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140 - Topic 6 Notes

14 or viable count figures 515 and 516 one of

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Unformatted text preview: tionship between turbidity and cell number. Fundamentals of Microbiology (Biology 140) Course notes Dr. Josh D. Neufeld So far, we have been considering growth only under ideal conditions. In the real world, most microorganisms are not growing in log phase (we know why that could not be possible!) and there are several factors, besides nutrient availability and growth inhibition by toxic substances, which can limit growth. In this lecture, we will look at some of these factors. Temperature Each type of microorganism has upper and lower temperature limits (Figure 5.18), beyond which they are not able to grow. Between these upper and lower limits, there is an optimum temperature at which growth is maximum. Maximum growth temperature: inactivation of at least one important protein. Minimum growth temperature: freezing of the cytoplasmic membrane. There is a wide variation in the temperature limits and optima for different microorganisms (Figure 5.19). Psychrophiles: low temperature optima Mesophiles: midrange temperature optima Thermophiles: high temperature optima Hyperthermophiles: very high temperature optima Low Temperature Growth Psychrophiles: optimal growth temperature 15C or lower, maximum growth temperature below 20C, minimal growth temperature 0C or lower Psychrotolerant: grow at 0C, optimal growth temperature 20-40C Many psychrophiles are actually killed by temperatures above 20C. They are often very difficult to study, since they must always be kept below r...
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