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Chapter 6: Growth and Culturing of Bacteria
Terms in this set (84)
AKA parent cell; a cell that has approximately doubled in size and is about to divide into 2 daughter cells
One of the to identical products of cell division
Increase in the number of cells due to cell division
the process in which a bacterial cell duplicates its components and divides into two cells
a mixture of nutritional substances on or in which microorganisms grow
Standard bacterial growth curve
a graph plotting the number of bacteria vs. time and showing the phases of bacterial growth
first of four major phases of the bacterial growth curve, in which organisms grow in size but do not increase in number
the rate of growth in a bacterial culture characterized by doubling of the population in a fixed interval of time
second of four major phases of the bacterial growth curve, in which cells divide at an exponential or logarithmic rate
time required for a population of organisms to double in number
hypothetical pattern of growth during the log phase in which all the cells in a culture divide at the same time
the third of four major phases of the bacterial growth curve in which new cells are produced at the same rate that old cells die, leaving the number of live cells constant
4th phase of bacterial growth curve; cells lose their ability to divide due to less supportive conditions in the medium, and die.
a group of descendants of an original cell
a polysaccharide extracted from certain marine algae and used to solidify medium for the growth of microorganisms
a method of measurement in which successive 1:10 dilutions are made from the original sample
a plate containing separate colonies and used to prepare a pure culture; used to prepare pure cultures using serial dilutions, each being mixed with melted agar and poured into a sterile petri plate
used to prepare pure cultures by placing a diluted sample of cells on the surface of an agar plate and spreading the sample evenly over the surface
Colony-forming unit (CFU)
live bacterial cells that can give rise to a colony
an acid-loving organism that grows best in an environment with a pH of 4 to 5.4
organisms that grow best in an environment with a pH of 5.4-8.5
base-loving; grows best in an environment with pH 7.0-11.5
requiring a particular environmental condition
able to tolerate the presence or absence of an environmental condition
cold-loving organism that grows best at temperatures 15-20ºC
grows best at temperatures between 25 and 40ºC; includes most bacteria
heat-loving; grows best at 50-60ºC
organism that uses oxygen; includes those that must have oxygen
enzyme that converts superoxide to molecular oxygen and hydrogen peroxide
organisms that do not use oxygen, including those that are killed by oxygen exposure
bacterium that grows best in the presence of a small amount of free oxygen
prefers CO2 gas for growth
can survive in the presence of oxygen but does not use oxygen in its metabolism
enzyme that converts hydrogen peroxide to water and molecular oxygen
lives under high hydrostatic pressure
salt-loving; requires moderate to large concentrations of salt
microorganisms that have special nutritional needs that are difficult to meet in the laboratory
communication system whereby bacteria communicate with other members of their species via inducer molecules signaling that there are enough of their kind to make a metabolic action take place
a substance that binds to and inactivates a repressor protein
a layer of one or more kinds of bacteria growing on a surface
formation of spores (endospores)
Streak plate method
used to prepare pure cultures in which bacteria are lightly spread over the surface of agar plates, resulting in isolated colonies
contains known specific kinds and amounts of chemical substances
growth medium that contains certain reasonably well-defined materials but varies slightly in chemical composition from batch to batch
encourages the growth of some organisms and suppresses growth of others
has a constituent that causes an observable change (in color or pH) in the medium when a particular chemical reaction occurs, making it possible to distinguish between organisms
contains special nutrients that allow growth of a particular organism
a reserve culture used to store an isolated organism in pure conditions for use in the laboratory
set of procedures used to minimize chances that cultures will be contaminated by organisms from the environment
How does the definition of microbial growth differ from growth of other organisms?
Microbial growth is an increase in the number of cells that occurs by cell division, not in terms of cell size. A mother cell divides into two daughter cells, which grow and subsequently divide. The cells grow larger only to divide into 2 new individuals. Normal organisms usually grow in terms of size, not number
What is the basic mechanism by which bacterial cells divide?
Binary fission - the cell duplicates its components and divides into two cells. The daughter cells split when a septum grows between them
Budding - a small, new cell develops from the surface of an existing cell and subsequently separates from the parent cell
Step 1 - lag phase
organisms are metabolically active, growing in size, synthesizing enzymes, and incorporating various molecules from the medium. Individual organisms increase in size and produce large quantities of energy (ATP) using nutrients within the environment. They must first pull the nutrients through the cell membrane, then metabolize them into ATP. The medium has plentiful nutrients. They are preparing for division.
Step 2 - log phase
organisms are dividing at their most rapid rate. Uses a lot of nutrients, can only go on for so long
Step 3 - stationary phase
when cell division decreases to the point at which new cells are produced at the same rate as old cells die, so the number of live cells remains constant
Step 4 - decline/death phase
as conditions become less and less supportive of cell division, many cells begin to lose their ability to divide, and die. Decrease in amount of nutrients and overgrowth of waste products in a small region.
Advantages of using serial dilutions and standard plate counts
- Able to count colonies and see what is in the sample without having a tremendous amount of colonies on the plate
- Able to use a calculation to quantify the amount of bacteria in a sample
Disadvantages of the serial dilution and standard plate counts method
- May miscount or discount some colonies in the sample
- May lose some diversity in the case of non-homogeneity during preparation of the serial dilution
- Some colonies will exist within the agar, not just on top
- Missing dead cells on plate
Advantages of direct microscope counts using a counting chamber
- More accurate counts due to grid
- Counting cells rather than colonies
Disadvantages of direct microscope counts using a counting chamber
- Cannot distinguish whether cells are alive or dead
Advantages of using measuring turbidity using a spectrophotometer method
- Fairly accurate, ease of use, useful for monitoring the rate of growth
Disadvantages of using measuring turbidity using a spectrophotometer method
- High enough density must be used for it to be effective, but too high will not work and dead cells can also be incorporated
How do physical factors such as pH, temperature, oxygen, moisture, hydrostatic pressure, osmotic pressure, and radiation affect bacterial growth?
