Archaea
Archaea are a group of single-celled microorganisms that constitute one of the three domains of life, alongside Bacteria and Eukaryota. They are known for their ability to thrive in extreme environments such as hot springs, salt flats, and deep-sea hydrothermal vents. Archaea play a crucial role in various biogeochemical cycles and have unique metabolic pathways.
8 Key excerpts on "Archaea"
eBook - ePub- Britannica Educational Publishing, Kara Rogers(Authors)
- 2010(Publication Date)
- Britannica Educational Publishing(Publisher)
...Woese called these two lineages the eubacteria and the archaebacteria. These names were subsequently changed to bacteria and Archaea (the Archaea being distinctly different from bacteria), but Woese’s splitting of the prokaryotes into two groups has remained, and all living organisms are now considered by many biologists to fall into one of three great domains: Archaea, Bacteria, and Eukarya. Further molecular analysis has shown that domain Archaea consists of two major subdivisions, the Crenarchaeota and the Euryarchaeota, and two minor ancient lineages, the Korarchaeota and the Nanoarchaeota. Archaea are found in a diverse range of extreme environments, including the salt deposits on the shores of the Dead Sea. Z. Radovan, Jerusalem H ABITATS OF THE A RCHAEA Archaea are microorganisms that define the limits of life on Earth. They were originally discovered and described in extreme environments, such as hydrothermal vents and terrestrial hot springs. They were also found in a diverse range of highly saline, acidic, and anaerobic environments. Although many of the cultured Archaea are extremophiles, these organisms in their respective extreme habitats represent only a minority of the total diversity of the Archaea domain. The majority of Archaea cannot be cultured within the laboratory setting, and their ubiquitous presence in global habitats has been realized through the use of culture-independent techniques. One commonly used culture-independent technique is the isolation and analysis of nucleic acids (i.e., DNA and RNA) directly from an environment, rather than the analysis of cultured samples isolated from the same environment. Culture-independent studies have shown that Archaea are abundant and fulfill important ecological roles in cold and temperate ecosystems...
eBook - ePubMarine Microbiology
Ecology & Applications
- Colin Munn, Colin B. Munn(Authors)
- 2019(Publication Date)
- CRC Press(Publisher)
...Although many of the most thermophilic and halophilic microbes are indeed members of the Archaea, species belonging to this domain are very abundant and diverse, and can be found everywhere in the marine environment, especially the sub-photic ocean. Here, they play critical roles in the carbon and nitrogen cycles. Recent advances in DNA sequencing and genomic methods are revealing an unexpected diversity of novel Archaeal lineages, leading to new ideas about the position of Archaea in the tree of life and the origins of eukaryotes. Key Concepts The basic metabolism and organization of cells of Archaea resembles those of Bacteria, but there are important differences in membrane structure, replication of DNA, and protein synthesis. Numerous new phyla of the Archaea have been described following discovery in environmental gene surveys and this has led to reorganization of phylogenetic trees, providing support for the evolution of the Eukarya from within the Archaea. Production of methane by members of the Euryarchaeota is the final step in the anaerobic biodegradation of organic material and leads to formation of massive reserves of methane in deep-sea sediments. Anoxic methane oxidation is carried out by members of the Euryarchaeota by reverse methanogenesis, in syntrophic association with sulfate-reducing bacteria. Numerous types of chemolithotrophic and organotrophic Euryarchaeota and Crenarchaeota show adaptations for growth at very high temperatures and high salinity. Thaumarchaeota are abundant in the deep sea, where their main function is oxidation of ammonia coupled to chemolithoautotrophy, making a major contribution to dark carbon fixation. Archaea, Archaea, EVERYWHERE The discovery that Archaea are a major component of ocean microbiota ranks as one of the most significant surprises to emerge from the application of methods to directly sequence 16S rRNA isolated from planktonic biomass (see p.42)...
eBook - ePubThe New Microbiology
From Microbiomes to CRISPR
- Pascale Cossart(Author)
- 2018(Publication Date)
- ASM Press(Publisher)
...PART I New Concepts in Microbiology CHAPTER 1 Bacteria: Many Friends, Few Enemies Bacteria are unicellular living organisms that make up one of the three domains of life: Bacteria, Archaea, and Eukaryota (Fig. 1). This model of three branches stemming from a common ancestor was first proposed by Carl Wo-ese in 1977. The absence of a nucleus is one major difference between prokaryotes and eukaryotes. Eukaryota or eukaryotes include animals, plants, fungi, and protozoa, which all have nuclei; bacteria and Archaea are prokaryotes and do not have a nucleus. The DNA of prokaryotes is non-membrane bound, unlike in eukaryotes. But do not assume that bacteria are merely small sacks full of disorderly contents. Their “interior” is in fact very well organized. Archaea, like bacteria, are unicellular organisms but differ from bacteria in that they have lipids that are not found in bacteria and an ensemble of compounds that are similar to those of eukaryotes, in particular the machinery that regulates gene expression. When they were discovered, Archaea were thought to exist only in extreme environments, such as very hot water springs, but we now know that they are present everywhere, including in our gut. Figure 1. The three large domains of life. Bacteria, Archaea, and Eukaryota have a common ancestor. Bacteria are extremely varied and make up the most diverse domain of life. They have been on Earth for billions of years and have evolved to survive in a great variety of conditions. There are more than 11,500 known species of bacteria in more than 2,000 genera (groupings of species). These numbers have so far been based only on gene comparisons, particularly the 16S RNA genes, and they keep rising. Classification methods are changing too. Now that we can compare entire genome sequences, the definition of “species” itself is evolving. Bacteria may have different shapes (Fig. 2)...
