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Appl. Environ. Microbiol. doi:10.1128/AEM.02741-07
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

The Thermo-acidophilic Cyanidiales: Biogeographic and Phylogenetic Diversity in Yellowstone National Park, Japan, and New Zealand

Center for Ecology and Evolutionary Biology, 5289 University of Oregon, Eugene, Oregon 97403-5289; Department of Chemistry and Biochemistry, California Polytechnic State University, San Luis Obispo, CA 93407; Thermal Biology Institute, and Department of Land Resources and Environmental Sciences, Montana State University, Bozeman, MT 59717

^* To whom correspondence should be addressed. Email: rcasten{at}uoregon.edu.

	Abstract

Members of the Rhodophytan order Cyanidiales are unique among phototrophs in their ability to live in an extreme environment that combines low pH (0.2-4.0) and moderately high temperatures of 40°-56°C. These unicellular algae occur in far-flung volcanic areas throughout the Earth. Three genera (Cyanidium, Galdieria, and Cyanidioschyzon) are recognized. The phylogenetic diversity of culture isolates of the Cyanidiales from habitats throughout Yellowstone National Park (YNP), three areas in Japan, and seven regions in New Zealand was examined, using the chloroplast RUBISCO large sub-unit gene (rbcL) and the 18S rRNA gene. Based on the nucleotide sequences of both genes, the YNP isolates fall into two groups, one with high identity to Galdieria sulphuraria (Type II) and another that is by far the most common and extensively distributed Yellowstone type (Type IA). The latter is a spherical, walled cell that reproduces by internal divisions with a subsequent release of smaller daughter cells. This type, nevertheless, shows a 99-100% identity to Cyanidioschyzon merolae (Type IB) that lacks a wall, divides by a "fission"-like cytokinesis into two daughter cells and is less than 5% of the cell volume of Type IA. The evolutionary and taxonomic ramifications of this disparity are discussed. Although 18S rRNA and rbcL genes did not reveal diversity among the numerous isolates of Type IA, chloroplast short sequence repeats (cpSSR) did show some variation by location within YNP. In contrast, Japanese and New Zealand strains showed considerable diversity using only the sequences of 18S and rbcL genes. Most exhibited identities closest to Galdieria maxima but which were commonly as low as 91-93%. Some of these strains probably represent undescribed species that diverged after long-term geographic isolation.