All bacteria require a specific range that they will grow best at for pH and temperature. It varies among groups. Some bacteria grow best in oxygen, while others will die in its presence.
What might it indicate that microbes have been discovered that live at the extreme of each of these variables?
It symbolizes their adaptability, because they evolved under conditions that were a lot more harsh and less favorable for life. They have been able to occupy every space because of their ability to adapt to changes and continue to reproduce. It also shows that they are ancient because they have been around for long enough to experience all of these changes. It also shows their diversity, because not all within that species will be able live in the extreme conditions of the environment
What are the different terms we use to classify bacteria based on their oxygen requirement?
Must have free oxygen for aerobic respiration; could not survive without it
Killed by free oxygen
Grow best in the presence of a small amount of free oxygen
Love carbon dioxide; thrive under low-oxygen, high CO2 areas
Ordinarily carry on aerobic metabolism when oxygen is present, but they shift to anaerobic metabolism when oxygen is absent
Can survive in the presence of oxygen, but do not use it in their metabolism.
What is the role of enzymes superoxide dismutase and catalase in determining the oxygen concentration requirements of bacteria?
Superoxide dismutase - takes the harmful oxygen substances and converts them into less-harmful molecules that we can use.
- Catalyzes the partitioning of the superoxide radical into ordinary molecular oxygen or hydrogen peroxide
Catalase - converts hydrogen peroxide into water and molecular oxygen. It is an enzyme that is common to all organisms that are exposed to/depend on oxygen. It also protects the cell from oxidative damage by reactive oxygen species
What features of a bacterial species would determine whether you could use a defined medium with relatively few ingredients compared to a rich complex medium?
Its nutritional complexity - number of nutrients it must obtain to grow. The kind and number of its enzymes is most important. A bacteria with many enzymes has simple nutritional needs because they can synthesize nearly all the substances they need. But a bacteria with fewer enzymes has complex nutritional needs because they lack the ability to synthesize many substances they need for growth
How can bacteria, single-celled organisms, communicate and coordinate with each other to perform complex behavior?
1 bacteria alone cannot produce enough light to attract attention - takes many together. Producing ineffective amounts of light is a waste of nutrients and energy so they can produce inducer molecules to turn on bioluminescence genes when they are present in a high enough concentration.
How do biofilms present challenges for treating bacterial infections with antibiotics?
They contain many different species, all responding differently. They are essentially a superorganism, enclosed in a matrix of DNA, proteins, and sugars. Cells at the bottom would be difficult to be reached by antibiotics because the antibiotics must penetrate the entire organism to reach those cells. The cells of different species are often exchanging genes through transduction, transformation, and conjugation. Because of this, they are far more diverse than the antibiotics we commonly use to treat normal bacterial infections.
What is the purpose of bacterial sporulation?
To ensure that the bacterial population does not die out when they exist in nutrient-poor environments
How does a cell accomplish spore formation?
1. In an environment starved of nutrients, the bacterium enters the sporulation pathway. Some cells enter the endospore pathway and others do not
2. Cells in the pathway form a spore coat, and produce killing factors and immunity factors. Cells out of the pathway do not produce any factors
3. The endospore bacterium contains immunity factors that block the killing factors from killing them.
4. Killing factors attack and destroy the cells that are not in the sporulation pathway
5. Cells out of the sporulation pathway die, releasing their nutrients into the environment
6. The endospore bacterium takes in the released nutrients, and exits the sporulation pathway, dividing into two bacterial cells
7. Once all the nutrients are used again, the bacterium will re-enter the sporulation pathway
How does a cell in sporulation return to normal vegetative growth?
Once favorable conditions return, the endospore develops into a vegetative cell, which lacks the endospore's resistant properties. It returns to its vegetative state via germination in three stages.
stages of germination
requires traumatic agent such as low pH or heat that damages the coat
requires water and a germination agent that penetrates the damaged coat. Peptidoglycan is broken down and its fragments are released into the medium. The living cell takes in large quantities of water and loses its resistance to heat and staining and its refractility.
in a medium with adequate nutrients. Proteins and RNA are synthesized, DNA synthesis begins, and the cell is a vegetative cell undergoing binary fission.
How can a medium be both selective and differential?
A selective medium encourages growth of some organisms, and suppresses the growth of others. A differential medium has a constituent that causes an observable change in the medium when a particular biochemical reaction occurs
A medium can be both because it can contain components that allow some organisms to grow, while others cannot, and also an indicator that shows that a reaction is occurring
Example of a medium being both selective and differential
MacConkey agar: contains crystal violet bile salts that inhibit growth of gram-positive bacteria and allow the growth of gram-negative. Contains sugar lactose and a pH indicator that turns colonies of lactose fermenters red and leaves colonies of non-fermenters colorless and translucent.
Why is it a significant problem that most bacteria on earth are considered "nonculturable organisms"?
Nonculturable organisms are those that we cannot grow within the lab. This is a significant problem because we are unable to observe their properties. For example, some may have antibiotic properties that we are simply unable to observe because we cannot grow them and see how they work. Others may be infectious, but we cannot understand how they are this way because we cannot grow them and observe them in culture.
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