Lecture 3- bacterial growth? Flashcards
What 4 things do bacteria need to grow?
- Carbon source- carbohydrates, usually glucose
- Nitrogen source- for protein synthesis
- S,P & Mg
- Growth factors- e.g. vitamins, nucleotides
How do bacteria grow in numbers?
Through binary fission. Exponential growth 2,4,8,16 etc.
When do bacteria divide?
When the cell is 2x as long
What is the mdt?
Mean doubling time (of population)
How does the bacteria know when to divide?
The FtsZ ring forms in the middle and stimulates division
Why is there a lag phase in the bacterial growth curve in batch culture?
The cells are making new components, may be old, injured, adjusting to new medium.
WHy does the growth phase give a straight line?
It’s plotted logorithmically and cells have exponential growth so straight line.
Why do cells stop dividing in the stationary phase?
Nutrient, limitation, accumulation of toxic waste
What are the 4 temperature classes of organisms?
- Psychrophiles- Low Topt (<15’C) oceans etc.
- Mesophiles- midrange Topt ( 15-45’C) animals
- Thermophiles- high Topt (45-80’C) soil etc.
- Hyperthermophiles- v.high Topt (80-100’C) hot springs
What are psychophiles’ unique adaptations?
- Semi fluid membranes at low temp- don’t become waxy and non functional at low temp.
- Altered proteins- more alpha helices give greater flexibility
- Anti freeze molecules which bind ice crystals (in animals).
What are thermophiles’ adaptations?
- Semi- fluid membranes at high temperatures
- Altered proteins- heat resistant folding conformations
What are hyperthomiles’ adaptions?
- No fatty acids in membrane
- Lipid monolayer NOT bilayer
In the measurement of heat killing, what is the D value?
The time required to kill 90% of cells.
What are the conditions in steam sterilisation by autoclaving?
- High temp - 121’C
- Long enough- 20 mins
- High pressure- 138 kPa
