microbe terms

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microbe terms
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2011-03-28 18:40:51
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microbiology glossary
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  1. AB toxins
    The structure and activity of many exotoxins are based on the AB model. In this model, the B portion of the toxin is responsible for toxin binding to a cell but does not directly harm it. The A portion enters the cell and disrupts its function.
  2. accessory pigments
    Photosynthetic pigments such as carotenoids and phycobiliproteins that aid chlorophyll in trapping light energy
  3. acid dyes
    Dyes that are anionic or have negatively charged groups such as carboxyls
  4. acid fast
    Refers to bacteria like the mycobacteria that cannot be easily decolorized with acid alcohol after being stained with dyes such as basic fuchsin.
  5. A staining procedure that differentiates between bacteria based on their ability to retain a dye when washed with an acid alcohol solution.
    acid-fast staining
  6. acidophile
    A microorganism that has its growth optimum between about pH 0 and 5.5.
  7. acquired immune deficiency syndrome (AIDS)
    An infectious disease syndrome caused by the human immunodeficiency virus and is characterized by the loss of a normal immune response, followed by increased susceptibility to opportunistic infections and an increased risk of some cancers.
  8. actinobacteria
    A group of gram-positive bacteria containing the actinomycetes and their high G 1 C relatives.
  9. actinomycete
    An aerobic, gram-positive bacterium that forms branching filaments (hyphae) and asexual spores.
  10. actinorhizae
    Associations between actinomycetes and plant roots.
  11. activated sludge (sluj)
    Solid matter or sediment composed of actively growing microorganisms that participate in the aerobic portion of a biological sewage treatment process. The microbes readily use dissolved organic substrates and transform them into additional microbial cells and carbon dioxide.
  12. acute infections
    Virus infections with a fairly rapid onset that last for a relatively short time.
  13. acyclovir
    A synthetic purine nucleoside derivative with antiviral activity against herpes simplex virus.
  14. adhesin
    A molecular component on the surface of a microorganism that is involved in adhesion to a substratum or cell. Adhesion to a specific host tissue usually is a preliminary stage in pathogenesis, and adhesins are important virulence factors.
  15. aerobe
    An organism that grows in the presence of atmospheric oxygen.
  16. aerobic anoxygenic photosynthesis
    Photosynthetic process in which electron donors such as organic matter or sulfide, which do not result in oxygen evolution, are used under aerobic conditions.
  17. aerotolerant anaerobes
    Microorganisms that grow equally well whether or not oxygen is present.
  18. agar
    A complex sulfated polysaccharide, usually extracted from red algae, that is used as a solidifying agent in the preparation of culture media.
  19. airborne transmission
    The type of infectious organism transmission in which the pathogen is truly suspended in the air and travels over a meter or more from the source to the host.
  20. akinetes
    Specialized, nonmotile, dormant, thick-walled resting cells formed by some cyanobacteria.
  21. alga
    A common term for a series of unrelated groups of photosynthetic eucaryotic microorganisms lacking multicellular sex organs (except for the charophytes) and conducting vessels.
  22. algicide
    An agent that kills algae.
  23. algology
    The scientific study of algae.
  24. alkalophile
    A microorganism that grows best at pHs from about 8.5 to 11.5.
  25. alpha-proteobacteria
    One of the five subgroups of proteobacteria, each with distinctive 16S rRNA sequences. This group contains most of the oligotrophic proteobacteria; some have unusual metabolic modes such as methylotrophy, chemolithotrophy, and nitrogen fixing ability. Many have distinctive morphological features.
  26. alveolar macrophage
    A vigorously phagocytic macrophage located on the epithelial surface of the lung alveoli where it ingests inhaled particulate matter and microorganisms.
  27. amensalism
    A relationship in which the product of one organism has a negative effect on another organism.
  28. amoeboid movement
    Moving by means of cytoplasmic flow and the formation of pseudopodia (temporary cytoplasmic protrusions of the cytoplasm).
  29. amphitrichous
    A cell with a single flagellum at each end.
  30. anaerobe
    An organism that grows in the absence of free oxygen.
  31. anoxygenic photosynthesis
    Photosynthesis that does not oxidize water to produce oxygen; the form of photosynthesis characteristic of purple and green photosynthetic bacteria.
