Bacterial Growth & Growth Requirements Flashcards
What does growth in bacteria refer to?
Reproduction
How do majority of bacterial cells reproduce?
By binary fission
the time it takes for cells to divide and produce a new generation of cells
Generation time
the time it takes for cells to double their population size
Doubling time
Many bacterial cells have a generation time of _____
20 mins
4 phases of bacterial growth
- lag phase
- logarithmic (exponential) phase
- stationary phase
- death phase
period of adaptation into a new environment or when bacterial cells are placed in a culture medium
Lag phase
lag phase is also known as _____
Phase of rejuvenescence or physiologic youth
True or False
There is little to no cell division taking place during lag phase, therefore no increase in population size
True
Are cells dormant during lag phase? Why or why not?
No, they are undergoing intense metabolic activity involving DNA and enzyme synthesis
What happens at the end of lag phase?
Cells have usually lost the reserve storage granules
In what phase are cells most active metabolically?
Log/logarithmic phase
True or False
There is minimal cell division taking place during log phase, therefore only a slight increase in population size can be observed
False, cell reproduction is more active in log phase, hence there is a notable increase in population size
True or False
Young cells during log phase are most susceptible to antimicrobial drugs that interfere with metabolism
True
In what phase is the population size stable?
Stationary phase
How does the population size remain stable during stationary phase when many cells are dying or already dead?
Cell division is still occurring which compensates for dead cells
Does the metabolic activity of surviving cells increase or decrease during stationary phase? Why?
Decrease because of the accumulation of waste products that are inhibitory for the cells
How can the stationary phase be postponed?
By continually removing the old medium with the waste and some cells using a chemostat and replenishing the medium so cells could still grow
cell division = cell death
In what phase does this equation apply to?
Stationary phase
phase wherein many of the cells have died and any cell division occurring can no longer compensate for the dead cells
Death/logarithmic decline phase
cell division < cell death
In what phase does this equation apply to?
Death/logarithmic decline phase
chemical and energy requirements for bacterial growth
- sources of carbon, energy, & electrons
- oxygen requirements
- nitrogen requirements
- other chemical requirements
a variety of chemicals organisms use for their energy needs and to build organic molecules and cell structures
Nutrients
necessary elements in nutrient compounds
CHON
2 broad groups of organisms based on their Carbon source
- autotrophs
- heterotrophs
organisms that can use inorganic carbon source (e.g., CO2) as their sole source of carbon
Autotrophs
organisms that catabolize reduced organic molecules (e.g., proteins, carbs, amino acids, fatty acids) acquired from other organisms
Heterotrophs
2 groups of organisms based their use of chemicals or light as energy source
- chemotrophs
- phototrophs
organisms that acquire energy from redox rxns involving inorganic and organic chemicals
Chemotrophs
organisms that use light as energy source
Phototrophs
4 groups of organisms based on their carbon and energy sources
- photoautotrophs
- chemoautotrophs
- photoheterotrophs
- chemoheterotrophs
organisms that use light as energy source and inorganic carbon as its carbon source
Photoautotrophs
examples of photoautotrophs
- plants
- some protozoans
- algae
- prokaryotes
organisms that use chemicals as energy source and inorganic carbon as its carbon source
Chemoautotrophs
example of chemoautotrophs
Prokaryotes
organisms that use light as energy source and organic carbon as its carbon source
Photoheterotrophs
example of photoheterotrophs
Prokaryotes
organisms that use chemicals as energy source and organic carbon as its carbon source
Chemoheterotrophs
example of chemoheterotrophs
- animals
- fungi
- other protozoans
- prokaryotes
2 groups of organisms based on their hydrogen source
- organotrophs
- lithotrophs
organisms that acquire electrons from the same organic molecules that provide them carbon & energy
Organotrophs
organisms that acquire electrons from inorganic hydrogen sources, e.g., H2, NO2, H2S, FE2+
Lithotrophs
5 groups of organisms based on oxygen requirement
- obligate aerobes
- obligate anaerobes
- facultative anaerobes
- aerotolerant anaerobes
- microaerophiles
Why is oxygen an essential nutrient for bacteria?
Because it serves as the final electron acceptor of electron transport chains which produce most of the ATP in bacteria
True or False
Obligate aerobes can still grow even without oxygen in their environment
False, oxygen must be present
examples of obligate aerobes
- algae
- most fungi
- protozoans
- many prokaryotes
True or False
Obligate anaerobes cannot grow without oxygen in their environment
False, oxygen must be absent
highly reactive O2 forms toxic for obligate anaerobes
- singlet oxygen (1 O2)
- superoxide radical (O2-)
- peroxide anion (O2 [2-])
- hydroxyl radical (OH-)
pigment that protects organisms from lethal oxidations of singlet oxygen, absent in obligate anaerobes
Carotenoid
enzyme necessary to prevent lethal accumulation of superoxide, absent in obligate anaerobes
Superoxide dismutase
enzyme that breaks down peroxide anion into water and oxygen, absent in obligate anaerobes
Catalase
enzyme that breaks down peroxide anion into water and NAD, absent in obligate anaerobes
Peroxidase
radical resulting from the incomplete reduction of H2O2 and ionizing radiation
Hydroxyl radical
What are facultative anaerobes?
