microbial growth Flashcards
what happens at the cellular level of binary fission
each bacterium reproduces by binary fission splits into two
what is binary fission
asexual reproduction by a separation of the body into two new bodies
What is microbial growth
An increase in the number of cells.
How to control microbial growth
Yoghurt
Anaerobic digested in wastewater treatment
Describe the growth by binary fission
At cellular level each bacterium reproduces by binary fission (splits in two).
The cells elongate to up to twice its length e.g E coli before forming a partition to seperate into two daughter cells.
Partition is called a septum. This results from growth of cytoplasmic membrane and cell wall.
1) cell elongated and dna is replicated
2) cell wall and plasma membrane begin to grow inward
3) cross wall forms completely around divided dna
4) cells separate
What is the time takes for one cell to become two in binary fission called
Generation time
How can an unbalanced growth occur in binary fission of the cells
Change in environment and nutritional conditions
This may lead to death of the culture
Describe the genetic mechanisms
- Fts proteins for the divisome
- polymerisation of ftsZ results in the building of a ring around the centre of the cell
- ZipA helps to anchor the ring to tbe cytoplasmic membrane
- Ftsl is involved in peptidoglycan synthesis
- FtsK helps chromosome separation
Describe the control of the divisome
- MreB proteins give shape to the bacteria
- MinC, D and E proteins spirals through the cell and stops the FtsZ ring by oscillating
- once the cell grows the Min proteins are stretched
- they no longer prevent FtsZ ring from forming
What is peptidoglycan made up from
Made up from NAM and NAG with a transpeptide on NAM
How is the new wall peptidoglycan built
Autolysins cut out the cell walls at the FtsZ ring.
Bactoprenol then transports new NAM-NAG across the cell membrane.
Glycolases then catalyse the bonding of new peptidoglycan.
How does peptidoglycan synthesis work
….
What is the time taken to get from one cell to two called
Generation time
What is exponential growth
Cell numbers get large very quickly
The number of cells can be calculated as 2n
N=N02n
How to calculate number of generations example
Bacteria time =0 and using serial dilutions calculate total number of cells to be 5000
After 6 hours we plate out the suspension again and find that there are 30000 cells
30000= 5000 x 2n 2n=6 Log10 2n =log10 6 n x 0.301=0.778 n = 0.778/0.301 n = 2.6
Another example of generations
Culture starts with 7000 how many cells will there be after 8 generations
N= N02n
N=7000x 2^8
N= 7000 * 256
N=1792000 or 1.8x10^6
How to calculate generation time
Generation time = time / number of generations
G=t/n
What is growth rate
Change in cell number per unit time
Defined as u (mu)
Number of cells N=e^ut
N=No x e^u (t-t0)
Why is it important to know growth kinetics
So we can replicate experiments with the exact same or proportional number of cells.
If u wanted to obtain particular conc of cells you woukd know how long to culture e.g 2 hours in the calculation.
In industrial setting wastewater treatment, number of microorganisms and growth kinetics determine how quick or.slow waste sources can be introduced.
Non sterilised food.products help determine shelf life
What are the two important factors about continuous culture
- dilution rate- how quickly you pump fresh media in and spent media out
- concentration of a limiting nutrient
Describe chemostat in continuous culture
….
What is dilution rate
Is the flow e.g. 500ml/h divided by the volume in the vessel e.g. 1000ml so 0.5ml/h .
Wide range of dilution rates allow for a steady state of growth.
If dilution rate is too slow then tbe cells begin to die of starvation increasing the doubling time.
If dilution rate is too fast the organism cannot grow fast enough to stop itself being diluted and washed out of the system.
What happens when the dilution rate is too slow
Not enough food being introduced, so population cannot increase.
Some product produced but not usable concentration.
Whag happens if dilutions is too fast
Population can increase however the new cells are lost to effluent
What happens if the dilution is just right
Population can increase, kept at a steady state by loss of cells to effluent.
All substrate converted to product
What happens at low concentrations of nutrient
The growth rate is sub maximal because the cells cannot get the nutrients in the cell to meet metabolic demand
What happens when there is a hugh concentration of nutrient
The growth rate plateaus since there is a competition for space. Yield will continue to rise however to a fixed limit ( solubility, enzymatic)
Describe the wastewater treatment
The waste water entering sewage cannot be discharged to the environment because of
-publix health consideration
-environmental consideration
-aesthetics
Wastewater treatment uses a number of processes to remove and neutralise contaminants
(^the above will be explained in a series of steps)
What is the primary treatment for wastewater treatment
- physical barrier
- series of gates which seperate large objects
- left with two outputs for solid and liquids
- liquid component still contains large concentration of both bacteria and food - soluble organic material
Describe the secondary treatment- (aerobic) for wastewater treatment
The liquid component is added to an aeration tank.
