Abstract

From acid seeps and deep-sea thermal vents to glacial ice and hypersaline lakes, extreme environments contain relatively simplified communities consisting of extremophiles that have evolved to survive and thrive under adverse abiotic conditions. In more neutral environments, microorganisms use dormancy as a common life history strategy to weather temporal fluctuations of resources or stresses until more 'optimal' conditions are present. It is unclear if dormancy is an essential survival mechanism for microorganisms in extreme environments; however, recent studies suggest that extreme environments may create stable conditions for extremophiles to the extent that dormancy is of less ecological importance. Using lake salinity levels as measurements of "extreme," we evaluated the dormancy of bacterial and archaeal phyla and lake chemistry in five hypersaline and five freshwater lakes across the western United States. Dormancy was calculated using targeted metagenomics to analyze 16S rDNA and rRNA tag sequences. It was hypothesized that bacteria and archaea in hypersaline lake communities would exhibit lower levels dormancy than bacterial and archaeal communities in geologically similar freshwater lake controls. It was also hypothesized that microbial dormancy would decrease as the dominant extreme environmental variable increased in the lakes. As hypothesized, overall dormancy decreased at least 2-fold in hypersaline compared to freshwater lakes for both bacteria and archaea. Of the predominant phyla and subclasses, Firmicutes, Bacteroidetes, and Gammaproteobacteria each demonstrated at least a seven-fold decrease in dormancy in hypersaline lakes compared to freshwater lakes. Specifically, species within the genus Clostridium were responsible for 85% of the dormancy observed in the phylum Firmicutes. Also as hypothesized, microbial dormancy decreased as salinity increased in the lakes. Lower dormancy in hypersaline lakes correlated with increasing salinity while lower dormancy in freshwater lakes correlated with increasing total phosphorus levels. These results suggest that dormancy is a less common life history strategy for microorganisms in extreme environments; it is proposed that this is due to the relatively stable environment in hypersaline lakes and the reduced number of available microbial niches. These results also suggest that the dominant extreme stress (i.e., salinity) may override other driving factors in an environment to ultimately determine microbial community composition, diversity and richness.

Degree

College and Department

Life Sciences; Microbiology and Molecular Biology

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