Measurement of bacteriophage infection kinetics in optically trapped, motile E. coli cells

We use a combination of optical trapping, microfluidics, and fluorescence microscopy to track individual, motile E. coli cells during infection by fluorescently labeled bacteriophages. Dual-trap optical tweezers immobilize swimming cells in a flow chamber, into which phages can be perfused. We measure the absorption of phages onto the cell surface with fluorescence imaging, while simultaneously monitoring the cell’s flagellar rotation with the optical traps. Utilizing the flagellar rotation frequency as a proxy for proton motive force, we examine phage-induced changes to E. coli’s membrane potential. These measurements reveal perturbations to host membrane integrity by phage attachment, followed by its recovery. This technique allows us to illuminate for the kinetics of viral infection of cells at the level of individual phages and bacteria.