CHAPTER 6
GROWTH AND CULTURING OF BACTERIA
F Chapter Overview
Many students have trouble understanding the speed with which bacteria multiply. It is difficult to recognize how bacteria can reproduce so rapidly that population numbers can be only expressed in logarithmic terms. A small container of milk or meat left on the counter overnight can be transformed from one virtually free of bacteria to a bacteria-rich sample.
With this in mind, the first part of this chapter deals with how bacteria divide, what a growth curve is, and how we can accurately measure the number of bacteria in a sample.
The second part presents the many factors that affect bacterial growth. This section helps to explain why bacteria cannot overpopulate the environment in spite of their ability to reproduce rapidly. This section also helps to explain how organisms adjust to changing environments. Sporulation is presented as an important strategy some bacteria use to survive unfavorable environmental conditions.
The last section presents methods used to culture bacteria. Much of the material presented in the text can and should be emphasized with interesting laboratory experiments.
F Chapter Objectives
· Define growth and note how it applies to bacteria.
· Describe the process of cell division in bacteria.
· List and describe the four phases of growth in a bacterial culture.
· List and describe at least four methods used to measure bacterial growth.
· List at least six physical factors that affect bacterial growth and explain the effects of each.
· List at least seven biochemical factors that affect bacterial growth and explain the effects of each.
· Describe the processes of sporulation and germination; note the importance of bacterial endospores.
· List and describe three methods to pure culture an organism in the laboratory.
· List several types of culture media and explain how each type provides the nutritional requirements for microbial growth.
· List and describe three types of special media used in selecting, differentiating, and/or enriching for certain bacteria.
Animations, videos and tutorials – online
A. Cells Alive! site illustrates bacterial growth and multiplication with an online video http://www.cellsalive.com/ecoli.htm
B. Simple animations of bacterial growth from Timothy Paustian http://www.bact.wisc.edu/Microtextbook/images/textbook/growth/bactdivision.swf
C. Annenberg Foundation (registration required) video on Microbial Ecology - http://www.learner.org/vod/vod_window.html?pid=1370
D. Annenberg Foundation (registration required) video on Microbial Diversity - http://www.learner.org/vod/vod_window.html?pid=1369
Web Destinations
· http://www.mansfield.ohio-state.edu/~sabedon/black06.htm
Ohio state site covers bacterial growth characteristics
· http://www.textbookofbacteriology.net/growth.html
Todar’s Online Textbook of Bacteriology, University of Wisconsin-Madison chapter on bacterial growth.
· http://www.bact.wisc.edu/Microtextbook/index.php?module=Book&func=displayarticle&art_id=112
Information and animations on bacterial growth.
· http://www.bact.wisc.edu/microtextbook/index.php?module=Book&func=displayarticlesinchapter&chap_id=43
University of Wisconsin online book of Microbiology and Bacteriology chapter on bacterial growth and nutrition.
Discussion Topics
· Bacteria can divide at incredible rates. What keeps them from overpopulating the world?
· Discuss the medical significance the endospore-forming bacteria Clostridium tetani and Clostridium botulinum.
Potential essay questions
· Water is essential for the survival of organisms. How can so many different bacteria survive in desert conditions?
· Enzymes are proteins and can be denatured by heat. How can organisms such as Pyrodictium survive at virtually boiling temperatures?
· Endospores are extremely resistant and can survive for long periods of time. How old are the oldest viable endospores and how much do they differ from present day cells?
F Chapter Outline
I. Growth and Cell Division
A. Definition of growth
B. Cell division
1. Binary fission
2. Budding
C. Phases of growth
1. Lag phase
2. Log phase
a. Logarithmic rate
b. Generation time
c. Synchronous growth
d. Chemostat
3. Stationary phase
4. Decline (death) phase
5. Growth in colonies
D. Measuring bacterial growth
1. Serial dilution and standard plate counts
a. Serial dilutions
b. Spread plate and pour plate techniques
c. Colony counter
2. Direct microscopic counts
3. Most probable number
4. Filtration
5. Other methods
a. Turbidity
b. Spectrophotometry
c. Metabolic action
d. Dry weight
II. Factors Affecting Bacterial Growth
A. Physical factors
1. pH
a. Acidophiles
b. Neutrophiles
c. Alkalinophiles
d. Effects of pH
2. Temperature
a. Obligate and facultative
b. Psychrophiles
c. Mesophiles
d. Thermophiles
e. Growth rate comparisons
f. Growth prevention
3. Oxygen
a. Aerobes
b. Obligate anaerobes
c. Microaerophiles
d. Capnophiles
e. Facultative anaerobes
f. Aerotolerant anaerobes
g. Superoxides
4. Moisture
5. Hydrostatic pressure
6. Osmotic pressure
a. Plasmolysis
b. Turgid
c. Osmosis in preservation
d. Halophiles
7. Radiation
B. Nutritional factors
1. Carbon sources
2. Nitrogen sources
3. Sulfur and phosphorus
4. Trace elements
5. Vitamins
6. Nutritional complexity
7. Locations of enzymes
a. Exoenzymes
1. Extracellular enzymes
2. Periplasmic enzymes
b. Endoenzymes
8. Adaptation to limited nutrients
III. Sporulation
A. Endospores
B. Endospore formation
1. Axial nucleoid
2. Core
3. Endospore septum
4. Cortex
5. Dipicolinic acid
6. Spore coat
7. Exosporium
C. Germination
1. Activation
2. Germination proper
3. Outgrowth
D. Vegetative and sporulation cycles
E. Other sporelike bacterial structures
1. Cyst formation
2. Conidia formation
IV. Culturing Bacteria
A. Methods of obtaining pure cultures
1. Definition of pure culture
2. Streak plate method
3. Pour plate method
B. Culture media
1. Types of media
a. Synthetic medium
b. Defined synthetic medium
c. Complex medium
2. Commonly used media
3. Diagnostic media
a. Selective
b. Differential
c. Enrichment
4. Controlling oxygen content of media
a. Culturing microaerophiles
b. Culturing obligate anaerobes
5. Maintaining cultures
a. Stock cultures
b. Aseptic technique
6. Special cultures
a. Preserved culture
b. Reference culture
C. Methods of performing multiple diagnostic tests
D. Living, but nonculturable, organisms
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