Kingdom Euryarchaeota Research Articles

A New Era of Methanogenesis Research

The reductive acetyl-CoA pathway coupled to methanogenesis is likely one of Earth's oldest metabolisms. Yet, until recently this metabolism had only been found in the kingdom Euryarchaeota. A study now suggests that distantly related Bathyarchaeota are also methanogens and that methane metabolism is more phylogenetically widespread than previously thought.

Rooting the domain archaea by phylogenomic analysis supports the foundation of the new kingdom Proteoarchaeota.

The first 16S rRNA-based phylogenies of the Archaea showed a deep division between two groups, the kingdoms Euryarchaeota and Crenarchaeota. This bipartite classification has been challenged by the recent discovery of new deeply branching lineages (e.g., Thaumarchaeota, Aigarchaeota, Nanoarchaeota, Korarchaeota, Parvarchaeota, Aenigmarchaeota, Diapherotrites, and Nanohaloarchaeota) which have also been given the same taxonomic status of kingdoms. However, the phylogenetic position of some of these lineages is controversial. In addition, phylogenetic analyses of the Archaea have often been carried out without outgroup sequences, making it difficult to determine if these taxa actually define lineages at the same level as the Euryarchaeota and Crenarchaeota. We have addressed the question of the position of the root of the Archaea by reconstructing rooted archaeal phylogenetic trees using bacterial sequences as outgroup. These trees were based on commonly used conserved protein markers (32 ribosomal proteins) as well as on 38 new markers identified through phylogenomic analysis. We thus gathered a total of 70 conserved markers that we analyzed as a concatenated data set. In contrast with previous analyses, our trees consistently placed the root of the archaeal tree between the Euryarchaeota (including the Nanoarchaeota and other fast-evolving lineages) and the rest of archaeal species, which we propose to class within the new kingdom Proteoarchaeota. This implies the relegation of several groups previously classified as kingdoms (e.g., Crenarchaeota, Thaumarchaeota, Aigarchaeota, and Korarchaeota) to a lower taxonomic rank. In addition to taxonomic implications, this profound reorganization of the archaeal phylogeny has also consequences on our appraisal of the nature of the last archaeal ancestor, which most likely was a complex organism with a gene-rich genome.

