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Lectures prepared by Christine L. Case
Chapter 6 Microbial Growth Lectures prepared by Christine L. Case © 2013 Pearson Education, Inc. 1
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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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Thermophiles Hyperthermophiles Mesophiles Psychrotrophs Psychrophiles
Figure 6.1 Typical growth rates of different types of microorganisms in response to temperature. Thermophiles Hyperthermophiles Mesophiles Psychrotrophs Psychrophiles
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Applications of Microbiology 6
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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Cell in isotonic solution. Plasmolyzed cell in hypertonic solution.
Figure 6.4 Plasmolysis. Plasma membrane Plasma membrane Cell wall H2O Cytoplasm Cytoplasm NaCl 0.85% NaCl 10% Cell in isotonic solution. Plasmolyzed cell in hypertonic solution.
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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 SO42– or H2S Phosphorus In DNA, RNA, ATP, and membranes PO43– 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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Clumps of bacteria adhering to surface Migrating clump of bacteria
Figure 6.5 Biofilms. Clumps of bacteria adhering to surface Migrating clump of bacteria Surface Water currents
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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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Envelope containing sodium bicarbonate and sodium borohydride
Figure 6.6 A jar for cultivating anaerobic bacteria on Petri plates. Clamp with clamp screw Lid with O-ring gasket Envelope containing sodium bicarbonate and sodium borohydride Palladium catalyst pellets Anaerobic indicator (methylene blue) Petri plates
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Figure 6.7 An anaerobic chamber.
Air lock Arm ports
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Capnophiles Microbes that require high CO2 conditions CO2 packet
Candle jar
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Differential Media Make it easy to distinguish colonies of different microbes
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Bacterial colonies Hemolysis
Figure 6.9 Blood agar, a differential medium containing red blood cells. Bacterial colonies Hemolysis
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Uninoculated Staphylococcus epidermis Staphylococcus aureus
Figure 6.10 Differential medium. Uninoculated Staphylococcus epidermis Staphylococcus aureus
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Selective Media Suppress unwanted microbes and encourage desired microbes
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Table 6.5 Culture Media
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Reproduction in Prokaryotes
Binary fission Budding Conidiospores (actinomycetes) Fragmentation of filaments ANIMATION Bacterial Growth: Overview
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(a) A diagram of the sequence of cell division
Figure 6.12a Binary fission in bacteria. Cell wall Cell elongates and DNA is replicated. Plasma membrane Cell wall and plasma membrane begin to constrict. DNA (nucleoid) Cross-wall forms, completely separating the two DNA copies. Cells separate. (a) A diagram of the sequence of cell division
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Partially formed cross-wall
Figure 6.12b Binary fission in bacteria. Partially formed cross-wall DNA (nucleoid) Cell wall (b) A thin section of a cell of Bacillus licheniformis starting to divide © 2013 Pearson Education, Inc.
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Figure 6.13b Cell division.
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Figure 6.15 Understanding the Bacterial Growth Curve.
Lag Phase Intense activity preparing for population growth, but no increase in population. Log Phase Logarithmic, or exponential, increase in population. Stationary Phase Period of equilibrium; microbial deaths balance production of new cells. Death Phase Population Is decreasing at a logarithmic rate. The logarithmic growth in the log phase is due to reproduction by binary fission (bacteria) or mitosis (yeast). Staphylococcus spp.
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