The organic components on the tank are eaten by microorganisms.
Microorganisms form flocks which are mix of organism and biofilm, heavy, kept suspended by aeration and settle in effluent.
What is the tertiary treatment for wastewater treatment
Some of the organisms are removed from the settling tank.
The remaining effluent can then be discharged to rivers and streams.
Rest can be sent for water treatment which is usually sedimentation and coordination
Then drinking water !!!!
Secondary digestion - anoxic
Solid material although separated cannot be simply allowed to pile up
We eag lots of fibre which are insoluble and also a good food source for bugs.
Polysacharides are broken down to smaller substrates
These can then be converted to methane- biogas
What are uses of anoxic secondary digestion
Production of insulin
Continuous culture
In exponential growth substrate is consumed and the product is insulin not from the substrate produced from growth
Why a batch culture?
Continuous culture has one flaw
One substrate in and one product out e.g insulin production/ wastewater and substrate is repaired to co2
Describe the stages of microbial growth cycle and draw a graph to show these stages
Lag phase
Log (exponential) phase
Stationary phase
Death ( decline) phase
Describe the lag phase in the microbial growth cycle
No population increase
Microbes synthesizing cell parts and enzymes
Microbes are adapting to new environment
Varies in length
In some cases can be very short or even absent for instance when sub cultures from an exponential culture.
Can be long when moving from a complex to a defined medium, biosynthesis of different enzymes.
Describe the logarithmic (exponential) phase
Population increasing at maximum rate Growth curve rises smoothly Population doubles at regular intervals ( generation time) Liquid media become turbid Colonies appear on solid media
Describe the stationary phase in microbial growth cycle
Many microbes dying Number of dead balances number of new Nutrients scarce Waste builds up Curve flattens
What are the possible reasons for entry into stationary phase
Nutrient limitation
Limited oxygen available
Toxic waste accumulation
Critical population density reached
What are the starvation responses
Morphological changes e.g. endospore formation
Decrease in size, protoplast shrinkage and nucleoid condensation
Production of starvation proteins
Long term survival
Increased virulence
How are bacterial endospore formed
Certain species of bacteria form endospores during the process of sporulation
Spores are resistant to heat , harsh chemicals, radiation or starvation
Regarded as a dormant stage ( vegetative cell - endosprore- vegetative cell )
Describe the death phase in microbial growth
Microbes dying rapidly
Death phase also an exponential function
Occasionally cells lyse
Capsules/ slime layers may buffer cells against environment
Spores may form
If there a use for the death phase in microbial growth cycles
Production of penicillin
As a starvation response penecillium produces antibiotic.
Would not get this is in continuous culture as sugar would not be depleted
What is used in alcohol production
Yeast not bacteria but same principle apples Add sachharomyces to Grapes - wine Makt/make hops-beer Apples - cider
How is Vinegar produced
Conversion of ethyl alcohol to acetic acid
E.g. wine beer fermented rice or cier can be used
Aceti acids vinegar
Acetobacter and gluconobacter are key genera
How is Yorgurt produced
Yoghurt production
Pasteurise the milk and add lactobacillus bulgaricus and streptococcus thermophilus
Converts lactose to lactic acid
Monitor the pH to 4.5
Stop the fermentation by booking to 7 degrees
How is kombucha produced - mixed batch culture
Traditional health drink
Fermentation of sugary tea
Charachterised by a symbiotic communities of bacteria and yeasts (scoby)
Sugar is converted to alcohol by first set of microbes
Alcohol is then converted to acetic acid by secondary set of microbes
Overview of the batch
Easy to set up and maintain
If contamination occurs only one batch is lost
Useful for production of secondary metabolites but growth rate is slower because of reducing nutrient levels.
Less efficient because it is not constantly in operation
Overview of continuous
Growth rate is higher because of constant nutrient addition
More efficient as constantly operational
More useful for primary metabolites
More difficult to set up but if contaminated lots of product lost
