PROKARYOTIC DIVERSITYBIOL 4125SPRING 2009LECTURE 22HyperthermophilicArchaeaPart II
• This viewpoint was established in thelate 1970s and was based on culturedorganisms (<20 rRNA gene sequences).• Based on the properties of the culturedorganisms, it appeared thatcrenarchaeotes were exclusively high-temperature organisms.• Left: the accumulation of archaealrRNA sequences submitted toGenBank.• The inset picture shows the proportionof archaeal rRNA sequences fromcultured versus environmental sources.• As environmental sequences haveaccumulated, it has become evidentthat Archaea are a cosmopolitan groupthat are not limited to ‘extreme’environments.The early overview of archaeal diversity was exemplified by a phylogenetic treethat had two main branches: the Euryarchaeota and the CrenarchaeotaRobertson et al. (2005) Curr. Opion. Microbiol. 6:638-642; plantphys.info/organismal/lechtml/archaea.html.
Cold-dwelling CrenarchaeotesIn contrast to hyperthermophiles, cold-dwelling crenarchaeotes have been identifiedfrom community sampling of 16S rRNA from many non-thermal environments,including frigid waters and sea ice near the Antarctic.They are estimated to represent1028cells in the world’s oceans and are likely to have a major role in biogeochemicalcycling.Until recently, there were no cultivated members of this group.
Nitrosopumilus maritimus: the first cold-temperature crenarchaeota incultivation and the first example of an archaea capable of nitrificationKonneke et al. (2005) Nature 437:543-546; Leininger et al. (2006) Nature 442:806-809Quantitative PCR studies demonstratedthe activity of the archaea in situ andsupported the numerical dominance ofarchaeal over bacterial ammoniaoxidizers, indicating that crenarchaeotamay be the most abundant ammonia-oxidizing organisms in soil on Earth!