  32. antibiotic
    A microbial product or its derivative that kills susceptible microorganisms or inhibits their growth.
  33. antimicrobial agent
    An agent that kills microorganisms or inhibits their growth.
  34. arbuscular mycorrhizal (AM) fungi
    The mycorrhizal fungi in a symbiotic fungus-root association that penetrate the outer layer of the root, grow intracellularly, and form characteristic much-branched hyphal structures called arbuscules.
  35. arbuscules
    Branched, treelike structures formed in cells of plant roots colonized by endotrophic mycorrhizal fungi.
  36. Archaea
    The domain that contains procaryotes with isoprenoid glycerol diether or diglycerol tetraether lipids in their membranes and archaeal rRNA (among many differences).
  37. ascocarp
    A multicellular structure in ascomycetes lined with specialized cells called asci in which nuclear fusion and meiosis produce ascospores. An ascocarp can be open or closed and may be referred to as a fruiting body.
  38. atomic force microscope
    A type of scanning probe microscope that images a surface by moving a sharp probe over the surface at a constant distance; a very small amount of force is exerted on the tip and probe movement is followed with a laser.
  39. autoclave
    An apparatus for sterilizing objects by the use of steam under pressure. Its development tremendously stimulated the growth of microbiology.
  40. autotroph
    An organism that uses CO2 as its sole or principal source of carbon.
  41. auxotroph
    A mutated prototroph that lacks the ability to synthesize an essential nutrient and therefore must obtain it or a precursor from its surroundings.
  42. axial filament
    The organ of motility in spirochetes. It is made of axial fibrils or periplasmic flagella that extend from each end of the protoplasmic cylinder and overlap in the middle of the cell. The outer sheath lies outside the axial filament.
  43. Bacteria
    The domain that contains procaryotic cells with primarily diacyl glycerol diesters in their membranes and with bacterial rRNA. Bacteria also is a general term for organisms that are composed of procaryotic cells and are not multicellular.
  44. bactericide
    bactericide
  45. bacteriocin
    A protein produced by a bacterial strain that kills other closely related strains.
  46. bacteriophage
    A virus that uses bacteria as its host; often called a phage.
  47. bacteriophage (phage) typing
    A technique in which strains of bacteria are identified based on their susceptibility to a variety of bacteriophages.
  48. bacteriostatic
    Inhibiting the growth and reproduction of bacteria.
  49. bacteroid
    A modified, often pleomorphic, bacterial cell within the root nodule cells of legumes; after transformation into a symbiosome it carries out nitrogen fixation.
  50. baeocytes
    Small, spherical, reproductive cells produced by pleurocapsalean cyanobacteria through multiple fission.
  51. balanced growth
    Microbial growth in which all cellular constituents are synthesized at constant rates relative to each other.
  52. basic dyes
    Dyes that are cationic, or have positively charged groups, and bind to negatively charged cell structures. Usually sold as chloride salts.
  53. basidiomycetes
    A division of fungi in which the spores are born on club-shaped organs called basidia.
  54. basidium
    A structure that bears on its surface a definite number of basidiospores (typically four) that are formed following karyogamy and meiosis. Basidia are found in the basidiomycetes and are usually club-shaped.
  55. basophil
    A phagocytic leukocyte whose granules stain bluish-black with a basic dye. It has a segmented nucleus. The granules contain histamine and heparin.
  56. beta-proteobacteria
    One of the five subgroups of proteobacteria, each with distinctive 16S rRNA sequences. Members of this subgroup are similar to the alpha-proteobacteria metabolically, but tend to use substances that diffuse from organic matter decomposition in anaerobic zones.
  57. binary fission
    Asexual reproduction in which a cell or an organism separates into two cells.
  58. biofilms
    Organized microbial systems consisting of layers of microbial cells associated with surfaces, often with complex structural and functional characteristics. Biofilms have physical/chemical gradients that influence microbial metabolic processes. They can form on inanimate devices (catheters, medical prosthetic devices) and also cause fouling (e.g., of ships' hulls, water pipes, cooling towers).
