Microbial Growth and Regulation
Taq polymerase
A DNA polymerase isolated from Thermus aquaticus that is used to automate the repetitive steps in the polymerase chain reaction
Biofilm
A attached polysaccharide matrix containing embedded bacterial cells; a common form for growth due to their protection from harmful chemicals and bacterial grazing
Bactericidal
A chemical agent that kills bacteria
Fungicidal
A chemical agent that kills fungi
Viricidal
A chemical agent that kills viruses
Thioglycolate
A complex medium containing a small amount of agar to make the medium viscous but still fluid; commonly used to test an organism's requirements for oxygen
Depth filter
A fibrous sheet made from an array of overlapping glass fibers that trap particles in their network; important in biosafety applications such as biological safety cabinets
Exponential phase
A growing cell population doubles at regular intervals and is typically at its healthiest state
Compatible solute
A highly water-soluble organic molecule (such as a sugar, alcohol, or amino acid derivative) that can be increased in the cell to maintain a positive water balance without inhibiting biochemical processes
Pour-plate method
A known volume of culture is pipetted into a sterile Petri plate; molten agar medium is then added and gently mixed before allowing the agar to solidify
Turbidity
A measure of how much light is scattered by cells in a suspension
Differential medium
A medium to which an indicator is added, which reveals by a color change whether a particular metabolic reaction has occurred during growth; widely used in clinical diagnostics and microbial taxonomy
Methanopyrus
A methane-producing genus of Archaea capable of growth up to 122 degrees Celsius
.2 micrometers
A minimum requirement for pore size when sterilizing via filtration; will not trap most viruses
Antimicrobial agent
A natural or synthetic chemical that kills or inhibits the growth of microorgainsms
Colony-forming units
A number of separable cells on the surface of a semisolid agar medium that create a visible colony
Circumneutral
A pH from 5.5 to 7.9
Pasteurization
A process developed by Louis Pasteur that uses heat to significantly reduce rather than totally eliminate the microorganisms found in liquids such as milk; kills pathogenic bacteria and increases the shelf life of perishable liquids
Disinfection
A process that directly targets pathogens, although it may not eliminate all microorganisms
Resazurin
A redox indicator dye present in thioglycolate broth to signal oxic reactions; pink when oxidized and colorless when reduced
Growth
A result of cell division; the ultimate process in the life of a microbial cell; an increase in the number of cells
Autoclave
A sealed heating device that uses steam under pressure to kill microorganisms
Aseptic technique
A series of steps to prevent contamination during manipulations of cultures and sterile culture media, both liquid and solid
Nucleopore filter
A type of membrane filter made from a polycarbonate film that is treated with radiation and then etched with a chemical, yielding very uniform holes; commonly used to isolate specimens for scanning electron microscopy
Cold shock proteins
A type of molecular chaperone that functions to maintain cold-sensitive proteins in an active form and bind specific mRNAs to facilitate their translation under cold conditions
Spread-plate method
A volume of an appropriately diluted culture is spread over the surface of an agar plate using a sterile glass spreader
Reducing agent
Added to anoxic vessels to remove traces of oxygen by reducing it to water
Microaerophiles
Aerobes that can use oxygen only when it is present at levels reduced from that in air due to their limited capacity for respiration or dependency on oxygen-sensitive molecules
Agar
An algal polysaccharide used to solidify solid media
Bacillus firmus
An alkaliphilic organism that has an unusually broad range for growth (pH 7.5 to 11); uses sodium rather than protons to drive transport reactions and rotate its flagellum but continues to rely on the proton motive force for its ATP synthesis
Superoxide reductase
An enzyme found in some strictly anaerobic Archaea and Bacteria that reduces superoxide to hydrogen peroxide without the production of oxygen gas
Superoxide dismutase
An enzyme that generates hydrogen peroxide and oxygen from two molecules of superoxide
Spectrophotometer
An instrument that passes light through a cell suspension and measures the unscattered light that emerges; used to measure turbidity
Continuous culture device
An open system in which a known volume of sterile medium is added at a constant rate while an equal volume of spent culture medium is removed at the same rate
Batch culture
An organism growing in an enclosed vessel, such as a tube or flask
Aerobes
Can grow at full oxygen tensions and respire oxygen in their metabolism
Binary fission
Cells elongate to approximately twice their original length and form a partition that constricts the cell into two daughter cells
Disinfectants
Chemicals that kill microorganisms but not necessarily endospores; primarily used on surfaces
Antiseptics/germicides
