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