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The Archaea Group Rolf Bernander Professor Department of Molecular Evolution Biomedical Center Uppsala University Husargatan 3 SE-751 24 Uppsala Sweden Phone: + 46-18-4714698 E-mail: Rolf.Bernander@icm.uu.se

• Archaea in global oceans use Cdv for cell division (comments in Nature Rev Microbiol and Mol Microbiol)


• Identification of an actin-based cytoskeleton in archaea (comments in Nature Rev Microbiol and CIB)


• Discovery of new Cdv cell division machinery (comments in PNAS and CIB)


• Global transcription map of an archaeal cell cycle (expression data web resource)


• Sulfolobus species contain three chromosome replication origins

Archaea Life on Earth is divided into three main evolutionary lineages: the Archaea, Bacteria and Eukarya domains. Archaeal organisms display a fascinating mixture of features from the other two domains. In particular, the replication, transcription and translation proteins are homologous to those of eukaryotes despite the fact that archaea, similar to bacteria, do not contain a cell nucleus. The archaea also display unique features, including distinct rRNA motifs, ether-linked membrane lipids and unique metabolic pathways, notably the ability of certain genera to produce methane gas.

Evolution In the universal Tree of Life, the shortest and deepest branches consist of hyperthermophiles (high-temperature organisms). This suggests that the last common ancestor of all life on Earth may have been a hyperthermophile, and most hyperthermophiles are archaea. Thus, by studying the archaea, it may be possible to deduce properties of the earliest cellular organisms. It has also been suggested that the eukaryotic lineage originated from cellular fusions between different bacteria and archaea. Archaea may therefore provide insights into the origin of the eukaryotes, and act as simple model systems for complex eukaryal processes.

Extremophiles and applied science Many archaea are extremophiles that thrive under conditions of extreme heat, acidity, salinity and/or pressure, and there is intense industrial interest in archaea as sources of thermostable enzymes and other biomolecules of unusual properties. In addition, proteins from thermophiles are often easier to crystallize than counterparts from lower-temperature organisms. Thus, a range of important structures, including the Cdc6 and Mcm replication proteins, the multisubunit RNA polymerase and the entire ribosome, have been solved with thermophiles as protein sources.

Ecology and biodiversity Although many archaea are extremophiles, rRNA gene amplification from environmental samples has made it clear that archaea are widespread also in non-extreme biotopes. Thus, they have ecological significance for large-scale circulation of energy, nutrients and biomass, as well as for global warming, since methanogenic archaea annually release in the order of half a billion tons of methane, a greenhouse gas 20 - 40 times more efficient than CO₂. In addition, increasing evidence is implicating archaea as largely responsible for nitrogen cycling in one of the largest habitats on Earth, the deep marine biosphere, as well as in many soil environments.

Exobiology All planets and moons in our solar system, except Earth, display environmental conditions that only extremophilic organisms can endure. Thus, knowledge about the biology of extremophiles is becoming increasingly releveant in searches for extraterrestrial life. We are co-founders of the Swedish Astrobiology Network which deals with astrobiology and exobiology issues.

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We are interested in regulatory, mechanistic and evolutionary aspects of the main cell cycle processes, i. e. chromosome replication, genome segregation and cell division. We investigate cell cycle features in a wide range of archaea with the main focus on the genus Sulfolobus, hyperthermophilic species that grow optimally in hot acid (80ºC and pH 3), found in geothermal hot springs areas all around Earth. The work has shown that several archaeal cell cycle features are eukaryotic in nature and that studies of archaea, consequently, can increase our understanding also of the eukaryotic cell cycle.

Our work rests on three main approaches. In the first, we use ultra-sensitive flow cytometry to characterize the general organization of the cell cycle, to determine DNA content and cell mass in exponential and stationary phase cultures, and to investigate the effects of mutations and drug treatments. In parallel, epifluorescence microscopy and computer-aided image analysis are used to study cell size and nucleoid dynamics during cell cycle progression, and in different growth phases. In addition, we have established several procedures for cell cycle synchronization of Sulfolobus species.

In a second main strategy, we have developed whole-genome DNA microarrays for two Sulfolobus species, in collaboration with Dr. Peter Nilsson at the Royal Institute of Technology (KTH) in Stockholm. The microarrays have been used for a series of functional genomics studies, including a genome-wide analysis of cell-cycle-specific gene expression in synchronized cell populations, and, in a pioneering study, a demonstration of the first instance of multiple chromosome replication origins in any prokaryote (see Research highlights).

In a third set of approaches, we investigate the molecular and biochemical details of archaeal chromosome replication, mitosis and cytokinesis machineries. This is to a large extent based on our previous identification of about 160 genes that display strong cell-cycle-dependent expression (above). Main outcomes of this work have been the discovery of the first novel cell division machinery, the Cdv system, since the bacterial FtsZ-based mechanism was identified several decades ago, as well as the identification of an archaeal cytoskeleton (see Research highlights).

We continue to explore deeper into the regulatory and mechanistic features of the archaeal cell cycle: see publications (link to the left) for a full account of our work.

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