  We investigate the properties of trapped Bose-Fermi mixtures for
experimentally relevant parameters in one dimension. The effect of the
attractive Bose-Fermi interaction onto the bosons is to deepen the parabolic
trapping potential, and to reduce the bosonic repulsion in higher order,
leading to an increase in bosonic coherence. The opposite effect was observed
in ${}^{87}$Rb - ${}^{40}$K experiments, most likely due to a sharp rise in
temperature. We also discuss low-temperature features, such as a bosonic Mott
insulator transition driven by the fermion concentration, and the formation of
composite particles such as polarons and molecules.