eBook - ePubThe Ancestor's Tale
A Pilgrimage to the Dawn of Evolution
- Richard Dawkins(Author)
- 2016(Publication Date)
- Mariner Books(Publisher)
...Instead, the immediate ancestry of most of our body lies among another major group of prokaryotes, the Archaea. It was the great American microbiologist Carl Woese of the University of Illinois who discovered and defined the Archaea (then called Archaebacteria) in the late 1970s. The deep separation from other bacteria was controversial at first because it was so different from previous ideas. But it is now very widely accepted, and Woese was justly honoured with prizes and medals, including the highly prestigious Crafoord Prize and the Leeuwenhoek Medal. The Archaea include species that thrive in different kinds of extreme conditions, whether it is very high temperatures, or very acid, alkaline or salty water. The Archaeans as a group seem to ‘push the envelope’ of what life can tolerate. Nobody knows whether Concestor 39 was such an extremophile, but it is an intriguing possibility. Archaeans join. Most experts believe the Archaeans are the sister group to the eukaryotes, on the basis of most of our nuclear DNA, as well as certain details of biochemistry and cellular morphology. However, if mitochondrial DNA were used, our closest relatives would be the α-proteobacteria, from whose ranks mitochondria emerged (see the Great Historic Rendezvous). As we develop tools for exploring the microscopic world around us, we are finding more and more microbial ‘species’, and more branches on the tree of life. One very recent example is the Lokiarchaeota, described here and represented by a single species of Lokiarchaeum above. Analyses of the Archaea are starting to suggest that we are more closely related to some than to others, as we show here. However, this idea is still controversial, as is the order of branching. To reflect this state of flux, the various rendezvous points with Archaea are labelled 39a, 39b, 39c, etc. and gathered into a single chapter...
eBook - ePub- Jennifer Stearns, Michael Surette(Authors)
- 2019(Publication Date)
- For Dummies(Publisher)
...It’s likely that many more Archaea will be discovered and that the current tree will change quite a bit. FIGURE 12-7: The phylogenetic tree of Archaea. Currently, there are two main phyla in the domain Archaea: the Euryarchaeota and the Crenarchaeota. However, within the Crenarchaeota, there may soon be a few new phyla, including the Thaumarchaeota, the Korarchaeota, and the Aigarchaeota. As new Archaeal strains are discovered, the gaps in what we know about how all Archaea are related get filled in. WHERE DO MY GENES COME FROM? The Archaea are interesting because they have many genes that resemble those in bacteria and others that resemble the genes in eukaryotes. This is part of the reason why they confounded microbiologists for years — they couldn’t squarely be placed within the domain of Bacteria or Eukarya. A great example of this is an archaeon (singular for Archaea) called Methanocaldococcus jannaschii, which has core metabolic genes that bear some resemblance to those in bacteria, but most of the genes for molecular processes (things like RNA transcription and protein translation) have similarities to those in eukaryotes. More than a third of its genome (40 percent) contains genes that don’t resemble those in either bacteria or eukaryotes. Archaea likely evolved around the same time as the earliest bacteria. It’s even possible that eukaryotes came from an early Archaeal ancestor. It’s mysteries like this that make the microbiology of the Archaea so fascinating. As with the Bacteria, there are far too many Archaeal species to describe them all here but you can go to www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=2157 for a complete list. In this section, we discuss representatives of the different forms of Archaeal life, filling you in on their ability to tolerate extremes of temperature, acidity, and salinity...
