Synthetic microbial communities : Microbial consortia engineering
Chapter 6 Microbial Growth © 2013 Pearson Education, Inc. Lectures prepared by Christine L. Case.
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Transcript of Chapter 6 Microbial Growth © 2013 Pearson Education, Inc. Lectures prepared by Christine L. Case.
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Chapter 6
Microbial Growth
© 2013 Pearson Education, Inc. Lectures prepared by Christine L. Case
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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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Figure 6.1 Typical growth rates of different types of microorganisms in response to temperature.
PsychrophilesPsychrotrophs
Mesophiles
Thermophiles
Hyperthermophiles
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Applications of Microbiology 6.1 A white microbial biofilm is visible on this deep-sea hydrothermal vent. Water is being emitted through the ocean floor at temperatures above 100°C.
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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
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Figure 6.4 Plasmolysis.
Plasma membraneCell wall
Cytoplasm
H2O
NaCl 10%
Cytoplasm
Plasma membrane
Cell in isotonic solution. Plasmolyzed cell in hypertonic solution.
NaCl 0.85%
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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
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Chemical Requirements
• Trace elements– Inorganic elements required in small amounts– Usually as enzyme cofactors
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Table 6.1 The Effect of Oxygen on the Growth of Various Types of Bacteria
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Organic Growth Factors
• Organic compounds obtained from the environment
• Vitamins, amino acids, purines, and pyrimidines
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Biofilms
• Microbial communities• Share nutrients• Sheltered from harmful factors
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Figure 6.5 Biofilms.
Clumps of bacteria adhering to surface
Surface Water currents
Migrating clump of bacteria
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Applications of Microbiology 3.2 Pseudomonas aeruginosa biofilm.
© 2013 Pearson Education, Inc.
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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
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Table 6.2 A Chemically Defined Medium for Growing a Typical Chemoheterotroph, Such as Escherichia coli
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Table 6.4 Composition of Nutrient Agar, a Complex Medium for the Growth of Heterotrophic Bacteria
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Anaerobic Culture Methods
• Reducing media– Contain chemicals (thioglycolate or oxyrase) that
combine O2
– Heated to drive off O2
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Figure 6.6 A jar for cultivating anaerobic bacteria on Petri plates.
Lid with O-ring gasket
Envelope containing sodium bicarbonate and sodium borohydride
Anaerobic indicator (methylene blue)
Petri plates
Clamp with clamp screw
Palladium catalyst pellets
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Figure 6.7 An anaerobic chamber.
Arm ports
Air lock
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Capnophiles
• Microbes that require high CO2 conditions
• CO2 packet
• Candle jar
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• Make it easy to distinguish colonies of different microbes
Differential Media
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Figure 6.9 Blood agar, a differential medium containing red blood cells.
Bacterial colonies
Hemolysis
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Figure 6.10 Differential medium.
Uninoculated
Staphylococcusepidermis
Staphylococcusaureus
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• Suppress unwanted microbes and encourage desired microbes
Selective Media
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Table 6.5 Culture Media
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• Binary fission• Budding• Conidiospores (actinomycetes)• Fragmentation of filaments
ANIMATION Bacterial Growth: Overview
Reproduction in Prokaryotes
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Figure 6.12a Binary fission in bacteria.
Cell elongates and DNA is replicated.
Cell wall and plasma membrane begin to constrict.
Cross-wall forms, completely separating the two DNA copies.
Cells separate.
Cell wall
Plasma membrane
DNA (nucleoid)
(a) A diagram of the sequence of cell division
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Figure 6.12b Binary fission in bacteria.
(b) A thin section of a cell of Bacillus licheniformis starting to divide
Cell wallDNA (nucleoid)
Partially formed cross-wall
© 2013 Pearson Education, Inc.
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Figure 6.13b Cell division.
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Lag PhaseIntense activity preparing for population growth, but no increase in population.
Log PhaseLogarithmic, or exponential, increase in population.
Stationary PhasePeriod of equilibrium; microbial deaths balance production of new cells.
Death PhasePopulation Is decreasing at a logarithmic rate.
The logarithmic growth in the log phase is due to reproduction by binary fission (bacteria) or mitosis (yeast).
Figure 6.15 Understanding the Bacterial Growth Curve.
Staphylococcus spp.