Viral Structure and Replication
Viruses are noncellular genetic elements that use a living cell for their replication and have an extracellular state. Viruses are ultramicroscopic particles containing nucleic acid surrounded by protein, and in some cases, other macromolecular components such as a membranelike envelope.At present, there are no technical names for viruses. International committees have recommended genus and family names for certain viruses, but the process is still in a developmental stage.
Viruses vary considerably in size and shape. The smallest viruses are about 0.02 μm (20 nanometers), while the large viruses measure about 0.3 μm (300 nanometers). Smallpox viruses are among the largest viruses; polio viruses are among the smallest.
Viral structure. Certain viruses contain ribonucleic acid (RNA), while other viruses have deoxyribonucleic acid (DNA). The nucleic acid portion of the viruses is known as the genome. The nucleic acid may be single-stranded or double-stranded; it may be linear or a closed loop; it may be continuous or occur in segments.
The genome of the virus is surrounded by a protein coat known as a capsid, which is formed from a number of individual protein molecules called capsomeres. Capsomeres are arranged in a precise and highly repetitive pattern around the nucleic acid. A single type of capsomere or several chemically distinct types may make up the capsid. The combination of genome and capsid is called the viral nucleocapsid.
A number of kinds of viruses contain envelopes. An envelope is a membranelike structure that encloses the nucleocapsid and is obtained from a host cell during the replication process. The envelope contains viral-specified proteins that make it unique. Among the envelope viruses are those of herpes simplex, chickenpox, and infectious mononucleosis.
The nucleocapsids of viruses are constructed according to certain symmetrical patterns. The virus that causes tobacco mosaic disease, for example, has helical symmetry. In this case, the nucleocapsid is wound like a tightly coiled spiral. The rabies virus also has helical symmetry. Other viruses take the shape of an icosahedron, and they are said to have icosahedral symmetry. In an icosahedron, the capsid is composed of 20 faces, each shaped as an equilateral triangle (Figure 1 ). Among the icosahedral viruses are those that cause yellow fever, polio, and head colds.
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Bacteriophages are viruses that multiply within bacteria. These viruses are among the more complex viruses. They often have icosahedral heads and helical tails. The virus that attacks and replicates in Escherichia coli has 20 different proteins in its helical tail and a set of numerous fibers and “pins.” Bacteriophages contain DNA and are important tools for viral research.
Viral replication. During the process of viral replication, a virus induces a living host cell to synthesize the essential components for the synthesis of new viral particles. The particles are then assembled into the correct structure, and the newly formed virions escape from the cell to infect other cells.
The first step in the replication process is attachment. In this step, the virus adsorbs to a susceptible host cell. High specificity exists between virus and cell, and the envelope spikes may unite with cell surface receptors. Receptors may exist on bacterial pili or flagella or on the host cell membrane.
The next step is penetration of the virus or the viral genome into the cell. This step may occur by phagocytosis; or the envelope of the virus may blend with the cell membrane; or the virus may “inject” its genome into the host cell. The latter situation occurs with the bacteriophage when the tail of the phage unites with the bacterial cell wall and enzymes open a hole in the wall. The DNA of the phage penetrates through this hole.
The replication steps of the process occur next. The protein capsid is stripped away from the genome, and the genome is freed in the cell cytoplasm. If the genome consists of RNA, the genome acts as a messenger RNA molecule and provides the genetic codes for the synthesis of enzymes. The enzymes are used for the synthesis of viral genomes and capsomeres and the assembly of these components into new viruses. If the viral genome consists of DNA, it provides the genetic code for the synthesis of messenger RNA molecules, and the process proceeds.
In some cases, such as in HIV infection (as discussed below), the RNA of the virus serves as a template for the synthesis of a DNA molecule. The enzyme reverse transcriptase catalyzes the DNA's production. The DNA molecule then remains as part of the host cell's chromosome for an unspecified period. From this location, it encodes messenger RNA molecules for the synthesis of enzymes and viral components.
