Bacterial Physiology PDF

# Bacterial Reproduction ## Binary Fission * Method of bacterial reproduction to increase their numbers. * One cell divides into two equal daughter cells similar to the parent cell. ## Bacterial generation time * The time it takes for a population to double in number. * For many common bacteria,...

# Bacterial Reproduction ## Binary Fission * Method of bacterial reproduction to increase their numbers. * One cell divides into two equal daughter cells similar to the parent cell. ## Bacterial generation time * The time it takes for a population to double in number. * For many common bacteria, the generation time is quite short, 20-60 minutes under optimum conditions. ## Diagram of Binary Fission The diagram shows the steps of binary fission: 1. **DNA replication:** The bacterial DNA replicates, and the two copies attach to the cell membrane. 2. **Cell elongation:** The cell wall begins to elongate, increasing the cell's surface area. 3. **Septum formation:** A septum forms between the two DNA copies, dividing the cell. 4. **Completion of septum with formation of distinct walls:** The septum continues to grow, forming two distinct cell walls. 5. **Cell separation:** The two daughter cells separate, each with their own copy of DNA and a complete cell wall. ## Bacterial Growth Curve * Bacteria are inoculated into a liquid nutrient medium, and the bacteria are counted at frequent intervals. * The results are plotted, showing a characteristic growth curve with four phases: ### Bacterial growth curve: 4 phases 1. **Lag phase:** The first phase where no cell division occurs as the bacteria adapt to the environment and form new enzymes and molecules for replication. 2. **Log (exponential) phase:** Rapid cell division occurs, increasing the number of bacterial cells steadily, making this the best stage for antibiotic action. Bacteria can be categorized as rapid or slow growers based on cell growth time in this phase. 3. **Stationary phase:** Nutrient exhaustion and the accumulation of toxic products slow down the growth rate until the number of dying cells equals the number of new cells, so the number of living bacteria remains constant. 4. **Death phase:** The exhaustion of nutrients and accumulation of toxic products continues, which causes the death rate to exceed the multiplication rate and the number of living bacteria to decline. ## Typical growth curve for a bacterial population The chart shows the typical growth curve for a bacterial cell population with the following characteristics: - **Lag phase:** Few live cells - **Exponential growth phase:** Many live cells - **Stationary phase:** Many live cells - **Death Phase:** Dead cells, some cells remain viable.