chapter3 Archea and Bacteria

Despite this visual similarity to bacteria, archaea possess genes and several metabolic pathways that are more closely related to those of eukaryotes: notably the enzymes involved in transcription and translation.

Other morphologies in the Crenarchaeota 泉古 生菌 include irregularly shaped lobed cells in Sulfolobus硫化叶菌属, thin needle-like filaments that are less than half a micrometer in diameter in Thermofilum热丝菌属, and almost perfectly rectangular rods in Thermoproteus热变形菌属 and Pyrobaculum 热棒菌属.
古细菌这个概念是1977年由卡尔· 和George Fox提出 沃斯

Archaea are further divided into four recognized phyla, but many more phyla may exist. Of these groups the Crenarchaeota and the Euryarchaeota are most intensively studied.
的，原因是它们在16S rRNA的系统发生树上和其它原核 生物的区别。这两组原核生物起初被定为古细菌 （Archaebacteria）和真细菌（Eubacteria）两个界或亚界。 Woese认为它们是两支根本不同的生物，于是重新命名其 为古菌（Archaea）和细菌（Bacteria），这两支和真核生 物（Eukarya）一起构成了生物的三域系统。
信使核糖核酸的形成和翻译
Haloquadra walsbyi




Other aspects of archaean biochemistry are unique, such as their reliance on ether lipids in their cell membranes. The archaea exploit a much greater variety of sources of energy than eukaryotes: ranging from familiar organic compounds such as sugars, to using ammonia, metal ions or even hydrogen gas as nutrients. Salt-tolerant archaea (the Halobacteria) use sunlight as a source of energy and other species of archaea fix carbon; however, unlike plants and cyanobacteria, no species of archaea is known to do both. Archaea reproduce asexually and divide by binary fission, fragmentation, or budding; in contrast to bacteria and eukaryotes, no species of archaea are known that form spores.
3.1.1 Morphology古菌的形态

Individual archaeans range from 0.1 micrometers (μm) to over 15 μm in diameter, and occur in various shapes, commonly as spheres, rods, spirals or plates.

古菌的分类

根据生活习性和生理特性可分为：
产甲烷菌 嗜热嗜酸菌 极端嗜盐菌


从rRNA进化树上，古菌分为两类：

泉古生菌(Crenarchaeota)

极端嗜热、嗜酸、代谢硫。
广古生菌(Euryarchaeota)

Yellowstone National Park.

Generally, archaea and bacteria are quite similar in size and shape, although a few archaea have very unusual shapes, such as the flat and square-shaped cells of Haloquadra walsbyi.
They have no cell nucleus or any other organelles within their cells.
Halobacteria sp. strain NRC-1，
每一细胞长度大约5μm


In the past they were viewed as an unusual group of bacteria and named archaebacteria but since the Archaea ቤተ መጻሕፍቲ ባይዱave an independent evolutionary history and show many differences in their biochemistry from other forms of life, they are now classified as a separate domain in the three-domain system. In this system the three main branches of evolutionary descent are the Archaea, Eukarya and Bacteria.
Colonies can also be produced by an association between different species: "string-of-pearls"

3.1.2 Cell structure



Archaea are similar to bacteria in their general cell structure, but the composition and organization of some of these structures set the archaea apart. Like bacteria, archaea lack interior membranes so their cells do not contain organelles. They also resemble bacteria in that their cell membrane is usually bounded by a cell wall and they swim by the use of one or more flagella. In overall structure the archaea are most similar to gram-positive bacteria, as most have a single plasma membrane and cell wall, and lack a periplasmic space; the exception to this general rule is the archaean Ignicoccus, which possess a particularly large periplasm that contains membrane-bound vesicles and is enclosed by an outer membrane.



Initially, archaea were seen as extremophiles that lived in harsh environments, such as hot springs and salt lakes, but they have since been found in a broad range of habitats, such as soils, oceans, and marshlands. Archaea are particularly numerous in the oceans, and the archaea in plankton may be one of the most abundant groups of organisms on the planet. Archaea are now recognized as a major part of life on Earth and may play an important role in both the carbon cycle and nitrogen cycle.


No clear examples of archaeal pathogens or parasites are known, but they are often mutualists or commensals. One example are the methanogenic archaea that inhabit the gut of humans and ruminants, where they are present in vast numbers and aid in the digestion of food. Archaea have some importance in technology, with methanogens used to produce biogas and as part of sewage treatment, and enzymes from extremophile archaea that can resist high temperatures and organic solvents are exploited in biotechnology.
Chapter 3 Archaea and Bacteria
3.1 Archaea The Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon (sometimes spelled "archeon").


Some species of archaea form aggregates or filaments of cells up to 200 μm in length, and these organisms can be prominent members of the communities of microbes that make up biofilms. An extreme example ： Thermococcus 嗜热球菌属
Classifying the Archaea is still difficult, since the vast majority have never been studied in the laboratory and have only been detected by analysis of their nucleic acids in samples from the environment.