Before microorganisms were known to exist, all life was classified as either animal or plant. The discovery of microbes in the late 17th century required developing a new classification system. Through the 1970s, scientists debated how to classify these new organisms. In 1978, Carl Woese proposed grouping all life into three domains based on cellular structure: Bacteria, Archaea, and Eukarya. This three domain system classified organisms as bacteria, archaea, which lack bacteria's peptidoglycan cell walls, or eukaryotes including plants, animals, fungi and protists.
Before microorganisms were known to exist, all life was classified as either animal or plant. The discovery of microbes in the late 17th century required developing a new classification system. Through the 1970s, scientists debated how to classify these new organisms. In 1978, Carl Woese proposed grouping all life into three domains based on cellular structure: Bacteria, Archaea, and Eukarya. This three domain system classified organisms as bacteria, archaea, which lack bacteria's peptidoglycan cell walls, or eukaryotes including plants, animals, fungi and protists.
Before microorganisms were known to exist, all life was classified as either animal or plant. The discovery of microbes in the late 17th century required developing a new classification system. Through the 1970s, scientists debated how to classify these new organisms. In 1978, Carl Woese proposed grouping all life into three domains based on cellular structure: Bacteria, Archaea, and Eukarya. This three domain system classified organisms as bacteria, archaea, which lack bacteria's peptidoglycan cell walls, or eukaryotes including plants, animals, fungi and protists.
Before microorganisms were known to exist, all life was classified as either animal or plant. The discovery of microbes in the late 17th century required developing a new classification system. Through the 1970s, scientists debated how to classify these new organisms. In 1978, Carl Woese proposed grouping all life into three domains based on cellular structure: Bacteria, Archaea, and Eukarya. This three domain system classified organisms as bacteria, archaea, which lack bacteria's peptidoglycan cell walls, or eukaryotes including plants, animals, fungi and protists.
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Early classification systems grouped organisms into two kingdoms - Monera and Protista. Later a three domain system was proposed dividing organisms into Bacteria, Archaea and Eukarya. Classification continues to evolve as new discoveries are made.
Initially microorganisms were classified as animals or plants. Later a two kingdom system was used, then a four kingdom system. In 1978 Carl Woese proposed the three domain system still used today, dividing organisms into Bacteria, Archaea and Eukarya based on cellular structure and genetics.
Bacteria have peptidoglycan in their cell walls while archaea do not. Archaea are more closely related to eukaryotes in terms of genetics and biochemistry. Bacteria are inhibited by certain antibiotics while archaea are not.
Classification of Microorganisms
Before the existence of microbes was known, all organisms
were grouped into either the animal kingdom or the plant kingdom.
When microscopic organisms with characteristics of animals and plants were discovered late in the seventeenth century, a new system of classification was needed. Still, biologists could not agree on the criteria for classifying these new organisms until the late 1970s. At the beginning : there are two kingdoms - Monera - Protista Earlier classification : Monera is oldest (earliest cell), prokaryotic & structurally simple cell Protista is youngest (latest cell), eukaryotic & more structurally complex cell The Protista developed to four kingdom : Protista, Fungi, plantae and animalia Table 10.2 In 1978, Carl Woese devised a system of classification based on the cellular organization of organisms. It groups all organisms in three domains as follows:
1. Bacteria (cell walls contain a proteincarbohydrate complex called peptidoglycan) 2. Archaea (cell walls, if present, lack peptidoglycan) 3. Eukarya, which includes the following: Protists (slime molds, protozoa, and algae) Fungi (unicellular yeasts, multicellular molds, and mushrooms) Plants (mosses, ferns, conifers, and flowering plants) Animals (sponges, worms, insects, and vertebrates The Three-Domain System Figure 10.1 Euryarchaeota Crenarchaeo ta Korarchaeota Domains Archaea In the late 1970s, a distinctive type of prokaryotic cell was discovered. Most strikingly, the cell walls of these prokaryotes lacked the peptidoglycan common to most bacteria. It soon became clear that they also shared many rRNA sequences, and the sequences were different from either those of the Domain Bacteria or the eukaryotic organisms. These differences were so significant that these organisms now constitute a new taxonomic grouping, the Domain Archaea. Bacteria and Archaea Bacteria and Archaea are both prokaryotes and their DNA is arranged in circular structures called plasmids (they have no nucleus and the DNA is not arranged in chromosomes). Prokaryote derived from the Greek Pro meaning before and karyon meaning a kernel [i.e. a nucleus].
However, they have substantial differences in their biochemistry, cell wall structure and other molecular details. Bacteria vs. Archaea Bacteria are inhibited by antibiotics Streptomycin and Chloramphenicol but Archaea are not.
Archaea in common with Eukarya have histone proteins associated with their DNA, have introns in their DNA, and have several kinds of RNA polymerase. Bacteria lack these features. Domain Bacteria Includes most of the bacteria people are familiar with including disease-causing species (Salmonella; Vibrio cholerae which causes cholera), nitrogen-fixing (Nitrosomonas) and parasites (Borrelia burgdorferi which causes Lyme disease). Bacteria play a major role in decomposition and many live symbiotically with other organisms including humans helping to break down or synthesize foods needed by the host.
contain unique genetic sequences in their rRNA seem more closely related to Domain Eukarya than to bacteria have unique membrane lipids & cell wall construction live in the most extreme habitats in nature, extremophiles adapted to heat salt acid pH, pressure & atmosphere includes: methane producers, hyperthermophiles, extreme halophiles, and sulfur reducers Domain Archaea Figure 11.27 Archaea. Pyrodictium abyssi, an unusual member of the archaea found growing in deep-ocean sediment at a temperature of 110C. The cells are disk-shaped with a network of tubules (cannulae). Most archaea are more conventional in their morphology. The Three-Domain System Table 10.1 Phyllogenetic tree of archaea Phylum/Class Order Important Genera Special Features
Euryarchaeota (Gram-Positive to Variable) Methanobacteriales Methanobacterium Methanogens Halobacteriales Halobacterium Require high salt concentration Halococcus Require high salt concentration
Phyllogenetic and Metabolic diversity of archaea A. B. for your kind attention Sahara desert Life in the extremes Yellowstone National park Lake Magadi, Tansania Yellowstone National Park Postulated Mars-Biosphere Mars from Pathfinder Liquid water only in deep subsurface regions Life either extinct or in subsurface niches: