  We study the effects of interaction between bosons and fermions in a
Bose-Fermi mixtures loaded in an optical lattice. We concentrate on the
destruction of a bosonic Mott phase driven by repulsive interaction between
bosons and fermions. Once the Mott phase is destroyed, the system enters a
superfluid phase where the movements of bosons and fermions are correlated. We
show that this phase has simultaneously correlations reminiscent of a
conventional superfluid and of a pseudo-spin density wave order.
