Microbial Taxonomic and Functional Diversity in Canadian Saline and Thermal Springs
Date
2019-07-15
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Abstract
By demonstrating a strong effect of salinity on microbial species diversity, this work expanded the known environmental parameters that influence microbial taxonomic diversity. Additionally, this work showed that environmental stress reduces both taxonomic and functional diversity of microbial communities. pH and temperature are strong drivers of microbial taxonomic diversity, with extreme environments supporting reduced diversity. To examine the effect of another environmental parameter, salinity, on diversity, 16S rRNA and 18S rRNA gene amplicon libraries constructed from 55 sediment samples ranging in conductivity from near-fresh to halite-saturated were sequenced on the Illumina platform. Increasing conductivity, as a proxy for salinity, was found to be correlated with a reduction in bacterial taxonomic diversity in a linear manner, with peak diversity occurring at the lowest salinities examined. Conductivity also influenced the diversity of Archaea and microbial Eukarya, and these trends were explained in terms of energetic costs of salinity tolerance and mechanisms of energy production in these organisms. A small number of studies suggest that functional diversity (all of the different metabolic functions within a community) declines with decreasing taxonomic diversity of microbial communities. This relationship was tested using a dataset of 12 geothermal springs ranging in temperature from 24 to 86 °C. Functional diversity was calculated by quantifying the Pfam (protein family) diversity contained within metagenomic libraries constructed from these samples. Functional diversity was found to decrease with temperature in a similar manner to taxonomic diversity. Lastly, a study of an uncultivated clade of Bacteria, GAL08, dominating microbial communities in a geothermal spring at Dewar Creek, British Columbia, was undertaken. Material from Dewar Creek was subjected to single-cell sorting and sequencing, resulting in the identification of 13 partial single-cell genomes belonging to GAL08. Analysis of the genomes revealed the presence of three species of GAL08 at Dewar Creek. Surveys of sediment from Dewar Creek showed that GAL08 is a persistent and stable member of the microbial community, and is thermophilic, with a temperature preference of 55 to 70 °C. Laboratory enrichment experiments determined that GAL08 is likely microaerophilic. By demonstrating that the effect of salinity on microbial species diversity can be explained in terms of energy constraints, this work expanded our understanding of how environmental parameters may drive microbial diversity. Furthermore, this work represented one of the few thorough investigations into the relationship between functional diversity and environmental stress in microbial communities. Elucidating how microbial taxonomic and functional diversity responds to changes in environmental parameters, such as temperature, is timely considering the ongoing changes in global climate.
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Keywords
Environmental stress, Thermophile, Salinity, Osmotic stress, GAL08, Microbial diversity
Citation
Ruhl, I. A. (2019). Microbial Taxonomic and Functional Diversity in Canadian Saline and Thermal Springs (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.