Ch. 2 (2.2 and 2.6 only) Flashcards
What does growth physiology include?
- Regulation of macromolecular synthesis, DNA division, etc.
- Adaptive responses to external environment
What is a growth curve?
Observation of the sequence of growth phases following inoculation into fresh media
What are the 4 phases in a growth curve?
- Lag phase
- Log phase/exponential growth
- Stationary phase
- Death phase
Draw a general growth curve.
What happens during the lag phase?
- Time required for physiological adaptation of stationary phase cells
- Preparing for growth
Why does the lag phase occur?
- Recovering from toxic waste products that have accumulated in media
- New enzymes/co-enzymes must be synthesized before growth
- Dead cells in inoculum may contribute to turbidity but not growth
What happens during the log phase/exponential growth?
Cell divide
What happens during the stationary phase?
Cells stop growing
Why does the stationary phase occur?
- Exhaustion of nutrients
- Limitation of oxygen
- Accumulation of toxic products
What happens during the death phase?
Cells start dying
Why does the death phase occur?
- Depletion of cellular energy
- Activity of autolytic enzymes
How do bacteria adapt to starvation conditions (2 general methods)?
- Some sporulate or form desiccation resistant cysts
- Others undergo adaptive changes and enter the stationary phase
What changes do bacteria undergo during starvation?
- Smaller cell size
- Change from rod to coccoid shape
- May become more adhesive
- Membrane phospholipids get converted to cyclopropyl derivatives
- Metabolic activity slows down
- New proteins with specific functions related to the decreased component
Under what conditions is sigma S activated?
- Starvation conditions
- Changes to resistance to environmental stress
Sigma S is also known as _____ or _____?
- rpoS
- σ38
What is a regulon?
Includes all the operons regulated by a single transcription factor
Why is sigma S considered a global regulator?
It’s required for a regulon that includes about 50 genes
How are rpoS levels regulated at each different levels?
- Transcriptional: increased transcription
- Post-transciptional: mRNA stability
- Post-translational: degradation by ClpXP
What factors regulate rRNA synthesis?
- ppGpp (guanosine tetra phosphate)
- Stringent reponse
What is the stringent response?
Temporary inhibition of rRNA and tRNA synthesis
- Results in production of ppGpp or pppGpp –> alarmone
- Mechanism: limited AA supply –> uncharged rRNA enters ribosome —> stalls ribosome –> activates enzyme on ribosome (RelA) –> RelA synthesizes ppGpp from GDP and PPi
What is diauxic growth?
Many bacteria preferentially grow on glucose even in the presence of other carbon sources
Explain catabolic repression by glucose.
- Glucose represses the synthesis of enzymes required to grow on alternatives
- Growth on other sources doesn’t occur until glucose is exhausted
- During the 2nd lag period, bacteria synthesize enzymes needed for growth on alternate