象山港网箱养殖区沉积物的古菌空间分布

PDF HTML阅读 XML下载 导出引用 引用提醒 象山港网箱养殖区沉积物的古菌空间分布 DOI: 10.5846/stxb201212041745 作者: 作者单位: 宁波大学海洋学院,宁波大学海洋学院,宁波大学海洋学院,宁波大学海洋学院,宁波大学海洋学院,宁波大学海洋学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金（41101234）；浙江省教育厅科研项目（Y201121499）；宁波大学学科项目（xkl11090）；国家863资助项目（2012AA092001） The archaeal spatial distribution in sediments of cage culture area in Xiangshan Bay, Zhejiang, China Author: Affiliation: School of Marine Science, Ningbo University,School of Marine Science,Ningbo University,School of Marine Science,Ningbo University,School of Marine Science,Ningbo University,School of Marine Science,Ningbo University,School of Marine Science,Ningbo University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:对象山港网箱养殖区及其周边沉积物中古菌群落的空间分布进行研究，应用基于16S rRNA基因的T-RFLP（末端限制性片段多态性分析）技术分析象山港网箱养殖区及其周边不同深度沉积物中古菌的群落结构和多样性，并构建克隆文库进行系统发育学分析。测定沉积物各项理化因子，通过PCA和RDA分析了古菌群落分布及其与环境因子之间的关系。结果表明，泉古菌是港口沉积物中的优势古菌群，占古菌群落的50%以上。网箱养殖区沉积物的古菌群落结构较非养殖区简单，多样性降低。非养殖区古菌群落随深度呈现有规律的变化。营养盐类和pH是造成养殖区域古菌群落结构区别于非养殖区域的主要环境因素。 Abstract:Archaea was distributed widely in marine environments. It plays an important role in nutrient and energy cycling in marine ecosystems. For studying the archaeal spatial distribution in sediment of cage culture area, archaeal community structures in sediments were investigated in July 2011, in Xiangshan Bay, Zhejiang Province, China. Sediments used in this paper were as the same as described previously[1]: a control or check site (CK), an intersection site 6-8 km from the aquaculture site (IS), and a cage culture site (AC). For sub-sampling, sediments were cut into several sections throughout their depth: a (0-5 cm), b (5-10 cm), c (10-15 cm), d (15-20 cm), e (20-25 cm) and f (50-55 cm). Physiochemical factors (NH4+, NO2-, NO3-, SiO32- and P) of sediments were analyzed in laboratory after transport with liquid nitrogen. Based on 16S rRNA gene, the structure and diversity of archaeal communities in sediments were analyzed by T-RFLP (Terminal Restriction Fragment Length Polymorphism), which was conducted after amplification of the archaeal 16S rRNA partial gene using a fluorescent primer pair 109F /934R-FAM and digestion by TaqI (T^CGA). Archaeal 16S rRNA gene clone library was constructed using DNA extracted from layer 0-5 cm sediment of the CK site, and the following phylogenetic analysis was carried out using ARB software. In agreement with other studies, Crenarchaeota is the dominant archaea in marine sediment. T-RFLP profiles showed that the dominant T-RF of 188 bp, affiliated to Crenarchaeota, occupied 80.3% in the cage culture site, more than it in the check site (61.2%). While, the kingdoms Euryarchaeota and Crenarchaeota were present equally in clone library and methanogens constituted a small proportion of the archaeal community. Because the check site is near to East Sea with a higher salinity, T-RF of 78 bp, belonged Halobacteriales, emerged in its upper layers (0-20 cm) sediments and was more abundant than it in other sites. Principal component analysis for the archaeal 16S rRNA gene T-RFLP using R software indicated a complete separation of archaeal communities of the cage culture sit from the check site. And archaeal communities of the intersection site were in the middle. An obvious difference of archaeal communities in the check site sediments at various depths was indicated by PCA. T-RFs of 78 bp, 88 bp, 383 bp and 188 bp related archaea may be the main microorganisms who made the difference among horizontal and vertical distribution. Although calculation of Shannon diversity index H' and evenness index E' showed large errors in parallels, comparing with the check site, the diversity of archaeal communities in cage culture sediments displayed a dropping tendency. Redundancy analysis of archaeal community compositions and environmental factors of sediments in different sites and depths suggested that nutritive salt and pH mainly affected the distribution of archaeal in horizontal by aquaculture. Eh and ammonium were tend to have a relation with archaeal vertical distribution, especially in the check site. In short, aquaculture affected the spatial distribution of uncultivated archaea. 参考文献 相似文献 引证文献

Phylogenetic ecology of widespread uncultured clades of the Kingdom Euryarchaeota

Despite its widespread distribution and high levels of phylogenetic diversity, microbes are poorly understood creatures. We applied a phylogenetic ecology approach in the Kingdom Euryarchaeota (Archaea) to gain insight into the environmental distribution and evolutionary history of one of the most ubiquitous and largely unknown microbial groups. We compiled 16S rRNA gene sequences from our own sequence libraries and public genetic databases for two of the most widespread mesophilic Euryarchaeota clades, Lake Dagow Sediment (LDS) and Rice Cluster-V (RC-V). The inferred population history indicated that both groups have undergone specific nonrandom evolution within environments, with several noteworthy habitat transition events. Remarkably, the LDS and RC-V groups had enormous levels of genetic diversity when compared with other microbial groups, and proliferation of sequences within each single clade was accompanied by significant ecological differentiation. Additionally, the freshwater Euryarchaeota counterparts unexpectedly showed high phylogenetic diversity, possibly promoted by their environmental adaptability and the heterogeneous nature of freshwater ecosystems. The temporal phylogenetic diversification pattern of these freshwater Euryarchaeota was concentrated both in early times and recently, similarly to other much less diverse but deeply sampled archaeal groups, further stressing that their genetic diversity is a function of environment plasticity. For the vast majority of living beings on Earth (i.e. the uncultured microorganisms), how they differ in the genetic or physiological traits used to exploit the environmental resources is largely unknown. Inferring population history from 16S rRNA gene-based molecular phylogenies under an ecological perspective may shed light on the intriguing relationships between lineage, environment, evolution and diversity in the microbial world.

