Related Research Articles
Carl Richard Woese was an American microbiologist and biophysicist. Woese is famous for defining the Archaea in 1977 through a pioneering phylogenetic taxonomy of 16S ribosomal RNA, a technique that has revolutionized microbiology. He also originated the RNA world hypothesis in 1967, although not by that name. Woese held the Stanley O. Ikenberry Chair and was professor of microbiology at the University of Illinois Urbana–Champaign.
In biology, a kingdom is the second highest taxonomic rank, just below domain. Kingdoms are divided into smaller groups called phyla.
In biological taxonomy, a domain, also dominion, superkingdom, realm, or empire, is the highest taxonomic rank of all organisms taken together. It was introduced in the three-domain system of taxonomy devised by Carl Woese, Otto Kandler and Mark Wheelis in 1990.
The three-domain system is a biological classification introduced by Carl Woese, Otto Kandler, and Mark Wheelis in 1990 that divides cellular life forms into three domains, namely Archaea, Bacteria, and Eukarya. The key difference from earlier classifications such as the two-empire system and the five-kingdom classification is the splitting of Archaea from Bacteria as completely different organisms. It has been challenged by the two-domain system that divides organisms into Bacteria and Archaea only, as Eukaryotes are considered as one group of Archaea.
The Thermoproteota are prokaryotes that have been classified as a phylum of the Archaea domain. Initially, the Thermoproteota were thought to be sulfur-dependent extremophiles but recent studies have identified characteristic Thermoproteota environmental rRNA indicating the organisms may be the most abundant archaea in the marine environment. Originally, they were separated from the other archaea based on rRNA sequences; other physiological features, such as lack of histones, have supported this division, although some crenarchaea were found to have histones. Until recently all cultured Thermoproteota had been thermophilic or hyperthermophilic organisms, some of which have the ability to grow at up to 113°C. These organisms stain Gram negative and are morphologically diverse, having rod, cocci, filamentous and oddly-shaped cells.
The last universal common ancestor (LUCA), on the basis of the RNA world concept, is hypothesized to have been a common ancestral cell from which the three domains of life, the Bacteria, the Archaea, and the Eukarya originated. It is suggested to have been a "cellular organism that had a lipid bilayer and used DNA, RNA, and protein". In general the LUCA is considered the point or stage at which the domains of life diverged from the precursing forms of life. The nature of this point of divergence remains a topic of research.
Mollicutes is a class of bacteria distinguished by the absence of a cell wall. The word "Mollicutes" is derived from the Latin mollis, and cutis. Individuals are very small, typically only 0.2–0.3 μm in size and have a very small genome size. They vary in form, although most have sterols that make the cell membrane somewhat more rigid. Many are able to move about through gliding, but members of the genus Spiroplasma are helical and move by twisting. The best-known genus in the Mollicutes is Mycoplasma. Colonies show the typical "fried-egg" appearance.
The two-empire system was the top-level biological classification system in general use before the establishment of the three-domain system. It classified cellular life into Prokaryota and Eukaryota as either "empires" or "superkingdoms". When the three-domain system was introduced, some biologists preferred the two-superkingdom system, claiming that the three-domain system overemphasized the division between Archaea and Bacteria. However, given the current state of knowledge and the rapid progress in biological scientific advancement, especially due to genetic analyses, that view has all but vanished.
Neomura is a possible clade composed of the two domains of life of Archaea and Eukaryota. The group was named by Thomas Cavalier-Smith in 2002. Its name means "new walls", reflecting his hypothesis that it evolved from Bacteria, and one of the major changes was the replacement of peptidoglycan cell walls with other glycoproteins. As of August 2017, the neomuran hypothesis is not accepted by most workers; molecular phylogenies suggest that eukaryotes are most closely related to one group of archaeans and evolved from them, rather than forming a clade with all archaeans, and that Archaea and Bacteria are sister groups.
Archaea is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria, but this term has fallen out of use.
Scientists trying to reconstruct evolutionary history have been challenged by the fact that genes can sometimes transfer between distant branches on the tree of life. This movement of genes can occur through horizontal gene transfer (HGT), scrambling the information on which biologists relied to reconstruct the phylogeny of organisms. Conversely, HGT can also help scientists to reconstruct and date the tree of life. Indeed, a gene transfer can be used as a phylogenetic marker, or as the proof of contemporaneity of the donor and recipient organisms, and as a trace of extinct biodiversity.
Evolution of cells refers to the evolutionary origin and subsequent evolutionary development of cells. Cells first emerged at least 3.8 billion years ago approximately 750 million years after Earth was formed.
