1. Chapter 6: Microbial Growth
August 15, 2013

2. Requirements for Growth
• There are two ways to microbial growth can be
divided
• Physical
• Chemical

3. Physical Requirements
• Temperature
• Hyperthermophiles –some members of Archaea,
“extreme thermophiles”
• Psychrophile-cold loving microbes
• Mesophile-moderate temperatures (most
common)
• Thermophile-heat loving microbes
• Psychrotrophs-capable of growing between 0
and 30 degrees Celsius (refrigerator
temperatures)

4. • pH – the acidity or basicity of a solution
• Most bacteria growth best at a pH between 6.5-7.5
• Neutral
• Osmotic pressure
• Microbes are 80-90% water
• Adding solutes to solutions can reduce the presence
of microbes (i.e. salt)

5. Chemical Requirements
• Carbon
•
•
Carbon is the structural backbone of all living matter
Organic compounds
• Nitrogen, Sulfur, Phosphorus
•
•
N2 and P required for synthesis of DNA and ATP
N2 required for protein synthesis
• Trace Elements
•
•
•
Needed for enzymatic functions
Can be added to media to culture microbes
Fe, Cu, Zn

6. • Oxygen
• Obligate Aerobes- require O2 to live
• Facultative Anaerobes – can use O2 to live if present,
but doesn’t require it for growth
• Obligate Anaerobes – do NOT require O2 to live,
harmed by it
• Aerotolerant Aerobes- can not use O2 for growth,
but they can handle it. Not necessarily harmed by the
presence of O2

7. Chapter 6 Continued
Microbial Growth

8. Page 166 in your Textbook

9. CULTURE MEDIA
• There are many different mediums that microbes
can grow in
• Some require specific requirements, whereas others
are more universal
• Culture Medium: a nutrient material prepared for
the growth of microorganisms in a laboratory

10. • To introduce microbes to a
media, you have to inoculate
them
• This is what we did when we
swabbed for microbes and put
them on the agar.
• If bacteria grows and
multiplies on the media, it is
referred to as a culture.

11. • A complex polysaccharide derived from a
marine algae is called agar.

12. Types of Media
• Chemically defined medium = the exact chemical
composition is known
• Complex media = a media that is made of
nutrients, chemical composition varies from plate to
plate; includes yeast, plant and meat extracts
• Nutrient broth or nutrient agar
• Reducing Media = anaerobic conditions and stored in
anaerobic jars to remove any oxygen

13. • Selective Media = Media used to
encourage growth of some organisms
while suppressing the growth of others
• Differential Media = Media used to
distinguish colonies of specific bacteria
from other organisms
• Enrichment Culture = media that mimics
environmental conditions that favor the
growth of a particular microbe but not
another

14. Obtaining Pure Cultures
• The most commonly used
method to get pure
cultures is the streak plate
method

15. Growth of Bacterial Cultures
• Bacterial cells divide by binary
fission, some by budding
• The time for a cell to divide is
called generation time
• 1-3 hours is typical for most
bacteria
• E.coli reproduces every 20
minutes!

16. Calculating Generation Time
(Initial # of cells )X (2 number of generations )= # of cells
• Example: A Taco Bell manager accidentally
inoculated 5 cells of E. coli into the burrito meat. How
many cells would there be after 4 hours if E.coli has a
generation time of 20 minutes.

17. Phases of Growth
• A bacterial growth
curve shows the
growth of cells over
time
• LAG PHASE
• EXPONENTIAL
PHASE
• STATIONARY PHASE
• DEATH PHASE

18. REVIEW CHAPTER 6 and
• Describe physical
• PAGE 185-186
• Review #’s: 2, 4, 10, 12
• Multiple Choice #’s: 8, 9
chemical requirements
for growth
• Label these test tubes
with the type of
oxygen-organism

19. GROUP TEACH
• Page 178-read first 2
paragraphs
• PLATE COUNTS-dilutions
• FILTRATION
• MPN
• DIRECT MICROSCOPE
COUNT
Each group tell me:
• Tell the method of measuring
cell growth
• Advantages/Disadvantages
• When is it used
• What is the process
• Picture or Diagram