Complete genome sequence of Methanocorpusculum labreanum type strain Z

Methanocorpusculum labreanum is a methanogen belonging to the order Methanomicrobiales within the archaeal kingdom Euryarchaeota. The type strain Z was isolated from surface sediments of Tar Pit Lake in the La Brea Tar Pits in Los Angeles, California. M. labreanum is of phylogenetic interest because at the time the sequencing project began only one genome had previously been sequenced from the order Methanomicrobiales. We report here the complete genome sequence of M. labreanum type strain Z and its annotation. This is part of a 2006 Joint Genome Institute Community Sequencing Program project to sequence genomes of diverse Archaea.

Diversity and distribution of the prokaryotic community in near-surface permafrost sediments in the Tianshan Mountains, China

The community structures and diversity of bacteria and archaea were investigated at 4 depths (1.5, 2.0, 2.5, and 3.0 m) in permafrost sediments in the Tianshan Mountains, using denaturing gradient gel electrophoresis of 16S rRNA gene amplified by polymerase chain reaction. Phylogenetic analysis of the dominant bands sequenced revealed the presence of rich diversity of bacteria, which could be related to the Proteobacteria, Actinobacteria, Acidobacteria, Gemmatimonadetes, Bacteroidetes, Firmicutes, and Chloroflexi. The Proteobacteria, consisting of the alpha, beta, gamma and epsilon subdivisions, were clearly the dominant group at all depths studied. Archaeal diversity was relatively low and archaeal 16S rRNA gene sequences were grouped into 3 phylogenetic clusters within the 2 kingdoms Euryarchaeota and Crenarchaeota. Within the Euryarchaeota, methanogen-related group II was most abundant at shallow depth (1.5 m), whereas halobacterium-related group I dominated at greater depths. The low-temperature Crenarchaeota group was detected only at 2.5 and 3.0 m. Specific-depth distribution of methanogen-related Euryarchaeota group II and denitrifying bacteria of the genus Pseudomonas dominated at 1.5 m depth, accompanied by a distinct peak in the ratio of NH4-N to NO3/NO2-N, implying the potential capacity of these organisms in near-surface permafrost to release the greenhouse gases N2O and CH4.

A novel repressor of nif and glnA expression in the methanogenic archaeon Methanococcus maripaludis.

Nitrogen assimilation in the methanogenic archaeon Methanococcus maripaludis is regulated by transcriptional repression involving a palindromic 'nitrogen operator' repressor binding sequence. Here we report the isolation of the nitrogen repressor, NrpR, from M. maripaludis using DNA affinity purification. Deletion of the nrpR gene resulted in loss of nitrogen operator binding activity in cell extracts and loss of repression of nif (nitrogen-fixation) and glnA (glutamine synthetase) gene expression in vivo. Genetic complementation of the nrpR mutation restored all functions. NrpR contained a putative N-terminal winged helix-turn-helix motif followed by two mutually homologous domains of unknown function. Comparison of the migration of NrpR in gel-filtration chromatography with its subunit molecular weight (60 kDa) suggested that NrpR was a tetramer. Several lines of evidence suggested that the level of NrpR itself is not regulated, and the binding affinity of NrpR to the nitrogen operator is controlled by an unknown mechanism. Homologues of NrpR were found only in certain species in the kingdom Euryarchaeota. Full length homologues were found in Methanocaldococcus jannaschii and Methanothermobacter thermoautotrophicus, and homologues lacking one or more of the three polypeptide domains were found in Archaeoglobus fulgidus, Methanopyrus kandleri, Methanosarcina acetivorans, and Methanosarcina mazei. NrpR represents a new family of regulators unique to the Euryarchaeota.

