Bacteria research Material V III Essay Research

  • Просмотров 508
  • Скачиваний 9
  • Размер файла 22
    Кб

Bacteria -research Material V. II,I Essay, Research Paper Archaebacteria, simple organisms that resemble ordinary bacteria in that they lack a well-formed nucleus and can therefore be characterized as procaryotes in the classification of living organisms. Their biochemistry differs in important ways from that of other bacteria, however, and some biologists place them in a kingdom of their own. According to these theories, archaebacteria may be ancestral to the main cellular body of eucaryotes, or organisms with well-formed cell nuclei, whereas ordinary bacteria are generally thought to be ancestral to the mitochondria and chloroplasts within eucaryotic cells.(Greek bakterion, “little staff”), large group of mostly microscopic, unicellular organisms that lack a distinct

nucleus and that usually reproduce by cell division. Bacteria are tiny, most ranging from 1 to 10 micrometers (1 micrometer equals 1/25,000 in), and are extremely variable in the ways they obtain energy and nourishment. They can be found in nearly all environments?from air, soil, water, and ice to hot springs; even the hydrothermal vents on the deep ocean floor are the home of sulfur-metabolizing bacteria (see MARINE LIFE). Certain types are found in nearly all food products, and bacteria also occur in various forms of symbiosis with most plants and animals and other kinds of life.the currently used five-kingdom scheme of classification, bacteria constitute the kingdom Monera, also known as Procaryotae?organisms in whose cells the nucleus is not enclosed by a membrane (see CELL).

About 1600 species are known. Generally, bacteria are classified into species on the basis of characteristics such as shape?cocci (spheres), bacilli (rods), spirochetes (spirals); cell-wall structure; differential staining GRAM’S STAIN; ability to grow in the presence or absence of air (aerobes and anaerobes, respectively); metabolic or fermentative capabilities; ability to form dormant spores under adverse conditions SPORE; serologic identification of surface components; and nucleic-acid relatedness. The most widely used reference for taxonomic classification of bacteria divides them into four major groups based on cell-wall characteristics. The division Gracilicutes encompasses bacteria with thin, gram-negative-type cell walls; the Firmicutes have thick, gram-positive cell

walls; the Tenericutes lack cell walls; and the Mendosicutes have unusual cell walls made of material other than typical bacterial peptidoglycan. Among the Mendosicutes are the archaebacteria, a group of unusual organisms that includes methanogens, strict anaerobes that produce methane from carbon dioxide and hydrogen; halobacteria, which grow at high salt concentrations; and thermoacidophiles, which are sulfur-dependent extreme thermophiles. It has been argued that the archaebacteria should be classified into a separate kingdom because recent biochemical studies have shown that they are as different from other bacteria as they are from eucaryotes (the nucleii of which are membrane-bound). The four major bacterial divisions are further subdivided into about 30 numbered sec tions,

some of which are divided into orders, families, and genera. Section 1, for example, is made up of spirochetes?long, corkscrew-shaped bacteria with gram-negative cell walls and internal (between the cell wall and cell membrane) filamentous flagella that provide the organisms with motility (ability to move). Treponema pallidum, causing syphilis, is a spirochete, a member of the order Spirochaetales, and the family Spirochaetaceae. Not all bacteria can move, but the mobile ones are generally propelled by screwlike appendages?flagella?that may project from all over the cell or from one or both ends, singly or in tufts. Depending on the direction in which the flagella rotate, the bacteria either move forward or tumble in place. The duration of runs versus tumbling is linked to