Lecture 4: Dynamics of
Prokaryotic Growth
Independent Study: Principles of Microbial Growth
• Increase in # (not size)
• Prokaryotic cells divide by
1.getting ready to divide
binary fission
needs protein all
2it begins to expend, dna is replicate
– Exponential growth:
population doubles each
division
– Generation time: time it
takes to double
• Varies among species
• Environmental conditions
E. coli → ~20’minutes
Mycobacterium tuberculosis → ~24h
first generation
Independent Study: Principles of Microbial Growth
Exponential growth has consequences!
Independent Study: Principles of Microbial Growth
GT
5 hours later
A. 30 cells/g
20 min. (bact)
B.
26 min. (yeast) ~100 thousand/g
C.
1 hour (mold)
~one million/g
~1 thousand/g
keep cold foods cold and hot foods hot
do you dont get sick
Microbial Growth in Lab vs. in Nature
→ Conditions in nature have
profound effect on microbial
growth, behavior
vs.
→ Cells sense change, adjust
to surroundings
→ Synthesize compounds
useful for growth
May be more beneficial to
live in a community
Microbial Growth in Nature
While bacterial cells can live
singly, most live in
polysaccharide-encased
communities called
Biofilms
_______________.
while bacterial cells can live singly (PLANKTONIC)
Biofilms
Biofilms have “architecture”
Channels through which nutrients
and wastes pass
Cells communicate by
synthesizing chemical signals
maybe
polysshacaries
or other proitein
EPS
Biofilms: Industry/Dental/Medical Implications
Biofilms are not only
important in nature
but are significant in
medicine and industry
as well
Factors that Influence Microbial Growth
• Environmental Factors (table 4.3)
– Temperature
– O2 availability
– pH
– Water availability
• Nutritional Factors
– Energy and C source are required (table 4.5)
– Other major elements (table 4.4)
– limiting nutrient
– Growth factors (some)
Pathogens?
Food spoilage in
refrigerator?
Dead Sea?
>30% NaCl
Environmental Factors: O2 availability
depending where
the organism grown
we can say where
they use oxygen
Environmental Factors: O2 availability
• Reactive Oxygen Species (ROS)
– byproducts of cellular respiration (discussed in
succeeding lectures)
• superoxide (O2-) and hydrogen peroxide (H2O2)
– Can damage many cellular components
– To protect from ROS: enzymes
–superoxide dismutase: inactivates superoxide
by converting O2- → O2 and H2O2
–catalase: converts H2O2 → O2 and H2O
Microbial Growth: Nutritional reqmts
To live/reproduce, all living things need:
an energy source + a C source
good source for
some bacteria
Microbial Growth: Nutritional reqmts
• To live/reproduce, all living things need:
• an energy source
• a source of carbon and other required elements
Energy sources
Carbon sources
• Chemicals (“chemo”)
• Organic (“organo”)
(ex. glucose)
• Inorganic (“litho”)
(ex. H2S)
• Sunlight (“photo”)
CO2 (“auto”)
(carbon fixation)
fix the co2 -> carbon
Organic cmpds (“hetero”)
troph = nourish
Microbial Growth: Nutritional reqmts
• To live/reproduce, all living things need:
• an energy source
• a source of carbon and other required elements
Note that I am simplifying groups here…when Dr. Gray talks to you about phototrophs,
he will tell you more about how they are classified based on source of electrons
Microbial Growth: Nutritional reqmts
Required elements:
Carbon sources
CO2
Organic cmpds
Nitrogen sources
•Organic nitrogen cmpds
•Inorganic nitrogen cmpds
•N2 (nitrogen fixation)
symbiotic bacteria
Nitrogen fixation is the process of converting atmospheric nitrogen (N2)
into a form that plants can use, such as ammonia (NH3). It's a vital step in
the nitrogen cycle and is essential for plant growth
Microbial Growth: Nutritional reqmts
Rhizobia: symbiotic N2
fixing bacteria, Fig 28.14
Microbial Growth: Nutritional reqmts
Recipe for 1 batch (6 pancakes)
What I Have
1000g flour
4 eggs
400 mL milk
1 gal olive oil
How many batches can I make? What is my limiting
ingredient? 2, milk
Microbial Growth: Nutritional reqmts
Required elements:
•Often a limiting nutrient in
the environment
cyanobacteria = blue-green “algae”
Seattle Times, Linda Mapes, 3/18/08
Algae-prone Green Lake is staying clean
Good news for Green Lake: It's clean and staying that way.
Efforts in 2004 to reduce algae growth in the lake by adding aluminum sulfate, or alum,
are still paying dividends. The alum binds with phosphorus in the water, tying up a key
nutrient algae need to thrive.
….the addition of nitrogen and phosphorus from fertilizers and other pollutants,
combined with warm, sunny days, can spell excessive growth.
And cyanobacteria, while quite beautiful, are toxic to small animals and dogs,…..
RCW 70.95L.020 (http://apps.leg.wa.gov/rcw/default.aspx?cite=70.95L.020)
Phosphorus content regulated.
(d) Beginning July 1, 2010, a person may not sell or distribute for sale a dishwashing
detergent that contains 0.5 percent or more phosphorus by weight in the state.
Microbial Growth: Nutritional reqmts
Required elements:
Carbon sources
Nitrogen sources
•Often a limiting nutrient
•Iron is often
sequestered in the body
to prevent microbial
growth
Growth factors
required by fastidious bacteria
fastidious=complicated nutritional reqmts
Obtaining a Pure Culture: Culture Medium
• Culture medium (liquid or solid)
– Nutrients necessary for bacterial
growth introduced
– Sterile
– Agar used to solidify
not destroyed by high temps
liquefies above 95c
solidifies below 45c
few microbes can degrade (eat them)
• Growth is measured by
– colony formation (solid media)
– turbidity (liquid media)
Studying Bacteria: Culture Medium
• Types of Culture
Medium
– Complex
– Chemically defined
– Differential
– Selective
– Enrichment
Studying Bacteria: Culture Medium
Complex vs.
chemicallydefined media
Minimal medium
Fastidious organisms – growth factors added
(eg. chocolate agar)
Studying Bacteria: Culture Medium
Differential vs. selective vs. differential AND selective
media
Differential
- ingredient added that
can be changed by
certain bacteria in a
recognizable way
Blood agar
hemolysis
Studying Bacteria: Culture Medium
Differential vs. selective vs. differential AND selective
media
Selective - ingredient added that inhibits growth of many
unwanted organisms
Antibiotic-containing medium
Selective and Differential
MacConkey agar
bile salts + dye
Inhibits all but GNR (Gram neg
rods) that typically reside in the
intestine
lactose + pH indicator
Lactose fermenters are reddish
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