The Effect of Tempurature on the Growth of Bacteria
by Ari Hest

Introduction
    My experiment was designed to test the rate of growth of four different bacteria in four different conditions. I wanted to answer the question of which bacteria would grow the fastest over a one day period. I hypothesized that the E. Coli bacteria would grow the fastest. I based this hypothesis on the fact that the E. Coli showed the greatest amount of growth of any bacteria in a prior class experiment using broth cultures. As a side experiment, I wanted to find out the temperature at which the growth of each bacteria was most abundant. I also hypothesized that all four bacteria would grow fastest in the warmest tempurature I experimented in which happened to be the lab room tempurature of 23 degrees celsius. I based this hypothesis on prior knowledge that objects tend to expand and grow better in heat rather than in cold tempurature.
METHODS AND MATERIALS
    MATERIALS USED IN MY PROJECT:
  1. bacteria loop
  2. lab dropper
  3. bunsen burner
  4. 16 petri dishes
  5. dextrose broth
  6. nutrient broth
  7. two incubators
  8. ruler
  9. black magic marker
  10. labels

    The first thing I wanted to do was to to find the broth in which each bacteria grows best. I judged which broth went with which bacteria according to data collected in a prior broth culture class experiment. I found that for the four bacteria I was testing, three of them grew best in the dextrose broth, while E. Coli grew best in the nutrient broth. Therefore, I was provided with six dextrose broth test tubes and two nutrient broth test tubes by my teacher, and I proceeded to streak different bacteria with a loop and put the bacteria in the appropriate test tube. I tried to put even amounts of each bacteria in each tube. These broths were then incubated over a weekend, and once they showed signs of growth (I knew what growth to expect with the help of the class experiment we did), I was ready to carry out the experiment.

    I was given sixteen petri dishes by Mr. Reiblein to use in my experiment. Each one was divided into four even parts using a magic marker. Here is what the petri dishes looked like before the bacteria was entered: [Not Available On Webpage!]

  11. Bacteria number one: B. Cereus
  12. Bacteria number two: B. Subtillis
  13. Bacteria number three: E. Coli
  14. Bacteria number four: S. Marcescens

    I took my incubated, labeled broths with bacteria to my table, and dropped one drop of the B. Cereus bacteria into one of the dishes using a dropper. I then cleaned out the dropper and dried it off, making sure that no excess broth was still present. I then repeated this dropping procedure for the next three bacteria, dropping each drop in its respective spot.

    Once I had dropped four different broth drops in a dish, I labeled the dish according to the trial number and the tempurature it would be placed in. A typical label looked like this:

    figure two - typical label
    -------------
    A. Hest
    2/7
    Trial Two
    30 degrees celsius
    -------------

    I then placed the dish in the tempurature I wanted to test it in, and observed them the next day for results.

RESULTS
    Each of these tables contains the starting diameter of the drop (approximately 6mm) of broth and the diameter of the broth after one day. Diameter measurements were made with a ruler, measuring the furthest diameter distance that a drop contained (in a couple of cases, the drop grew better around certain edges than others).

    table one - results of first tempurature
    tempurature one - incubator one - 30 degrees celsius
    * - ALL MEASUREMENTS IN MILLIMETERS
    BACTERIA TRIAL 1 TRIAL 2 TRIAL 3 TRIAL 4
    B.Cereus 6/7 6/6 6/7 6/7
    B. Subtillis 6/8 6/7 6/8 6/7
    E. Coli 6/15 6/14 6/18 6/16
    S. Marcescens 6/9 6/10 6/10 6/7
    -----------------------------------------------

    table two - results of second tempurature
    tempurature two - incubator two - 45 degrees celsius
    BACTERIA TRIAL 1 TRIAL 2 TRIAL 3 TRIAL 4
    B. Cereus 6/6 6/6 6/6 6/6
    B. Subtillis 6/7 6/7 6/6 6/7
    E. Coli 6/9 6/10 6/10 6/10
    S. Marcescens 6/7 6/8 6/8 6/9
    -----------------------------------------------

    table three - results of third tempurature
    tempurature three - room temp. - approx. 23 degrees cel.
    BACTERIA TRIAL 1 TRIAL 2 TRIAL 3 TRIAL 4
    B. Cereus 6/8 6/8 6/9 6/8
    B. Subtillis 6/9 6/8 6/10 6/9
    E. Coli 6/15 6/16 6/16 6/15
    S. Marcescens 6/11 6/13 6/10 6/10
    -------------------------------------------------------------------------------
    * - since tempurature four(next to window tempurature) showed no results, there is no table for growth. -------------------------------------------------------------------------------

DISCUSSION
    According to my results, the E. Coli bacteria showed the most growth in every tempurature (except the window temp) over a one day period. In fact, the E. Coli exceeded the other three bacteria by a landslide, especially the B. Cereus and B. Subtillis bacteria. The S. Marcescens ran a distant second to the E. Coli, but managed to distance itself from the final two bacteria pretty well. The B. Subtillis showed little growth in each tempurature, and the B. Cereus showed next to nothing in terms of diamter growth.

    There were a couple of interesting results in these tables. First off, the S. Marcescens broth in trial four of the 30 degree celsius tempurature was quite different from the prior three results. This may have been due to a shortage of bacteria within the broth drop, an error in dropping the original broth into the dish, or an error in measurement. The second results of interest was also an S. Marcescens trial, three two of the room tempurature data. This result exceeds the diameters of the other three trials by a good margin as well, and any of the before mentioned problems could have triggered this result.

    The most interesting thing about my data is that the diameters of the broths in the room tempurature experiment exceeded the those of the incubator one tempurature experiment. This is peculiar because the tempurature of the room was colder than that of the incubator, and judging from the lack of growth of the dishes by the window, which were subject to the coldest tempuratures, these results appear to go against my hypothesis that the warmest tempurature will yield the most growth. However, the tempurature in the room may have been changing throughout the day, causing the bacteria to grow at awkward paces. If I ran my experiment again, I would place the dishes in all set tempuratures so that no change in tempurature could occur.

    Overall, there is enough evidence to conclude that E. Coli shows the best growth over a one day period of these four bacteria, and this supports my hypothesis. On the other hand, the data on the tempuratures didnšt really conclude anything, probably because of error in the experimental design.

CONCLUSION
    The E. Coli bacteria showed the greatest amount of growth over a one day period than any bacteria tested. The next three, in order of most to least growth, were S. Marcescens, B. Subtillis, and B. Cereus. The tempurature may have an effect on the growth of the bacteria, but there was insufficient evidence in my experiment to prove this.
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