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Bacterial Cultivation & Growth

Learn about bacterial cultivation techniques, binary fission, and sporulation processes. Explore the factors influencing bacterial growth in various media types, from batch to continuous cultures. Discover the significance of endospores and how they protect bacterial DNA during stressful conditions. Dive into the mechanisms of spore germination and the importance of culturing microorganisms in different environmental conditions.

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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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