Abstract:
Growth rates play a central role in microbiology and are used to address questions regarding the physiology, ecology, and evolution of microbial populations. There is an inherent capacity for organisms to produce more of themselves and increase the size of the population. Quantification of variations in cell density over time allows microbiologists to compare growth rates between genotypes and species across a range of conditions. Growth rates are thought to be sensitive to environmental conditions and are therefore a useful measure of changes in microbial communities. Being able to accurately determine growth rates from existing population curves is therefore important. Escherichia coli populations were grown at room temperature in the presence of individual spice aqueous extracts: ginger, clove, coriander, green tea, oregano, herbes de Provence, and za’atar. A microplate reader was used to determine absorbances of the populations every 30 minutes for 36 hours. For most of the populations, growth appeared to be logistic (density-dependent). Four separate approaches were used to estimate the population growth rate, while two approaches were used to estimate the carrying capacity. The first involved curve fitting the logistic equation to the data using the software GrowthCurver. The second was to determine the highest growth rate calculated from the growth rates for each 30 minute time interval. The third was extracted from a regression fit to the population data below one half of the carrying capacity. The last method involved regressing the change in population size for each interval onto the previous population size. The calculated population growth values varied inconsistently across method. GrowthCurver estimates were consistently the highest, while the slope method estimates were consistently the lowest. Potential explanations for the differences in growth estimates will be discussed.
Team Members
Emilie Hillard | (Michael Ganger, Geoff Dietz) | Gannon University
Download the Project Summary
