  We study the superfluid response, the energetic and structural properties of
a one-dimensional ultracold Bose gas in an optical lattice of arbitrary
strength. We use the Bose-Fermi mapping in the limit of infinitely large
repulsive interaction and the diffusion Monte Carlo method in the case of
finite interaction. For slightly incommensurate fillings we find a superfluid
behavior which is discussed in terms of vacancies and interstitials. It is
shown that both the excitation spectrum and static structure factor are
different for the cases of microscopic and macroscopic fractions of defects.
This system provides a extremely well-controlled model for studying
defect-induced superfluidity.