Once the viral genomes and capsomeres have been synthesized, they are assembled to form new virions. This assembly may take place in the cytoplasm or in the nucleus of the host cell. After the assembly is complete, the virions are ready to be released into the environment (Figure 2 ).
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Lysogeny. Not all viruses multiply by the lytic cycle of reproduction. Certain viruses remain active within their host cells for a long period without replicating. This cycle is called the lysogenic cycle. The viruses are called temperate viruses, or proviruses, because they do not bring death to the host cell immediately.
In lysogeny, the temperate virus exists in a latent form within the host cell and is usually integrated into the chromosome. Bacteriophages that remain latent within their bacterial host cell are called prophages. This process is a key element in the recombination process known as transduction.
An example of lysogeny occurs in HIV infection. In this case, the human immunodeficiency virus remains latent within the host T-lymphocyte. An individual whose infection is at this stage will not experience the symptoms of AIDS until a later date.
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(1) Chapter Title: Growth and Culturing of Bacteria
(a) "Because individual cells grow larger only to divide into new individuals, microbial growth is defined not in terms of cell size but as the increase in the number of cells, which occurs by cell division."
(b) This emphasis has practical application since it is typically far easier to measure increases in cell number than it is to measure increases in cell size
(c) Furthermore, unless cell division is synchronized, cells will typically vary in size across an even homogeneous population, thus making measurement of cell size almost irrelevant as a means of measuring microbial growth
(d) Some general external links: [microbial growth (Google Search)] [microbial growth (with nice graphics) (David H. Demezas )] [Microbial Growth Dynamics (a book)] [microbial growth theory for biotreatment] [effects of random motility on microbial growth and competition in a flow reactor] [index]
(a) The majority of bacteria reproduce by a mechanism termed binary fission
(b) Binary fission is much simpler than the mechanisms of cell division seen in eucaryotic cells
(c) See Figure 6.1, Binary fission
(d) [binary transverse fission] [binary fission (nice cartoon illustration)] [index]
(e) (if there are two fish in a lake, and one of them is dead, that�s called binary fishin�)
(f) [binary fission (Google Search)] [index]
(a) Tetrads are a cell arrangement that is a consequence of binary fission not resulting in complete separation of cells, and that occurs in two planes, thus producing a square consisting of four cocci, one at each corner
(a) Sarcina are a cell arrangement that is a consequence of binary fission that does not result in complete separation of cells, and that occurs in three planes, thus producing cubes consisting of eight cocci, one coccus at each corner
(a) Bacteria added to fresh media typically go through four more-or-less distinct phases of growth
(i) Lag phase (A)
(iii) Stationary phase (C)
(iv) Decline (death) phase (D)
(b) 
(d) See Figure 6.3, A standard bacterial growth curve
(a) Transfers of bacteria from one medium to another, where there exist chemical differences between the two media, typically results in a lag in cell division
(b) This lag in division is associated with a physiological adaptation to the new environment, by the cells, prior to their resumption of division
(c) That is, cells may increase in size during this time, but simply do not undergo binary fission
(d) [lag phase (Google Search)] [index]
(a) Lag phase is followed by log phase during which binary fission occurs
(b) This phase of growth is called logarithmic or exponential because the rate of increase in cell number is a multiplicative function of cell number
(c) This can be seen in a graph of cell number versus time where cell numbers increase at ever increasing rates with time or generation; that is, the rate of increase is a function of absolute cell number such that the more cells present, the faster the population of cells increases in size (at least, during log phase)
(d) See Figure 6.4, Nonsynchronous growth
(e) When graphed on semi-log graph paper (Figure 6.3, i.e., log cell number versus time), log-phase growth produces a straight line
(f) [log phase, exponential phase, logarithmic phase (Google Search)] [illustration, exponential growth] [exponential growth rate (a student activity)] [index]
(a) A means of keeping cultures in log phase can be accomplished either by employing a chemostat or via serial transfer