Diversity, abundance, and activity of archaeal populations in oil-contaminated groundwater accumulated at the bottom of an underground crude oil storage cavity.

Fluorescence in situ hybridization has shown that cells labeled with an Archaea-specific probe (ARCH915) accounted for approximately 10% of the total cell count in oil-contaminated groundwater accumulated at the bottom of an underground crude oil storage cavity. Although chemical analyses have revealed vigorous consumption of nitrate in cavity groundwater, the present study found that the methane production rate was higher than the nitrate consumption rate. To characterize the likely archaeal populations responsible for methane production in this system, fragments of 16S ribosomal DNA (rDNA) were amplified by PCR using eight different combinations of universal and Archaea-specific primers. Sequence analysis of 324 clones produced 23 different archaeal sequence types, all of which were affiliated with the kingdom EURYARCHAEOTA: Among them, five sequence types (KuA1, KuA6, KuA12, KuA16, and KuA22) were obtained in abundance. KuA1 and KuA6 were closely related to the known methanogens Methanosaeta concilii (99% identical) and Methanomethylovorans hollandica (98%), respectively. Although no closely related organism was found for KuA12, it could be affiliated with the family METHANOMICROBIACEAE: KuA16 and KuA22 showed substantial homology only to some environmental clones. Both of these branched deeply in the Euryarchaeota, and may represent novel orders. Quantitative competitive PCR showed that KuA12 was the most abundant, accounting for approximately 50% of the total archaeal rDNA copies detected. KuA1 and KuA16 also constituted significant proportions of the total archaeal rDNA copies (7 and 17%, respectively). These results suggest that limited species of novel archaea were enriched in the oil storage cavity. An estimate of specific methane production rates suggests that they were active methanogens.

RNomics in Archaea reveals a further link between splicing of archaeal introns and rRNA processing.

The bulge-helix-bulge (BHB) motif recognised by the archaeal splicing endonuclease is also found in the long processing stems of archaeal rRNA precursors in which it is cleaved to generate pre-16S and pre-23S rRNAs. We show that in two species, Archaeoglobus fulgidus and Sulfolobus solfataricus, representatives from the two major archaeal kingdoms Euryarchaeota and Crenarchaeota, respectively, the pre-rRNA spacers cleaved at the BHB motifs surrounding pre-16S and pre-23S rRNAs subsequently become ligated. In addition, we present evidence that this is accompanied by circularization of ribosomal pre-16S and pre-23S rRNAs in both species. These data reveal a further link between intron splicing and pre-rRNA processing in Archaea, which might reflect a common evolutionary origin of the two processes. One spliced RNA species designated 16S-D RNA, resulting from religation at the BHB motif of 16S pre-rRNA, is a highly abundant and stable RNA which folds into a three-stem structure interrupted by two single-stranded regions as assessed by chemical probing. It spans a region of the pre-rRNA 5' external transcribed spacer exhibiting a highly conserved folding pattern in Archaea. Surprisingly, 16S-D RNA contains structural motifs found in archaeal C/D box small RNAs and binds to the L7Ae protein, a core component of archaeal C/D box RNPs. This supports the notion that it might have an important but still unknown role in pre-rRNA biogenesis or might even target RNA molecules other than rRNA.

Halocins and sulfolobicins: The emerging story of archaeal protein and peptide antibiotics

