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MICROBIAL NUTRITION & GROWTH
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Result of microbial growth is discrete colony
Growth Requirements Microbial growth Increase in a population of microbes Result of microbial growth is discrete colony An aggregation of cells arising from single parent cell Reproduction results in growth 2
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Microbes obtain nutrients from variety of sources
Growth Requirements Organisms use a variety of nutrients for their energy needs and to build organic molecules and cellular structures Most common nutrients contain necessary elements such as carbon, oxygen, nitrogen, and hydrogen Microbes obtain nutrients from variety of sources 3
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Nutrients: Chemical and Energy Requirements
Growth Requirements LEARNING OBJECTIVES Describe the roles of carbon, hydrogen, oxygen, nitrogen ,trace elements, and, vitamins in microbial growth and reproduction Compare the four basic categories of organisms based on their carbon and energy sours Distinguish among anaerobes, and microaerophiles Explain how oxygen can be fatal to organisms by discussing singlet oxygen, superoxide radical, peroxide anion, and hydroxyl, radical and describe how organisms protect themselves from toxic from of oxygen Defined nitrogen fixation and explain its importance Nutrients: Chemical and Energy Requirements Sources of carbon, energy, and electrons Two groups of organisms based on source of carbon Autotrophs Heterotrophs Two groups of organisms based on source of energy Chemotrophs Phototrophs 4
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Four basic groups of organisms
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Nutrients: Chemical and Energy Requirements
Growth Requirements Nutrients: Chemical and Energy Requirements Oxygen requirements Oxygen is essential for obligate aerobes Oxygen is deadly for obligate anaerobes How can this be true? Toxic forms of oxygen are highly reactive and excellent oxidizing agents Resulting oxidation causes irreparable damage to cells 6
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Nutrients: Chemical and Energy Requirements
Growth Requirements Nutrients: Chemical and Energy Requirements Oxygen requirements Four toxic forms of oxygen Singlet oxygen Superoxide radicals Peroxide anion Hydroxyl radical 7
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Catalase test
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Nutrients: Chemical and Energy Requirements
Growth Requirements Nutrients: Chemical and Energy Requirements Oxygen requirements Aerobes Anaerobes Facultative anaerobes Aerotolerant anaerobes Microaerophiles 9
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Oxygen requirements of organisms - overview
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Nutrients: Chemical and Energy Requirements
Growth Requirements Nutrients: Chemical and Energy Requirements Nitrogen requirements Anabolism often ceases because of insufficient nitrogen Nitrogen acquired from organic and inorganic nutrients All cells recycle nitrogen from amino acids and nucleotides Nitrogen fixation by certain bacteria is essential to life on Earth 11
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Nutrients: Chemical and Energy Requirements
Growth Requirements Nutrients: Chemical and Energy Requirements Other chemical requirements Phosphorus Sulfur Trace elements Required only in small amounts Growth factors Necessary organic chemicals that cannot be synthesized by certain organisms 12
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Physical Requirements
Growth Requirements LEARNING OBJECTIVE Explain how extremes of temperature, pH, and osmotic and hydrostatic pressure limit microbial growth Physical Requirements Temperature Effect of temperature on proteins Effect of temperature on membranes of cells and organelles If too low, membranes become rigid and fragile If too high, membranes become too fluid 13
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Microbial growth - overview
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Four categories of microbes based on temperature ranges for growth
Psychrophiles Mesophiles Thermophiles Hyperthermophiles Growth rate Temperature (°C) Four categories of microbes based on temperature ranges for growth
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An example of psychrophile - overview
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Physical Requirements
Growth Requirements Physical Requirements pH Organisms are sensitive to changes in acidity H+ and OH– interfere with H bonding Neutrophiles grow best in a narrow range around neutral pH Acidophiles grow best in acidic habitats Alkalinophiles live in alkaline soils and water 17
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Physical Requirements
Growth Requirements Physical Requirements Physical effects of water Microbes require water to dissolve enzymes and nutrients Water is important reactant in many metabolic reactions Most cells die in absence of water Some have cell walls that retain water Endospores and cysts cease most metabolic activity Two physical effects of water Osmotic pressure Hydrostatic pressure 18
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Physical Requirements
Growth Requirements Physical Requirements Physical effects of water Osmotic pressure Pressure exerted on a semipermeable membrane by a solution containing solutes that cannot freely cross membrane Hypotonic solutions have lower solute concentrations Hypertonic solutions have greater solute concentrations Restricts organisms to certain environments Obligate and facultative halophiles 19
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Physical Requirements
Growth Requirements Physical Requirements Physical effects of water Hydrostatic pressure Water exerts pressure in proportion to its depth Barophiles live under extreme pressure Their membranes and enzymes depend on pressure to maintain their shape 20
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Associations and Biofilms
Growth Requirements LEARNING OBJECTIVE Describe how quorum sensing can lead to formation. Associations and Biofilms Organisms live in association with different species Antagonistic relationships Synergistic relationships Symbiotic relationships 21