(b) A chemostat involves adding fresh medium to a culture, mixing, and then allowing an equal volume of culture to drain from the vessel; this is typically done continuously (i.e., a steady stream of fresh medium is added)
(c) Serial transfer means taking a volume of culture and diluting that volume into fresh media
(a) Generation time it takes a bacterial population to double in size (number) during log-phase growth
(b) Note that the time it takes for the population to double in size does not change with cell number (so long as cells remain in log phase)
(c) That is, with exponential growth, the absolute increase in cell number increases as cell number increases while the relative increase remains invariant
(d) Typically, generation times range from 20 minutes to 20 hours depending on the bacterial species/strain and the conditions during which log-phase growth is occurring
(e) ["generation time" and bacteria (Google Search)] [index]
(a) Stationary phase is a steady-state equilibrium where the rate of cell growth (division) is exactly balanced by the rate of cell death (i.e., increase in cell number due to cell divisions exactly balanced by a decrease in cell number due to death)
(b) Cell death (or, at least, lack of cell growth) occurs because of a loss of limiting nutrients (due to their incorporation into cells during log-phase growth) or a build-up of toxins (due to their release during log-phase growth, e.g., fermentative products)
(c) Note that the simplest conditions that will result in a stationary phase is when both the rate of cell increase and the rate of cell death together equal zero (i.e., cells neither die nor are born)
(d) [stationary phase (Google Search)] [index]
(a) Stationary phase, in a standard bacterial growth curve, is followed by a die-off of cells
(b) Cell death in bacteria cultures basically means that the cells are unable to resume division following their transfer to new environments
(c) Typically this die-off occurs exponentially, i.e., such that cell number graphed against time, using a semi-log scale for cell number, results in a straight line (i.e., see Figure 6.3)
(d) This death occurs because vegetative cells can survive exposure to harsh conditions (few nutrients or too-many toxins) for only so long
Stop material covered this day; Start material below next day
(a) Solid media contains agar, which is a compound that goes into water solution at temperatures approaching boiling, and then, once in solution, solidifies the medium at room (<40�C) temperature
(b) Subsequent exposure to high temperature (i.e., boiling) will melt the medium
(c) Exposure to relatively low temperatures (i.e., >40�C), however, will not melt the medium, thus allowing incubation of solid medium at various temperatures (compare to gelatin which liquefies at 37�C)
(d) Once boiled, agar-containing medium will stay liquid at 45�C
(e) This allows solid medium to be poured into various vessels at temperatures that will not kill most cells (nor melt vessels), followed by a solidification of the medium
(f) 
(g) ["solid medium" and bacteria (Google Search)] [index]
(a) Colonies represent piles of cells descended, assuming pure culture technique and sufficiently few colonies on a single plate, from a single parent cell, all growing on or in a solid medium
(b) 
(c) The four phases of bacterial growth can be observed within a single colony, with the edges displaying lag and log phases and the interior can display stationary and then decline phases
(d) Various colony morphologies (no need to memorize):
(e) 
(f) 
(g) [bacterial colony (Google Search)] [index]
(a) The pour-plate method is employed for bacterial-cell enumeration and isolation
(b) In the pour-plate method of addition of cells to solid medium contained within a petri dish, cells are added to melted (but not too hot) solid medium
(c) The melted solid medium is then poured into a petri dish and allowed to harden
(d) Colonies appear both within, beneath, and on top of the agar
(e) See Figure 6.7, Calculation of the number of bacteria per milliliter of culture using serial dilution
(f) [pour plate (Google Search)] [index]
(a) The spread plate method is employed for bacterial-cell enumeration and isolation
(b) In the spread-plate method of addition of cells to solid medium, a small volume of culture is dropped onto the surface of agar that has already hardened in a petri dish
(c) The volume is then spread around the agar surface
(d) Colonies will grow solely on the surface of the agar
(e) This technique is advantageous particularly when cells are sensitive to exposure to relatively high temperatures plus the method does not require a prior melting of the solid medium
(f) See Figure 6.7, Calculation of the number of bacteria per milliliter of culture using serial dilution
(g) [spread plate (Google Search)] [index]
