Microbial Growth Flashcards
(34 cards)
How is growth defined in microbiology according to the course-book? Can growth be defined in other ways?
According to the course book, microbial growth is defined as an increase in the number of cells.
microbial growth can also be defined as the proliferation of a bacterial cell into two daughter cells in a process called binary fission.
What is binary fission?
the extension of a cell into approximately twice its length and a constriction leading to its division into two identical daughter cells.
What is generation time?
It is the time that is required for a cell to divide into two daughter cells.
Describe lag-phase. Why is there a lag-phase?
It is the period between inoculation of bacteria into new/fresh media and the onset of growth, it is an initial pause where cells do not grow.
It occurs because transfer to fresh medium means new conditions and a new environments which the bacteria needs time to adjust to.
Describe the exponential phase of growth.
This is the period in which the bacteria doubles regularly at intervals, cell divisions are maximal and the cells are as close as possible to being metabolically identical as they can be and continues until the conditions in the culture can no longer sustain growth.
Describe stationary phase of growth. Why does the stationary phase occur?
in this phase there is no net increase nor decrease of the cell population, and the growth rate is zero. Cellular metabolism shifts from growth as the cell prepares for maintenance and survival.
it occurs due to nutrient depletion, accumulation of waste products, change in oxygen levels and production of secondary metabolites.
Describe death-phase. Why does the death-phase occur?
The total number of cells decline due to cell death. It occurs due to nutrients becoming scarcer and toxic waste products accumulating.
What factors are required for bacteria to grow?
Nutritional access
Temperature
Water
pH
What are obligate aerobic-, obligate anaerobic-, facultative anaerobic- and aerotolerant bacteria? What does it mean that bacteria are microaerophilic?
obligate aerobic: require oxygen and use it for cellular respiration, e.g micrococcus luteus, found in skin/dust
facultative anaerobic: does not require oxygen to grow but grows better with it, e.g escerichia coli, found in mammalian large intestine
microaerophilic anaerobic: requires oxygen but at levels lower than atmospheric. e.g spirilium volutans, found in lake water.
aerotolerant: does not require oxygen and grows no better with it. e.g streptococcus mutans, found in oral cavity
obligate anaerobic: dies in the presence of oxygen. e.g, methanobacterium formicicum, found in sewage sludge, anoxic lake sediments
How can you test if a bacteria is obligate aerobic, obligate anaerobic, etc?
by adding bacteria to thioglycolate broth, and using the redox dye indicator resazurin to give visual representation.
How does temperature affect bacterial growth?
The lowest temperature that allows growth is called minimum temperature and the maximum temperature that allows growth is called maximum temperature. Anything below the minimum temperature causes the cell wall to harden, inhibiting the entrance of nutrients into the cell, ceasing growth and anything above the maximum causes the cell to dentaure also ceasing growth.
What are psychrophilic-, mesophilic-, thermophilic- and hyperthermophilic bacteria?
psychrophilic- below 15
mesophilic- between 20 to 45
thermophilic- above 45
hyperthermophilic-above 80
What is happening to a bacterial cell when the temperature increases very much (boiling point)?
the cellular enzymes and proteins denature.
How does pH affect growth?
It affects the ionic properties of a bacterial cell thus affecting growth, some thrive in acidic or basic enviroments, while most grow at neutral environment.
What is hyperosmotic shock?
it is when a cell becomes dysfunctional due to a sudden increase in the concentration extracellular environment
When plotting total bacterial cell number in a logarithmic scale as a function of time exponential growth and death-phase appears as straight lines. Why?
because the straight line reflects that the population is increasing or decreasing exponentially.
What is post-exponential and early stationary phase of growth?
The period where cells have stopped growing and changes are taking place in the cell
What is continuously culturing?
Continuous culture is a set of techniques used to reproducibly cultivate microorganisms at submaximal growth rates at different growth limitations in such a way that microorganisms remain in a steady state over long periods of time
How does a chemostat work?
fresh sterile medium is added to the culture vessel at the same time as spent culture is tapped out, the supply medium is controlled by the dilution rate(f/v, with f being flow rate and v being volume of the culture) , and the growth rate is controlled by the concentration of the limiting nutrient.
What is steady-state when considering continuous growth?
An exponential growth over an extended period of time.
What dangerous oxygen species exist, when are they formed and how do bacteria circumvent these?
superoxide anion, hydroden peroxide, hydroxyl radical
with the enzymes: catalase, peroxidase, superoxide dismutase, superoxide reductase
What are cathalase- and oxidase-tests?
The oxidase test is an assay for the presence of cytochrome c oxidase, an enzyme present in many respiring bacteria.
The catalase test assays for the enzyme catalase, which detoxifies hydrogen peroxide and is commonly found in bacteria able to grow in the presence of oxygen.
How can you count the total number of bacteria in a sample?
Microscopes, plating method of koch and turbidity measurement (using a spectrophotometer)
What are the limitations when using microscopic counting to estimate the number of bacteria in a solution?
a microscope is required, small cells can be missed, counting both living and dead cells.
