Phylogenetic characterization of alpine soil microbial diversity.

摘要

I explored the diversity of all domains of life in the dry meadow tundra of Niwot Ridge in the Colorado Rocky Mountains, comparing this diversity between the winter and summer. Using molecular, culture-independent techniques, I examined the phylogenetic relationships of the Bacteria, Archaea, and Eucarya populating this ecosystem. Within their respective domains, Proteobacteria, Crenarchaeota Group 1.1b, and Fungi dominate this soil; also abundant are Verrucomicrobia and Acidobacteria, among the Bacteria, and Viridiplantae, Metazoa, and Cercozoa, among the Eucarya. Statistical tests indicate that the winter and summer eucaryal communities are significantly different with the Viridiplantae and the Basidiomycetes driving this difference. This is the first ever molecular study examining the diversity within all three domains of biologic life in one ecosystem.; I also examined the metabolic and phylogenetic characteristics of 17 cold-tolerant Pseudomonas isolates from the same dry meadow tundra of Niwot Ridge. I characterized their ability to grow on a variety of carbon sources and their phylogenetic relationships based on 16S ribosomal DNA sequencing. I found high prevalence of Pseudomonas in my soil and isolates exhibited extensive metabolic diversity. In addition, my data revealed that many of the isolates form a unique cold-adapted clade, representatives of which are also found in the Swedish tundra, Baltic Sea, and Antarctica. Interestingly, my data also show a lack of concordance between the carbon-source metabolic properties and 16S phylogeny, indicating that some of the metabolic diversity of these organisms cannot be predicted by phylogeny.; Finally, I studied the phylogenetic characteristics of a microbe-dominated ecosystem in the talus fields of Niwot Ridge. I sampled this site during the most stable and wettest period of the year, beneath the late winter snow pack. Again using culture-independent techniques, I examined the diversity of eukaryotes there. I show that this high elevation (3700 meters) soil system contains eight eukaryotic kingdoms, and is dominated by the Fungi and Cercozoa. Most significantly, I discovered that this seemingly barren system supports many unique microbial lineages, including a new, high-level clade distinct from known kingdoms and several class-level and order-level clades among the chytrid fungi and cercozoa. One explanation for the novelty and diversity of the organisms I discovered is that isolated, high elevation systems may be refugia for cold-adapted eukaryotic microorganisms that dominated the earth during colder epochs, i.e. "snowball Earth" periods. In addition, my results significantly extend our knowledge of Mars-like terrestrial systems and suggest that our understanding of eukaryotic diversity on Earth may still be quite limited.