(a) When bacteria are placed on a solid medium, ideally each colony is founded by only a single bacterial cell (obviously, given clumping and various cell arrangements, this ideal is not always met)
(b) Thus, addition of a known quantity of bacterial cells to a solid medium should produce the same number of colonies
(c) This result can be employed backward so that the number of colonies grown on solid medium can be used to estimate the number of individual bacteria that were added to the solid medium
(d) This number, in turn, may be employed to estimate the concentration of bacteria present in a culture
(a) Whether a single cell or a clump of cells or whatever, what grows into an isolated colony is termed a colony-forming unit
(b) When doing standard plate counts, what is being estimated are numbers of colony-forming units
(c) The number of colonies that may be counted per petri dish (and therefore the number CFUs that may be enumerated) is limited by statistics (at the low end) and space on the dish (at the upper end) to between 30 and 300 colonies/CFUs per plate
(d) See Figure 6.8, Counting colonies
(e) [colony-forming unit (Google Search)] [index]
(a) For a given agar surface, there are only so many colonies that may be present before it becomes impossible to accurately count the number of colonies present
(b) This number serves as a limit on the concentration of bacteria in cultures that may be enumerated using the standard plate-count technique
(c) How to get around this limitation? This may be achieved by diluting cultures before enumerating them
(d) By keeping track numerically of the degree of diluting employed, the concentration of bacteria in the pre-diluted culture may be estimated
(e) Due to limitations in the size of the volumes that may be conveniently handled (i.e., both very large volumes and very small volumes are difficult to handle), relatively large dilutions are typically handled serially
(f) For example, a 10-fold dilution followed by a second 10-fold dilution (i.e., 1 ml from a parent culture diluted to 9 ml diluent followed by mixing followed by 1 ml from the diluted culture diluted to an additional 9 ml diluent followed by mixing) gives a total of a 100-fold dilution
(g) 
(h) See Figure 6.6, Serial dilution
(i) See Figure 6.7, Calculation of the number of bacteria per milliliter of culture using serial dilution
(j) [serial dilution (Google Search)] [index]
(a) A more direct means of enumerating bacteria is done by viewing them through a microscope
(b) This method's limitations are that only relatively high concentrations of bacteria may be enumerated and the method cannot distinguish living from dead bacteria
(c) See Figure 6.9, The Petroff-Hausser counting chamber
(d) [direct microscopic count (Google Search)] [index]
(a) Organisms that cannot grow on solid media can still be enumerated using the most probable number method
(b) Once again, cultures are diluted, here into a suitable broth medium
(c) "The more tubes that show growth, especially at greater dilutions, the more organisms were present in the sample."
(d) Particularly, at some greater dilution there will be on average no organisms added per tube of broth, while at lesser dilutions there will be organisms in every tube; the middle dilution at which the transition is made from all tubes inoculated with organism to few or none represents approximately the inverse of the concentration of organisms in the original culture
(e) See Figure 6.10, A most probable number (MPN) test
(a) The degree of turbidity (cloudiness) exhibited by a broth culture gives an indication of the number of organisms present
(b) Degree of turbidity varies with organisms, conditions, and phase of growth so use of turbidity as a form of enumeration requires previous standardization
(c) As with direct microscopic counts, use of turbidity is limited to relatively high cell concentrations
(d) [culture turbidity (Google Search)] [microbial growth monitors] [index]
(a) The rate of use of substrates or liberation of metabolic products also can be employed as methods of enumeration, though just as with turbidity, prior standardization is necessary
(a) A time-consuming method of culture-mass determination involves drying cells (removing water) and then weighing them
(b) ["dry weight" and bacteria (Google Search)] [index]
(a) "The kinds of organisms found in a given environment and the rates at which they grow can be influenced by a variety of factors, both physical and biochemical. Physical factors include pH, temperature, oxygen concentration, moisture, hydrostatic pressure, osmotic pressure, and radiation. Nutritional (biochemical) factors include availability of carbon, nitrogen, sulfur, phosphorus, trace elements, and, in some cases, vitamins."