Production of antibiotic peptides and proteins is a near-universal feature of living organisms regardless of phylogenetic classification. Bacteriocins (proteinaceous antimicrobials from the domain Bacteria) have been studied for over 75 years, and the eucaryocins (proteinaceous antimicrobials from the domain Eucarya) since the early 1960s. However, one domain of organisms, the Archaea, containing hyperthermophiles, extreme halophiles and the methanogens, is just beginning to be scrutinized for the production of peptide antibiotics. Production of archaeal proteinaceous antimicrobials (archaeocins) from extreme halophiles (halocins) is a nearly universal feature of the rod-shaped haloarchaea. Halocin activity is first detectable in culture supernatants at the beginning of the transition into stationary phase, concomitant with an induction of transcription of the structural gene. Halocins are diverse in size, consisting of proteins as large as 35 kDa and peptide "microhalocins" as small as 3.6 kDa. The 36 amino acids of microhalocin HalS8 are located in the interior of a 311-residue pro-protein from which they are liberated by an unknown mechanism. Microhalocins are hydrophobic and robust, withstanding heat, desalting and exposure to organic solvents. Unlike the peptide bacteriocins and the eucaryocins, microhalocins possess a large number of neutral residues and are not cationic, leaving their mechanism(s) of action mostly a mystery. While microhalocins affect a variety of haloarchaeal genera (kingdom Euryarchaeota), they also exhibit cross-kingdom toxicity, inhibiting or killing Sulfolobus species (kingdom Crenarchaeota). Finally, archaeocins also are produced by the hyperthermophile "Sulfolobus islandicus". These 20-kDa protein antibiotics are not excreted into the environment, but are associated with small particles apparently derived from the cell's S-layer.

Phylogenetic diversity of the archaeal component in microbial mats on coral-like structures associated with methane seeps in the Black Sea

With the use of molecular ecology methods, the archaea component of microbial mats on coral-like structures associated with methane seeps occurring at a depth of about 200 m in the Black Sea was investigated without the isolation of pure cultures. Using archaea-specific 16S rRNA-targeted oligonucleotide primes, long fragments of genes were amplified, cloned, and sequenced and their phylogenetic analysis was carried out. It was shown that archaea in microbial mats on coral-like structures are represented by two dominant phylotypes that belong to the kingdoms Crenarchaeota and Euryarchaeota and are not specifically related to any described archaea species. The possible role of the revealed archaea in the process of anaerobic methane oxidation is discussed.

Effect of temperature on structure and function of the methanogenic archaeal community in an anoxic rice field soil.

Soil temperatures in Italian rice fields typically range between about 15 and 30 degrees C. A change in the incubation temperature of anoxic methanogenic soil slurry from 30 degrees C to 15 degrees C typically resulted in a decrease in the CH4 production rate, a decrease in the steady-state H2 partial pressure, and a transient accumulation of acetate. Previous experiments have shown that these changes were due to an alteration of the carbon and electron flow in the methanogenic degradation pathway of organic matter caused by the temperature shift (K. J. Chin and R. Conrad, FEMS Microbiol. Ecol. 18:85-102, 1995). To investigate how temperature affects the structure of the methanogenic archaeal community, total DNA was extracted from soil slurries incubated at 30 and 15 degrees C. The archaeal small-subunit (SSU) rRNA-encoding genes (rDNA) of these environmental DNA samples were amplified by PCR with an archaeal-specific primer system and used for the generation of clone libraries. Representative rDNA clones (n = 90) were characterized by terminal restriction fragment length polymorphism (T-RFLP) and sequence analysis. T-RFLP analysis produced for the clones terminally labeled fragments with a characteristic length of mostly 185, 284, or 392 bp. Sequence analysis allowed determination of the phylogenetic affiliation of the individual clones with their characteristic T-RFLP fragment lengths and showed that the archaeal community of the anoxic rice soil slurry was dominated by members of the families Methanosarcinaceae (185 bp) and Methanosaetaceae (284 bp), the kingdom Crenarchaeota (185 or 284 bp), and a novel, deeply branching lineage of the (probably methanogenic) kingdom Euryarchaeota (392 bp) that has recently been detected on rice roots (R. Grosskopf, S. Stubner, and W. Liesack, Appl. Environ. Microbiol. 64:4983-4989, 1998). The structure of the archaeal community changed when the temperature was shifted from 30 degrees C to 15 degrees C. Before the temperature shift, the clones (n = 30) retrieved from the community were dominated by Crenarchaeota (70%), "novel Euryarchaeota" (23%), and Methanosarcinacaeae (7%). Further incubation at 30 degrees C (n = 30 clones) resulted in a relative increase in members of the Methanosarcinaceae (77%), whereas further incubation at 15 degrees C (n = 30 clones) resulted in a much more diverse community consisting of 33% Methanosarcinaceae, 23% Crenarchaeota, 20% Methanosaetaceae, and 17% novel Euryarchaeota. The appearance of Methanosaetaceae at 15 degrees C was conspicuous. These results demonstrate that the structure of the archaeal community in anoxic rice field soil changed with time and incubation temperature.

