Chapter 9: Microbial Growth
Halophiles
"salt-loving" archaea that live in environments that have very high salt concentrations
environmental factors that influence microbes
-Oxygen requirements -Temperature -pH -Osmotic pressure -Barometric pressure
Media used for bacterial growth
-chemically defined media -complex media -selective media -Differential media -Enriched media
most cells have developed enzymes that neutralize these chemicals:
-superoxide dismutase -catalase
Atmospheric CO2
0.03%
binary fission process
1. DNA replication 2. formation of division septum 3. cell separation
organisms exhibit 3 distinct temperatures:
1. Minimum 2.Maximum 4. Optimum
oxygen requirements for microbial growth
Aerobes: utilize oxygen Anaerobe: does not utilize oxygen
Capnophiles
Microbes that require high CO2 conditions (3%-10%)
most bacteria are:
Neutrophiles AND they grow best at near-neutral pH
Chemostat
addition and removal of fluids adjusted to maintain the culture in the log phase.
binary fission
asexual reproduction in which a cell divides into two equal parts
Bacteria normally reproduce by
binary fission
Barophiles
can survive under extreme pressure and will rupture if exposed to normal atmospheric pressure
complex media
chemical composition is not known
Psychrophiles
cold-loving microbes. grows at 0°C and below; optimum temp <15°C
Direct (total) cell count
counting chambers electronic counters
measurement of bacterial growth
direct counts, plate count methods, indirect methods
Osmotolerant
do not require high concentration of solute but can tolerate it when it occurs
enriched media
encourages the growth of most bacteria
chemically defined media
exact chemical composition is known
4. Death/decline phase
exponential decrease in number of living bacterial cells
2. Log phase
exponential increase in number of living bacterial cells
Acidophiles pH
grow at extreme acid pH values near 3
Alkaliphiles pH
grow optimally at pH above 9
most microbes exist under:
hypotonic or isotonic conditions
Microbial growth
increase in cell and population size
serial dilution
involves diluting a fixed volume of cells to calculate the concentration of microorganisms.
what if a microbe is not capable of dealing w/ toxic oxygen?
it's forced to live in oxygen-free (anaerobic) habitats
microbial growth curve
lag phase, log phase, stationary phase, death phase
differential media
makes it easy to distinguish colonies of different microbes
1. lag phase
no increase in number of living cells
Mesophiles
optimum temperature 20°C-45°C
Thermophiles
optimum temperature of 50°C to maximum of 80°C
direct viable cell count
plating methods - spread plate -pour plate membrane filtration method. start w/ a serial dilution
Hyperthermophiles
ranges from 80°C to maximum of 110°C
3. Stationary Phase
rate of cell division and death roughly equal
selective media
suppress unwanted microbes and encourage desired microbes
exponential growth
the increase of a population by a factor of 2
pour plate method
the sample is mixed in liquid warm agar. The resulting colonies are counted
spread plate method
the sample is poured onto solid agar. The resulting colonies are counted and provide an estimate of the number of cells in the sample.
generation/doubling time
the time required for a population to double in size
Indirect cell count
turbidity, metabolic activity, dry weight