(a) Recall that the pH scale measures hydrogen ion (H+) concentration and that low pHs correspond with high concentrations of hydrogen ion, neutral pH with equal numbers of hydrogen and hydroxyl ions (OH-), and high pHs correspond to low concentrations of hydrogen ion
(a) Optimum pH is that pH at which a given organism grows best
(b) The range over which most organisms can grow tends to vary over no more than a single pH unit in either direction (e.g., from pH 6 to pH 8 for an organism whose pH optimum is pH 7)
(c) ["optimum pH" and bacteria (Google Search)] [index]
(a) Organisms whose optimum pH is relatively to highly acidic
(b) [acidophile (Google Search)] [index]
(a) Organisms whose optimum pH ranges about pH 7, plus or minus approximately 1.5 pH units
(b) [neutrophile and bacteria (Google Search)] [index]
(a) Organisms whose optimum pH is relatively to highly basic
(b) [alkaphile (very few hits) (Google Search)] [index]
(a) Optimum temperature is the temperature at which an organism grows best
(b) See Figure 6.14, Growth rates of psychrophilic, mesophilic, and thermophilic bacteria
(c) Typically the range in temperature over which a bacterium can grow is about 30�C
(a) Cold-adapted organisms are called psychrophiles
(b) The cut-off temperature for a psychrophile is a 20�C or colder temperature optimum
(c) Psychrophiles may additionally be termed obligate or facultative with obligate psychrophiles unable to grow above 20�C, but facultative psychrophiles are able to
(d) [psychrophile (Google Search)] [index]
(a) Organisms whose optimum growth temperatures is found between 20�C to 40�C are termed mesophiles
(b) Human pathogens, which must be able to grow at the approximately 37�C body temperature, are mesophiles
(c) [mesophile (Google Search)] [index]
(a) Mesophilic organisms that can endure brief exposures to relatively high temperatures are termed thermoduric
(b) These are one category of the organisms that survive following inadequate heating of foods and may thereby contribute to the spoilage of foods that have been heated (e.g., Pasteurization) to kill microorganisms
(c) [thermoduric (Google Search)] [index]
(a) High-temperature-adapted organisms are called thermophiles
(b) [thermophile (Google Search)] [index]
(a) Organisms differ in their requirements of molecular oxygen (i.e., O2) as well as other atmospheric gasses (e.g., carbon dioxide)
(b) Categories of oxygen requirements include:
(i) Obligate aerobes
(ii) Obligate anaerobes
(iii) Microaerophiles
(vi) Strict anaerobes
(c) See Figure 6.15, Patterns of oxygen use
(a) Organisms that are unable to generate ATP via fermentation are termed obligate aerobes
(b) This term is somewhat misleading because some of these organisms can still grow in the absence of molecular oxygen by employing alternative final electron acceptors to their electron transport systems
(c) The bottom line, then, for an obligate aerobe is a dependence on an electron transport system for their generation of ATP as well as a tolerance for atmospheric oxygen (which otherwise can serve as a poison)
(d) [obligate aerobe (Google Search)] [index]
(a) Organisms that are unable to detoxify atmospheric oxygen are termed obligate anaerobes because they cannot grow (nor, often, even survive) in the presence of oxygen
(b) Obviously, obligate anaerobes must possess means for ATP generation that do not require molecular oxygen, e.g., fermentation pathways
(c) [obligate anaerobe (Google Search)] [index]
(a) These are organisms that grow best when small amounts of oxygen are present
(b) That is, less (typically much less) than atmospheric concentrations, but more than those concentrations tolerable by obligate anaerobes
(c) [microaerophile (Google Search)] [index]
(a) Facultative anaerobes can generate ATP by either aerobic or anaerobic means and have the means to detoxify oxygen