Chemicals that kill or inhibit the growth of microorganisms but are sufficiently nontoxic to be applied to living tissues; used for hand washing or for treating surface wounds
Buffers
Commonly added to culture media along with nutrients required for growth in order to keep the media at an optimal pH
Selective medium
Contains compounds that inhibit the growth of some microorganisms but to others
Viable
Describes a cell that is able to divide and form offspring
Bacteriostatic
Describes a chemical agent that does not kill but only inhibits the growth of bacteria
Fungistatic
Describes a chemical agent that does not kill but only inhibits the growth of fungi
Viristatic
Describes a chemical agent that does not kill but only inhibits the growth of viruses
Bacteriolytic
Describes a chemical agent that lyses cells
Halotolerant
Describes organisms that can tolerate some level of dissolved solutes but grow best in the absence of the added solute
pH
Describes the acidity or alkalinity of a solution on a logarithmic scale
Sterilants
Destroy all microorganisms, including endospores
Budding division
Division that occurs as a result of unequal cell growth; forms a totally new daughter cell with the mother cell retaining its original identity
Ionizing radiation
Electromagnetic radiation of sufficient energy to produce ions and other reactive molecular species from molecules with which the radiation particles collide; typically generated from X-ray sources or radioactive nuclides
Cold sterilization
Employs gases such as ethylene oxide or aldehydes such as formaldehyde or glutaraldehyde to sterilize medical devices
Catalase
Enzyme that attacks hydrogen peroxide to form oxygen
Peroxidase
Enzyme that attacks hydrogen peroxide to form water
Viable/plate count
Estimation of the size of a microbial population based upon the number of colonies formed when diluted samples are plated onto agar media
Dilution rate
Expressed as the flow rate divided by the culture volume
Instantaneous growth rate constant
Expresses the rate at which the population is growing at any instant; expressed in units of reciprocal hours; a function of the number of cells at a given time multiplied by k
Water activity (aw)
Expresses water availability as a ratio of the vapor pressure of air in equilibrium with a substance or solution to the vapor pressure of pure water
Intercalary growth
Formation of new cell wall material throughout the whole cell, as in binary fission
Polyunsaturated fatty acids
Found in the membranes of some psychrophilic bacteria; remain flexible even at very cold temperatures
Extreme halophiles
Halophiles capable of growth in very salty environments; typically require 15-30% NaCl for optimal growth
Ultraviolet radiation
Has a wavelength between 220 to 300 nanometers; is absorbed by DNA and can cause mutations that lead to death of the exposed organisms; useful for disinfecting surfaces and air but has very poor penetrating power
Yellowstone National Park, Wyoming
Has the largest concentration of hot springs in the world
HEPA filter
High-efficiency particulate air filter; typically remove .3-micrometer or larger particles from an airstream with an efficiency of greater than 99.9%; a type of depth filter
Hydrothermal vents
Hot springs at the bottom of the ocean
Cryoprotectants
Include dedicated antifreeze proteins or specific solutes that are produced in large amounts at cold temperatures to prevent the formation of ice crystals that can puncture the cytoplasmic membrane
Lag phase
Intense activity preparing for population growth, but no increase in population
Sanitizers
Less harsh than disinfectants and reduce microbial numbers but do not sterilize; widely used in the food industry
Complex media
Made from digests of microbial, animal, or plant products (such as casein, beef extract, tryptic soy broth, or yeast extract); disadvantage of using it is that its exact nutritional composition is unknown
Psychrotolerant
Microbes that grow at zero degrees Celsius but have optima of 20 to 40 degrees Celsius
Alkaliphiles
Microorganisms showing pH optima of 8 or higher; typically found in highly alkaline habitats such as soda lakes and high-carbonate soils
Facultative aerobes
Microorganisms that respire oxygen but can survive the absence of oxygen under appropriate nutrient and culture conditions
Thermophiles
Microorganisms with high temperature optima
Psychrophiles
Microorganisms with low temperature optima
Mesophiles
Microorganisms with midrange temperature optima
Hyperthermophiles
Microorganisms with very high temperature optima
Microbial mats
Multilayered biofilm sheets with different organisms present in the individual layers
Culture media
Nutrient solutions tailored to the particular organism to be grown
Microscopic cell count
Observing and enumerating the cells present in a culture or natural sample by looking through a microscope; a quick and easy way of estimating cell numbers
Death phase
Occurs as an exponential function (though typically more slowly than the exponential phase) in which the number of cells dying begins to overwhelm the number of new cells being produced
Planktonic growth
Occurs in microbial cells living in suspension
Sessile growth
