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MICROBIAL GROWTH

MICROBIAL GROWTH. Microbial growth = increase in the number of cells Requirements for growth: Physical: temperature, pH, osmotic pressure Chemical: the necessary chemical elements. Physical Requirements for Growth. Temperature minimum growth temp - lowest temp at which organism can grow

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MICROBIAL GROWTH

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  1. MICROBIAL GROWTH

  2. Microbial growth = increase in the number of cells • Requirements for growth: • Physical: temperature, pH, osmotic pressure • Chemical: the necessary chemical elements

  3. Physical Requirementsfor Growth • Temperature • minimum growth temp - lowest temp at which organism can grow • optimum growth temp - where the organisms grows the best (usually toward upper end of range) • maximum growth temp - highest temp at which organism can grow

  4. Psychrophiles (cold-loving) grows at 0 C with optimum at 15 C • Psychrotrophs (cold-loving) grows at 0 C with optimum of 20-30 C (grows well at refrigerator temp - causes food spoilage) • Mesophile (moderate-temp loving) 25-40 C with optimum around 37 C • Thermophiles (heat-loving) optimum at around 50-60 C • extreme thermophiles

  5. pH • Optimum 6.5 - 7.5 • a few will grow under 4.0 (mostly fungi) • some can grow in a pH as low as 1.0 (acidophiles) • use acid food, pickling to inhibit bacteria • bacteria produce acids that interfere with growth - must use buffers in media

  6. Osmotic Pressure • Bacteria in hypertonic environment produces plasmolysis (isotonic is OK; hypotonic is OK if cell wall is strong) • Halophiles - live in high salt • facultative and extreme • Agar percentatge in media is 1.5 - more would be hypertonic to bacteria

  7. CARBON • Source: CO2; organic carbon • Use: organic carbon

  8. NITROGEN • Source: N2; NH3; NO3 (N fixation) organic • Use: amino acids, nucleotides

  9. PHOSPHORUS • Source: PO4 (phosphate); organic • Use: nucleotides; ATP; phospholipids

  10. SULFUR • Source: SO4 (sulfate); H2S (hydrogen sulfide); organic • Uses: 2 amino acid R groups

  11. OTHER CHEMICAL ELEMENTS • Calcium, Potassium, Magnesium are used as cofactors • Iron, Copper, Zinc, Molybdenum are trace elements required in very small quantities • Organic Growth Factors: molecules that the microorganism can’t make - some vitamins and amino acids

  12. OXYGEN • Oxygen gas in atmosphere • A highly corrosive and harmful gas that can oxidize organic matter • Early life on earth did not have to contend with oxygen in air • After photosynthesis evolved, organisms had to deal with oxygen gas or die • Respiration was one way to handle oxygen

  13. OYXGEN REQUIREMENTS • Aerobes: can use oxygen in respiration • obligate aerobes: must have oxygen • Facultative anaerobes: can use oxygen if present but can live without it • Obligate anaerobes: can not survive if oxygen is present • Aerotolerant: can live in presence of oxygen but does not use it

  14. Microaerophilic: grows in oxygen concentrations less than atmosphere (likes a little oxygen)

  15. CULTURE MEDIA REQUIREMENTS • Culture media: all of the things that are necessary for a microorganism to grow • Must have: • nutrients • right environment (temp, pH, solute, O2, H2O) • must be sterile • may use agar to solidify

  16. WHY AGAR? • liquefies at 100 degrees C • stays liquid until 40 degrees C • few microorganisms digest it (this was major problem with gelatin solidifiers)

  17. TYPES OF MEDIA • chemically defined media: exact composition is known since elements are measured out; Fig 6.2, 6.3, 6.4 • complex media: exact composition is not known (varies slightly with each batch) • components: partially digested protein (peptone), yeast extract, beef extract

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