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Chapter 7
Microbial Growth
| Term | Definition |
|---|---|
| acidophile | microorganism that has its optimum growth between pH values 0 and about 5.5 |
| aerobe | organism that grows in the presence of atmospheric oxygen |
| aerotolerant anaerobe | microbe that grows equally well whether or not oxygen is present |
| alkaliphile (alkalophile) | microorganism that grows best at pH values about 8.5-11.5 |
| anaerobe | organism that can grow in absence of free oxygen |
| batch culture | population of microorganisms growing in closed culture vessel containing single batch of medium |
| biofilm | organized microbial communities consisting of layers of cells associated with surfaces and surrounded by an extracellular polymeric matrix |
| chemostat | a continuous culture apparatus that feeds medium into the culture vessel at the same rate as medium containing microorganisms is removed; the medium contains a limiting quantity of one essential nutrient |
| colony forming units (CFU) | number of microorganisms that form colonies when cultured using spread plates or pour plates; used as a measure of the number of viable microorganisms in a sample |
| cytokinesis | processes that apportion the intracellular contents, synthesize a septum, and divide a cell into two daughter cells during cell division |
| exponential (log) phase | phase of growth curve during which the microbial population is growing at a constant and maximum rate, dividing and doubling at regular intervals |
| extremophiles | microorganisms that grow under harsh or extreme environments |
| facultative anaerobe | microorganism that does not require oxygen for growth but grows better in its presenxe |
| generation (doubling) time | time required for a microbial population to double in number |
| halophile | microorganism that requires high levels of sodium chloride for growth |
| hyperthermophile | a bacterium or archaeon with a growth optimum above 85 degrees Celsius |
| lag phase | period following the introduction of microorganisms into fresh batch culture medium when there is no increase in cell numbers of mass |
| mesophile | microorganism growth optimum temperature around 20-45 Celsius |
| microaerophile | microorganism that requires low levels of oxygen for growth (2-10%) but is damaged by normal atmospheric oxygen levels |
| most probable number (MPN) | method for determining number of viable cells in a liquid sample. Samples are incubated in a suitable liquid medium in dilution series, the most dilute sample to show growth is between 1-10 cells |
| neutrophile | microorgnism that grows best at neutral pH range between 5.5-8.0 |
| obligate aerobe | organism that grows only when oxygen is present |
| obligate anaerobe | organism that grows only when oxygen is absent |
| osmotolerant | organisms that grow over a wide range of water activity or solute concentration |
| psychrophile | microorganism that grows well at 0 degrees C, optimum growth temperature of 15 degrees C or lower |
| quorum sensing | exchange of extracellular molecules that allows microbial cells to sense cell density |
| stationary phase | phase of microbial growth in batch culture when population growth ceases and the growth curve levels off |
| thermophile | microorganism that can grow at temperatures 55 degrees Celsius or higher |
| water activity (aw) | quantitative measure of water availability in a habitat |
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