Transcript Microbial Growth

Microbial Growth
What do they need to grow?
• Physical needs
– Temperature, proper pH,
etc.
• Chemical needs
– Molecules for food, ATP
production, coenzymes, etc.
• Growth = increase in
number, not size
– Binary fission, some by
budding
– E coli growing
• Generation time: doubling
time
– 1-2 hrs for most bacteria
– E. coli can divide in 20
minutes in optimum
conditions!
What is the bacterial growth curve?
• Graph shows a closed system
• Lag phase
– Cells acclimating
– Preparing to divide
• Log phase
– Exponential growth
– Generation time reaches constant
minimum
– Must susceptible to adverse
conditions
• Heat, radiation, drugs
– Total growth
• = # of cells X 2n
• (n = number of generations)
• Stationary phase
– # dividing = # dying
– Population stabilizes
– Decrease in nutrients,
increase in wastes
• Death phase
– # deaths > # new cells
How can I measure bacterial growth directly?
• Direct count
– Plate
counts
– Serial
dilutions
• Then
either
pour
plates or
spread
plates
– Pro: only
measures
viable cells
– Con: time
consuming!
Pro: only measures viable cells
– Con: time consuming!
How can I measure bacterial growth directly?
• Direct
microscopic
count
– Use gridded
slide to count
• Pro: no
incubation time
• Con: counts
dead cells, too;
hard to count
moving bacteria
– Take average
and calculate
back from
dilution
• Coulter counter
How can I measure bacterial growth indirectly?
• Turbidity
– Cloudiness and more bacteria present
– Use spectrophotometer
• Percentage of transmission
• Only works if you have at least a 1M cells per milliliter
What are the physical requirements for growth?
• Temperature
– Each species has
preferred temp
range (over about
30 degrees C
spread)
– Dies quickly
outside range
• Minimum growth
temp
• Maximum growth
temp
• Optimum growth
temp
– Usually near top
of range (close to
max)
What are the physical requirements for growth?
• Temperature: Three
groups
• Psychrophiles (cold
loving): 5-20 degrees C
– Psychrotrophs: 20-30
degrees C
• Contribute to food
spoilage in
refrigerator
• Mesophiles (mod.temp): 25-40 degrees C
– Most common
– Often in animals
• Thermophiles (hot): 4560 degrees C
– Obligate thermophiles:
only above 50 degrees
C
– Extreme thermophiles:
above 80 degrees C
• Archaea
What are the physical requirements for
growth?
• pH
– Most bacteria prefer 6.5-7.5
• When growing, pH changes
• Additive to growth medium buffer pH
– Phosphate salts, amino acids
– Yeast, molds more tolerant of greater range
• Optimum 5-6
• Acidophiles
– Not many
What are the physical requirements for
growth?
• Osmotic pressure
– Bacteria are 80% to 90% water
– Hypertonic solutions ________
water ____ cell
• Results in plasmolysis
– PM pulls away from
cell wall
– Retards bacterial
growth
– Why meat, butter, etc.
salted
– Extreme halophiles
• Obligate halophiles
– Bacteria in Dead Sea,
30% salt
• Facultative halophiles
– Can grow in up to 2%
salt
– Some in up to 15%
– Salt not required for
growth
Anaerobic Culture Methods
• Reducing media
– Anaerobic jar
– Contain chemicals (thioglycollate or oxyrase)
that combine O2
– Heated to drive off O2
What are all the different “troph” types?
Energy source:
nonliving
environment
• Photoautotroph
• Chemoautotroph
Energy source: other
organisms or sunlight
• Photoheterotroph
• Chemoheterotroph
• Saprobe
• Parasite
What are the chemical requirements for growth?
• Oxygen
– Aerobe
– Obligate aerobe
– Anaerobe
– Obligate anaerobe
• Often harmed by oxygen
• Clostriudium
– Facultative anaerobe
• Uses O2 when present
• Can use anaerobic path or fermentation
• E. coli
– Aerotolerant anaerobes
• Tolerate oxygen but don’t use it
• Lactobacilli for cheese, pickles
– Microaerophiles
• Require oxygen at low concentration
• Others include nitrogen, sulfur, phosphorus, etc.
What are symbiotic relationships?
• Mutualism
– lichen
• Commensalism
–
–
–
–
Satellitism
Microbial flora
Lactobacillus
E. coli
• Parasitism
What are non-symbiotic relationships?
• Synergism
– Roots &
bacteria
• Antagonism
– Penicillium
Photo from: http://scientificteaching.wisc.edu/products/PeanutFiles/imagesforsite/penicillium.jpg