Presentation

1. Energy source,and a source of carbon and other required nutrients, and some physical conditions such as o 2 conc.,temp,and ph,moisture based on their patterns of growth under various chemical (nutritional) or physical conditions. For example phototrophs are organisms that use light as an energy source; anaerobes are organisms that grow without oxygen; thermophiles are organisms that grow at high temperatures.

2. According to these conditions they can grow. The growth is measured in a graph. The growth curve has 4 phases: Lag phase Log or exponential phase Stationary phase Death or decline phase

3. Growth curve

4. Lag phase A Bacteria do not grow during the lag phase. They do adjust to their environment and metabolize, that is, produce vitamins and amino acids needed for division. They begin making copies of their DNA, and if the environment supplies plenty of nutrients, the lag phase may be very short. Then the bacteria will proceed to the next phase of their life. This phase occurs slowly.

5. Log phase During the log phase, bacteria multiply rapidly, even exponentially. The time it takes for a culture to double is called "generation time," and under the best conditions, the fastest bacteria can double in about 15 minutes. Other bacteria take days. Metabolic activity and some physiological characteristics were done much more fastly .

6. The generation time g (the time required for the population to double) can be determined from the number of generations n that occur in a particular time interval t the generation time is calculated by the formula: g= t/n=t/3.3(log 10 N-log 10 N ) It is for e.coli because e.coli is a basic bacteria. Not all bacteria have the same generation time.

7. During exponential growth, the growth rate ( ie ., the generations per hour), termed as R is the reciprocal of the generation time g. R=3.3 (log 10 N-log 10 N o )/t

8. Stationary phase: During this phase bacteria growth dwindles. It is due to some growth-limiting factor such as the depletion of an essential nutrient, or the formation of an inhibitory product (organic acid). This results in a “smooth,” horizontal linear part of the curve during the stationary phase. The population remains constant.

9. Death phase: With the exhaustion of nutrients and build-up of waste and secondary metabolic products, the growth rate has slowed to the point where the growth rate equals the death rate. Effectively, there is no net growth. T he bacteria may die faster than new cells produced.