  We study experimentally and numerically the dynamics of colloidal beads
confined by a harmonic potential in a bath of swimming E. coli bacteria. The
resulting dynamics is well approximated by a Langevin equation for an
overdamped oscillator driven by the combination of a white thermal noise and an
exponentially correlated active noise. This scenario leads to a simple
generalization of the equipartition theorem resulting in the coexistence of two
different effective temperatures that govern dynamics along the flat and the
curved directions in the potential landscape.