Purification and Characterization of a Proteasome from the Hyperthermophilic Archaeon Pyrococcus furiosus

A 640-kDa proteasome consisting of (alpha) (25-kDa) and (beta) (22-kDa) subunits, and with a temperature optimum of 95(deg)C, was purified from crude cell extracts of a hyperthermophilic archaeon, Pyrococcus furiosus. Although this is the fourth member of the kingdom Euryarchaeota (and the first hyperthermophile) found to contain a proteasome, none has been identified among the members of the kingdom Crenarchaeota.

Picrophilus oshimae and Picrophilus torridus fam. nov., gen. nov., sp. nov., Two Species of Hyperacidophilic, Thermophilic, Heterotrophic, Aerobic Archaea

We describe two species of hyperacidophilic, thermophilic, heterotrophic, aerobic archaea that were isolated from solfataric hydrothermal areas in Hokkaido, Japan. These organisms, Picrophilus oshimae and Picrophilus torridus, represent a novel genus and a novel family, the Picrophilaceae, in the kingdom Euryarchaeota and the order Thermoplasmales. Both of these bacteria are more acidophilic than the genus Thermoplasma since they are able to grow at about pH 0.

Viruses, plasmids and other genetic elements of thermophilic and hyperthermophilic Archaea.

We review and update the work on genetic elements, e.g., viruses and plasmids (exluding IS elements and transposons) in the kingdom Crenarchaeota (Thermoproteales and Sulfolobales) and the orders Thermococcales and Thermoplasmales in the kingdom Euryarchaeota of the archael domain, including unpublished data from our laboratory. The viruses of Crenarchaeota represent four novel virus families. The Fuselloviridae represented by SSVI of S. shibatae and relatives in other Sulfolobus strains have the form of a tailed spindle. The envelope is highly hydrophobic. The DNA is double-stranded and circular. Members of this group have also been found in Methanococcus and Haloarcula. The Lipothrivciridae (e.g., T TV1 to 3) have the form of flexible filaments. They have a core containing linear double-stranded DNA and DNA-binding proteins which is wrapped into a lipid membrane. The "Bacilloviridae" (e.g., TTV4 and SIRV) are stiff rods lacking this membrane, but also featuring linear double-stranded DNA and DNA-binding proteins. Both virus types carry on both ends structures involved in the attachment to receptors. Both types are represented in Thermoproteus and Sulfolobus. The droplet-formed novel Sulfolobus virus SNDV represents the "Guttaviridae" containing circular double-stranded DNA. Though head and tail viruses distantly resembling T phages or lambdoid phages were seen electronmicroscopically in solfataric water samples, no such virus has so far been isolated. SSV1 is temperate, TTV1 causes lysis after induction, the other viruses found so far exist in carrier states. The hosts of all but TTV1 survive virus production. We discuss the implications of the nature of these viruses for understanding virus evolution. The plasmids found so far range in size from 4.5 kb to about 40 kb. Most of them occur in high copy number, probably due to the way of their detection. Most are cryptic, pNOB8 is conjugative, the widespread pDL10 alleviates in an unknown way autotrophic growth of its host Desulfurolobus by sulfur reduction. The plasmid pTIK4 appears to encode a killer function. pNOB8 has been used as a vector for the transfer of the lac S (beta-galactosidase) gene into a mutant of S. solfataricus.

A comparison of the DNA binding properties of histone-like proteins derived from representatives of the two kingdoms of the Archaea

The nucleoid protein composition, the enhancement of DNA electrophoretic mobility, the toroidal wrapping and the helical period of DNA complexed with nucleoid proteins from species within the archaeal kingdom Euryarchaeota was shown to contrast with the composition and properties of nucleoid proteins from Sulfolobus solfataricus, a member of the archaeal kingdom Crenarchaeota. This result was seen to support the hypothesis that archaeal histones with homology to the eukaryal hi stone consensus are a diagnostic feature of the Euryarchaeota.

