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Aerotaxis
Aerotaxis is the movement caused by oxygen gradients. Positive aerotaxis involves the movement toward higher concentration of environmental oxygen, while negative aerotaxis involves the movement towards a lower concentration of environmental oxygen. Aerotactic bacteria gather around sources of air forming aerotactic bands. Discovery The discovery of aerotaxis was first reported by Theodor Wilhelm Engelmann, as he showed microaerophilic ''Spirillum tenue'' were attracted by low oxygen concentrations. Ten decades after the first discovery of this movement, it was observed that bacteria are actually bound to areas with optimal oxygen concentrations; resulting in the formation of bands. It was concluded that the creations of these bands was largely in part to oxygen's important role in metabolic pathways as they allowed for surveying aerotaxis in many bacterial species. This ability proves to be important for survival as efficient metabolism directly relates to growth. Aerotaxis not o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bacteria
Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among the first life forms to appear on Earth, and are present in most of its habitats. Bacteria inhabit the air, soil, water, Hot spring, acidic hot springs, radioactive waste, and the deep biosphere of Earth's crust. Bacteria play a vital role in many stages of the nutrient cycle by recycling nutrients and the nitrogen fixation, fixation of nitrogen from the Earth's atmosphere, atmosphere. The nutrient cycle includes the decomposition of cadaver, dead bodies; bacteria are responsible for the putrefaction stage in this process. In the biological communities surrounding hydrothermal vents and cold seeps, extremophile bacteria provide the nutrients needed to sustain life by converting dissolved compounds, suc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Theodor Wilhelm Engelmann
Theodor Wilhelm Engelmann (14 November 1843 – 20 May 1909) was a German botanist, physiologist, microbiologist, university professor, and musician whose 1882 experiment measured the effects of different colors of light on photosynthetic activity and showed that the conversion of light energy to chemical energy took place in the chloroplast A chloroplast () is a type of membrane-bound organelle, organelle known as a plastid that conducts photosynthesis mostly in plant cell, plant and algae, algal cells. Chloroplasts have a high concentration of chlorophyll pigments which captur .... Academic history Engelmann studied natural science and medicine first at the University of Jena, from 1861 to 1862, and later at the University of Heidelberg, the University of Göttingen and the University of Leipzig. In 1867, he received a doctoral degree in medicine at Leipzig. From 1870 he taught physiology at the University of Utrecht, becoming a professor in 1877. In 1897, he began ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electron
The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up quark, up and down quark, down quarks. Electrons are extremely lightweight particles that orbit the positively charged atomic nucleus, nucleus of atoms. Their negative charge is balanced by the positive charge of protons in the nucleus, giving atoms their overall electric charge#Charge neutrality, neutral charge. Ordinary matter is composed of atoms, each consisting of a positively charged nucleus surrounded by a number of orbiting electrons equal to the number of protons. The configuration and energy levels of these orbiting electrons determine the chemical properties of an atom. Electrons are bound to the nucleus to different degrees. The outermost or valence electron, valence electrons are the least tightly bound and are responsible for th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Proton
A proton is a stable subatomic particle, symbol , Hydron (chemistry), H+, or 1H+ with a positive electric charge of +1 ''e'' (elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an electron (the proton-to-electron mass ratio). Protons and neutrons, each with a mass of approximately one Dalton (unit), dalton, are jointly referred to as ''nucleons'' (particles present in atomic nuclei). One or more protons are present in the Atomic nucleus, nucleus of every atom. They provide the attractive electrostatic central force which binds the atomic electrons. The number of protons in the nucleus is the defining property of an element, and is referred to as the atomic number (represented by the symbol ''Z''). Since each chemical element, element is identified by the number of protons in its nucleus, each element has its own atomic number, which determines the number of atomic electrons and consequently the chemical characteristi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Taxis
A taxis (; : taxes ) is the motility, movement of an organism in response to a Stimulus (physiology), stimulus such as light or the presence of food. Taxes are innate behavioural responses. A taxis differs from a tropism (turning response, often growth towards or away from a stimulus) in that in the case of taxis, the organism has motility and demonstrates guided movement towards or away from the stimulus source. It is sometimes distinguished from a Kinesis (biology), kinesis, a non-directional change in activity in response to a stimulus. Taxis can be positive (moving towards the stimulus) or negative (moving away from the stimulus). Classification Taxes are classified based on the type of stimulus, and on whether the organism's response is to move towards or away from the stimulus. If the organism moves towards the stimulus the taxis are positive, while if it moves away the taxis are negative. For example, flagellate protozoans of the genus ''Euglena'' move towards a light so ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shewanella Oneidensis