(b) These organisms tend to exist in environments in which oxygen concentrations are uncertain, and serve as the oxygen scavengers in environments displaying relatively low oxygen concentrations
(c) For example, the lumen of the large intestine is mostly anaerobic because (i) the body does not actively oxygenate the lumen of the large intestine and (ii) oxygen scavengers such as Escherichia coli remove what oxygen manages to leak into this environment
(d) Facultative anaerobes tend to grow better/faster when O2 is present
(e) [facultative anaerobe (Google Search)] [index]
(a) These are organisms that are unable to utilize molecular oxygen in their ATP generation but otherwise possess the means to detoxify oxygen
(b) This allows, if nothing else, the safe passage of these organisms through aerobic environments
(c) Lactobacillus spp. for example generate their ATPs by fermentation regardless of the oxygen concentrations of the environment
(d) [aerotolerant anaerobe (Google Search)] [index]
(a) A strict anaerobe is unable to replicate, and may even die given the presence of oxygen
(b) This inability or fragility results from a lack of enzymes necessary to detoxify molecular oxygen
(c) [strict anaerobe (Google Search)] [index]
| Sample question: Full credit for 13 entered correctly (with credit off for incorrect entries):
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(a) These are organisms whose optimum growth requires relatively high concentrations of carbon dioxide
(b) [capnophiles (Google Search)] [index]
(a) The concentration of dissolved substances in the environment can impact on the growth and survival of cells
(a) Environments containing large concentrations of dissolved substances draw water out of cells, causing a shrinkage of the cytoplasm volume, a phenomenon termed plasmolysis
(b) Plasmolysis interferes with growth and this is why highly osmotic environments prevent bacterial growth (e.g., brine, the high sugar concentrations in jellies and jams, salting of meats)
(c) [plasmolysis and bacteria (Google Search)] [index]
(a) Organisms that require high concentrations of dissolved salts to grow are termed halophiles
(b) Depending on organism, the salt concentrations required range from those of sea water on up to those of brine
(c) [halophiles (Google Search)] [index]
(a) All microorganisms require the following nutrients to grow, repair themselves, and to replicate:
(i) Carbon
(ii) Nitrogen
(iii) Sulfur
(iv) Phosphorus
(v) Various trace elements
(b) In addition, some microorganisms require various vitamins as well as additional organic factors (e.g., specific amino acids)
(c) "Although we are concerned with ways microorganisms satisfy their own nutritional needs, we can note that in satisfying such needs, they also help recycle elements in the environment."
(i) That is, microorganisms are typically able to obtain nutrients from sources that macroorganisms are not
(a) Microorganisms whose nutritional needs are unusually complex are termed fastidious
(b) [fastidious and bacteria (Google Search)] [index]
(a) Nitrogen may be obtained from inorganic sources (e.g., nitrate ions, NO3-, or ammonium ion, NH4+) or from organic sources (i.e., amino acids or nucleotides)
(b) In contrast, organisms such as ourselves obtain nitrogen solely from organic sources
(c) Many microorganisms (e.g., E. coli) can satisfy all of their nitrogen needs from inorganic sources
(d) Fastidious microorganisms may require one or more amino acid in their growth medium because they are unable to synthesize that amino acid (just as we have various essential amino acids that we must obtain from our diet because we are unable to synthesize them ourselves)
(a) Like nitrogen, sulfur may be obtained from organic sources (sulfur-containing amino acids) or from inorganic sources
(a) Unlike nitrogen and sulfur, phosphorous is typically obtained by microorganisms in its inorganic form, i.e., the phosphate ion (PO43-).