A comparison of the DNA binding properties of histone-like proteins derived from representatives of the two kingdoms of the Archaea

The nucleoid protein composition, the enhancement of DNA electrophoretic mobility, the toroidal wrapping and the helical period of DNA complexed with nucleoid proteins from species within the archaeal kingdom Euryarchaeota was shown to contrast with the composition and properties of nucleoid proteins from Sulfolobus solfataricus, a member of the archaeal kingdom Crenarchaeota. This result was seen to support the hypothesis that archaeal histones with homology to the eukaryal hi stone consensus are a diagnostic feature of the Euryarchaeota.

Nucleotide sequence of a DNA region comprising the gene for elongation factor 1α (EF-1α) from the ultrathermophilic archaeotePyrococcus woesei: Phylogenetic implications

The gene encoding elongation factor 1 alpha (EF-1 alpha, 1290 bp) of the ultrathermophilic, sulfur-reducing archaeote Pyrococcus woesei was localized within a Bg/II fragment of chromosomal DNA. Sequence analysis showed that the EF-1 alpha gene is the upstream unit of a three-gene cluster comprising the genes for ribosomal protein S10 (306 bp) and transfer RNAser (GGA). The three genes follow each other immediately in the order EF-1 alpha.S10.tRNA(ser) after a putative promoter located 55 bp upstream of the EF-1 alpha gene. Alignment of the derived EF-1 alpha sequence with the corresponding sequences from Eukarya, Bacteria/organelles, and with available archaeal sequences (Sulfolobus, Thermococcus, Methanococcus, Halobacterium) showed that Pyrococcus EF-1 alpha is highly homologous (89% identity) to Thermococcus celer EF-1 alpha, both being strikingly more similar to eukaryotic EF-1 alpha than to bacterial EF-Tu. Unrooted dendrograms computed from aligned sequences by distance matrix and DNA parsimony methods, including evolutionary parsimony, showed the Archaea to be a monophyletic-holophyletic cluster closer to Eukarya than to Bacteria. Both distance matrix and DNA parsimony--although not evolutionary parsimony--support the partition of the known archaeal lineages between the kingdoms Crenarchaeota and Euryarchaeota, and the affiliation of the Pyrococcus-Thermococcus lineage to the Euryarchaeota, of which it is the most primitive offspring. A closer relation of Pyrococcus to Euryarchaeota than to Crenarchaeota was also inferred from sequence analysis of S10 ribosomal proteins.

Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya.

Molecular structures and sequences are generally more revealing of evolutionary relationships than are classical phenotypes (particularly so among microorganisms). Consequently, the basis for the definition of taxa has progressively shifted from the organismal to the cellular to the molecular level. Molecular comparisons show that life on this planet divides into three primary groupings, commonly known as the eubacteria, the archaebacteria, and the eukaryotes. The three are very dissimilar, the differences that separate them being of a more profound nature than the differences that separate typical kingdoms, such as animals and plants. Unfortunately, neither of the conventionally accepted views of the natural relationships among living systems--i.e., the five-kingdom taxonomy or the eukaryote-prokaryote dichotomy--reflects this primary tripartite division of the living world. To remedy this situation we propose that a formal system of organisms be established in which above the level of kingdom there exists a new taxon called a "domain." Life on this planet would then be seen as comprising three domains, the Bacteria, the Archaea, and the Eucarya, each containing two or more kingdoms. (The Eucarya, for example, contain Animalia, Plantae, Fungi, and a number of others yet to be defined). Although taxonomic structure within the Bacteria and Eucarya is not treated herein, Archaea is formally subdivided into the two kingdoms Euryarchaeota (encompassing the methanogens and their phenotypically diverse relatives) and Crenarchaeota (comprising the relatively tight clustering of extremely thermophilic archaebacteria, whose general phenotype appears to resemble most the ancestral phenotype of the Archaea.