  We present GMRT HI observations of an eXtremely Metal Deficient (XMD) galaxy
SBS 1129+576 (12 + log(O/H) = 7.41). Our HI observations show that the galaxy
is strongly interacting with a companion galaxy, SBS 1129+577. A third, smaller
galaxy, SDSS J113227.68+572142.3, is also present in the data cube. Our
low-resolution map shows a bridge of emission connecting the two larger
galaxies and a large one-armed spiral distortion of the disc of SBS 1129+577.
Assuming that most of the bridge gas originally came from SBS 1129+576, ~1/3 of
its original gas mass has been stripped off. The third smaller galaxy does not
show any sign of interaction with the other two galaxies. The higher resolution
maps show that SBS 1129+577 has a central bar and a ring surrounding the bar;
there is also a hint of an integral-shaped warp in SBS 1129+576. All these
features are very likely to have been induced by the tidal interaction. In both
SBS 1129+576 and SBS 1129+577, there is, in general, a good correspondence
between regions with high HI column density and those with ongoing star
formation. The inclination-corrected HI column density in the two brightest HII
regions in SBS 1129+576 and near the HII regions in SBS 1129+577 is generally
above the threshold density for star formation observed in other blue compact
galaxies. (abridged)
