Chapter 6: Microbial Nutrition and Growth
Growth Requirements
Nutrients: Chemical Energy Requirements
-Sources of carbon, energy, and electrons:
1. Photoautotrophs2. Chemoautotrophs3. Photoheterotrophs4. Chemoheterotrophs5. Organotrophs-.
6. Lithotrophs-Oxygen requirements:
1. Obligate Aerobes-
2. Obligate Anaerobes-singlet oxygen (1O2)-
-superoxide radical (O2-)-
-peroxide anion (O22-)-hydroxyl radical (OH-)-
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3. Facultative Anaerobes-
4. Aerotolerant anaerobes-
5. Microaerophiles-
-Nitrogen Requirements-Nitrogen is needed in amino acids (proteins and enzymes) and
nucleotide bases (DNA and RNA), if low, anabolism stops.
-Nitrogen is acquired from organic and inorganic nutrients.
-Many organisms cannot use atmospheric Nitrogen (79% of
atmosphere), a few bacteria reduce N2 to NH3 (ammonia); nitrogen
fixation.
-Nitrogen fixation is essential for life on Earth.
-Other Chemical Requirements
-C, H, O, N make up 95% of the dry weight of cells
-phosphorus, sulfur, calcium, manganese, copper, iron, and a few
other elements constitute the other 5%, trace elements.
-growth factors-
Physical Requirements:
-Temperature- temperature plays an important role in microbial life, due
to its effects on the 3-D configurations of biological molecules
-Organisms usually have a minimum, maximum, and optimum
growth temperature.
-Psychrophiles-
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-Mesophiles-Thermophiles-Hyperthermophiles-pH- organisms are sensitive to changes in acidity
-Neutrophiles-Acidophiles-Alkalinophiles-Physical Effects of Water- water is essential for growth and metabolism
-Osmotic pressure-
-There are some cells that can withstand hypertonic solutions:
-obligate halophiles-facultative halophiles-Hydrostatic pressure is related to the pressure found at various
depths under water.
-barophilesEcological Associations- all organisms live in relationships with other organisms
-Antagonistic relationship-Synergistic relationship-
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-Symbiotic relationship-
-Biofilms-quorum sensing-
Culturing Microorganisms
InoculumMedium- a
-culture tubes-petri dish-use of solid media allows the determination of a bacteria’s colony growth
characteristics:
Clinical SamplingObtaining Pure Cultures-CFU (colony forming unit)-Streak Plates-Pour PlatesCulture Media- can be very general or very specific in their growth requirements
-Defined Media-
-Complex Media-
-Selective Media-
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-Enrichment Culture-
-Differential Media-
-Anaerobic Media-
-Transport MediaSpecial Culture Techniques
-Animal and Cell Culture-Low-Oxygen CulturePreserving Cultures
-refrigeration is the best technique for storing bacteria for short periods of
time.
-deep-freezing and lyophilization used for long term storage of bacterial
cultures.
Growth of Microbial Populations
Mathematical Considerations in Population Growth-the number of cells arising from a single cell reproducing by binary fission
is calculated as 2n, where n is the number of generations.
[15 generations from 1 cell will be 215 = 32,768 cells]
[15 generations from 3 cells will be 3 x 215 = 98,304 cells]
-scientific notation is used when writing down bacterial population
[1,073,741,824 is written as 1.07 x 109]
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Generation Time-optimal conditions can allow some bacteria (E. coli and S. aureus) to
have a generation time of 20 minutes or less (that’s fast!)
-most bacteria have a generation time of 1-3 hours
-some slow growing bacteria (Mycobacterium leprae) need more than 10
days before they double.
Phases of Microbial Growth-There is a general pattern to bacterial growth, even though the rate may
differ from species to species.
-Lag phase-Log phase-Stationary Phase-Death PhaseMeasuring Microbial Growth
-Direct Methods include viable plate counts, membrane filtration,
microscopic counts, electronic counters, and most probable number.
-Microscopic Counters-Electronic Counters-Viable Plate Counts-Membrane Filtration-
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-Most Probable Number-
-Indirect methods include metabolic activity, dry weight, and turbidity
-Turbidity-Metabolic Activity-Dry Weight-Genetic Methods-
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