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12-13_Microbial_Growth___Metabolism_Combo

2 obligate anaerobic bacteria gather at bottom to

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2: Obligate anaerobic bacteria gather at bottom to avoid oxygen. 3: Facultative anaerobes gather mostly at the top, since aerobic respiration is most beneficial; but as lack of oxygen does not hurt them, they can be found all along the test tube. 4: Microaerophiles gather at upper part of test tube, not at top. Require O 2 , but at low concentration. 5: Aerotolerant bacteria are not affected by oxygen, and they are evenly spread along the test tube. Image: Microbial oxygen requirements , Pixie From the Virtual Microbiology Classroom on ScienceProfOnline.com
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Using oxygen (1/2 O 2 ) in metabolism creates toxic waste. Microbes that are able to use aerobic respiration produce enzymes to detoxify oxygen: Catalase : H 2 O 2 --- H 2 0 and 0 2 Superoxide dismutase (SOD): oxygen radical --- H 2 0 and O 2 Microbes that don’t make these enzymes cannot exist in the presence of oxygen. Microbes & Oxygen Image: Catalase enzyme structure , Vossman; Superoxide dismutase enzyme structure , Fvasconcellos From the Virtual Microbiology Classroom on ScienceProfOnline.com
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Microbes & Temperature _____________ Three-dimensional shape because of the temperature sensitive hydrogen bonds. These bonds will usually break at higher temperatures, and protein become ________. Denatured proteins lose function. ____________ Also temperature sensitive. Become brittle if temperature is too low. If temperature too high, lipids will be more liquid in form. Outside membrane cannot preserve the integrity of the cell and it will disintegrate. Images: Superoxide dismutase enzyme structure , Fvasconcellos; Phospholipids & Cholesterol , Cytochemistry.net From the Virtual Microbiology Classroom on ScienceProfOnline.com
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Effects of Temperature on Growth 95 o F 77 o F 40 o F Most of our plates are incubated at 37 o C (98.6 o F). Conversion C to F = 1.8 x C + 32 From the Virtual Microbiology Classroom on ScienceProfOnline.com
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Categories of Microbes Based on Temperature Range
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Gram positive , rod-shaped _________________. L. monocytogenes is widely distributed; found in soil, water, animals, birds, insects. Responsible for disease listeriosis. Rarely pathogenic in healthy adults (mild flu-like symptoms). Can be lethal in pregnant women, fetuses, newborns, elderly and immune compromised, causing meningitis or bacteremia. Transmitted from environment (contaminated food & water) to human, except in the case of pregnant woman passing on to fetus. In vulnerable populations can have a case fatality rate of 25%. Facultative intracellular pathogen. Triggers its own phagocytosis. Listeria are very hardy. Can grow in temperatures ranging from 39°F (refrigerator) to 99°F. Q: What microbes have we discussed in previous lecture that are at the other end of the temperature spectrum? Image: Listeria monocytogenes , PHIL #2287, Cantaloupe , USDA photo by Scott Bauer. Image Number K7355-11 Meet the Microbe!
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