SCIENCE CHINA Life Sciences © The Author(s) 2012. This article is published with open access at Springerlink.com life.scichina.com www.springer.com/scp email: huangl@sun.im.ac.cn May 2012 Vol.55 No.5: 375–376 • EDITORIAL • doi: 10.1007/s11427-012-4323-x Unveiling the beauty of Archaea HUANG Li State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China Received April 15, 2012 Citation: Huang L. Unveiling the beauty of Archaea. Sci China Life Sci, 2012, 55: 375–376, doi: 10.1007/s11427-012-4323-x One of the greatest achievements in the life sciences in the 20th century was the recognition of three forms, or domains, of cellular life, i.e., Bacteria, Archaea, and Eukarya, in the three-domain theory put forward by Carl Woese and George Fox in 1977 [1]. According to their theory, Archaea, which were previously regarded as a peculiar group of bacteria, are no more closely related to Bacteria than to the Eucarya from a phylogenetic viewpoint and, thus, represent the third form of life. This theory was not widely accepted until 1996 when the genome sequence of Methanocaldococcus jan- naschii, a methane-producing archaeon, was published [2]. The genetic blueprint of this organism offered strong sup- port for the three-domain theory. By some estimates, Archaea account for 20% of the total biomass on Earth [3]. The majority of known Archaea are extremophiles thriving in extremes of temperature, pH, salin- ity, etc. [4]. A number of hyperthermophilic Archaea have been isolated from hot springs and hydrothermal vents, halophilic Archaea from salt lakes, and acidophilic Archaea from acid mine drainage. Archaea also exist in “non-ex- treme” environments, including soils, wetlands, oceans, and the human colon [5]. Archaea are capable of a wide range of metabolic activities and are believed to serve important roles in driving the C, N, and S cycles on the planet [6]. Despite their resemblance in size and morphology, Archaea and Bacteria differ markedly in many important aspects, such as cell wall and membrane composition and DNA transactions [7–10]. Strikingly, Archaea employ genetic mechanisms similar to, but simpler than, those found in Eucarya [11]. Furthermore, a surprising variety of mobile genetic elements (e.g., viruses and plasmids) have been found in the domain Archaea [12]. Some archaeal viruses have unusual shapes that are never seen in bacteriophages or eucaryal viruses [13]. The landmark discovery of Archaea drew much attention to this new form of life. There was a further boost of inter- est in Archaea after the sequencing of the M. jannaschii genome. A number of laboratories have since become in- volved, at least partially, in studying Archaea for clues on the fundamentals and evolution of life or for enzymes or functions with potential applications. In the short period of less than 20 years since the end of the last century, our un- derstanding of Archaea has significantly increased [13–21]. To date, nearly 200 archaeal genomes have been sequenced. Because of their unusual stability, proteins from thermo- philic Archaea are favored for biochemical and structural biological studies. Some 5500 crystal structures of archaeal proteins, 60% of which are derived from thermophiles, are now available in PDB. Over 80% of them were obtained in the past decade. In China, research on Archaea started in the late 1970s when the first extremophile laboratory was established at the Institute of Microbiology, Chinese Academy of Sciences (IMCAS). The laboratory isolated halophilic microorgan- isms from salt lakes in Qinghai province, China [22]. In the 1980s, scientists from IMCAS isolated the first thermoaci- dophilic archaeon, Acidianus tengchongenses, from hot springs in Tengchong, Yunnan Province [23,24]. From the late 1990s to the early 2000s, the pace of archaeal research accelerated and entered the molecular and genomic phase. Several archaeal laboratories devoted entirely to research on thermophilic, halophilic, or methanogenic Archaea were set SPECIAL TOPIC 376 Huang L. Sci China Life Sci May (2012) Vol.55 No.5 up at IMCAS as well as at several universities. Their re- search covers chromosomal organization, genetic mecha- nisms, viruses and plasmids, synthesis of polyhydroxyalka- noates (PHAs), quorum sensing, enzyme stability, etc. [25–36]. Although moderate in size, the Chinese archaeal community has made important contributions to the understanding of Archaea and is now well respected in the field. 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