Enhanced diffusion of stretching DNA chains in active baths

Abstract Biological molecules interact with their active and living surroundings, playing a crucial role in a variety of biofunctional processes. However, experimental studies on the morphological changes and diffusion behavior of real bio-macromolecules under active forces remain challenging. Here, suspensions of swimming bacteria at varying number densities are employed as an active bath, with fluorescently dyed DNA chains serving as model biopolymers. Our results show that DNA chains in bacterial baths undergo significant stretching and exhibit repetitive stretching and coiling dynamics, distinctly different from their behavior in thermal baths. The extent of elongation increases linearly with the bacteria density and the correlation length of the flow disturbed by motile bacteria. Furthermore, DNA chains exhibit short-time super-diffusion and long-time normal diffusion, with an effective diffusion coefficient surpassing that of rigid particles with hydrodynamic radii comparable to DNA macromolecules. The stretching deformation also induces anisotropic diffusion in the DNA body frame, characterized by faster transport along the elongated direction attributed to the chain’s incapability to resist bending forces. These findings provide valuable insights into the behavior of chain-like biopolymers in active environments and enhance our understanding of the coupling between the deformation and diffusion of polymers in active systems.