Organisms that can grow with or without oxygen
examples of facultative anaerobes
- Escherichia coli
- few yeasts
- many prokaryotes
- many bacterial pathogens
organisms that do not use aerobic metabolism but tolerate oxygen by having some of the enzymes that detoxify toxic oxygen forms
Aerotolerant anaerobes
examples of aerotolerant anaerobes
- Lactobacilli
- few yeasts
- many prokaryotes
- few protozoans
organisms that require oxygen levels of 2-10%
Microaerophiles
Where does Helicobacter pylori thrive?
In the stomach
What oxygen concentration would damage microaerophiles?
21% concentration of atmospheric O2
examples of microaerophiles
- many prokaryotes
- protozoans
___% of the dry weight of microbial cells is nitrogen
14%
Why is nitrogen also a growth-limiting nutrient?
Because anabolism stops when there is insufficient nitrogen to build proteins and nucleotides
Where can cells recycle nitrogen from?
From their amino acids and nucleotides
process wherein a few bacteria (e.g., cyanobacteria & Rhizobium) reduce nitrogen gas to ammonia
Nitrogen fixation
Why are nitrogen fixing bacteria essential?
They provide usable nitrogen to other organisms
other chemical requirements
- phosphorous
- sulfur
- calcium, copper, iron
- manganese
- magnesium
- trace elements
- growth factors
essential organic compounds organisms cannot produce, therefore have to be supplied to them
Growth factors
growth factors
- B complex vitamins
- amino acids
- purines & pyrimidines
How are growth factors supplied to bacteria in a culture medium?
Through yeast extracts, whole blood, or serum
physical requirements for bacterial growth
- temperature
- pH
- physical effects of water
- CO2
3 groups of bacteria based on temperature dependence
- psychrophiles/cryophilic
- mesophiles
optimum temperature for psychrophiles
15°C
temperature range for psychrophile growth
0-20°C
examples of psychrophiles
- algae
- fungi
- bacteria in snow fields, ice, & cold water
- bacteria that cause spoilage of food in fridges
optimum temperature range for mesophiles
20-40°C
What are thermoduric organisms?
Mesophiles that can survive high temperatures for brief periods
What group of bacteria based on temperature do bacteria for man belong in?
Mesophiles as they grow best at 37°C
optimum temperature range for thermophiles
temperatures above 45°C
members of archaea that grow in water above 80°C or above 100°C
Hyperthermophiles
bacteria that grows in 113°C and can survive 121°C for an hour
Pyrodictium
a measure of the concentration of hydrogen ions in a solution
pH
3 groups of bacteria based on pH requirement
- neutrophiles
- acidophiles
- alkalinophiles
optimum pH range for neutrophile growth
6.5 - 7.5
examples of neutrophiles
- most bacteria
- most protozoans
- including pathogens
2 types of acidophiles
- obligate acidophiles
- acid tolerant microbes
acidophiles that require an acidic pH and die when pH reaches 7
Obligate acidophiles
acidophiles that merely survive acid without preferring it
Acid tolerant microbes
examples of acidophiles
- other bacteria
- most fungi
True or False
Low pH acts as a preservative by preventing any further bacterial growth
True
optimum pH for alkalinophiles
11.5
examples of alkalinophiles
Vibrio cholerae - goes best outside the body in water at pH 9
How can organisms remain metabolically active?
They must be in a moist environment
Why is it detrimental for an organism if it loses water?
80% of its cells’ cytoplasm is made up of water
dissolves enzymes and nutrients and is an important reactant in many metabolic rxns
Water
example of an organism that can survive dry conditions
Mycobacterium tuberculosis
component in Mycobacterium tuberculosis that aids in retention of water
High lipid and mycolic acid content
the pressure exerted on a semi-permeable membrane by a solution containing solutes that cannot cross the membrane
Osmotic pressure
What happens when cells are placed in hypotonic solutions?
Cells gain water and swells
- if cell wall is absent, cell bursts
What happens when cells are placed in hypertonic solutions?
Cells lose water and shrink (plasmolysis)
If there is high external osmotic pressure, the cells are in what kind of solution?
Hypertonic solution
If there is low external osmotic pressure, the cells are in what kind of solution?
Hypotonic solution
What does halophile mean?
Salt-loving
organisms adapted for growth under high osmotic pressure and can grow in 30% salt
Obligate halophiles
organisms that do not require high salt concentration but can tolerate it
Facultative halophiles
example of facultative halophiles
Staphylococcus aureus
the pressure exerted by water in proportion to its depth
Hydrostatic pressure
for every additional 10 meters depth, water pressure increases by ___ atmosphere
1
organisms that are living in the ocean basins and trenches which are under extreme pressure
Barophiles
organisms that would require CO2 to initiate growth
Capnophiles
carbon dioxide is usually supplied in ____ concentration
5-10%
How is CO2 supplied in the lab?
- CO2 incubator
- candle jar
