Each growing culture is carefully kept at the appropriate, and constant, temperature for the length of the experiment. At regular intervals of time, small samples of the growing culture are taken from the flask and all reproduction of the microbes stopped by some poison or inhibitor they can also be chilled or frozen.
The size of the population at each time point is then determined. M endel's M other shows you -- how bacteria grow. The results of each of your investigations should be recorded as a table a Table of Results. In these tables you should indicate the name of the microbe being studied, the temperature growth, and make an accurate record of either the growth data growth curve , or the value of the generation time generations per minute , as required.
The logatithmic value of the generations per hour should also be recorded on your table of results. The results of each investigation should then be presented as a graph. The horizontal axis of the graph should be the intervals of the different temperatures at which the microbes were grown. The vertical axis should represent the logarithmic value of the generations per hour determined for that sample. This is called a Arrhenius plot.
The shape of these graphs or plots is characteristic for each species of microbe, but each organism will show an optimum temperature where growth proceeds most rapidly, and as the temperatures either exceed, or fall below that optimum, growth slows down.
Above or below the maximum and minimum permissive temperatures, all growth stops. Each investigation is carried out under a specific set of growth conditions. A species of microbe is chosen first.
It is then necessary to chose a temperature. Use the thermometer sliding scale to set the chosen temperature. The value chosen will appear in the box. Growth Factors - Microbes can exist in a great many environments because they are small, easily dispersed, need only small quantities of nutrients, are diverse in their nutritional requirements.
Physical Factors. Lactobacilllus ferments milk. Vibrio cholerae causes cholera. Halophiles salt lovers inhabit the oceans. Some bacteria have enzyme systems that can repair some mutations. Oxygen Requirements. Clostridium tetani. Methods of Obtaining Pure Cultures a culture that contains only 1 species of organism. The loop is flamed and a few bacteria are picked up from the region already deposited and streaked onto a new region.
Fewer and fewer bacteria are deposited as the streaking continues, and the loop is flamed after each streaking. Individual organisms individual cells are deposited in the region streaked last. After the plate is incubated at a suitable growth temperature for the organism, small colonies each derived from a single bacterial cell appear.
The loop is used to pick up a portion of an isolated colony and transfer it to another medium for study. The use of aseptic technique assures that the new medium will contain organisms of a single species. Neisseria gonorrhoeae. Water is added to the gas-pak.
Water is converted into hydrogen gas and carbon dioxide. The hydrogen gas can then bind with any oxygen in the jar to form water. A methylene blue test strip is included in the jar to ensure that anaerobic conditions are reached.
When oxidized oxygen is present the strip is blue; when reduced no oxygen , the strip is clear. Return to Chp. Two Types of Asexual Reproduction in Microbes: 1. Microbial Growth A. Inorganic carbon autotrophs - carbon dioxide. Microaerobic formally called microaerophils. If these organism need increased carbon dioxide they are called capnophilic. Exception, Helicobacter pylori which inhabits the stomach with a pH approaching pH 1.
This organism makes ammonia to neutralize the stomach acid around it. Temperature -- Psychrophiles have a low temperature optimum Listeria monocytogenes grows best at low temperatures and cultures can be enriched by incubation at refrigerator temperature. Mesophiles have an optimum growth temperature around human body temperature. Thermophiles have a hot optimum growth temperature. Cold temperatures are often used to slow microbial growth and thus preserve foods.
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