Microbial Growth Flashcards
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
