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25 Cards in this Set
- Front
- Back
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Bulk transport
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endocytosis, phagocytosis, pinocytosis
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Environmental Factors Influencing Growth
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temperature
oxygen pH osmotic pressure others: radiation, atmospheric pressure |
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Temperature Optima
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o Psychrophiles: cold-loving
o Mesophiles: moderate temperature-loving o Thermophiles: heat-loving o Each has a minimum, optimum, and maximum growth temperature |
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Temperature Optima
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o Optimum growth temperature is usually near the top of the growth range
o Death above the maximum temperature comes from inactivation of enzymes o Mesophiles most common group of organisms o 40ºF (5°C) slows or stops growth of most microbes o Fig 6.2-6.3 illustrate parameters of refrigeration |
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Microbe of the Day
o Listeria monocytogenes |
o Gram + rod
o Common in environment o Lives in monocytes o Intracellular o Can move through cell membrane to spread from cell to cell o Psychrophile o Listeriosis: fever, aches, GI or CNS symptoms o Pregnant women may suffer miscarriage o Listeriosis: – 2500 cases/yr – 500 fatal o Prevention – Pasteurization – Avoidance |
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Oxygen Requirements
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o Obligate aerobes – require O2
o Facultative anaerobes – can use O2 but also grow without it o Obligate anaerobes – die in the presence of O2 |
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Oxygen Tolerance
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o Aerotolerant – do not use O2 but can grow when it is present
– Often ferment glucose to lactic acid o Microaerophiles – require O2 but grow only in concentrations lower than air |
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Toxic Forms of Oxygen
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o Singlet oxygen (O2) – very reactive
o Superoxide free radicals (O2.) – Neutralized by superoxide dismutase (SOD) o Peroxide anions (O2-2) – H2O2 broken down by catalase and peroxidase o Hydroxyl radical (OH-) –very reactive Growth of anaerobes: Brewer's Jar Growth of Microaerophiles: Candle jar |
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pH
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o Most bacteria grow between pH 6.5 and 7.5
o Acid (below pH 4) good preservative for pickles, sauerkraut, cheeses o Acidophiles can live at low pH o Lab media contain phosphate buffers to keep pH near neutrality o Many bacteria and viruses survive low pH of stomach to infect intestines o Helicobacter pylori lives in stomach under mucus layer |
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Osmotic Pressure
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o Bacteria 80-90% water
o High salt in surrounding environment leads to water loss and plasmolysis o Cell’s plasma membrane shrinks, cell growth inhibited |
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Drying and High Osmolarity
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o Salted fish, jerky, honey, sweetened condensed milk are preserved by pulling water out of bacteria
o Hypotonic medium (low osmolarity) may lyse bacteria without cell walls |
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Ecological Associations
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Symbiotic: close nutritional realtionship
mutualism: both benefit commensalism: commensal benefits, host not harmed parasitism: parasite benefits, host is harmed |
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Bacterial Division
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o Bacteria divide by binary fission
o Alternative means – Budding – Conidiospores (filamentous bacteria) – Fragmentation |
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Generation Time
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o Time required for cell to divide/for population to double
o Average for bacteria is 1-3 hours o E. coli generation time = 20 min – 20 generations (7 hours), 1 cell becomes 1 million cells! |
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Bacterial Growth Curve
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Phases of Growth
o Lag phase – making new enzymes in response to new medium o Log phase – exponential growth – Desired for production of products – Most sensitive to drugs and radiation during this period o Stationary phase – – nutrients becoming limiting or waste products becoming toxic – death rate = division rate o Death phase – death exceeds division |
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Measuring Growth
Direct Methods Plate counts |
oGrow on plates, each colony comes from one original cell (cfu = colony forming units)
oSerial dilutions to give reasonable #s to count oTakes 24 hours to grow colonies oDetects living cells |
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Measuring Growth
Direct Methods Direct Microscopic Count |
o Measured amount of suspension placed on special slide
o Several fields counted under oil immersion and average calculated o Same technique used for manually counting blood cells |
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Measuring Growth
Indirect Methods Turbidity : |
oBacterial cells scatter light
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Measuring Growth
Indirect Methods Metabolic activity |
o Measure amount of product produced
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Measuring Growth
Indirect Methods Dry weight : |
o Best for filamentous organisms (fungi)
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Measuring Growth
Direct Methods Plate counts |
oGrow on plates, each colony comes from one original cell (cfu = colony forming units)
oSerial dilutions to give reasonable #s to count oTakes 24 hours to grow colonies oDetects living cells |
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Measuring Growth
Direct Methods Direct Microscopic Count |
o Measured amount of suspension placed on special slide
o Several fields counted under oil immersion and average calculated o Same technique used for manually counting blood cells |
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Measuring Growth
Indirect Methods Turbidity : |
oBacterial cells scatter light
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Measuring Growth
Indirect Methods Metabolic activity |
o Measure amount of product produced
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Measuring Growth
Indirect Methods Dry weight : |
o Best for filamentous organisms (fungi)
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