Chapter 5 Flashcards
Microbes have both the fastest and slowest
growth rates
• Some hot springs bacteria double in as little as 10 min
• Some deep-sea sediment microbes take as long as 100 years)
What determines the differences in growth rate?
- Nutrition
- Temperature
- pH
- Osmolarity
What are “normal” growth conditions?
sea level, 20-40C, neutral pH, salt concentration 0.9%, and many nutrients
Fastest growth rate occurs
at temp where all proteins work most efficiently
• Rising temperatures cause enzymes or cell membrane to fail
at colder temperatures
enzymatic processes become too sluggish and the cell membrane becomes too rigid
Arrhenius equation
k=Ae^-Ea/RT. growth rate roughly doubles every 10C
Mesophiles:
15-45C
Psychrophiles (0-20C)
- Proteins are more flexible
* Require less energy (heat) to function
Thermophiles (40-80C)
- Enzymes are more stable
- Chaperone
- Membranes are more rigid
Barophiles or piezophiles
grow at high pressures
Barotolerant
grow over 1-50 MPa but their growth falls off
Water activity (aw)
is a measure of how much water is available for use
Osmolarity
# of solute molecules in soln and inversely related to a(w) • The more particles in a solution=greater osmolarity and the lower the water activity
aquaporins
allow water to cross the membrane faster than by diffusion
• Help protect the cell from osmotic stress
- Hypertonic
* Hypotonic
– external osmolarity is higher
– internal osmolarity is higher
When in a hypertonic solution, bacteria
try to protect their internal water from leaving by importing more solutes (proline, potassium)
Halophiles
• Require high salt (NaCl) concentrations to grow
Neutralophiles
pH 5-8
acidophiles
pH 0-5
• Often chemoautotrophs
• tetraether lipids
Alkaliphiles
pH 9-11
• in soda lakes
• Use Na motive force and Na+/H+ antiporters
Nutrient deprivation and starvation
- Growth rates slow
- stress responses
- Cells begin to make/store glycogen
- Programmed cell death – members of pop sacrifice themselves to save others – dying cells release nutrients for other cells
sterilization
killing of all living organisms
disinfection
killing pathogens from inanimate objects
antisepsis
killing pathogens from the surface of living tissues
sanitation
reducing microbial pop to safe levels
Cells treated with antimicrobials die at a logarithmic rate
• D-value (decimal reduction time)-
time it takes the agent to kill 90% of population
2 D-values
time to kill 99% of cells
Physical agents that kill microbes
- Temperature
- Temperature + Pressure
- Irradiation
- Filtration
- Chemical agents
temperature and time
LTLT (low temperature/long time): 63C for 30 min
• HTST (high temperature/short time): 72C for 15 seconds
• UHT (ultra high temperature): 150C for 3 seconds,
immediate cooling
other methods
freezing, irradiation, filtration
- Bacteriostatic
* Bacteriocidal
- inhibits growth
- kills cells
