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Microbial Growth

Microbial Growth. Growth of Microbes. Orderly increase of all of the chemical constituents of the cell. Bact.growth-both an increase in the size and no. of the cells. Net effect an increase in the total mass i.e.biomass. Bacteria divide by binary fission.

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Microbial Growth

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  1. Microbial Growth

  2. Growth of Microbes Orderly increase of all of the chemical constituents of the cell. Bact.growth-both an increase in the size and no. of the cells. Net effect an increase in the total mass i.e.biomass. Bacteria divide by binary fission. Nuclear division precedes cell division.

  3. Factors Regulating Growth • Chemical requirements( macro n micronutrients) • Growth factors(essential n accessory) like thiamine, riboflavin,nicotinic acid, folic acid, B12. • Physical factors: Environmental conditions: temperature, pH, osmotic pressure,oxygen,co2,moisture n drying,light, mechanical n sonic stresses. • Energy sources( photo n chemotrophs) • Generation time( interval of time between two cell divisions or time required for a bacterium to give rise to two daughter cells under optimal conditions.)

  4. I.Nutritional Requirements • Major elements (CHONPS + K, Mg, Fe, Ca) Carbon, oxygen, hydrogen, nitrogen, sulfur, phosphorus, potassium, magnesium, iron, and calcium Organisms classified based on carbon usage • Heterotrophs Use organic carbon as nutrient source. • Autotrophs Use inorganic carbon (CO2) as carbon source • Trace elements (Co, Cu, Ni, Zn, Se, Mg, Wo) • Cobalt, zinc, copper, molybdenum and manganese • Required in minute amounts • Assist in enzyme function • Nutritional diversity • Different organisms require the same nutrients but may require different forms of the nutrients

  5. Major elements

  6. Nutritional Categories • Carbon sources • CO2 = autotroph • organic = heterotroph • Energy sources • sunlight = phototroph • organic = chemotroph • Derive both carbon and energy from organic compnds(chemohetero)

  7. A “Chemoorganicautotroph would be…. Derives energy from organic compounds and carbon source from inorganic compounds A related ancient group….. Lithoautotroph Neither sunlight nor organics used, rather it relies totally on inorganics

  8. Nutritional Categories • Saprobe – lives on organic matter of dead organisms • Parasite – lives on organic matter of living host = pathogens

  9. II.Environmental Factors Influencing Growth • Temperature • O2 • CO2 • pH • Osmotic Pressure(plasmolysis n plasmotysis) • Moisture n drying( lyophilization or freeze drying) • Light • Mechanical n sonic stresses.(grinding n vigorous shaking with glass beads)

  10. Temperature Optima • Psychrophiles: cold-loving • Mesophiles: moderate temperature-loving • Thermophiles: heat-loving • Each has a minimum, optmum, and maximum growth temperature

  11. Temperature Optima • Optimum growth temperature is usually near the top of the growth rang • Death above the maximum temp. comes from enzyme inactivation • Mesophiles most common group of organisms • 40ºF (5°C) slows or stops growth of most microbes

  12. Oxygen Requirements • Obligate aerobes – require O2.e.g pseudomonas,vibrio. • Facultative anaerobes – can use O2 but also grow without it.ecoli n staph. • Obligate anaerobes – die in the presence of O2.clostridia n bacteroides.

  13. pH • Most bacteria grow between pH 6.5 and 7.5 • Acid (below pH 4) good preservative for pickles n cheeses • Acidophiles can live at low pHe.g lactobacillus. • Vibrio grows at alkaline pH

  14. Bacterial Division • Bacteria divide by binary fission. • No mitosis • Colony: clone of cell derived from a single parent..millions of bacteria in a single colony • Colonies on soid media • Diffuse growty in liquid media • Logarithmic growth,geometric progression or exponential growth

  15. Fig. 7.13

  16. Generation Time • Time required for cell to divide/for population to double • Average for bacteria is 1-3 hours • E. coli generation time = 20 min • 20 generations (7 hours), 1 cell becomes 1 million cells! • Tubercle bacilli 20 hrs • Lepra bacilli 20 days

  17. Fig. 7.14a

  18. Plotting growth on graphs

  19. Standard Growth Curve

  20. Phases of Growth 1.Lag phase After inoculation of microorg.in fresh culture medium, no immediate increase in cell no. • Increase in cell size but no cell division, cells r not dormant • making new enzymes in response to new medium(adaptation) • Variable in length 2.Log phase : exponential growth • Desired for production of products • Most sensitive to drugs and radiation during this period • Population is most uniform in physiological n chemical properties

  21. Phases of Growth • Stationary phase – • nutrients becoming limiting or waste products becoming toxic,changes in Ph,decreased o2 tension • death rate = division rate • Death phase – death exceeds division

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