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The aim of this investigation is to investigate how changing the temperature affects growth and survival of bacteria. The bacterium's Escherichia coli, Bacillus stearothermophilus, Bacillus subtilis, Pseudomonas fluorescens and Enterococcus

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Student: N009834 The Effect of Heat on Growth and Survival of Bacteria Abstract The aim of this investigation is to investigate how changing the temperature affects growth and survival of bacteria. The bacterium's Escherichia coli, Bacillus stearothermophilus, Bacillus subtilis, Pseudomonas fluorescens and Enterococcus faecalis will be investigated. Each of the bacteria were loop inoculated into glucose nutrient broths, then incubated at five different temperatures, 4OC, 25OC, 37OC, 45OC and 55OC for seven days to see where growth, if any has occurred at which particular temperature. Results showed that bacterium Pseudomonas fluorescens grew best at the lower temperatures and Bacillus subtilis grew paramount at the higher temperatures. Another experiment was carried out where the aim of the investigation was to show the relationship between the temperature and the time to kill for a number of species of bacteria. Each of the bacterium's nutrient broth bottles were placed in four waterbaths at 40OC, 60OC, 80OC and 100OC. Each bottle was then removed one by one at 0, 2, 5, 30 and 90 minutes, then incubated for seven days. Bacillus stearothermophilus broths were incubated at 55OC. Escherichia coli and Enterococcus faecalis broths were incubated at 37OC. Bacillus subtilis and Pseudomonas fluorescens broths were incubated at 30OC. ...read more.


Psychrophiles have largely unsaturated fatty acids in their plasma membranes which makes them adapted to their environment. 'The degree of unsaturation of a fatty acid correlates with its solidification temperature or thermal transition stage (i.e., the temperature at which the lipid melts or solidifies); unsaturated fatty acids remain liquid at low temperature but are also denatured at moderate temperature'. www2. Within the membrane of the Thermophiles are saturated fatty acids which are stable at high temperatures; however they too solidify at relatively high temperatures. The fluidity of the membrane is affected by the fatty acids in the membrane, whether they are solid or liquid, this affects its ability to function. Enzymes are contained within Psychrophiles which continue functioning although at condensed rate, near temperatures of 0O. Psycrophile proteins/membranes adapt to low temperatures, but at 37OC (body temperature of warm blooded animals) they do not function. Thermophiles are adapted to their function of temperatures over 60OC in a number of ways. They have a high Cytosine and Guanine content in their DNA which is at least as high as the optimum temperature for the organisms' growth. 'But this is not always the case, and the correlation is far from perfect, so thermophile DNA must be stabilized in these cells by other means. ...read more.


No growth at the highest temperature but very faint growth shown at 4oC. Discussion As you can see from the results of the experiment, the five different bacterium's can now be categorised into psychrophiles, mesophiles and thermophiles. Escherichia coli appears to be a mesophile as it grows in moderate temperatures, growing greatest at human body temperature of 37oC, indicating that this organism is obviously present within our human bodies. Bacillus stearothermophilus appears to be a thermophile but also is able to grow in mesophile conditions. There was very faint growth at 55oC indicating that if the temperature had increased further, more growth will have occurred. Bacillus subtilis also appears as a mesophile as it grows greatest within moderate temperatures of 37oC and 45oC, yet fails to grow at extreme temperatures of 55oC and faintly at low temperatures. The only psychrophile from these five bacterium's is Pseudomonas fluorescens as this grows very heavily at low temperatures of 4oC and 25oC, yet faintly and none at when the temperature increases to 37oC and above. Finally another mesophile is the Enterococcus faecalis as this also grows best at 37oC and at moderate temperatures it showed medium growth. It showed very little growth at 4oC and no growth at the extreme of 55oC. Results The effect of heat on survival of bacteria The following tables indicate the effect of heat on the survival of the five different bacterium's. ...read more.

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