''Shewanella oneidensis'' is a bacterium notable for its ability to reduce metal ions and live in environments with or without oxygen. This proteobacterium was first isolated from Lake Oneida, NY in 1988, hence its name. ''Shewanella oneidensis'' is a facultative bacterium, capable of surviving and proliferating in both aerobic and anaerobic conditions. The special interest in ''S. oneidensis'' MR-1 revolves around its behavior in an anaerobic environment contaminated by heavy metals such as iron, lead and uranium. Experiments suggest it may reduce ionic mercury to elemental mercury and ionic silver to elemental silver. Cellular respiration for these bacteria is not restricted to heavy metals though; the bacteria can also target sulfates, nitrates and chromates when grown anaerobically. Name This species is referred to as ''S. oneidensis'' MR-1, indicating "manganese reducing", a special feature of this organism. It is a common misconception to think that MR-1 refers to "me ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gram-negative
Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelope consists of a thin peptidoglycan cell wall sandwiched between an inner ( cytoplasmic) membrane and an outer membrane. These bacteria are found in all environments that support life on Earth. Within this category, notable species include the model organism '' Escherichia coli'', along with various pathogenic bacteria, such as '' Pseudomonas aeruginosa'', '' Chlamydia trachomatis'', and '' Yersinia pestis''. They pose significant challenges in the medical field due to their outer membrane, which acts as a protective barrier against numerous antibiotics (including penicillin), detergents that would normally damage the inner cell membrane, and the antimicrobial enzyme lysozyme produced by animals as part of their innate immune system. Furthe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Facultative Bacteria
A facultative anaerobic organism is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent. Some examples of facultatively anaerobic bacteria are ''Staphylococcus'' spp., ''Escherichia coli'', ''Salmonella'', ''Listeria'' spp., '' Shewanella oneidensis'' and ''Yersinia pestis''. Certain eukaryotes are also facultative anaerobes, including pupfish, fungi such as ''Saccharomyces cerevisiae'' and many aquatic invertebrates such as nereid polychaetes. It has been observed that in mutants of '' Salmonella typhimurium'' that underwent mutations to be either obligate aerobes or anaerobes, there were varying levels of chromatin-remodeling proteins. The obligate aerobes were later found to have a defective DNA gyrase subunit A gene ('' gyrA''), while obligate anaerobes were defective in topoisomerase I (''topI''). This indicates that topoisomerase I and its associated relaxation of chromosomal DNA is requi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electron Donor
In chemistry, an electron donor is a chemical entity that transfers electrons to another compound. It is a reducing agent that, by virtue of its donating electrons, is itself oxidized in the process. An obsolete definition equated an electron donor and a Lewis base. In contrast to traditional reducing agents, electron transfer from a donor to an electron acceptor may be only fractional. The electron is not completely transferred, which results in an Delocalized electron, electron resonance between the donor and acceptor. This leads to the formation of charge transfer complexes, in which the components largely retain their chemical identities. The electron donating power of a donor molecule is measured by its ionization potential, which is the energy required to remove an electron from the highest occupied molecular orbital (HOMO and LUMO, HOMO). The overall energy balance (ΔE), i.e., energy gained or lost, in an electron donor-acceptor transfer is determined by the difference bet ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electron Acceptor
An electron acceptor is a chemical entity that accepts electrons transferred to it from another compound. Electron acceptors are oxidizing agents. The electron accepting power of an electron acceptor is measured by its redox potential. In the simplest case, electron acceptors are reduced by one electron. The process can alter the structure of the acceptor substantially. When the added electron is highly delocalized, the structural consequences of the reduction can be subtle. The central C-C distance in the electron acceptor tetracyanoethylene elongates from 135 to 143 pm upon acceptance of an electron. In the formation of some donor-acceptor complexes, less than one electron is transferred. TTF-TCNQ is a charge transfer complex. Biology In biology, a ''terminal electron acceptor'' often refers to either the last compound to receive an electron in an electron transport chain, such as oxygen during cellular respiration, or the last cofactor to receive an electron within ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phase-contrast Microscopy
__NOTOC__ Phase-contrast microscopy (PCM) is an optical microscopy technique that converts phase shifts in light passing through a transparent specimen to brightness changes in the image. Phase shifts themselves are invisible, but become visible when shown as brightness variations. When light waves travel through a medium other than a vacuum, interaction with the medium causes the wave amplitude and phase to change in a manner dependent on properties of the medium. Changes in amplitude (brightness) arise from the scattering and absorption of light, which is often wavelength-dependent and may give rise to colors. Photographic equipment and the human eye are only sensitive to amplitude variations. Without special arrangements, phase changes are therefore invisible. Yet, phase changes often convey important information. Phase-contrast microscopy is particularly important in biology. It reveals many cellular structures that are invisible with a bright-field microscope, as exem ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oxygen
Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), nonmetal, and a potent oxidizing agent that readily forms oxides with most elements as well as with other chemical compound, compounds. Oxygen is abundance of elements in Earth's crust, the most abundant element in Earth's crust, making up almost half of the Earth's crust in the form of various oxides such as water, carbon dioxide, iron oxides and silicates.Atkins, P.; Jones, L.; Laverman, L. (2016).''Chemical Principles'', 7th edition. Freeman. It is abundance of chemical elements, the third-most abundant element in the universe after hydrogen and helium. At standard temperature and pressure, two oxygen atoms will chemical bond, bind covalent bond, covalently to form dioxygen, a colorless and odorless diatomic gas with the chemical formula ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
