This chapter discusses the requirements for microbial growth, including physical factors like temperature, pH, and osmotic pressure as well as chemical requirements like carbon, nitrogen, and oxygen. It also covers culture media that can be used to grow microbes in the lab, including nutrient broth, selective media, and differential media. The chapter describes how to obtain pure cultures using the streak plate method and calculates microbial generation time. It outlines the phases of a bacterial growth curve, including the lag, exponential, stationary, and death phases.

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