Dynamics of lipid analogs in the E. coli outer membrane

Alyssa Jeanne Cramer Garrelts, Purdue University

Abstract

While there have been many studies on the diffusion of membrane lipids in eukaryotic cells, which have given insight into the structure and organization of these membranes, little is known to date of their mobility in bacterial membranes, specifically the Gram negative bacteria, Escherichia coli. The E. coli outer envelope consists of inner and outer lipid membranes that are separated by a periplasmic space containing the cell wall. The outer membrane is unique in that it is thinner than mammalian plasma membranes and consists of a phospholipid inner leaflet with a predominantly lipopolysaccharide (LPS) outer leaflet. Here we look at the diffusion of the fluorescent lipid analogs DiI, FAST DiO, and TopFluor-PC in the outer membrane of liveE. coli cells using single molecule imaging/tracking techniques. Lipid analog dynamics are compared in several cells – E. coli with no O antigen (wild type),E. coli with no core oligosaccharids (ΔrfaC), and a mammalian cell line (KB) – at several sampling rates. Lipid analogs deviate from free diffusion at time scales smaller than 30 fps for FAST DiO and smaller than 260 fps for TopFluor-PC. The diffusion of lipid analogs differs according to the charge of the headgroup and fatty acid composition. These differences give evidence for predictions that LPS plays a role in membrane structure and organization and may imply lipid phase separation in E. coli.

Degree

Ph.D.

Advisors

Ritchie, Purdue University.

Subject Area

Microbiology|Biophysics

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