archaea in terrestrial hot springs. In addition to training undergraduate and graduate students, Zhang will bring high school teachers and students to the field each year and incorporate this research into his community seminars on life in extreme environments in Augusta, GA, which has interested both children and adults.