Sulfolobus islandicus L.D.8.5
   
   
 

Biogeographic structure among S. islandicus strains (Mutnovsky and Uzon/Geyser Valley populations are both from the Kamchtka Russia.)

The questions that can be addressed by genome sequencing projects depend upon the level of evolutionary divergence being analyzed [1]. While single representatives of divergent phyla have provided evidence that lateral gene transfer has occurred on ancient time scales, the importance of genetic exchange processes to the structure and function of microbial communities over recent evolutionary time scales can only be determined by comparative genomic analysis among closely related individual strains. To investigate genome dynamics at the population level, we propose sequencing 8 strains from a highly structured model system in which biogeographically isolated populations have been defined. High-resolution multilocus sequence analysis of 130 Sulfolobus islandicus strains cultured from geothermal regions in North America, the Kamchatka peninsula, and Iceland revealed that S. islandicus is the dominant cultivable Sulfolobus species in the Northern Hemisphere, and that there are at least five endemic populations of Sulfolobus that are isolated from one another by geographic distance (Figure) [2]. Due to their geographic isolation, evolutionary events are likely to have occurred in each of five geothermal communities independently, and therefore may be correlated with the unique geologic history of their individual locale. Based on nucleotide divergence between populations, we estimate that Yellowstone and Lassen populations have been isolated for about 700,000 years, whereas the North American and Kamchatkan populations have been isolated for about 2,000,000 years - relatively short time scales compared to the 3.5 billion years of evolution that have created the diversity represented in the 16S rRNA tree of life. Interestingly the dating of divergence of these population correlates with the history of geothermal activity in each region providing excellent basis for linking evolutionary dynamics with geologic events in this system. We recommend the following set of strains be sequenced to facilitate comparisons in gene content and structure within and between these populations. Specifically, we anticipate this sequencing project would allow quantification of rates of lateral gene transfer, genome rearrangements, and recombination relative to mutation over geologically defined time scales.

References
1. Miller, W., et al., Comparative Genomics. Annual Review of Genomics and Human Genetics, 2004. 5(15-56).
2. Whitaker, R.J., D.W. Grogan, and J.W. Taylor, Geographic barriers isolated endemic population of hyperthermophilic archaea. Science, 2003. 301: p. 976-978.