  Anisotropic macromolecules exposed to non-equilibrium (active) noise are very
common in biological systems, and an accurate understanding of their
anisotropic dynamics is therefore crucial. Here, we experimentally investigate
the dynamics of isolated chains assembled from magnetic microparticles at a
liquid-air interface and moving in an active bath consisting of motile E. coli
bacteria. We investigate both the internal chain dynamics and the anisotropic
center-of-mass dynamics through particle tracking. We find that both the
internal and center-of-mass dynamics are greatly enhanced compared to the
passive case, i.e., a system without bacteria, and that the center-of-mass
diffusion coefficient $D$ features a non-monotonic dependence as a function of
the chain length. Furthermore, our results show that the relationship between
the components of $D$ parallel and perpendicular with respect to the direction
of the applied magnetic field is preserved in the active bath compared to the
passive case, with a higher diffusion in the parallel direction, in contrast to
previous findings in the literature. We argue that this qualitative difference
is due to subtle differences in the experimental geometry and conditions and
the relative roles played by long-range hydrodynamic interactions and
short-range collisions.
