An open microscopy framework suited for tracking dCas9 in live bacteria

Abstract

Super-resolution microscopy is frequently employed in the life sciences, but the number of freely accessible and affordable microscopy frameworks, especially for single particle tracking photo-activation localization microscopy (sptPALM), remains limited. To this end, we designed the miCube: a versatile super-resolution capable fluorescence microscope, which combines high spatiotemporal resolution, good adaptability, low price, and easy installation. By providing all details, we hope to enable interested researchers to build an identical or derivative instrument. The capabilities of the miCube are assessed with a novel sptPALM assay relying on the heterogeneous expression of target genes. Here, we elucidate mechanistic details of catalytically inactive Cas9 (dead Cas9) in live Lactococcus lactis. We show that, lacking specific DNA target sites, the binding and unbinding of dCas9 to DNA can be described using simplified rate constants of kbound[->]free = 30-80 s-1 and kfree[->]bound = 15-40 s-1. Moreover, after providing specific DNA target sites via DNA plasmids, the plasmid-bound dCas9 population size decreases with increasing dCas9 copy number via a mono-exponential decay, indicative of simple disassociation kinetics.