  59. bioinsecticide
    A pathogen that is used to kill or disable unwanted insect pests. Bacteria, fungi, or viruses are used, either directly or after manipulation, to control insect populations.
  60. bright-field microscope
    A microscope that illuminates the specimen directly with bright light and forms a dark image on a brighter background.
  61. budding
    A vegetative outgrowth of yeast and some bacteria as a means of asexual reproduction; the daughter cell is smaller than the parent.
  62. burst size
    The number of phages released by a host cell during the lytic life cycle.
  63. capsid
    The protein coat or shell that surrounds a virion's nucleic acid.
  64. capsule
    A layer of well-organized material, not easily washed off, lying outside the bacterial cell wall.
  65. cellular slime molds
    Slime molds with a vegetative phase consisting of amoeboid cells that aggregate to form a multicellular pseudoplasmodium; they belong to the division Acrasiomycota.
  66. cell wall
    The strong layer or structure that lies outside the plasma membrane; it supports and protects the membrane and gives the cell shape.
  67. chemolithotrophic autotrophs
    Microorganisms that oxidize reduced inorganic compounds to derive both energy and electrons; CO2 is their carbon source. Also called chemolithoautotrophs.
  68. chemoorganotrophic heterotrophs
    Organisms that use organic compounds as sources of energy, hydrogen, electrons, and carbon for biosynthesis.
  69. chemotaxis
    The pattern of microbial behavior in which the microorganism moves toward chemical attractants and/or away from repellents.
  70. chemotrophs
    Organisms that obtain energy from the oxidation of chemical compounds.
  71. chlamydiae
    Members of the genus Chlamydia: gram-negative, coccoid cells that reproduce only within the cytoplasmic vesicles of host cells using a life cycle that alternates between elementary bodies and reticulate bodies.
  72. cilia
    Threadlike appendages extending from the surface of some protozoa that beat rhythmically to propel them; cilia are membrane-bound cylinders with a complex internal array of microtubules, usually in a 9 1 2 pattern.
  73. coaggregation
    The collection of a variety of bacteria on a surface such as a tooth surface because of cell-to-cell recognition of genetically distinct bacterial types. Many of these interactions appear to be mediated by a lectin on one bacterium that interacts with a complementary carbohydrate receptor on another bacterium.
  74. coccus
    A roughly spherical bacterial cell.
  75. coenocytic
    Refers to a multinucleate cell or hypha formed by repeated nuclear divisions not accompanied by cell divisions.
  76. colonization
    The establishment of a site of microbial reproduction on an inanimate surface or organism without necessarily resulting in tissue invasion or damage.
  77. colony
    A cluster or assemblage of microorganisms growing on a solid surface such as the surface of an agar culture medium; the assemblage often is directly visible, but also may be seen only microscopically.
  78. colorless sulfur bacteria
    A diverse group of nonphotosynthetic proteobacteria that can oxidize reduced sulfur compounds such as hydrogen sulfide. Many are lithotrophs and derive energy from sulfur oxidation. Some are unicellular, whereas others are filamentous gliding bacteria.
  79. commensal
    Living on or within another organism without injuring or benefiting the other organism.
  80. commensalism
    A type of symbiosis in which one individual gains from the association and the other is neither harmed nor benefited.
  81. competent
    A bacterial cell that can take up free DNA fragments and incorporate them into its genome during transformation.
  82. complex viruses
    Viruses with capsids having a complex symmetry that is neither icosahedral nor helical.
  83. confocal scanning laser microscope (CSLM)
    A light microscope in which monochromatic laser-derived light scans across the specimen at a specific level and illuminates one spot at a time to form an image. Stray light from other parts of the specimen is blocked out to give an image with excellent contrast and resolution.
  84. conjugation
    1. The form of gene transfer and recombination in bacteria that requires direct cell-to-cell contact. 2. A complex form of sexual reproduction commonly employed by protozoa.
  85. contractile vacuole (vak_u-øol)
    In protists and some animals, a clear fluid-filled cell vacuole that takes up water from within the cell and then contracts, releasing it to the outside through a pore in a cyclical manner. Contractile vacuoles function primarily in osmoregulation and excretion.
  86. cyanobacteria
    A large group of bacteria that carry out oxygenic photosynthesis using a system like that present in photosynthetic eucaryotes.
