In conducting our research, we crossed two species of bacteria — Micrococcus luteus and Micrococcus roseus — and used ultraviolet light to trigger their transformation. We added citric acid to one test tube of crossed bacteria and left the other tube untreated. We then streaked plates, four with low pH and four with neutral pH. We placed two plates from each of the two acidity levels under a fume hood (essentially a room-temperature environment), and the other four in an incubator. After forty-eight hours, we counted the white, crossed colonies that appeared in each plate and recorded our data. We analyzed the effects of each factor, acidity and temperature, and their interaction with a two-factor Design of Experiment to determine which factor had a greater effect on the growth of the cultures. We found that acidity had a significant effect, a lower environmental pH promoting growth in the plates. The interaction of both acidity and temperature also had a significant effecting the reverse direction—as both of the factors increased, the number of colonies decreased.

Research Done By:

Michael DeRamo
Cousino High School

Jill Samp
Cousino High School