bacterial growth power point presentation

1. Bacterial Growth

2. Growth of Microbes
 Microbial Growth
Defined:
 Increase in number of
cells, not cell size
 One cell becomes
colony of millions of
cells

3. Bacterial growth:
Binary fission
Generation time
Phases of growth

4. Binary Fission:

5. 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!

7. Phases of Growth:
4 Phases:
1) Lag phase-
2) Log (logarithmic) phase
3) Stationary phase
4) Decline phase or death phase

8. Standard Growth Curve:

9. Phases of Growth:
 Lag phase – making new enzymes in response to new medium
 Log phase – exponential growth
 Desired for production of products
 Most sensitive to drugs and radiation during this period
 Stationary phase –
 nutrients becoming limiting or waste products becoming toxic
 death rate = division rate
 Death phase – death exceeds division

10. Factors Regulating Growth
 Nutrients
 Environmental conditions:
temperature, pH, osmotic
pressure
 Generation time

11. Physical Requirements
Temperature
Oxygen requirement
pH
Water availability

12. Factors Affecting Bacterial Growth
The Requirements for Growth:
Physical Requirements
 Temperature
 Minimum growth temperature
 Optimum growth temperature
 Maximum growth temperature

13. Temperature
 Psychrophile
 0o to 18o C
 Psychrotroph
 20°C to 30°C
 Important in food spoilage
 Mesophile
 25°C to 45°C
 More common
 Disease causing
 Thermophiles
 45°C to 70°C
 Common in hot springs and hot water heaters
 Hyperthermophiles
 70°C to 110°C

14. The Requirements for Growth:
Physical Factors - Chemical Requirements
Oxygen (O2)

15. • Oxygen is a very reactive molecule and can affect cells in several ways. The effect of oxygen
is often determined using thioglycollate broth, a special medium that contains a reducing
agent (thioglycollate) that removes oxygen so that a gradient occurs within the tube.
• Obligately aerobic bacteria can obtain energy only through aerobic respiration and have to
have oxygen available. Thus, they will grow only at the surface of thioglycollate broth.
• Obligately anaerobic bacteria die in the presence of oxygen and can only grow at the
bottom of thioglycollate broth.
• Microaerophiles require oxygen for growth but the 20% in air is too toxic. As a result, they
grow near the top but beneath the surface of thioglycollate broth where the oxygen
concentration is typically 4 – 10%.
• Facultative anaerobes can use oxygen for aerobic respiration but can switch to fermentative
metabolism in the absence of oxygen. As a result, they will grow throughout thioglycollate
broth.
• Aerotolerant anaerobes are anaerobic bacteria that can grow in the presence of air.

16. pH
 Neutrophiles grow best around neutral pH (7)
 Acidophiles grow best at pH < 7
 Alkophiles grow best at pH > 7
 Acidotolerant grow best at pH 7 but can also grow at
lower pH
 Alkotolerant grow best at pH 7 but can also grow at
higher pH

17. Water Activity
 Microbes that require a high water activity (near or at 1) are
termed nonhalophiles. (Halophile = salt-loving)
 Some bacteria require salt to grow and are called halophiles. If a
very high concentration of salt is required (around saturation), the
organisms are termed extreme halophiles.
 A nonhalophile that can grows best with almost no salt but can
still grow with low levels of salt (~ 7%) is called halotolerant.
 In general, fungi are more tolerant of low water activity.

18. The Requirements for Growth:
Nutritional Factors - Chemical Requirements
 Carbon
 Structural organic molecules, energy source
 Chemo heterotrophs use organic carbon sources
 Autotrophs use CO2

19. The Requirements for Growth:
Nutritional Factors - Chemical Requirements
 Nitrogen
 In amino acids and proteins
 Most bacteria decompose proteins
 Some bacteria use NH4
+ or NO3
–
 Sulfur
 In amino acids, thiamine and biotin
 Some bacteria use SO4
2– or H2S
 Phosphorus
 In DNA, RNA, ATP, and membranes
 PO4
3– is a source of phosphorus

20. The Requirements for Growth:
Nutritional Factors - Chemical Requirements
 Trace elements
 Inorganic elements required in small amounts
 Usually as enzyme cofactors
 Vitamins- organic substances and growth factors

21. The End