Cyanidiales ecology : biodiversity and transcriptomics in Yellowstone National Park

Abstract

The work presented in this thesis investigated the ecology of a unicellular, and asexual red algae belonging to the order Cyanidiales which are the only phototrophs occurring in low pH (0.5-3.5) and high temperature (38-56°C) geothermal environments. These algae exhibit a dynamic seasonal biomass fluctuation referred to as 'mat decline,' where viability drastically decreases as seasonal ultra-violet (UV) and visible (VIS) irradiance intensify. Temporal experiments coupling UV irradiance filtering with whole-community transcription profiling revealed significant cyanidial gene expression changes occurring as a result of exposure to UV, and that patterns of response adjusted across low and high irradiance time periods. Separate analyses examined genes responding to either increasing seasonal UV or VIS intensity, or by the combined effects of both irradiance wavelengths (UV and VIS). Results not only corroborated known physiological changes to solar irradiance, but also suggested the strategies employed to deal with excess VIS and UV intensity may be highly integrated. Comparative analysis determined that environmental microarrays are highly sensitive in their detection of transcript diversity, and in situ gene expression changes. Proteomic work identified several dominant cyanidial proteins which were also abundantly transcribed, suggesting there is good correspondence between highly abundant proteins and gene transcriptional activity for these algae. Additionally, a study is presented which examined the biodiversity and distribution of the Cyanidiales in Yellowstone National Park (YNP). Phylogenetic reconstruction using the rbcL gene sequence identified two well-supported YNP lineages: Cyanidioschyzon and Galdieria-A, and showed the separation of taxa based on ecophysiological conditions. Galdieria-A phylotypes were found exclusively in soil and endolithic habitats. Cyanidioschyzon was the sole phylotype found in aqueous environments, but was also detected in all soil and endolithic habitats investigated. Culturing efforts demonstrated that moisture availability controls cyanidial viability and distribution in soil habitats, while alternative environmental factors influence endolithic populations. In addition, autotrophic and heterotrophic viable cell counts in combination with rbcL gene sequencing determined that Galdieria dominates the species composition in soil environments, while the endolithic habitat contains both Cyanidioschyzon and Galdieria.