copyright © 2010 pearson education, inc. microbial growth chapter 6
TRANSCRIPT
Copyright © 2010 Pearson Education, Inc.
MICROBIAL GROWTH
Chapter 6
Copyright © 2010 Pearson Education, Inc.
QUESTION OF THE DAY…
Oxygen in the atmosphere is essential for human life. Can some bacteria grow in the absence of oxygen - how?
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Microbial Growth
Increase in number of cells, not cell size Populations Colonies
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The Requirements for Growth
Physical requirements Temperature pH Osmotic pressure
Chemical requirements Carbon Nitrogen, sulfur, and phosphorous Trace elements Oxygen Organic growth factor
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Physical Requirements
Temperature Minimum growth temperature Optimum growth temperature Maximum growth temperature
Copyright © 2010 Pearson Education, Inc. Figure 6.2
Food Preservation Temperatures
Psychrotrophs: Grow between 0°C and 20–30°CCause food spoilage
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pH
Most bacteria grow between pH 6.5 and 7.5 Molds and yeasts grow between pH 5 and 6 Acidophiles grow in acidic environments
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Osmotic Pressure
Hypertonic environments, or an increase in salt or sugar, cause plasmolysis
Extreme or obligate halophiles require high osmotic pressure
Facultative halophiles tolerate high osmotic pressure
Copyright © 2010 Pearson Education, Inc. Figure 6.4
Plasmolysis
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Chemical Requirements
Carbon Structural organic molecules, energy source Chemoheterotrophs use organic carbon sources Autotrophs use CO2
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Chemical Requirements
Nitrogen In amino acids and proteins Most bacteria decompose proteins Some bacteria use NH4+ or NO3–
A few bacteria use N2 in nitrogen fixation
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Chemical Requirements
Sulfur In amino acids, thiamine, and biotin Most bacteria decompose proteins Some bacteria use SO4
2– or H2S
Phosphorus In DNA, RNA, ATP, and membranes PO4
3– is a source of phosphorus
QUESTION: If bacterial cells were given a sulfur source containing radioactive sulfur (35S) in their culture media, in what molecules would the 35S be found in the cells?
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Chemical Requirements
Trace elements Inorganic elements required in small amounts Usually as enzyme cofactors
Copyright © 2010 Pearson Education, Inc. Table 6.1
The Effect of Oxygen (O2) on Growth
QUESTION: How would one determine whether a microbe is a strict anaerobe?
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Singlet oxygen: O2 boosted to a higher-energy state
Superoxide free radicals: O2–
Peroxide anion: O22–
Hydroxyl radical (OH•)
2 2 2 2 2superoxide dismutase O O 2H H O O
2 2 2 2
2 2 2
catalase
peroxidase
2H O 2H O O
H O 2O 2H O
Toxic Oxygen
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QUESTION OF THE DAY….
Oxygen in the atmosphere is essential for human life. How can some bacteria grow in the absence of oxygen?
Copyright © 2010 Pearson Education, Inc.
Organic Growth Factors
Organic compounds obtained from the environment Vitamins, amino acids, purines, and pyrimidines
Copyright © 2010 Pearson Education, Inc. Figure 6.5
Biofilms
Microbial communities Form slime or
hydrogels Bacteria attracted by
chemicals via quorum sensing
Share nutrients Sheltered from harmful
factors
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Biofilm Application Question
Patients with indwelling catheters received contaminated heparin Bacterial numbers in contaminated heparin were too low to cause
infection 84–421 days after exposure, patients developed infections Pseudomonas fluorescens was cultured from the catheters What happened?
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Culture Media
Culture medium: Nutrients prepared for microbial growth
Sterile: No living microbes Inoculum: Introduction of microbes into medium Culture: Microbes growing in/on culture medium
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Agar
Complex polysaccharide Used as solidifying agent for culture media in Petri
plates, slants, and deeps Generally not metabolized by microbes Liquefies at 100°C Solidifies at ~40°C
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Culture Media
Chemically defined media: Exact chemical composition is known
Complex media: Extracts and digests of yeasts, meat, or plants Nutrient broth Nutrient agar
QUESTION: Could Louis Pasteur, in the 1800s, have grown rabies viruses in cell culture instead of in living animals?
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Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
Anaerobic Culture Methods
Reducing media Contain chemicals (thioglycolate or oxyrase) that combine
O2
Heated to drive off O2
Anaerobic Jar Anaerobic Chamber
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Capnophiles
Microbes that require high CO2 conditions CO2 packet Candle jar
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1: No special precautions 2: Lab coat, gloves, eye
protection 3: Biosafety cabinets to
prevent airborne transmission
4: Sealed, negative pressure Exhaust air is filtered
twice
Biosafety Levels
QUESTION: Which biosafety level is observed in the photo?
Copyright © 2010 Pearson Education, Inc. Figure 6.10
Selective Media
Suppress unwanted microbes and encourage desired microbes
Copyright © 2010 Pearson Education, Inc. Figure 6.9
Differential Media
Make it easy to distinguish colonies of different microbes.
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Enrichment Culture
Encourages growth of desired microbe Assume a soil sample contains a few
phenol-degrading bacteria and thousands of other bacteria Inoculate phenol-containing culture medium with the soil,
and incubate Transfer 1 ml to another flask of the phenol medium, and
incubate Transfer 1 ml to another flask of the phenol medium, and
incubate Only phenol-metabolizing bacteria will be growing
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Obtaining Pure Cultures
A pure culture contains only one species or strain A colony is a population of cells arising from a
single cell or spore or from a group of attached cells A colony is often called a colony-forming unit
(CFU) The streak plate method is used to isolate pure
cultures
Copyright © 2010 Pearson Education, Inc. Figure 6.11
The Streak Plate Method
QUESTION: Can you think of any reason why a colony does not grow to an infinite size, or at least fill the confines of the Petri plate?
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Preserving Bacterial Cultures
Deep-freezing: –50° to –95°C Lyophilization (freeze-drying): Frozen (–54° to –
72°C) and dehydrated in a vacuum
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Binary fission Budding Conidiospores (actinomycetes) Fragmentation of filaments
Reproduction in Prokaryotes
Copyright © 2010 Pearson Education, Inc. Figure 6.12a
Binary Fission
Copyright © 2010 Pearson Education, Inc. Figure 6.13b
Cell Division
Copyright © 2010 Pearson Education, Inc. Figure 6.14
Bacterial Growth Curve
Copyright © 2010 Pearson Education, Inc. Figure 6.15
Phases of Growth
Copyright © 2010 Pearson Education, Inc. Figure 6.16
Serial Dilutions
Copyright © 2010 Pearson Education, Inc. Figure 6.17
Plate Counts
Copyright © 2010 Pearson Education, Inc. Figure 6.16
Plate Counts
After incubation, count colonies on plates that have 25–250 colonies (CFUs)
Copyright © 2010 Pearson Education, Inc. Figure 6.18
Counting Bacteria by Membrane Filtration
Copyright © 2010 Pearson Education, Inc. Figure 6.19
Most Probable Number
Multiple tube MPN test Count positive tubes Compare with statistical tables
Copyright © 2010 Pearson Education, Inc. Figure 6.20
Direct Microscopic Count
Copyright © 2010 Pearson Education, Inc. Figure 6.21
Turbidity
QUESTION: How did bacterial growth affect absorbance - why?
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Measuring Microbial Growth
Direct Methods Plate counts Filtration MPN Direct microscopic count
Indirect Methods Turbidity Metabolic activity Dry weight