Thursday, March 25, 2010

bacterial fluorescence vs time

03.24.10. A major contributor to the explosion of quantitative data in microbiology in the past 10-20 years has been the advent of the fluorescent protein. Originally extracted from jellyfish, fluorescent proteins can be designed to be coupled to (either produced along with or literally bound to) other intracellular molecules of interest. Under a microscope the brightness then provides a proxy for molecular concentration. This fluorescent "tagging" procedure has elucidated scads of time-, space-, and concentration-dependent molecular processes inside individual living cells. As a class we observed two movies of bacterial cells whose fluorescence intensity changed as a function of time: (1) a movie taken by Mr. Mugler at Caltech's Bootcamp, in which bacteria were photobleached, causing the fluorescence to decrease exponentially with time, and (2) the movie shown here, from Stricker et al, Nature, 2008, in which bacteria were synthetically engineered to oscillate in fluorescence over time. Students were then presented with two sets of fluorescence vs time data and asked which data set corresponded to which movie, a question that they answered definitively by constructing a double-line graph. This exercise reinforced the preceding class discussion that line graphs are appropriate for visualizing and comparing changes over time.