Microbial population growth Flashcards
What is the most dominant life form?
Prokaryotes
Do microbes grow in isolation or together in nature?
Together, in ‘cities’
Are all prokaryotes pathogenic?
No, only a small fraction of them are.
Why are prokaryotes so dominant?
They have a very fast growth rate (13 min doubling time) = evolve/ adapt fast
- While it takes us a long time to evolve, a bacterial cell can evolve very quickly
- Responds to environmental cues very fast as can adapt very quickly
- Because of this they can take over most ecosystems in the environment
What is binary fission?
Prokaryotes reproduce asexually by cell division through binary fission
- Results in two genetically identical offspring (cloning)
- Will make a copy of chromosomes and segregate them off to two poles of the cell, and splits the cell in half to make two cells
- Can split very fast and under variable conditions
For how many years were prokaryotes the sole form of life on earth, and what did this lead to?
Prokaryotes were the sole inhabitants for 1.7 billion years
- This results in colonization of most habitats
- Extreme ecological and metabolic diversity
- Fast growth + 3.5 billion years = colonization of all ecosystems
What is a closed batch culture system?
A single batch of organisms growing in a closed system
- No inflow or outflow
- Defined by limited supply of nutrients
- Once nutrients are used cells cannot proliferate
- Dictated by method not by shape of flask
- Standard method of studying microorganisms in culture
What is a closed system bias towards?
Fast growing organisms like pathogens (some organisms don’t proliferate as fast, sometimes once or twice a year, and can’t wait that long to study these so it’s not as useful)
What is the lag phase of microbial growth?
Lag between adding cell to the media, and when it starts growing.
- Length determined by history of the cell
- If a cell has been starved for a long time, it won’t proliferate as fast because it doesn’t have the resources to
- Take a cell that is actively growing, to will immediately start to proliferate
What is the exponential phase (log phase) of microbial growth?
Cells are actively dividing and nothing is limiting for growth.
- Population is doubling in a constant interval (under ideal conditions)
- Cells have no limitations Growing at there maximum
What is stationary phase of microbial growth?
Cells stop growing and cryptic growth is observed (when the organism platus)
- Organisms run out of nutrients and they can no longer proliferate at a maximum
Cryptic growth occurs in this stage
- Is when organisms survive by consuming lysed cell constituents of other dead cells within the culture
- This is not a static population but a dynamic population
Some cells are dying and some cells continue to grow = growth/ death is in equilibrium
What is death phase in microbial cell growth?
Cell death.
- Equilibrium between growing and dying cells is skewed towards death
Are all cells doing the same thing during microbial cell growth?
No, some cells will be actively growing and some will not
- Graph shows the average observation across the cells
- No growth actually means death rate and growth rate are in balance
What is the importance of differentiating between alive and growing cells?
Because penicillin kills bacteria by blocking cell wall synthesis, so only growing or about to divide cells are targeted
What are persisters?
Persisters are not targeted by antibiotics as they are in the non-dividing, dormant phase. Penicillin only kills bacteria when they are about to divide.
- Similar to that of bacteria that are in the lag phase of the growth curve
