The Effect of pH and Bacteria Concentrations on Pseudomonas Fluorescens Colonies

The experiment we performed focused on the concentration of Pseudomonas fluorescens bacteria contamination of Arabidopsis thaliana under varying soil acidities and infection rates. Our hypothesis was that if the bacteria concentration was at the lowest dilution and the pH was lowest (acidic), then the number of bacteria colonies observed would be the highest. To test this hypothesis, we grew fifty Arabidopsis thaliana plants, and divided them into five groups. The soil pH was adjusted by watering with solutions of different pH levels (6.5, 7.0, and 7.5). The plant leaves were then inoculated with different concentrations of bacteria, high, standard, and low concentration. The day after inoculation, four dilutions were created from each leaf, a small sample of each was plated on nutrient agar, and the number of Pseudomonas fluorescens bacteria colonies were then counted, using the appropriate dilution. The data from three trials was used to perform a two-factor Design of Experiment (DOE). The results showed that there was a possible interaction between variations of pH and bacteria concentrations on the growth of Pseudomonas fluorescens colonies, although the high range of standards suggested there was error in our experiment; all our factors were rendered irrelevant in the parsimonious equation. Unfortunately, time did not allow us to collect more data. Further research on this topic could be conducted to determine how other factors affect the bacteria growth, such as the use of various chemical or biological disease control agents.

Research Done By:

LeighAnna Beach
Lakeview High School

Nick Triglia
Warren Woods Tower