Chapter 7: Microbial Growth Flashcards
FtsZ
The protein that directs the process of cytokinesis and cell division.
Z Ring
Defines the division plate between the two daughter cells; is composed of FtsZ.
Divisome
Activates to produce a peptidoglycan cell wall and build a septum that divides the two daughter cells.
Septum
Where all of the cells’ outer layers (the cell wall and outer membranes, if present) must be remodeled to complete division.
Generation Time (Doubling Time)
The time it takes for the population to double through one round of binary fission.
Closed Culture (Batch Culture)
No nutrients are added and most waster is not removed from a culture.
Growth Curve
A reproductive growth pattern.
Culture Density
The number of cells per unit volume.
Inoculum
A small number of cells.
Culture Medium
A nutritional broth that supports growth.
Lag Phase
Number of cells does not change. Cells grow larger and are metabolically active, synthesizing proteins needed to grow within the medium.
Logarithmic (Log) Growth Phase (Exponential Growth Phase)
The cells are actively dividing by binary fission and their number increases exponentially.
Intrinsic Growth
The generation time under specific growth conditions (nutrients, temperature, pH, and so forth) is genetically determined.
Stationary Phase
The number of new cells created by cell division is now equivalent to the number of cells dying; thus, the total population of living cells is relatively stagnant.
Death Phase
When the number of dying cells exceeds the number of dividing cells, leading to an exponential decrease in the number of cells.
Persisters
Surviving cells that form endospores.
Direct Microscopic Cell Count
The simplest way to count bacteria; involves transferring a known volume of a culture to a calibrated slide and counting the cells under a light microscope.
Petroff-Hausser Chamber
A calibrated slide that has counting chambers etched into squares of various sizes.
Hemocytometer
A type of slide used to count red blood cells.
Electronic Cell Counting Device (Coulter Counter)
Detects and counts changes in electrical resistance in a saline solution.
Viable
Live cells.
Viable Plate Count (Plate Count)
A count of viable or live cells.
Colony-Forming Units
Rather than cells per milliliter because more than one cell may have landed on the same spot to give rise to a single colony.
Serial Dilution
The goal is to obtain plates with CFUs in the range of 30-300, and the process usually involves several dilutions.
Turbidity
The cloudiness of a sample of bacteria in liquid suspension.
Spectrophotometer
The laboratory instrument used to measure turbidity.
Calibration Curve
Generated by plotting turbidity as a function of cell density.
Planktonic Cells
Free-floating microbial cells that live in an aquatic environment.
Dispersal
Cells on the periphery of the biofilm revert to a planktonic lifestyle, sloughing off the mature biofilm to colonize more sites.
Quorum Sensing
The mechanism by which cells in a biofilm coordinate their activities in response to environmental stimuli.
Candle Jar
Consists of a jar with a tight-fitting lid that can accommodate the cultures and a candle.
Capnophiles
Bacteria that grow best in a higher concentration of CO2 and a lower concentration of oxygen present in the atmosphere.
Maximum Permissive Oxygen Concentration
The highest tolerated concentration of oxygen.
Minimum Permissive Oxygen Concentration
The lowest concentration of oxygen that allows growth.
Optimum Oxygen Concentration
The ideal concentration of oxygen for a particular microorganism.
Anaerobic Chamber
An enclosed box from which all oxygen is removed.
Anaerobic Jar
Include chemical packs that remove oxygen and release CO2.
Microaerophiles
Bacteria that require a minimum level of oxygen for growth, about 1%-10%, well below the 21% found in the atmosphere.
Aerotolerant Anaerobes
Can’t use the oxygen but can tolerate its presence which is facilitate by enzymes like the superoxide dismutase.
Facultative Anaerobes
Organisms that thrive in the presence of oxygen but also grow in its absence by relying on fermentation or anaerobic respiration, if there is a suitable electron acceptor other than oxygen and the organism is able to perform anaerobic respiration.
Obligate Anaerobes
Killed by oxygen.
Obligate (Strict) Aerobes
Cannot grow without an abundant supply of oxygen.
Thioglycolate Medium
Contains a low percentage of agar to allow motile bacteria to move throughout the medium.
Alkaliphiles
Microorganisms that grow best at pH between 8.0 and 10.5.
Acidophiles
Microorganisms that grow optimally at less than 5.55 pH.
Neutrophiles
They grow optimally at a pH within one or two pH units of the neutral pH of 7.
Maximum Growth pH
The highest pH value that an organism can tolerate.
Minimum Growth pH
The lowest pH value that an organisms can tolerate.
Optimum Growth pH
The most favorable pH for the growth of an organism.
Hyperthermophiles
Characterized by growth ranges from 80°C to a maximum of 110°C, with some extreme examples that survive temperatures above 121°C.
Thermophiles
Organisms that grow at optimum temperatures of 50° C to a maximum of 80°C.
Psychrophiles
Microorganisms that can grow at 0° C and below, have an optimum growth temperature close to 15°C, and usually do not survive at temperatures above 20°C.
Psychrotrophs (Psychrotolerant)
Prefer cooler environments, from a high temperature of 25°C to refrigeration temperature about 4°C.
Mesophiles
Adapted to moderate temperatures, with optimal growth temperatures ranging from room temperature (about 20°C) to about 45°C.
Maximum Growth Temperature
The highest temperature at which the organism can survive and replicate.
Minimum Growth Temperature
The lowest temperature at which the organism can survive and replicate.
Optimum Growth Temperature
The temperature range where the organism’s growth rates are the highest.
Differential Media
Make it easy to distinguish colonies of different bacteria by a change in the color of the colonies or the color of the medium.
MacConkey Agar
Contains bile salts and crystal violet, which interfere with the growth of many gram-positive bacteria and favor the growth of gram-negative bacteria, particularly the Enterobacteriaceae.
Selective Media
Media that inhibit the growth of unwanted microorganisms and support the growth of the organisms of interest by supplying nutrients and reducing competition.
Complex Media
Contain extracts and digests of yeasts, meat, or plants, the precise chemical composition of the medium is not known.
EZ Medium
All individual chemical components are identified and the exact amounts of each is known.
Chemically Defined Medium
When the complete composition of a medium is known.
Fastidious Organisms
Organisms that cannot make certain nutrients and require them to be added to the medium.
Enriched Media
Contains growth factors, vitamins, and other essential nutrients to promote the growth of fastidious organisms.
Tryptic Soy Broth (TSB)
A general all-purpose media and support growth of a large variety of organisms.
Halobacteria
Use light energy to drive their sodium pumps.
Barophiles
Microorganisms that require high atmospheric pressure for growth.
Water Activity
The ratio of the vapor pressure of the medium of interest to the vapor pressure of pure distilled water.
Halophiles
Require high salt concentrations for growth.
Plasmolysis
The shrinking of the protoplasm away from the intact cell wall causing cell death.
Osmotic Pressure
The pressure that would have to be applied to a pure solvent to prevent it from passing into a given solution by osmosis, often used to express the concentration of the solution.