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Associations and Biofilms
Growth Requirements Associations and Biofilms Biofilms Complex relationships among numerous microorganisms Develop an extracellular matrix Adheres cells to one another Allows attachment to a substrate Sequesters nutrients May protect individuals in the biofilm Form on surfaces often as a result of quorum sensing Many microorganisms more harmful as part of a biofilm 22
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Plaque (biofilm) on a human tooth
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Culturing Microorganisms
Inoculum introduced into medium Environmental specimens Clinical specimens Stored specimens Culture Act of cultivating microorganisms or the microorganisms that are cultivated 24
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Characteristics of bacterial colonies - overview
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Culturing Microorganisms
LEARNING OBJECTIVE Describe the two most common methods by which microorganisms can be isolated for culture. Obtaining Pure Cultures Cultures composed of cells arising from a single progenitor Progenitor is termed a CFU Aseptic technique prevents contamination of sterile substances or objects Two common isolation techniques Streak plates Pour plates 26
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Streak plate method of isolation - overview
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Pour plate method of isolation - overview
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Culturing Microorganisms
LEARNING OBJECTIVE Describe six types of general culture media available for bacterial culture Culture Media Majority of prokaryotes have not been grown in culture medium Six types of general culture media Defined media Complex media Selective media Differential media Anaerobic media Transport media 29
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Slant tube containing solid media
Butt Slant tube containing solid media
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An example of the use of a selective medium
Bacterial colonies Fungal colonies pH 7.3 pH 5.6 An example of the use of a selective medium
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The use of blood agar as a differential medium
Beta-hemolysis Alpha-hemolysis No hemolysis (gamme-hemolysis) The use of blood agar as a differential medium
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The use of carbohydrate utilization tubes as differential media
Durham tube (inverted Tube to trap gas) No fermentation Acid fermentation with gas The use of carbohydrate utilization tubes as differential media
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Use of MacConkey agar as a selective and differential medium - overview
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An anaerobic culture system
Clamp Airtight lid Chamber Palladium pellets to catalyze reaction removing O2 Envelope containing chemicals to release CO2 and H2 Methylene blue (anaerobic indicator) Petri plates An anaerobic culture system
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Culturing Microorganisms
LEARNING OBJECTIVE Discuss the use of special culture methods including animal and cell culture, low-oxygen culture, and enrichment culture Special Culture Techniques Techniques developed for culturing microorganisms Animal and cell culture Low-oxygen culture Enrichment culture 36
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Culturing Microorganisms
LEARNING OBJECTIVE Contrast refrigeration, deep freezing, and lyophilization as methods for preserving culture of microbes Preserving Cultures Refrigeration Stores for short periods of time Deep-freezing Stores for years Lyophilization Stores for decades 37
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Binary fission events - overview
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Comparison of arithmetic and logarithmic growth - overview
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Growth of Microbial Populations
LEARNING OBJECTIVE Explain what is meant by the generation time op bacteria Generation Time Time required for a bacterial cell to grow and divide Dependent on chemical and physical conditions 40
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Two growth curves of logarithmic growth - overview
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Typical microbial growth curve
Stationary phase Death (decline) phase Log (exponential) phase Number of live cells (log) Lag phase Time Typical microbial growth curve
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Schematic of chemostat
Fresh medium with a limiting amount of a nutrient Flow-rate regulator Sterile air of other gas Culture vessel Culture Overflow tube Schematic of chemostat
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Growth of Microbial Populations
Measuring Microbial Reproduction Direct methods Serial dilution and viable plate counts Membrane filtration Most probable number Microscopic counts Electronic counters 44
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Estimating microbial population size - overview
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Use of membrane filtration to estimate microbial population - overview
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The most probable number (MPN) method for estimating microbial numbers
1.0 ml 1.0 ml Undiluted 1:10 1:100 Inoculate 1.0 ml into each of 5 tubes Phenol red, pH color indicator, added Incubate Results 4 tubes positive 2 tubes positive 1 tube positive The most probable number (MPN) method for estimating microbial numbers
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The use of a cell counter for estimating microbial numbers - overview
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Growth of Microbial Populations
LEARNING OBJECTIVE Contrast direct and indirect methods of measuring bacterial Measuring Microbial Growth Indirect methods Metabolic activity Dry weight Turbidity 49
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Spectrophotometry - overview
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Growth of Microbial Populations
Measuring Microbial Reproduction Genetic methods Isolate DNA sequences of unculturable prokaryotes Used to estimate the number of these microbes 51
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