Name: Blessy B Martin Subject: Microbiology and Parasitology Date: June 10 2021 Instructor: Prof. Brandon Estigoy Worksheet No. 3 Exponential Growth and Death of Bacteria Introduction Bacteria divide asexually through a process called binary fission. One bacteria can split into two new identical copies. Since bacteria are very small and simple cells, they are able to grow and reproduce very quickly under the right conditions. For this worksheet, we will follow a population of 100 bacteria on a petri dish as they grow and die. Lag Phase During this phase, the bacteria are getting used to their environment. They are adapting, ingesting food, and growing in size. Most of the individual bacteria are not fully mature and cannot divide yet. Hours # of Bacterial Cells Hours # of Bacterial Cells 1 2 3 4 5 100 100 102 106 144 6 7 8 9 10 131 144 159 178 200 1. Sketch the basic shape the graph of the lag phase would take. Make sure you label each axis. Y WORKSHEET IN MICROBIOLOGY__BME 1 2. If you were looking at a petri dish in lag phase, would you be able to see any bacterial colonies? Why? The number of cells does not change during the lag phase; however, cells grow larger and are metabolically active, synthesizing proteins needed to grow within the medium. Exponential Phase During this phase, cell doubling occurs. This growth will continue, unrestricted, as long as the bacteria have sufficient space, water, and food. Hours # of Bacterial Cells Hours # of Bacterial Cells 11 12 13 14 15 16 200 400 800 1600 3200 6400 17 18 19 20 21 22 12800 25600 51200 102400 204800 409600 3. Sketch the basic shape the graph of the exponential phase would take. Make sure you label each axis. 4. Would it be realistic to expect this kind of growth to continue endlessly? Explain. In exponential growth does not continue indefinitely and ceases after some time because of two reasons: a) The culture medium becomes so over-populated that, essential nutrients present in it are used up and become unavailable after sometime and b) Due to overpopulation, toxic waste metabolites produced by the bacteria accumulate to inhibitory levels. These lead to the beginning of death of the bacteria cells in the culture. Although cells WORKSHEET IN MICROBIOLOGY__BME 2 reproduce by binary fission and growth continues unabated, the number of cells produced almost equals the number of cells dying. This leads to the stationary phase. 3. If you were looking at a petri dish during this phase, how would you expect its appearance to change? Why? When the bacteria have already made colonies because the cells are dividing by binary fission and doubling in numbers after each generation time. Stationary Phase Eventually, the bacteria begin to experience limits to their growth. They may start to run out of space and crowd against each other, water and food may start to become depleted, and their waste products, which are toxic to growth, begin to accumulate. Hours # of Bacterial Cell Hour # of Bacterial Cell 23 410000 26 411000 24 411000 27 410500 25 411000 28 410000 6. Sketch the basic shape the graph of the stationary phase would take. Make sure you label each axis. 7. If you were looking at a petri dish during this phase, how would you expect its appearance to change? Explain. When the number of cells in the culture remains almost constant even though some cells continue to divide and others begin to die because during the stationary phase, the rate of bacterial cell growth is equal to the rate of bacterial cell death. Death Phase As the waste products of the bacteria accumulate and the bacteria run out of nutrients, they quickly begin to die. All of the colonies that were produced during the exponential growth phase die off in huge numbers. WORKSHEET IN MICROBIOLOGY__BME 3 Hours 29 30 31 32 33 Data Analysis # of Bacterial Cells Hours # of Bacterial Cells 410000 380000 340000 300000 250000 34 35 36 37 38 200000 140000 75000 30000 0 Make a line graph to show the growth and death of the bacteria in this petri dish. Time should go on the x-axis, and population on the y-axis. Label each of the four phases of bacterial growth on this graph. WORKSHEET IN MICROBIOLOGY__BME 4 8. Explain why it takes so long for the bacteria to start growing. What is happening in the lag phase? They take in nutrients and reproduce by dividing – one bacteria splits and becomes two bacteria, two become four, four become eight and so on. Doubling can occur quickly if the conditions – enough nutrients, proper temperature, adequate moisture, etc. Each type of bacteria has its own preferred conditions for growth. During lag phase, bacteria adapt themselves to growth conditions. It is the period where the individual bacteria are maturing and not yet able to divide 9. What form of reproduction is occurring in the bacteria during the exponential phase? Why is this so much faster than animal and plant reproduction? During exponential phase asexual reproduction is formed (bacterial reproduction) it is faster than animal and plant reproduction because all of them offspring have the same genetic information, individuals are more susceptible to disease. 10. What limiting factors eventually restrict the bacterial growth during the stationary phase? Stationary phase is the one which follows the period of active growth, known as exponential phase. During this phase with the cells growing at their most vigorous they are using up nutrients, growing in size and number, accumulating waste products and they enter stationary phase because the nutrient supply is becoming limited, the accumulation of waste products is having an inhibitory effect, the cells are becoming “squeezed” for space, O2 supply is depleted in short depletion of an essential nutrient, and/or the formation of an inhibitory product such as an organic acid. 11. What causes the eventual demise of the bacterial colonies during the death phase? Death occurs because cell have depleted intracellular ATP reserves. 12. Describe a real-life example of this kind of bacterial growth outside of a petri dish. In real life example of bacterial growth not all bacteria grows harmful. In fact, some even are involved in the production of foods consumed by humans. For example, bacteria that cause milk to become sour are used in making cottage cheese, buttermilk, and yogurt. Vinegar and sauerkraut also are produced by the action of bacteria on ethyl alcohol and cabbage, respectively. Other bacteria, most notably Escherichia coli ( E. coli ) in the human intestines, make it possible for animals to digest foods and even form vitamins in the course of their work. Others function as decomposers aiding in the chemical breakdown of organic materials, while still others help keep the world a cleaner place by consuming waste materials, such as feces. Despite its helpful role in the body, certain strains of E. coli are dangerous pathogens that can cause diarrhea, bloody stools, and severe abdominal cramping and pain. The affliction is rarely fatal, though in late 1992 and 1993 four people died during the course of an E. coli outbreak in Washington, Idaho, California, and Nevada. More often the outcome is severe illness that may bring on other conditions; for example, two teenagers among a group of 11 who became sick while attending a Texas cheerleading camp had to receive emergency appendectomies. The pathogen is usually transmitted through under-cooked foods, and sometimes through other means; for example, a small outbreak in the Atlanta area in the late 1990s occurred in a recreational water park. WORKSHEET IN MICROBIOLOGY__BME 5