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Chapter 5

Biological Sciences 55-237 Chapter 5: Microbiology Topic 5


Department
Biological Sciences
Course Code
BIOL 2070
Professor
tanyanoel
Chapter
5

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Microbiology Topic 5
Microbial Growth and Growth Control
Growing BacteriaRequirements and Media
All living organisms eat, or at least they have nutritional needs
This is true for growing plants, cultivating livestock, and when we grow bacteria,
they need to be fed as well
Overview of Catabolic Diversity
There is a diversity of nutritional strategy and capabilities of microbes
Depending on the organism, the carbon and the energy source will vary, as will the
conditions under which they can grow
Feeding and Watering Your Microbes
Culture media must provide necessary nutrients for microbes we want to culture
Common ways we grow microbes:
o Broth (liquid) medium: tubes, flasks
o Solid medium (includes agar): Petri dishes, test tubes (slants)
If we want to keep microbes alive in the lab, we need to provide them with
appropriate nutrients and conditions
We use culture (or growth) medium to supply most, if not all, of the nutrient s
Sometimes we grow bacteria in liquid media; other times we use solid media, which
would be slants in a test tube or agar plates
There is growth on the surface of slants on the left
Many tubes look cloudy turbid
o Reflects that there are bacteria growing there
On the tube on the right hand side, it does not look as cloudy
o The bacteria are at the bottom of the tube
There are a number of recipes for different types of growth media
The exact ingredients will vary depending on which culture of organisms we are
making, as different organisms will have different needs
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Macronutrients are Required in Larger Amounts
In all cases, organisms are going to need some nutrients in larger amounts
These are the macronutrients
Need for carbon, hydrogen, oxygen, nitrogen, and phosphorous
o The other elements are also important
Micronutrients are Required in Trace Amounts
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Micronutrients are required in much lower amounts
In some cases, just the tiny contaminants in water can provide an adequate supply
These include certain elements and growth factors
Chemical Composition of Growth Media
Chemically defined media: exact chemical composition known
Complex media: includes ingredient(s) where exact composition not known (usually
mixture of proteins, carbohydrates, etc.)
Enriched media: contains complex organic substances and special growth factors
required by certain species
Most bacterial growth media can be categorized chemically
Most of it would be chemically defined or complex
Chemically defined media have known compositions that are precisely defined
o Pure organic or inorganic ingredients are used in carefully measured
quantities
o Defined media are most often used to culture known microbes with highly
specific nutritional needs, which would be the case for something like
Leuconostoc and Thiobacillus
Complex media contain at least one ingredient of which the exact chemical
composition is unknown
o This is often an extract or digest of something like yeast, beef, soy or blood
o These sorts of things, when digested, provide rich sources or proteins, carbs,
and growth factors
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