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. Element
% dry wgt
Source
Carbon 50
organic compounds or CO2
Oxygen 20
H2O, organic compounds, CO2, and O2
Nitrogen 14
NH3, NO3, organic compounds, N2
Hydrogen 8
H2O, organic compounds, H2
Phosphorus 3
inorganic phosphates (PO4)
Sulfur 1
SO4, H2S, So, organic sulfur compounds
Potassium
Potassium salts
Magnesium
0.5
Magnesium salts
Calcium
Calcium salts
Iron
0.2
Iron salts

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

8. A “Chemoorganic autotroph 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

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

10. 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)

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

12. 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

13. 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.

14. 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

16. 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

17. Fig. 7.13

18. 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

19. Fig. 7.14a

20. Plotting growth on graphs

21. Standard Growth Curve

22. 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

23. 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