Microbial Community Assembly and Diversification of the Genus Chloroflexus along an Alkaline Hot Spring Gradient

This research aims to achieve a greater understanding of the structure of bacterial communities present in alkaline hot springs in Yellowstone National Park. I focus specifically on White Creek and Rabbit Creek in the Lower Geyser Basin. I show that, overall, the bacterial communities of both creeks are non-randomly assembled. However, at finer taxonomic scales, bacterial groups differ in their community assembly patterns. Specifically, phototrophic groups show the strongest evidence for non-random assembly, most likely due to competition for light. A major exception to this pattern is the genus Chloroflexus, a major member of these communities. Members of this genus primarily grow phototrophically, yet they did not show evidence of non-random assembly, as only one major 16S ribosomal RNA (rRNA) sequence was detected. Therefore, I next explored whether this single 16S rRNA sequence represents a single, broadly-distributed generalist or several cryptic specialist lineages. I isolated eleven strains of Chloroflexus from White Creek and determined that these isolates are members of a group without previously cultured representatives. I show that strains isolated from different temperatures have recently diverged within White Creek, as they can be differentiated genetically by the propionyl Co-A synthase gene, as well as phenotypically by differences in thermotolerance.