  87. cyst
    A general term used for a specialized microbial cell enclosed in a wall. Cysts are formed by protozoa and a few bacteria. They may be dormant, resistant structures formed in response to adverse conditions or reproductive cysts that are a normal stage in the life cycle.
  88. cytoproct
    Site on a protozoan where undigestible matter is expelled.
  89. cytostome
    A permanent site in the protozoan ciliate body through which food is ingested.
  90. dark-field microscopy
    Microscopy in which the specimen is brightly illuminated while the background is dark.
  91. death phase
    The decrease in viable microorganisms that occurs after the completion of growth in a batch culture.
  92. decimal reduction time (D or D value)
    The time required to kill 90% of the microorganisms or spores in a sample at a specified temperature.
  93. delta-proteobacteria
    One of the five subgroups of proteobacteria, each with distinctive 16S rRNA sequences. Chemoorganotrophic bacteria that usually are either predators on other bacteria or anaerobes that generate sulfide from sulfate and sulfite.
  94. deuteromycetes
    In some classification systems, the deuteromycetes or Fungi Imperfecti are a class of fungi. These organisms either lack a sexual stage or it has not yet been discovered.
  95. diatoms
    Algal protists with siliceous cell walls called frustules. They constitute a substantial subfraction of the phytoplankton.
  96. diauxic growth (di-awk_sik)
    A biphasic growth pattern or response in which a microorganism, when exposed to two nutrients, initially uses one of them for growth and then alters its metabolism to make use of the second.
  97. differential interference contrast (DIC) microscope
    A light microscope that employs two beams of plane polarized light. The beams are combined after passing through the specimen and their intereference is used to create the image.
  98. dinoflagellate
    An algal protist characterized by two flagella used in swimming in a spinning pattern. Many are bioluminescent and an important part of marine phytoplankton, some also are important marine pathogens.
  99. dipicolinic acid
    A substance present at high concentrations in the bacterial endospore. It is thought to contribute to the endospore's heat resistance.
  100. ectomycorrhizal
    Referring to a mutualistic association between fungi and plant roots in which the fungus surrounds the root tip with a sheath.
  101. ectoplasm
    The outer stiffer portion or region of the cytoplasm in a protozoan, which may be differentiated in texture from the inner portion or endoplasm.
  102. endocytosis
    The process in which a cell takes up solutes or particles by enclosing them in vesicles pinched off from its plasma membrane.
  103. endomycorrhizal
    Referring to a mutualistic association of fungi and plant roots in which the fungus penetrates into the root cells and arbuscules and vesicles are formed.
  104. endotoxin
    The heat-stable lipopolysaccharide in the outer membrane of the cell wall of gram-negative bacteria that is released when the bacterium lyses, or sometimes during growth, and is toxic to the host.
  105. envelope
    1. All the structures outside the plasma membrane in bacterial cells. 2. In virology it is an outer membranous layer that surrounds the nucleocapsid in some viruses.
  106. epsilon-proteobacteria
    One of the five subgroups of proteobacteria, each with distinctive 16S rRNA sequences. Slender gram-negative rods, some of which are medically important (Campylobacter and Helicobacter).
  107. Eucarya
    The domain that contains organisms composed of eucaryotic cells with primarily glycerol fatty acyl diesters in their membranes and eucaryotic rRNA.
  108. euglenoids
    A group of algae (the division Euglenophyta) or protozoa (order Euglenida) that normally have chloroplasts containing chlorophyll a and b. They usually have a stigma and one or two flagella emerging from an anterior gullet.
  109. Eumycota
    A division of fungi in some classification systems. These are the true fungi consisting of the Zygomycetes, Ascomycetes, Basidiomycetes, and Chytridiomycetes.
  110. excystation
    The escape of one or more cells or organisms from a cyst.
  111. exogenote
    The piece of donor DNA that enters a bacterial cell during gene exchange and recombination.
  112. extreme environment
    An environment in which physical factors such as temperature, pH, salinity, and pressure are outside of the normal range for growth of most microorganisms; these conditions allow unique organisms to survive and function.
  113. extremophiles
    Microorganisms that grow under harsh or extreme environmental conditions such as very high temperatures or low pHs.
