(339f) Compression Affects Short-Time Subdiffusion of Loci and Inclusion Bodies in E. coli Cells

We have tracked the loci and inclusion bodies (μNS particles) motions in E. coli cells under compression on a microfabricated device systematically in real time. We observed that both fluorescently labeled loci and GFP-μNS particles performed subdiffusion in E. coli cells. This subdiffusion may arise from an intrinsic viscoelasticity of bacterial cytoplasm, as extensive research has demonstrated that proteins, inclusion bodies, and loci all exhibit subdiffusion in a crowded cytoplasm. However, our experiments show that compression affects the subdiffusion of loci and inclusion bodies in very different ways. As the main external compression force might be exerted on the cell membranes of high modulus, the structure of nucleoid contributing to the loci subdiffusion can remain unchanged. Thus, whilst the cytoplasmic diffusion is slowed down significantly under compression, as evidenced by notable reductions in both the diffusion coefficient and travel distance of μNS particles, the diffusion coefficient of DNA loci remains almost the same under compression. These results suggest that the dynamics of bacterial chromosome is decoupled from the viscoelastic environment of the cytoplasm, in contrast to some previous ideas proposed in literature. It would seem that DNA elasticity and organization (which are probably weakly affected by the deformation) play a more important role in loci subdiffusion. In addition, since the compression on a cell has similar cytoplasmic effects as suppressing metabolic activities in a cell, i.e. the onset of glass-like behavior, these particle tracking experiments in compressed cells provide new insights into the physical properties of the cytoplasm.