22 - PROKARYOTIC DIVERSITY BIOL 4125 SPRING 2009 LECTURE 22...

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PROKARYOTIC DIVERSITY BIOL 4125 SPRING 2009 LECTURE 22 Hyperthermophilic Archaea Part II
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• This viewpoint was established in the late 1970s and was based on cultured organisms (<20 rRNA gene sequences). • Based on the properties of the cultured organisms, it appeared that crenarchaeotes were exclusively high- temperature organisms. • Left: the accumulation of archaeal rRNA sequences submitted to GenBank. • The inset picture shows the proportion of archaeal rRNA sequences from cultured versus environmental sources. • As environmental sequences have accumulated, it has become evident that Archaea are a cosmopolitan group that are not limited to ‘extreme’ environments. The early overview of archaeal diversity was exemplified by a phylogenetic tree that had two main branches: the Euryarchaeota and the Crenarchaeota Robertson et al. (2005) Curr. Opion. Microbiol. 6:638-642; plantphys.info/organismal/lechtml/archaea.html.
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Cold-dwelling Crenarchaeotes In contrast to hyperthermophiles, cold-dwelling crenarchaeotes have been identified from community sampling of 16S rRNA from many non-thermal environments, including frigid waters and sea ice near the Antarctic. They are estimated to represent 10 28 cells in the world’s oceans and are likely to have a major role in biogeochemical cycling. Until recently, there were no cultivated members of this group.
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: the first cold-temperature crenarchaeota in cultivation and the first example of an archaea capable of nitrification Konneke et al. (2005) Nature 437:543-546; Leininger et al. (2006) Nature 442:806-809 Quantitative PCR studies demonstrated the activity of the archaea in situ and supported the numerical dominance of archaeal over bacterial ammonia oxidizers, indicating that crenarchaeota may be the most abundant ammonia- oxidizing organisms in soil on Earth! Nitrifying Crenarchaeota are important to global carbon and nitrogen cycling.
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22 - PROKARYOTIC DIVERSITY BIOL 4125 SPRING 2009 LECTURE 22...

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