  114. F factor
    The fertility factor, a plasmid that carries the genes for bacterial conjugation and makes its E. coli host cell the gene donor during conjugation.
  115. fimbria
    A fine, hairlike protein appendage on some gram-negative bacteria that helps attach them to surfaces.
  116. flagellin
    The protein used to construct the filament of a bacterial flagellum.
  117. flagellum
    A thin, threadlike appendage on many procaryotic and eucaryotic cells that is responsible for their motility.
  118. fluorescence microscope
    A microscope that exposes a specimen to light of a specific wavelength and then forms an image from the fluorescent light produced. Usually the specimen is stained with a fluorescent dye or fluorochrome.
  119. fomite
    An object that is not in itself harmful but is able to harbor and transmit pathogenic organisms. Also called fomes.
  120. saprophyte
    An organism that takes up nonliving organic nutrients in dissolved form and usually grows on decomposing organic matter.
  121. saprozoic nutrition
    Having the type of nutrition in which organic nutrients are taken up in dissolved form; normally refers to animals or animal-like organisms.
  122. scale
    A platelike organic structure found on the surface of some cells (chrysophytes).
  123. scanning electron microscope (SEM)
    An electron microscope that scans a beam of electrons over the surface of a specimen and forms an image of the surface from the electrons that are emitted by it.
  124. scanning probe microscope
    A microscope used to study surface features by moving a sharp probe over the object's surface (e.g., the scanning tunneling microscope).
  125. scanning tunneling microscope
    A type of scanning probe microscope used to image a surface by moving a fine probe over it at a constant height, which is maintained by keeping a constant electron flow (tunneling current) between the tip and surface.
  126. schizogony
    Multiple asexual fission.
  127. secondary metabolites
    Products of metabolism that are synthesized after growth has been completed.
  128. secondary treatment
    The biological degradation of dissolved organic matter in the process of sewage treatment; the organic material is either mineralized or changed to settleable solids.
  129. selective media
    Culture media that favor the growth of specific microorganisms; this may be accomplished by inhibiting the growth of undesired microorganisms.
  130. selective toxicity
    The ability of a chemotherapeutic agent to kill or inhibit a microbial pathogen while damaging the host as little as possible.
  131. sepsis
    Systemic response to infection. This systemic response is manifested by two or more of the following conditions as a result of infection: temperature .38 or ,36°C; heart rate .90 beats per min; respiratory rate .20 breaths per min, or pCO2 ,32 mm Hg; leukocyte count .12,000 cells per ml3 or .10% immature (band) forms. Sepsis also has been defined as the presence of pathogens or their toxins in blood and other tissues.
  132. septic shock
    Sepsis associated with severe hypotension despite adequate fluid resuscitation, along with the presence of perfusion abnormalities that may include, but are not limited to, lactic acidosis, oliguria, or an acute alteration in mental status. Gram-positive bacteria, fungi, and endotoxin-containing gram-negative bacteria can initiate the pathogenic cascade of sepsis leading to septic shock.
  133. serotyping
    A technique or serological procedure that is used to differentiate between strains (serovars or serotypes) of microorganisms that have differences in the antigenic composition of a structure or product.
  134. sex pilus
    A thin protein appendage required for bacterial mating or conjugation. The cell with sex pili donates DNA to recipient cells.
  135. sheath
    A hollow tubelike structure surrounding a chain of cells and present in several genera of bacteria.
  136. S-layer
    A regularly structured layer composed of protein or glycoprotein that lies on the surface of many bacteria. It may protect the bacterium and help give it shape and rigidity.
  137. slime
    The viscous extracellular glycoproteins or glycolipids produced by staphylococci and Pseudomonas aeruginosa bacteria that allows them to adhere to smooth surfaces such as prosthetic medical devices and catheters. More generally, the term often refers to an easily removed, diffuse, unorganized layer of extracellular material that surrounds a bacterial cell.
  138. slime layer
    A layer of diffuse, unorganized, easily removed material lying outside the bacterial cell wall.
  139. slime mold
    A common term for members of the divisions Acrasiomycota and Myxomycota.
