  The equilibrium structure and dynamics of a single polymer chain in a thermal
solvent is by now well-understood in terms of scaling laws. Here we consider a
polymer in a bacterial bath, i.e. in a solvent consisting of active particles
which bring in nonequilibrium fluctuations. Using computer simulations of a
self-avoiding polymer chain in two dimensions which is exposed to a dilute bath
of active particles, we show that the Flory-scaling exponent is unaffected by
the bath activity provided the chain is very long. Conversely, for shorter
chains, there is a nontrivial coupling between the bacteria intruding into the
chain which may stiffen and expand the chain in a nonuniversal way. As a
function of the molecular weight, the swelling first scales faster than
described by the Flory exponent, then an unusual plateau-like behaviour is
reached and finally a crossover to the universal Flory behaviour is observed.
As a function of bacterial activity, the chain end-to-end distance exhibits a
pronounced non-monotonicity. Moreover, the mean-square displacement of the
center of mass of the chain shows a ballistic behaviour at intermediate times
as induced by the active solvent. Our predictions are verifiable in
two-dimensional bacterial suspensions and for colloidal model chains exposed to
artificial colloidal microswimmers.