Bacterial taxonomy is subfield of taxonomy devoted to the classification of bacteria specimens into taxonomic ranks.
Woese's dogma is a principle of evolutionary biology first put forth by biophysicist Carl Woese in 1977. It states that the evolution of ribosomal RNA was a necessary precursor to the evolution of modern life forms. This led to the advancement of the phylogenetic tree of life consisting of three domains rather than the previously accepted two. While the existence of Eukarya and Prokarya were already accepted, Woese was responsible for the distinction between Bacteria and Archaea. Despite initial criticism and controversy surrounding his claims, Woese's three domain system, based on his work regarding the role of rRNA in the evolution of modern life, has become widely accepted.
The eocyte hypothesis in evolutionary biology proposes that the eukaryotes originated from a group of prokaryotes called eocytes. After his team at the University of California, Los Angeles discovered eocytes in 1984, James A. Lake formulated the hypothesis as "eocyte tree" that proposed eukaryotes as part of archaea. Lake hypothesised the tree of life as having only two primary branches: Parkaryoates that include Bacteria and Archaea, and karyotes that comprise Eukaryotes and eocytes. Parts of this early hypothesis were revived in a newer two-domain system of biological classification which named the primary domains as Archaea and Bacteria.
Microbial phylogenetics is the study of the manner in which various groups of microorganisms are genetically related. This helps to trace their evolution. To study these relationships biologists rely on comparative genomics, as physiology and comparative anatomy are not possible methods.
Otto Kandler was a German botanist and microbiologist. Until his retirement in 1986 he was professor of botany at the Ludwig Maximilian University of Munich.
The initial version of a classification system of life by British zoologist Thomas Cavalier-Smith appeared in 1978. This initial system continued to be modified in subsequent versions that were published until he died in 2021. As with classifications of others, such as Carl Linnaeus, Ernst Haeckel, Robert Whittaker, and Carl Woese, Cavalier-Smith's classification attempts to incorporate the latest developments in taxonomy., Cavalier-Smith used his classifications to convey his opinions about the evolutionary relationships among various organisms, principally microbial. His classifications complemented his ideas communicated in scientific publications, talks, and diagrams. Different iterations might have a wider or narrow scope, include different groupings, provide greater or lesser detail, and place groups in different arrangements as his thinking changed. His classifications has been a major influence in the modern taxonomy, particularly of protists.
Microbial DNA barcoding is the use of DNA metabarcoding to characterize a mixture of microorganisms. DNA metabarcoding is a method of DNA barcoding that uses universal genetic markers to identify DNA of a mixture of organisms.
The two-domain system is a biological classification by which all organisms in the tree of life are classified into two big domains, Bacteria and Archaea. It emerged from development in the knowledge of archaea diversity and challenge over the widely accepted three-domain system that defines life into Bacteria, Archaea, and Eukarya. It was predicted by the eocyte hypothesis of James A. Lake in the 1980s, which was largely superseded by the three-domain system due to better compelling evidences at the time. Better understanding of archaea, especially in their roles in the origin of eukaryotes by symbiogenesis with bacteria, led to the revival of the eocyte hypothesis in the 2000s. The two-domain system became widely appreciated after the discovery of a large group (superphylum) of archaea called Asgard in 2017, evidences of which suggest to be the evolutionary root of eukaryotes – implying that eukaryotes are members of the domain Archaea.
References
- ↑ Bothamley, Jennifer (2002). Dictionary of Theories . p. 557. ISBN 9781578590452.
- ↑ Woese, C.R.; Kandler, O.; Wheelis, M.L. (1990). "Towards a natural system of organisms: Proposal for the domains Archaea, Bacteria, and Eucarya". Proceedings of the National Academy of Sciences of the United States of America. 87 (12): 4576–79. Bibcode:1990PNAS...87.4576W. doi: 10.1073/pnas.87.12.4576 . PMC 54159 . PMID 2112744.
- ↑ Woese, C.R. (1996). "Phylogenetic trees: Whither microbiology?". Current Biology. 6 (9): 1060–63. doi: 10.1016/s0960-9822(02)70664-7 . PMID 8805350.
- ↑ Sapp, Jan (2009). The new foundations of evolution: on the tree of life. Oxford University Press.
- ↑ Morell, V (1997). "Microbial Biology: Microbiology's scarred revolutionary". Science. 276 (5313): 699–702. doi:10.1126/science.276.5313.699. PMID 9157549. S2CID 84866217.