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8/14/2019 BIO 205 Chapter 5 Powerpoint
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BIO 205
Chapter 5
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Prokaryotic Growth and
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Prokaryotic ReproductionMost Prokaryotes Reproduce by Binary Fission
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A false color TEM of a cell ofBacillus licheniformis undergoing binary fission
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Prokaryotes ReproduceAsexually
The generation (ordoubling) time is theinterval of timebetween successivebinary fissions
In pathogens, ashorter doubling time
means a shorterincubation period ofdisease
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A Bacterial Growth Curve Illustrates the Dynamics of Growth
During the lag phase, no cell division occurs while bacteria
adapt to their new environment
Exponential growth of the population occurs during thelogarithmic (log) phase
Human disease symptoms usually develop during the logphase
When reproductive and death rates equalize, the population
enters the stationary phase
The accumulation of waste products and scarcity ofresources causes the population to enter the decline(exponential death) phase
Prokaryotic Growth
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When reproductive and death rates equalize, the population entersthe stationary phase
The accumulation of waste products and scarcity of resourcescauses the population to enter the decline (exponential death) phase
Prokaryotic Growth Continued
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Endospores
Endospores Are a Response to Nutrient Limitation
Endospores are a highly resistant structure formed by species ofBacillus and Clostridium when nutrient supplies are low
Core
Coat
Layers
Cortex
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The Formation ofa BacterialEndospore
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Factors Affecting Bacteria Growth:2. Temperature3. Oxygen Levels4. pH5. Hydrostatic Pressure
6. Osmotic Pressure
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Temperature
Each prokaryotic species has an optimal temperature forgrowth and about a 30 range of acceptable
temperatures
Psychrophiles grow optimally below 15C, and make upthe largest portion of all prokaryotes on Earth
Thermophiles multiply best around 60C, living incompost heaps and hot springs
Hyperthermophiles areArchaea that grow optimallyabove 80C, found in seafloor hot-water vents
Mesophiles thrive at the medium temperature range of10 to 45C, including pathogens that thrive in the humanbody
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Oxygen
Many prokaryotes are obligate aerobes, which
require oxygen to grow
Anaerobes do not or cannot use oxygen;aerotolerant species are insensitive to oxygen, butobligate anaerobes are inhibited or killed by oxygen
Facultative prokaryotes grow either with oxygen, orin reduced oxygen environments
Thioglycollate broth can be used to test an
organisms oxygen sensitivity
Carnophilic bacteria require an atmosphere low inoxygen and rich in carbon dioxide
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The effect of oxygen on prokaryotic
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pH
The majority of species grow optimally at neutral (~7.0) pH.
Acidophiles are acid-tolerant prokaryotes.
For example, those used to turn milk into buttermilk, sourcream, and yogurt
Hydrostatic and Osmotic Pressure
Barophiles can withstand incredibly high hydrostatic pressure.
For example, psychrophiles living at the bottom of the
ocean.
Halophiles are salt-tolerant prokaryotes.
They can maintain optimal osmotic pressure withoutsuffering from plasmolysis
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Culture Media and Growth
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Culture Media Are of Two Basic Types:
1. A complex mediumis a chemically unidentified
medium such as a nutrient broth or nutrient agar.
2. In a synthetic medium, the chemical composition of
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A selective medium contains ingredients to inhibitgrowth of certain species and allow the growth of others
A differential medium contains specific chemical toindicate species that possess or lack a biochemicalprocess
Some fastidious organisms require an enriched
medium containing specific nutrients
Many prokaryotes cannot be cultured in a laboratory
Culture Media Can Be Devised to Select for or Differentiatebetween Prokaryotic Species
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Bacterial Population Measurements Are Made Using PureCultures
A pure culture is apopulation consisting of onlyone species of prokaryote
The pour-plate isolationmethod allows separation ofspecies through dilution of asample
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The streak-plate isolation method spreads out individual cellsto form discrete colonies of species
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End of Chapter 5