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Microbial Nutrition and
Growth
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
© 2012 Pearson Education Inc.
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
© 2012 Pearson Education Inc.
Growth Requirements
• 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
© 2012 Pearson Education Inc.
Figure 6.1 Four basic groups of organisms
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
© 2012 Pearson Education Inc.
Growth Requirements
• Nutrients: Chemical and Energy Requirements– Oxygen requirements
– Four toxic forms of oxygen– Singlet oxygen– Superoxide radicals– Peroxide anion– Hydroxyl radical
© 2012 Pearson Education Inc.
Growth Requirements
• Nutrients: Chemical and Energy Requirements– Oxygen requirements
– Aerobes– Anaerobes– Facultative anaerobes– Aerotolerant anaerobes– Microaerophiles
© 2012 Pearson Education Inc.
Figure 6.3 Oxygen requirements of organisms-overview
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
© 2012 Pearson Education Inc.
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
© 2012 Pearson Education Inc.
Growth Requirements
• 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
© 2012 Pearson Education Inc.
Figure 6.4 Microbial growth-overview
Figure 6.5 Four categories of microbes based on temperature ranges for growth
Psychrophiles
Mesophiles
Thermophiles
Hyperthermophiles
Gro
wth
rate
Temperature (°C)
Figure 6.6 An example of psychrophile-overview
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
© 2012 Pearson Education Inc.
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
© 2012 Pearson Education Inc.
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
© 2012 Pearson Education Inc.
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
© 2012 Pearson Education Inc.
Growth Requirements
• Associations and Biofilms– Organisms live in association with different species
– Antagonistic relationships– Synergistic relationships– Symbiotic relationships
© 2012 Pearson Education Inc.
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
© 2012 Pearson Education Inc.
Figure 6.7 Plaque (biofilm) on a human tooth
Culturing Microorganisms
• Inoculum introduced into medium– Environmental specimens– Clinical specimens– Stored specimens
• Culture – Act of cultivating microorganisms or the
microorganisms that are cultivated
© 2012 Pearson Education Inc.
Figure 6.8 Characteristics of bacterial colonies-overview
Culturing Microorganisms
• 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
© 2012 Pearson Education Inc.
Figure 6.9 Streak plate method of isolation-overview
Figure 6.10 Pour plate method of isolation-overview
Culturing Microorganisms
• 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
© 2012 Pearson Education Inc.
Figure 6.11 Slant tube containing solid media
Slant
Butt
Figure 6.12 An example of the use of a selective medium
Fungal coloniesBacterial colonies
pH 7.3 pH 5.6
Figure 6.13 The use of blood agar as a differential medium
Beta-hemolysisAlpha-hemolysis
No hemolysis(gamme-hemolysis)
Figure 6.14 The use of carbohydrate utilization tubes as differential media
No fermentation Acid fermentationwith gas
Durham tube(inverted tubeto trap gas)
Figure 6.15 Use of MacConkey agar as a selective and differential medium-overview
Figure 6.16 An anaerobic culture system
Clamp
Chamber
Petri plates
Airtight lid
Envelopecontainingchemicals torelease CO2and H2
Palladium pelletsto catalyze reactionremoving O2
Methylene blue(anaerobicindicator)
Culturing Microorganisms
• Special Culture Techniques– Techniques developed for culturing
microorganisms– Animal and cell culture– Low-oxygen culture– Enrichment culture
© 2012 Pearson Education Inc.
Culturing Microorganisms
• Preserving Cultures– Refrigeration
– Stores for short periods of time – Deep-freezing
– Stores for years – Lyophilization
– Stores for decades
© 2012 Pearson Education Inc.
Growth of Microbial Populations
ANIMATION Bacterial Growth: Overview
© 2012 Pearson Education Inc.
Growth of Microbial Populations
© 2012 Pearson Education Inc.
ANIMATION Binary Fission
Figure 6.17 Binary fission events-overview
Figure 6.18 Comparison of arithmetic and logarithmic growth-overview
Growth of Microbial Populations
• Generation Time– Time required for a bacterial cell to grow
and divide– Dependent on chemical and physical
conditions
© 2012 Pearson Education Inc.
Figure 6.19 Two growth curves of logarithmic growth-overview
Figure 6.20 Typical microbial growth curve
Stationary phase
Death(decline)phaseLog
(exponential)phase
Lag phase
Time
Num
ber o
f liv
e ce
lls (l
og)
Growth of Microbial Populations
© 2012 Pearson Education Inc.
ANIMATION Bacterial Growth Curve
Figure 6.21 Schematic of chemostat
Fresh medium witha limiting amountof a nutrient
Sterile airof othergas
Culture
Culturevessel
Flow-rateregulator
Overflowtube
Growth of Microbial Populations
• Measuring Microbial Reproduction– Direct methods
– Serial dilution and viable plate counts– Membrane filtration– Most probable number– Microscopic counts– Electronic counters
© 2012 Pearson Education Inc.
Figure 6.22 Estimating microbial population size-overview
Figure 6.23 Use of membrane filtration to estimate microbial population-overview
Figure 6.24 The most probable number (MPN) method for estimating microbial numbers
1.0 ml 1.0 ml
1:1001:10Undiluted
Inoculate 1.0 ml intoeach of 5 tubes
Phenol red, pHcolor indicator,added
Incubate
Results
4 tubes positive 2 tubes positive 1 tube positive
Figure 6.25 The use of a cell counter for estimating microbial numbers-overview
Growth of Microbial Populations
• Measuring Microbial Growth– Indirect methods
– Metabolic activity– Dry weight– Turbidity
© 2012 Pearson Education Inc.
Figure 6.26 Spectrophotometry-overview
Growth of Microbial Populations
• Measuring Microbial Reproduction– Genetic methods
– Isolate DNA sequences of unculturable prokaryotes
– Used to estimate the number of these microbes
© 2012 Pearson Education Inc.