Lecture 5 Flashcards
Growth
Increase in cell number
Growth = reproduction
Population
Total cells from one microbe
Applications of cell division
Infectious diseases and food preservation
Binary fission
Division of one fell into two
Elongation to septum formation
Generation time typically 30 min to 6 hours
Generation time is affected by
Environmental factors (nutrient availability and temperature) and genetic factors (particular to different microbial species)
Divisome
Directs cell division in prokaryotes
Embedded in cytoplasmic membrane
Comprises of Fts (filamenting temperature-sensitive) proteins
FtsZ
Forms a ring around the center of the dividing cell
In bacteria and archaea
Relates to tubulin
ZipA
Connects to FtsZ ring to the cytoplasmic membrane
The anchor
FtsA
Attracts other Fts protein to the divisome
The recruiter
FtsI
Peptidoglycan synthesis
- implications for drug design (new antibiotics)
MreB protein
Form cellular cytoskeleton
Absent in coccoid bacteria
Present in rod-shapes bacteria (if it’s inactive they become coccoid)
Exponential growth
Cells double each generation
Rate of cell production increases each generation
Healthiest state of cells for study
App. Standards for bacterial counts in food
Microbial growth cycle
Lag phase, exponential phase, stationary phase, and death phase
Lag phase
Growth rate= positive (low)
Recovery phase from previous conditions
Stationary phase
Growth rate = zero
Nutrient depletion and waste accumulation
Cryptic growth
Few cells still dividing
Few cells dying
Average of two makes stationary phase
Death phase
Growth rate = negative (cell death)
Continuous culture
Chemostat- constant conditions over time
Controls- dilution rate and nutrient concentration
Applications- ecology and physiology
Microscopic counts
Cell counts
Adv: simple method
Dis: counts live and dead cells & difficulties with low cell numbers and motile cells
Viable counts
Plate counts
Adv: high sensitivity and counts viable cells
Dis: possible errors (plating consistencies, incubation length, cell “clumps”
Turbidimetric methods
Cell mass -> cell number
Adv: simple method & non-destructive
Dis: possible errors, cell clumps and films
Cardinal temperatures
Minimum (no growth), optimal (fastest growth), maximum (cell death)
Extremophiles
Live in very cold or very hot environments
- deep ocean, glaciers, polar regions
- hot springs, surface soils, and water
Psychrophiles
Optimal temperature <15C
Typical slow growing
“Pockets” of water
Ex. Snow algae and seaice diatoms
Molecular adaptations:
- cytoplasmic membrane (high in unsaturated/short-chain FAs and fluidity at low temperature)
- cyroprotectants (“cold-shock” proteins, like anti-freeze for the cell)
Life in the heat
Optimal temperature:
- >45C thermophiles
- > 80C hyperthermophiles
Ex. Boiling springs bacteria, hot spring Cyanobacteria, and hydrothermal vent microbes
Molecular adaptations:
- cytoplasmic membrane (high saturated FAs and stability at high temps)
Heat protectants (heat shock proteins through more ionic bonds)
Polymerase chain reaction
cyclical heating of DNA to 94C and requires a heat-resistant polymerase
Taq polymerase
Thermus aquaticus and hot spring bacterium
Acidophiles
optimal growth < pH 5.5
Alkaliphiles
optimal growth > pH 8