  140. slow virus disease
    A progressive, pathological process caused by a transmissible agent (virus or prion) that remains clinically silent during a prolonged incubation period of months to years after which progressive clinical disease becomes apparent.
  141. Southern blotting technique
    The procedure used to isolate and identify DNA fragments from a complex mixture. The isolated, denatured fragments are transferred from an agarose electrophoretic gel to a nitrocellulose filter and identified by hybridization with probes.
  142. spermosphere
    The region surrounding a germinating seed where released organic matter stimulates microbial growth.
  143. spheroplast
    A relatively spherical cell formed by the weakening or partial removal of the rigid cell wall component (e.g., by penicillin treatment of gram-negative bacteria). Spheroplasts are usually osmotically sensitive.
  144. spirillum
    A rigid, spiral-shaped bacterium.
  145. spirochete
    A flexible, spiral-shaped bacterium with periplasmic flagella.
  146. spongiform encephalopathies
    Degenerative central nervous system diseases in which the brain has a spongy appearance; they appear due to prions.
  147. spontaneous generation
    The hypothesis that living organisms can arise from nonliving matter.
  148. spore
    A differentiated, specialized form that can be used for dissemination, for survival of adverse conditions because of its heat and dessication resistance, and/or for reproduction. Spores are usually unicellular and may develop into vegetative organisms or gametes. They may be produced asexually or sexually and are of many types.
  149. spread plate
    A petri dish of solid culture medium with isolated microbial colonies growing on its surface, which has been prepared by spreading a dilute microbial suspension evenly over the agar surface.
  150. stalk
    A nonliving bacterial appendage produced by the cell and extending from it.
  151. starter culture
    An inoculum, consisting of a mixture of carefully selected microorganisms, used to start a commercial fermentation.
  152. stationary phase
    The phase of microbial growth in a batch culture when population growth ceases and the growth curve levels off.
  153. sterilization
    The process by which all living cells, viable spores, viruses, and viroids are either destroyed or removed from an object or habitat.
  154. stigma
    A light-sensitive eyespot, which is found in some algae and photosynthetic protozoa; it is believed to be involved in phototaxis, at least in some cases.
  155. stoneworts
    A group of approximately 250 species of algae that have a complex growth pattern, with nodal regions from which whorls of branches arise; they are abundant in fresh to brackish waters.
  156. strain
    A population of organisms that descends from a single organism or pure culture isolate.
  157. streak plate
    A petri dish of solid culture medium with isolated microbial colonies growing on its surface, which has been prepared by spreading a microbial mixture over the agar surface, using an inoculating loop.
  158. stroma
    The chloroplast matrix that is the location of the photosynthetic carbon dioxide fixation reactions.
  159. stromatolite
    Dome-like microbial mat communities consisting of filamentous photosynthetic bacteria and occluded sediments (often calcareous or siliceous). They usually have a laminar structure. Many are fossilized, but some modern forms occur.
  160. superantigen
    Superantigens are bacterial proteins that stimulate the immune system much more extensively than do normal antigens. They stimulate T cells to proliferate nonspecifically through simultaneous interaction with class II MHC proteins on antigen-presenting cells and variable regions on the b chain of the T-cell receptor complex. Examples include streptococcal scarlet fever toxins, staphylococcal toxic shock syndrome toxin-1, and streptococcal M protein.
  161. superinfection
    A new bacterial or fungal infection of a patient that is resistant to the drug(s) being used for treatment.
  162. syntrophism
    The association in which the growth of one organism either depends on, or is improved by, the provision of one or more growth factors or nutrients by a neighboring organism. Sometimes both organisms benefit. This type of mutualism is also known as cross-feeding or the satellite phenomenon.
  163. teichoic acids (ti-ko_ik)
    Polymers of glycerol or ribitol joined by phosphates; they are found in the cell walls of gram-positive bacteria.
  164. temperate phages
    Bacteriophages that can infect bacteria and establish a lysogenic relationship rather than immediately lysing their hosts.
  165. test
    A loose-fitting shell of an amoeba.
  166. thallus
    A type of body that is devoid of root, stem, or leaf; characteristic of some algae, many fungi, and lichens.
