Teaching the microbial growth curve concept using microalgal cultures and flow cytometry

Abstract

The microbial growth curve is widely studied within microbiology classes and bacteria are usually the microbial model used. Here, we describe a novel laboratory protocol involving flow cytometry to assess the growth dynamics of the unicellular microalgae Isochrysis galbana. The algal model represents an appropriate alternative to bacteria because its slower growth rate allows a better visualization of the growth phases, which makes the logistic of the laboratory sessions easier. Flow cytometry is a technique commonly used for cell enumeration in ecology, microbiology, and medical sciences because of its accuracy and speed. In this experiment, microbial growth was observed under two light conditions and cell abundance was monitored using a flow cytometer and a haemocytometer. The chlorophyll a fluorescence of each cell was also measured by the flow cytometer and was used as an index of cellular content of photosynthetic pigments. Students were asked to compare the results obtained with the two techniques and to explain the effect of light conditions on the growth curve shape and dynamics.