(a) Trace elements are required in relatively small quantities
(b) Typically these elements are employed as enzyme cofactors, e.g., metals to which enzymes must complex with in order to function properly
(a) Vitamins are essentially organic equivalents of trace elements, i.e., organic molecules required in relatively small amounts which various enzymes must complex with in order to function properly
(b) While many microorganism can synthesize vitamins, others cannot and an inability to synthesize vitamins contributes to an organism's fastidiousness since vitamins consequently must be supplied in the organism's growth medium
(a) Microorganisms employ enzymes as well as transport proteins to bring substances into their cytoplasm to either be broken down in catabolic reactions or used as building blocks to produce more complex substances via anabolic pathways
(b) If an organism possesses sufficient kinds of enzymes, they can break down or build up just about anything, though no organism possesses all possible enzymes so consequently no organism is capable of breaking down nor building up everything
(c) In addition to enzymes found within their cells, many bacteria (as well as fungi and ourselves) produce enzymes that are secreted from cells into the surrounding medium
(d) These enzymes typically are employed to break down nutrients found outside of cells (extracellularly) so that the breakdown products may be taken up into the cell and used
(e) Many of these enzymes are harmful and represent exotoxins produced by disease-causing microorganisms, especially Gram-positive bacteria
(f) [exoenzyme (Google Search)] [index]
(a) To some extent equivalent to the exoenzymes used by Gram-positive bacteria, Gram-negative bacteria employ enzymes secreted into their periplasm to break down large molecules before those molecules are brought across the plasma membrane and into the cytoplasm
(b) [periplasmic enzymes (Google Search)] [index]
(a) To successfully grow microorganisms, one must employ a culture medium that contains all of the nutrients required by an organism (as well as conditions that meet an organism's physical requirements)
(b) Media may be differentiated in various ways
(c) [culture medium (Google Search)] [index]
(a) Broth media is liquid while solid media typically has agar added as a solidifying agent
(b) Semi-solid media also exists that contains insufficient quantities of agar to fully solidify the media
(a) A synthetic medium is prepared in the laboratory from reasonably well-defined ingredients
(b) By contrast, a not synthetic medium could be something like soil or sewage or ocean mud, i.e., something obtained directly from the environment
(c) [synthetic medium (Google Search)] [index]
(a) A defined synthetic medium is produced only from well-defined, relatively pure ingredients
(b) See Table 6.2, A defined synthetic medium for growing Proteus vulgaris
(c) See Table 6.3, A defined synthetic medium for growing the fastidious bacterium Leuconostoc mesenteroides
(d) [defined synthetic medium (Google Search)] [index]
(a) A second approach to producing a synthetic medium is to employ ingredients that are not well-defined nor pure
(b) Such ingredients additionally may vary from batch to batch
(c) For example, complex media may contain extracts from animals (e.g., beef, hearts, milk, etc.), plants (e.g., soy beans), or microorganisms (e.g., yeast)
(d) Complex media may additionally include very complex ingredients such as blood
(e) ["complex media" and bacteria (Google Search)] [index]
(a) Selective media acts to inhibit the growth of certain kinds of microorganisms while allowing the growth of other
(b) [selective media (Google Search)] [index]
(a) Differential media contains ingredients that allow different microorganisms to look reproducibly different
(b) Consequently, one may determine whether a given organism is present in a culture on the basis of colony morphology alone
(c) Confusingly, many media employed in microbiological laboratories are both differential and selective
(d) That is, many media both inhibit the growth of certain microorganisms while making those organisms that it allows to grow produce easily differentiated colony morphologies
(e) See Table 6.5, Selected examples of diagnostic media
(f) [differential media (Google Search)] [index]
(a) Acidophiles
(c) Alkaphiles
(d) Binary fission
(g) Capnophiles
(h) CFU
(j) Colonies
(l) Complex media
(n) Culture medium
(o) Death phase
(p) Decline phase
(t) Dry weight
(u) Exoenzymes
(y) Fastidious
(z) Generation time
(aa) Halophiles
(bb) Lag phase
(cc) Log phase
(dd) Logarithmic phase
(ee) Mesophile
(ff) Microaerophile
(gg) Microbial growth
(ii) MPN
(jj) Neutrophiles
(kk) Nitrogen sources
(ll) Nutritional factors
(mm) Obligate aerobe
(nn) Obligate anaerobe
(oo) Optimum pH
(pp) Optimum temperature
(rr) Oxygen requirements
(ss) Periplasmic enzymes
(tt) pH
(uu) Phosphorous
(vv) Plasmolysis
(xx) Psychrophile
(yy) Sarcinae
(zz) Selective media
(aaa) Serial dilution
(bbb) Serial transfer
(ccc) Solid medium
(ddd) Spread plate
(fff) Standard plate count
(ggg) Stationary phase
(hhh) Strict anaerobe
(iii) Sulfur
(kkk) Tetrad
(mmm) Thermophile
(nnn) Trace elements
(ooo) Turbidity
(ppp) Vitamins
