Unusual bacterial morphologies

One of the most intriguing morphologies that I've seen in the scanning electron microscopy images that we've done from cave samples is the beads-on-a-string (you'll find several in the Gruta da Terra Mole album). They are the right size for bacteria (1 micron in diameter), but they don't really match anything in Bergey's. A colleague found a very similar morphology in soil from Germany. Because the "beads" are spaced out, they are different than those seen in such species as the Streptococcus. We have usually found them in the ferromanganese deposits in caves, but have recently discovered an abundance of them in the Azorean lava tubes in the white bacterial mats.

I'm intrigued by the spacers between the "beads"--any ideas what these are? Also, I've seen those "spacers" turn into what looks like a hold-fast on the carbonate surface.

Anyone seen anything like this?