I'm betting you need a metal catalyst and Acetic acid to make it work.
Of course, the bacteria might themselves be making the Acetic acid (Vinegar).
Maybe there are 3 separate species of bacteria involved along with a metal catalyst (Iron?). 1 species makes H2 and CO2, species 2 makes Acetic acid, species 3 makes methane...
Ironicly, An oil spill into ground water near the iron range of Minnesota is what apears to have spurred the research in this area!
Oh well... Back to accounting (God am I bored today)