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Bacterial Cultivation & Growth

Bacterial Cultivation & Growth. Culturing Microorganisms Binary fission & sporulation What determines growth? Media Types Batch vs Continuous Culture Growth. Binary Fission in Prokaryotes. Dividing vegetative cells But what happens when stressed or starved?. Endospores:.

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Bacterial Cultivation & Growth

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  1. Bacterial Cultivation & Growth • Culturing Microorganisms • Binary fission & sporulation • What determines growth? • Media Types • Batch vs Continuous Culture Growth

  2. Binary Fission in Prokaryotes

  3. Dividing vegetative cellsBut what happens when stressed or starved?

  4. Endospores: • Resting stage during “lean or stressful times”. • Resistant protein coat! • Develop in different locations of vegetative cell: • Schaeffer – Fulton Stain: free; sub-terminal; central; terminal Young (24 h) Old (96 h)

  5. Endospores & Sporulation (cortex) Dipicolinic Acid & Calcium protects DNA from heat. Spore coat proteins resist toxic chemicals. exosporium

  6. Spore Germination:activation; germination; outgrowth

  7. Culturing Microorganisms • Tolerance to All Environmental Factors (Shelford’s Law of Tolerance) • Growth Limiting Resource (Liebig’s Law of the Minimum): Nutrient in least supply relative to bacterial needs will cap growth yield. • Temperature • Solute Concentration / Water Activity • pH (acidity versus alkalinity) • Oxygen Concentration • Barometric Pressure • Electromagnetic Radiation

  8. Closed (“batch”) Culture Systems“growth curve” Unbalanced Growth Balanced Growth: Rates of RNA = Protein = DNA = binary fission

  9. Exponential Growth PhaseNt = No + 2n Number of generations (n) = (log Nt – log No) / log 2 Growth Rate Constant (k) = n/t It is expressed in units of generations per hours (h-1) Generation time (g) = 1/k; it is expressed in units of hours (h).

  10. Time (hours) k = (log Nt – log No) / 0.301 t Generation time (g) = doubling time

  11. Nutrient Concentration Effects in Batch Cultures: • Total growth will increase until limiting nutrients are exhausted (included oxygen for aerobes) or metabolic byproducts accumulate that change environmental conditions to inhibit growth (toxicity). • Growth rate will also increase with increasing nutrient concentration up to a some maximum value, beyond which there is no effect (transporters are saturated with there substrate.

  12. Open (“continuous”) Culture Systems Chemostat: growth rate = dilution rate (D = f/V); constant dilution rate with nutrient limiting growth. Turbidostat: dilution rates varies to maintain constant turbidity (cell density); no limiting nutrient. Flow (f) Wash out! Volume (V)

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