  Abundance studies of solar-type stars revealed a small fraction of objects
with extreme depletion of beryllium. We investigate the possible link between
the beryllium depletion and the presence of companions. The classical methods
(radial velocity, astrometry, imaging) used to search for binary companions
were exploited. We also performed a chemical analysis to identify binaries by
the alteration in abundances that is produced by the accretion of material lost
by a former evolved companion. We found that all the four previously
investigated stars that were found to be ultra--depleted in Be are binaries. In
two cases the companion is a white dwarf, and in the other two cases the
companion might be a white dwarf or a main-sequence star. One new barium star
was identified. We speculate that the interaction with the white dwarf
progenitor caused an alteration in the abundance pattern of the star, which
resulted in severe beryllium depletion. Possible mechanisms such as
thermohaline mixing, episodic accretion, and rotational mixing are discussed.
We also briefly discuss predictions for validating this scenario
