Post on 31-Dec-2015
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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)
• 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): 45-60 degrees C
– Obligate thermophiles: only above 50 degrees C
– Extreme thermophiles: above 80 degrees C
• Archaea
What are the physical requirements for growth?
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