Of course the most logical group to study here would be the
parabasalians of termite guts. Grosovsky and Margulis 1982 and several
papers by Michael Yamin explore the cellulose digesting capabilities of
these protists but there is still some discussion as to whether it is
the protists themselves doing the breakdown or if it is the associated
bacteria. The chapter on Parabasalians in the Handbook of the
Protoctista has the full references for these papers.
Mark Farmer