Download Microbial growth

**Microbial Growth**
• Growth= an increase in the number of
cells, not an increase in size
• Generation=growth by binary fission
• Generation time=time it takes for a cell to
divide and the population to double
Bacteria divide by binary fission
Generation times vary for each
organism
• E. coli
• Mycobacterium tuberculosis
**Bacterial growth curve**
*Primary and Secondary
metabolites
I will ask you
about secondary
metabolites – know
what they are,
when they are
produced and
why.
**Requirements for bacterial
growth**
• Environmental factors that influence
– Temperature, pH, osmotic pressure, oxygen
• Nutritional factors
– Carbon, nitrogen, sulfur, and phosphorous
– Trace elements
*Optimum Growth Temperatures
•
•
•
•
Psychrophiles-optimum -5 to 15oC
Psychrotrophs- range from 20-30oC
Mesophiles- range from 25-45oC
Thermophiles-range from 45-70oC
Growth rates in different temperatures
pH influences the growth
• Bacteria-prefer a pH range of 6.5-7.5
• Molds prefer a pH range of 5.0-6.0
Osmotic environment influences growth
**Oxygen preferences of
organisms**
• Obligate aerobes require oxygen for growth
• Facultative anaerobes: can grow in aerobic
or anaerobic environments
• Obligate anaerobes: unable to grow in the
presence of oxygen
**Why can some organisms grow
in the presence of oxygen?**
• Because they have the ability to neutralize
toxic oxygen molecules (superoxide,
oxygen radicals)
• Toxic forms of oxygen need to be
neutralized by enzymes
– Superoxide dismutase
– Catalase
*Oxygen Preferences of Bacteria
Candle jars increase CO2 levels for
growing capnophiles
How does a candle jar create a
CO2-enriched/O2-depleted
environment? Is it an anaerobic
environment?
Anaerobic jars
eliminate the
oxygen for
anaerobes to
grow.
How does the hydrogen gas
generator create an anaerobic
environment?
Chemical requirements: Carbon
• What are possible sources of carbon?
• Bacteria are classified based on the source
of carbon as either heterotrophs or
autotrophs
Classification based on Energy and
Carbon sources
Chemical Requirements: Nitrogen
• Why do bacteria need nitrogen?
Chemical requirements: Sulfur
and Phosphorous
• Why do bacteria need sulfur?
• Why do bacteria need phosphorous?
Chemical requirements: trace
elements
• Small amounts of minerals
• Usually function as cofactors
*Culture Media
• Chemically defined
– GSA
A chemically defined medium is one where we
know EXACTLY what the ingredients are. An
undefined medium is one where we don’t know the
exact chemical makeup (for instance, it may
contain “protein digest”
Chemically defined media
Culture Media
• Complex
– Nutrient Agar
– TSA
– BHI
*Culture Media
• Selective
• Differential
• Selective and
Differential
*Ways to measure bacterial
growth
• Direct Count
• Plate Count/Viable Cell Count
• Measure Turbidity
Direct Counts
Plate counts require dilutions to
obtain colonies
Plate Counts: pour plate
Plate Count-spread plate
*Turbidity gives a rough estimate