1. Bacterial Growth

2. I. Determine in terms of population size. Nature there is a mixture of organisms living together. Nature there is a mixture of organisms living together. How can we get a certain type of bacteria? How can we get a certain type of bacteria? Pure Culture - separating the progeny of a single bactium from all others. Pure Culture - separating the progeny of a single bactium from all others.

3. Koch - interested in disease causing bacteria (major contributor to pure culture techniques). Initially grew bacteria on potato surface but had problem: Not enough nutrition for bacterial growth. Added gelatin as a solidifying agent. (Warm - pour, cool - solid) Streak-plate method - simplest & most common method to isolate a single bacterium. Hesse (Koch’s assistant) agar (polysaccharide extract from marine algae) - easier to work with then gelatin (solid over a wider range then gelatin). Julius Petri - Petri dish

4. Streak-Plate Method

5. II. Bacterial growth formula to determine population size: formula to determine population size: b = B2 n B= Number of cells at time zero (beginning). b= number a cells at any later time. n = number of cell generations.

6. A. Growth can be measured as an increase in mass (weight) of the population. A. Growth can be measured as an increase in mass (weight) of the population. B. Growth can be measured as an increase in cell number. B. Growth can be measured as an increase in cell number. 1. Plate count method - count the number of colonies on the medium. 2. Direct microscopic count - counting the number of bacterium in an known volume of liquid.

7. III. Factors that influence microbial growth. A. Temperature 1. Most bacteria grow within or near 30C. 2. Four groups of bacteria based upon their optimum growth temperatures. a. Psychrophiles 5C - 20C b. Mesophiles 20C - 50C c. Thermophiles 50C - 80C d. Hyperthermophiles +80C

8. 3. Food Preservation Refrigerators retards food spoilage because most of the microorganism that cause spoilage are mesophiles. 4. Temperature & Human diseases. Human body 37C (brain, heart, gastrointestinal tract). 20C - 25C (fingertips, ears, feet, hands, scrotum). Ex - leprosy (Mycobacterium leprae)- involves the coolest regions of the body.

9. B. Oxygen Requirements 1. Strict Aerobes - require free oxygen to grow. 2. Strict (obligate)Anaerobes - will not grow in the presence of free oxygen, may even be killed. 3. Micro-aerophilic -prefers the presence of low oxygen (2% - 10% Oxygen). 4. Facultative Aerobes or Facultative Anaerobes - lives in the presence of both: Growth occurs more rapidly in the presence of oxygen. 5. Aerotolerant - will grow in the presence of oxygen but do not posse an oxidative metabolism: Derive no benefit from the presence of oxygen.

10. Why can some bacteria thrive in the presence of oxygen but others are killed by it? Oxygen can be converted into a toxic form like hydrogen peroxide (H2O2) & Superoxide (O2-). Cells that do not die in the presence of oxygen produce enzymes (Superoxide dismutase) into a harmless form (H20 & O2).

11. C. pH Most bacteria grow best in an medium with a pH of 7 (neutral). Can live in a wider range - 5 - 8. Ex. Helicobacter pylori - live in very low acidic environments (humans stomach’s) & may cause ulcers. Acidophilic. Bacteria produce metabolic products that may acidic or basic. Need a BUFFER (pH stabilizer) to grow bacteria.

12. 4. Osmotic Pressure - pressure that is required to prevent the net flow of water across the cell membrane. Salt concentration effect water movement. Use salt as an growth inhibiting factor in food preservation.

13. IV Cell multiplication requires a source of energy & raw material for synthesis of cell components. A. Bacterial Nutrients Raw Materials Organic Compounds Carbon, Nitrogen, Oxygen, Hydrogen. Inorganic Compounds all other compounds including ions. Two Purposes of nutrition 1. Build up (Synthesize) protoplasm. 2. Supply energy to life processes.

14. B. Energy Source C. Mineral Requirements D. Growth Factors Small organic molecules other than carbon that bacteria must provide in order to grow (amino acids & vitamins).

15. V. Dynamics of population growth.