Measuring Bacterial Growth Curves Under Different Resource Conditions

Alice Kraiza 

Advisor:  Dr. Gregory KrukonisAlice Kraiza

Bacillus subtilis is a Gram-positive rod-shaped soil bacterium, commonly used in microbiological studies. As the Gram-positive model organism equivalent of E. coli (which is Gram-negative), many different strains of B. subtilis have been isolated. These vary in function, morphology, growth rate, and susceptibility to viruses. In our lab, we are interested in the competitive interactions among B. subtilis strains as well as the interactions between Bacillus phages and different B. subtilis hosts. To facilitate these studies, I am developing a protocol to measure colony growth rate using a spectrophotometer. Optical density can be used as a measure of the concentration of bacteria in a suspension. Thus measuring changes in optical density through time can be used to measure colony growth rate. I am comparing five Bacillus strains, available in Dr. Krukonis’ lab, which have been already sequenced. Thus, I may be able to relate variation in bacterial phenotypes (e.g., growth rate) to variation in their genotypes. Further studies will explore whether variation in nutrient requirements or susceptibility to particular phages can be correlated to particular genotypes (e.g., presence or absence of specific genes, differences in specific genes).