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64 terms

Microbiology - Chapter 6: Microbial Growth

Some definitions from the Microbiology book from Chapter 6 on Microbial Gworth.
cold-loving microbes
moderate-temperature-loving microbes
heat-loving microbes
Minimum growth temperature
the lowest temperature at which the species will grow
Optimum growth temperature
the temperature at which the species grows best
Maximum growth temperature
the highest temperature at which growth is possible
Organisms that are likely to be encountered in low-temperature food spoilage because they grow fairly well at refrigerator temperatures
Hyperthermophiles/extreme thermophiles
Microbes that have an optimum growth temperature of 80 degrees celsius or higher
Bacteria that are remarkably tolerant of acidity
Shrinkage of the cell's cytoplasm
Extreme halophiles
Organisms that have adapted well to high salt concentrations
Obligate halophiles
Organisms that require high salt concentrations for growth
Facultative halophiles
Organisms that do not require high salt concentrations but are able to grow at salt concentrations up to 2%, a concentration that inhibits growth of many other organisms
Nitrogen fixation
When important bacteria use gaseous Nitrogen (N2) directly from the atmosphere
Trace elements
A chemical element (mineral) required in small amounts for growth, such as iron, copper, molybdenum, and zinc
Obligate aerobes
Organisms that require oxygen to live
Facultative anaerobes
Aerobic bacteria that have developed, or retained, the ability to continue growing in the absence of oxygen
Obligate anaerobes
Bacteria that are unable to use molecular oxygen for energy-yielding reactions
Singlet oxygen (1^O2-)
Normal molecular oxygen (O2) that has ben boosted into a higher-energy state and is extremely reactive
Superoxide radicals/superoxide anions (O2.-)
A toxic anion (O2-) with an unpaired electron
Superoxide dismutase (SOD)
An enzyme that destroys superoxide: O2- + O2- + 2H+ --> H2O2 + O2
Peroxide anion
An oxygen anion consisting of two atoms of oxygen; O2^2-
An enzyme that breaks down hydrogen peroxide: 2 H2O2 --> 2 H2O + O2
An enxyme that destroys hydrogen peroxide: H2O2 + 2 H+ --> 2 H2O
Hydroxyl radical
A toxic form of oxygen (OH.) formed in cytoplasm by ionizing radiation and aerobic respiration
Aerotolerant anaerobes
An organism that does not use molecular oxygen (O2) but is not affected by its presence
Organisms that are aerobic (require oxygen) but grow only in oxygen concentrations lower than those in air (small amounts of oxygen).
Organic growth factors
Essential organic compounds an organism is unable to synthesize
Microbial community that usually forms as a slimy layer on a surface
Culture medium
A nutrient material prepared for the growth of microorganisms in a laboratory
Microbes that are introduced into a culture medium to initiate growth
The microbes that grow and multiply in or on a culture medium
A complex polysaccharide derived from a marine alga
Chemically defined medium
A medium whose exact chemical composition is known
Complex media
Culture medium in which the exact chemical composition is not known
Nutrient broth
Complex medium in liquid form
Nutrient agar
Nutrient broth containing agar
Reducing media
Media contain ingredients such as sodium thioglycolate that chemically combine with dissolved oxygen and deplete the oxygen in the culture medium
Microbes that grow better at high CO2 concentrations
Selective media
Media that suppress growth of unwanted bacteria and encourage the growth of the desired microbes
Differential media
Media that make it easier to distinguish colonies of the desired organism from other colonies growing on the same plate
Enrichment culture
Culture medium used for preliminary isolation that favors the growth of one particular microorganism but not others.
A visible mass of microbial cells arising from one cell or from a group of the same microbes
Streak plate method
A method of isolating a culture by spreading microorganisms over the surface of a solid culture medium
Process in which a pure culture of microbes is placed in a suspending liquid and quick-frozen at temperatures ranging from -50 degrees C to -95 degrees C
Lyophilization (freeze-drying)
A suspension of microbes is quickly frozen at temperatures ranging from -54 degrees C to -72 decrees C, and the water is removed by a high vacuum (sublimation)
Binary fission
Reproduction of a cell by division of a cell into two daughter cells
Bacteria form a small initial outgrowth (a bud) that enlarges until its size approaches that of the parent cell, then it separates
Generation time
The time required for a cell to divide (and its population to double)
Bacterial growth curve
A graph indicating the growth of a bacterial population over time
Lag phase
Period of little or no cell division
Log phase/exponential growth phase
When the cells begin to divide and enter a period of growth, or logarithmic increase
Stationary phase
Period of equilibrium in which the growth rate slows, the number of microbial deaths balances the number of new cells, and the population stabilizes
Death phase/logarithmic decline phase
When the number of deaths eventually exceeds the number of new cells formed
Plate count
A method of determining the number of bacteria in a sample by counting the number of colony-forming unites on a solid culture medium
Colony-forming units (CFU)
Plate counts that count the short segments of a chain of bacterial clump; don't assume each live bacterium grows and divides to produce a single colony like a plate count
Serial dilution
The process of diluting a sample several times
Pour plate method
A method of inoculating a solid nutrient medium by mixing bacteria in the melted medium and pouring the medium into a Petri dish to solidify
Spread plate method
A plate count method in which inoculum is spread over the surface of a solid culture medium
The passage of a liquid or gas through a screenlike material; a 0.45- µm filter removes most bacteria
Most probable number (MPN) method
The greater the number of bacteria in a sample, the more dilution is needed to reduce the density to the point at which no bacteria are left to grow in the tubes in a dilution series.
Direct microscopic count
Enumeration of cells by observation through a microscope
The cloudiness of a suspension