You may use algae, protozoa, yeasts, or fungi. However, many of these may not grow on the QST medium and some will be killed by the temperature of the melted agar. Also not all bacteria will grow on this medium. For example, some pathogens don't grow well unless blood is included in the medium Expected Observations Methylene blue will be colorless in oxygen-free regions of the tube and blue where oxygen is present. Phonel red will be yellow in acidic regions of the tube and red in alkaline regions of the tube.
Some organisms produce gas by fermentation and the gas ruptures the agar.
All these traits will help you identify unknown bacteria. Add a discussion of oxidative vs fermentive metabolism. This experiment is one of a series testing the ability of bacteria to grow in various environments. We plan other experiments in this series. It is interesting to accumulate a set of bacteria and test the response of each in the different experiments.