  We investigate how a symmetric penetrable object immersed in an active fluid
becomes motile due to a negative drag acting in the direction of its velocity.
While similar phenomena have been reported only for active fluids that posses
polar or nematic order, we demonstrate that such motility can occur even in
active fluids without any preexisting order. The emergence of object motility
is characterized by both continuous and discontinuous transitions associated
with the symmetry-breaking bifurcation of the object's steady-state velocity.
Furthermore, we also discuss the relevance of the transitions to the
nonmonotonic particle-size dependence of the object's diffusion coefficient.
