Many types of secretion systems are known and these structures are often essential for the virulence of pathogens, so are intensively studied. [199][200], Because of their importance for research in general, samples of bacterial strains are isolated and preserved in Biological Resource Centers.
[87], Bacteria exhibit an extremely wide variety of metabolic types. As a result bacteria can be distinguished based on their morphology and staining properties. in ancient "amitochondrial" protozoa). One species of Rickettsia causes typhus, while another causes Rocky Mountain spotted fever. [210], Louis Pasteur demonstrated in 1859 that the growth of microorganisms causes the fermentation process, and that this growth is not due to spontaneous generation (yeasts and molds, commonly associated with fermentation, are not bacteria, but rather fungi). The classification of bacteria serves a variety of different functions. [208] In fact, his Bacterium was a genus that contained non-spore-forming rod-shaped bacteria,[209] as opposed to Bacillus, a genus of spore-forming rod-shaped bacteria defined by Ehrenberg in 1835. It allows a large proportion of clinically important bacteria to be classified as either. In his research into tuberculosis Koch finally proved the germ theory, for which he received a Nobel Prize in 1905. Some tests are used routinely for many groups of bacteria (oxidase, nitrate reduction, amino acid degrading enzymes, fermentation or utilization of carbohydrates); others are restricted to a single family, genus, or species (coagulase test for staphylococci, pyrrolidonyl arylamidase test for Gram-positive cocci).
pilus) are cellular appendages, slightly larger than fimbriae, that can transfer genetic material between bacterial cells in a process called conjugation where they are called conjugation pili or sex pili (see bacterial genetics, below). Classification of bacteria based on flagella presence. See the figure above for details.
These biofilms and mats can range from a few micrometres in thickness to up to half a metre in depth, and may contain multiple species of bacteria, protists and archaea.
Chemotrops are further divided into two groups on the basis of source of electron. [32] Among the smallest bacteria are members of the genus Mycoplasma, which measure only 0.3 micrometres, as small as the largest viruses. [37][38], Many bacterial species exist simply as single cells, others associate in characteristic patterns: Neisseria form diploids (pairs), Streptococcus form chains, and Staphylococcus group together in "bunch of grapes" clusters. Facultative anaerobes can switch between fermentation and different terminal electron acceptors depending on the environmental conditions in which they find themselves. [80], Endospores show no detectable metabolism and can survive extreme physical and chemical stresses, such as high levels of UV light, gamma radiation, detergents, disinfectants, heat, freezing, pressure, and desiccation.
Phototrops: Those bacteria which gain energy from light; Phototrops are further divided into two groups on the basis of source of electron. Due to their small size, commensal bacteria are ubiquitous and grow on animals and plants exactly as they will grow on any other surface. Those bacteria which uses carbondioxide as sole source of carbon to prepare its own food. [72], Fimbriae (sometimes called "attachment pili") are fine filaments of protein, usually 2–10 nanometres in diameter and up to several micrometres in length. Disinfectants such as bleach are used to kill bacteria or other pathogens on surfaces to prevent contamination and further reduce the risk of infection. Home » Basic Microbiology » Classification of Bacteria, Last Updated on January 5, 2020 by Sagar Aryal. 43 16
[109] The final phase is the death phase where the bacteria run out of nutrients and die. A primary distinguishing characteristic is whether an organism grows aerobically, anaerobically, facultatively (i.e., in either the presence or absence of oxygen), or microaerobically (i.e., in the presence of a less than atmospheric partial pressure of oxygen). Pointer Publishers; First edition.
There are approximately 5×1030 bacteria on Earth,[10] forming a biomass which exceeds that of all plants and animals. For the genus, see. "DNA repair as the primary adaptive function of sex in bacteria and eukaryotes". [63], Around the outside of the cell membrane is the cell wall. Either they may remain as a single cell or may aggregate together for various configurations. [41], Bacteria often attach to surfaces and form dense aggregations called biofilms, and larger formations known as microbial mats. [91] Chemotrophs use chemical compounds as a source of energy by transferring electrons from a given electron donor to a terminal electron acceptor in a redox reaction. Bacteria were among the first life forms to appear on Earth, and are present in most of its habitats.
[1], The word bacteria is the plural of the New Latin bacterium, which is the latinisation of the Greek βακτήριον (bakterion),[17] the diminutive of βακτηρία (bakteria), meaning "staff, cane",[18] because the first ones to be discovered were rod-shaped. 43 0 obj <>
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There are many types of antibiotics and each class inhibits a process that is different in the pathogen from that found in the host. 0000018135 00000 n
Chemotrophs are further divided by the types of compounds they use to transfer electrons. [155], The identification of bacteria in the laboratory is particularly relevant in medicine, where the correct treatment is determined by the bacterial species causing an infection.
Photoautotrophs and chemoautotrophs.
[217] Ehrlich had been awarded a 1908 Nobel Prize for his work on immunology, and pioneered the use of stains to detect and identify bacteria, with his work being the basis of the Gram stain and the Ziehl–Neelsen stain. By making mutations in bacterial DNA and examining the resulting phenotypes, scientists can determine the function of genes, enzymes and metabolic pathways in bacteria, then apply this knowledge to more complex organisms. [140], Bacteria often function as multicellular aggregates known as biofilms, exchanging a variety of molecular signals for inter-cell communication, and engaging in coordinated multicellular behaviour. Specimens that are normally sterile, such as blood, urine or spinal fluid, are cultured under conditions designed to grow all possible organisms. 0000014937 00000 n
This commonly involves Bacillus thuringiensis (also called BT), a Gram-positive, soil dwelling bacterium. During log phase, nutrients are metabolised at maximum speed until one of the nutrients is depleted and starts limiting growth. Bacteria can be classified on the basis of cell structure, cellular metabolism or on differences in cell components, such as DNA, fatty acids, pigments, antigens and quinones. startxref
[11] Bacteria are vital in many stages of the nutrient cycle by recycling nutrients such as the fixation of nitrogen from the atmosphere.
So high concentration of Na+ ion concentration is required to shield the –ve charge. Those bacteria that have optimum temperature of growth above 80C. [55] These light-gathering complexes may even form lipid-enclosed structures called chlorosomes in green sulfur bacteria. The general lack of internal membranes in bacteria means these reactions, such as electron transport, occur across the cell membrane between the cytoplasm and the outside of the cell or periplasm. [206] His observations had also included protozoans which he called animalcules, and his findings were looked at again in the light of the more recent findings of cell theory. [70] This layer provides chemical and physical protection for the cell surface and can act as a macromolecular diffusion barrier.
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