Single Cell Examination of Membrane Fluidity and Cellular Respiration

Abstract

Bulk measurements of oxygen consumption rates by bacteria have previously been shown to be related to the cells' average membrane fluidity (as measured by the diffusion of fluorescently-labeled molecules). Within a bacterial population, there is also significant cell-to-cell variation in both the diffusion coefficient of membrane probes and oxygen consumption rates of individual cells. One possibility is the diffusion of ubiquinone, an electron carrier in the electron transport chain (ETC), is being limited by the fluidity of the membrane which is causing the heterogeneity.We describe Fluorescence Recovery After Photobleaching (FRAP) measurements to monitor cell-to-cell variation in membrane diffusion coefficient. These results are compared to two approaches to look at what influence it might have on respiration at the single cell level. The first uses a fluorescent indicator of the activity of the ETC. The second directly measures the consumption of oxygen by individual cells using a phosphorescent Pt-porphyrin dye.