Occurs in microbial cells that live attached to the surface
Xerophiles
Organisms able to grow in very dry environments
Osmophiles
Organisms able to live in environments high in sugar
Obligate anaerobes
Organisms that are inhibited or even killed by oxygen gas
Anaerobes
Organisms that cannot respire oxygen
Aerotolerant anaerobes
Organisms that cannot respire oxygen but can still grow in its presence
Acidophiles
Organisms that grow best below a pH of 5.5
Neutrophiles
Organisms that grow optimally at a pH value in the neutral range
Halophiles
Organisms that thrive best in environments with high NaCl concentrations
The great plate count anomaly
Plate counts can be highly unreliable when used to assess total cell numbers in natural samples
Semilogarithmic graph
Plots cell number on a log10 scale as a function of time; produces a straight line in cases of exponential growth; useful for estimating generation time
Defined media
Prepared by adding precise amounts of pure inorganic or organic chemicals to distilled water; the exact composition of the medium is known
Exponential growth
Repetitive pattern in which the number of cells doubles in a constant time interval
Ultrahigh-temperature (UHT) pasteurization
Requires heat treatment at 135 degrees Celsius for 1-2 seconds and actually sterilizes the milk such that it can be stored at room temperature for long periods without spoilage
Anoxic glove bags
Special enclosures that permit work with open cultures in completely anoxic atmospheres
Lag, exponential, stationary, death
Stages of the growth cycle
Phylogenetic stains
Stain only species of Bacteria or only species of Archaea
Steady state
The culture volume, cell number, and nutrient/waste product status remain constant
Polar growth
The formation of new cell wall material from a single point, as in budding division
Sterilization
The killing or removal of all microorganisms
Cardinal temperatures
The minimum, optimum, and maximum temperatures at which an organism grows
Picrophilus oshimae
The most acidophilic microbe known; a species of Archaea that grows optimally at a temperature of 60 degrees Celsius and a pH of .7; inhabits extremely acidic thermal soils associated with volcanic activity
Membrane filter
The most common filter used for liquid sterilization in the microbiology laboratory; composed of high-tensile-strength polymers manufactured in such a away as to contain a large number of tiny pores
Chemostat
The most common type of continuous culture; a device wherein both specific growth rate and cell density can be controlled independently
Septum
The partition that forms between dividing cells during binary fission
1.1 kilograms/centimeters squared (15 pounds per inch)
The pressure of the steam applied by the autoclave
Flow rate
The rate at which fresh medium is pumped in and spent medium is removed from a chemostat
Minimum inhibitory concentration (MIC)
The smallest amount of an agent needed to inhibit the growth of a test organism; used to assess antimicrobial activity
Absorbed radiation dose
The standard for sterilization using ionizing radiation
121 degrees Celsius
The temperature applied by an autoclave
-15 to 122 degrees Celsius
The temperature range over which microbial growth has been shown to be possible
Generation time
The time it takes for one cell to separate to form two cells; variable and depends on nutritional and genetic factors as well as temperature
Thermal death time
The time it takes to kill all cells at a given temperature; a way to characterize the heat sensitivity of an organism; measured by taking samples of a cell suspension, heating them for different times, mixing them with a culture medium, and incubating them to observe whether or not there is growth; greatly affected by population size
Decimal reduction time (D)
The time required for a 10-fold reduction in the viability of a microbial population at a given temperature; used to measure the effectiveness of heat as a sterilant
15 minutes
The time required to achieve sterilization of small amounts of endospore-containing material at 121 degrees Celsius
Decontamination
The treatment of an object or surface to make it safe to handle
Dilution rate, concentration of a limiting nutrient
The two factors that cover the specific growth rate and cell density of the chemostat
Optical density (OD)
The unit for turbidity at the wavelength specified on a spectrophotometer; proportional to cell number in unicellular organisms
Roentgen
The unit of ionizing radiation
Superoxide anion, hydrogen peroxide, hydroxyl radical
Toxic oxygen byproducts produced during the reduction of oxygen gas to water in respiration
rads/grays
Units for the absorbed radiation dose
Enriched medium
Used for the culture of nutritionally demanding microbes; a complex medium to which additional highly nutritious substances are added
Flash pasteurization
Using a tubular heat exposure, the temperature of the milk is raised to 71 degrees Celsius for 15 seconds
Stationary phase
When growth ceases because an essential nutrient in the culture medium is depleted or an organism's waste products accumulate
Positive water balance
When water diffuses into the cytoplasm of a cell due to its higher solute concentration