  167. thermoacidophiles
    A group of bacteria that grow best at acid pHs and high temperatures; they are members of the Archaea.
  168. thermophile
    A microorganism that can grow at temperatures of 55°C or higher; the minimum is usually around 45°C.
  169. toxin
    A microbial product or component that can injure another cell or organism at low concentrations. Often the term refers to a poisonous protein, but toxins may be lipids and other substances.
  170. transduction (trans-duk_shun)
    The transfer of genes between bacteria by bacteriophages.
  171. transfer host (trans_fer)
    A host that is not necessary for the completion of a parasite's life cycle, but is used as a vehicle for reaching a final host.
  172. transformation (trans_for-ma_shun)
    A mode of gene transfer in bacteria in which a piece of free DNA is taken up by a bacterial cell and integrated into the recipient genome.
  173. transmission electron microscope (trans-mish_un)
    A microscope in which an image is formed by passing an electron beam through a specimen and focusing the scattered electrons with magnetic lenses.
  174. transposon
    A DNA segment that carries the genes required for transposition and moves about the chromosome; if it contains genes other than those required for transposition, it may be called a composite transposon. Often the name is reserved only for transposable elements that also contain genes unrelated to transposition.
  175. trichome
    A row or filament of bacterial cells that are in close contact with one another over a large area.
  176. tropism
    The movement of living organisms toward or away from a focus of heat, light, or other stimulus.
  177. tumble
    Random turning or tumbling movements made by bacteria when they stop moving in a straight line.
  178. ultramicrobacteria
    Bacteria that can exist normally in a miniaturized form or which are capable of miniaturization under low-nutrient conditions. They may be 0.2 mm or smaller in diameter.
  179. vaccine
    A preparation of either killed microorganisms; living, weakened (attenuated) microorganisms; or inactivated bacterial toxins (toxoids). It is administered to induce development of the immune response and protect the individual against a pathogen or a toxin.
  180. vector
    1. In genetic engineering, another name for a cloning vector. A DNA molecule that can replicate (a replicon) and is used to transport a piece of inserted foreign DNA, such as a gene, into a recipient cell. It may be a plasmid, phage, cosmid or artificial chromosome. 2. In epidemiology, it is a living organism, usually an arthropod or other animal, that transfers an infective agent from one host to another.
  181. vibrio
    A rod-shaped bacterial cell that is curved to form a comma or an incomplete spiral.
  182. viricide
    An agent that inactivates viruses so that they cannot reproduce within host cells.
  183. virion
    A complete virus particle that represents the extracellular phase of the virus life cycle; at the simplest, it consists of a protein capsid surrounding a single nucleic acid molecule.
  184. virioplankton
    Viruses that occur in waters; high levels are found in marine and freshwater environments.
  185. viroid
    An infectious agent of plants that is a single-stranded RNA not associated with any protein; the RNA does not code for any proteins and is not translated.
  186. virulent bacteriophages (vir_u-lent bak-te_re-o-føajs²)
    Bacteriophages that lyse their host cells during the reproductive cycle.
  187. virus
    An infectious agent having a simple acellular organization with a protein coat and a single type of nucleic acid, lacking independent metabolism, and reproducing only within living host cells.
  188. water mold
    A common term for a member of the division Oomycota.
  189. whole-organism vaccine
    A vaccine made from complete pathogens, which can be of four types: inactivated viruses; attenuated viruses; killed microorganisms; and live, attenuated microorganisms.
  190. xerophilic microorganisms (ze²ro-fil_ik)
    Microorganisms that grow best under low aw conditions, and may not be able to grow at high aw values.
  191. yeast
    A unicellular fungus that has a single nucleus and reproduces either asexually by budding or fission, or sexually through spore formation.
  192. zooflagellates
    Flagellate protozoa that do not have chlorophyll and are either holozoic, saprozoic, or symbiotic.
  193. zooplankton
    A community of floating, aquatic, minute animals and nonphotosynthetic protists.
  194. zooxanthella
    A dinoflagellate found living symbiotically within cnidarians and other invertebrates.
  195. zygomycetes
    A division of fungi that usually has a coenocytic mycelium with chitinous cell walls. Sexual reproduction normally involves the formation of zygospores. The group lacks motile spores.

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