eBook - ePub- Simon Baker, Jane Nicklin, Caroline Griffiths(Authors)
- 2011(Publication Date)
- Taylor & Francis(Publisher)
...Techniques such as DGGE (denaturing gradient gel electrophoresis), SCCP (single-stranded conformation polymorphism), DNA chips, and in situ hybridization now give us the tools to study microbial community ecology at the molecular level. Microbiology has returned to its roots! Bacteria, Archaea, and eukaryotes The microbial world has three main cell lineages within it, all of which are thought to have evolved from a single progenitor (Figure 1). The lineages are formally known as domains and were established from the DNA sequence of genes common to all organisms (Section B3). The three domains are the Bacteria (previously called the Eubacteria), the Archaea (previously called the Archaeabacteria), and the Eukarya. The defining property of the Eukarya compared to the Archaea and Bacteria is the presence of a nucleus. It is convenient to group the annucleate lineages (the Bacteria and Archaea) together as the prokaryotes. The prokaryotes are, with a very few exceptions (Section C6), all microorganisms, but the Eukarya include not only microbial fungi, chlorophyta, and protists (Sections H and I) but also macroorganisms such as higher plants and animals. Figure 1. The three cell lineages evolved from a common ancestor. Prokaryotic cell structure is characterized by the absence of a nucleus, but it also lacks energy-generating organelles such as mitochondria and chloroplasts. Instead, prokaryotes generate energy by cytoplasmic substrate-level phosphorylation and oxidative phosphorylation across their cell membranes (Section E). Apart from these major differences, there are a multitude of distinctive biochemical and physiological properties, the most important of which are listed in Table 1...
eBook - ePub- Thomas D. Pollard, William C. Earnshaw, Jennifer Lippincott-Schwartz, Graham Johnson(Authors)
- 2016(Publication Date)
- Elsevier(Publisher)
...A molecular view of microbial diversity and the biosphere. Science. 1997;276:734–740. B, Based on multiple sources, including Adl SM, Simpson AG, Lane CE, et al. The revised classification of eukaryotes. J Eukaryot Microbiol. 2012;59:429–493; and Spang A, Saw JH, Jørgensen SL, et al. Complex Archaea that bridge the gap between prokaryotes and eukaryotes. Nature. 2015;521:173–179.) Abetted by rapid proliferation and large populations, natural selection allowed prokaryotes to explore many biochemical solutions to life on the earth. Some Bacteria and Archaea (and some eukaryotes too) thrive under inhospitable conditions, such as anoxia and temperatures greater than 100°C as found in deep-sea hydrothermal vents. Other Bacteria and Archaea can use energy sources such as hydrogen, sulfate, or methane that are useless to eukaryotes. Far less than 1% of Bacteria and Archaea have been grown successfully in the laboratory, so many varieties escaped detection by traditional means. Today, sequencing DNA samples from natural environments has revealed vast numbers of new species in the ocean, soil, human intestines, and elsewhere. Only a very small proportion of bacterial species and no Archaea cause human disease. Chlorophyll-based photosynthesis originated in Bacteria around 3 billion years ago. Surely this was one of the most remarkable events during the evolution of life on the earth, because photosynthetic reaction centers (see Fig. 19.8) require not only genes for several transmembrane proteins, but also genes for multiple enzymes, to synthesize chlorophyll and other complex organic molecules associated with the proteins. Chapter 19 describes the machinery and mechanisms of photosynthesis. Even more remarkably, photosynthesis was invented twice in different bacteria. A progenitor of green sulfur bacteria and heliobacteria developed photosystem I, while a progenitor of purple bacteria and green filamentous bacteria developed photosystem II...
eBook - ePub- Michael J. Benton, Michael J. Benton(Authors)
- 2019(Publication Date)
- Wiley-Blackwell(Publisher)
...3 The Origin of Eukaryotes In This Chapter For the first half of Earth’s history, life consisted of prokaryotes (Archaea and Bacteria), but the evolution of eukaryotes (cells with nuclei) changed the biological world forever. Eukaryotes have complex cells resulting from a symbiosis, or stable evolutionary partnership, between an Archaeal host cell and one or more bacterial endosymbionts. These are major steps in evolution and we discuss how they happened. While most eukaryotes are single‐celled microbes, multicellularity evolved several times and gave rise to the most familiar eukaryotic groups, including animals, plants, and fungi. In this chapter, we also explore how biologists and paleontologists make sense of the huge diversity of species on Earth – the secret has been the revolution in cladistics and genomics in reconstructing the tree of life. Single‐Celled Life The microbes that were Earth’s first life evolved into two different major groups or domains: Archaea and Bacteria. They shared much the same body plan, however, and we group them together as prokaryotes (Figure 3.1). Prokaryotes were and are very successful in an incredible range of habitats, from stinking swamps to the hindgut of termites and from hot springs in the deep sea to the ice desert of Antarctica, and deep in rocks underground. They occur in numbers averaging 500 million/l in surface ocean waters, 1 billion/l in fresh water, and about 300 million on the skin of the average human. The evolutionary success of prokaryotes is due to their metabolic versatility, resilience to a broad range of environmental conditions, and large population sizes. With such large populations, adaptive evolution to new nutrient sources and environmental challenges typically proceeds much faster in prokaryotes than in eukaryotes – the cellular lineage to which we belong. Figure 3.1 A prokaryotic cell. The DNA (blue cords) is twisted and folded to fit into the cell and floats free in the cell cytoplasm (orange)...
