This isn't the first time fungus has been suggested. But, the more the merrier. It would be interesting to see some data on the rate, of biofuel production and I note that the new fungus directly excretes/produces biofuels. A paper on the fungus in the Journal Biochemistry and Molecular Biology says:
Certainly, it is both timely and interesting that G. roseum
can utilize cellulose for the production of hydrocarbons
given the enormous volumes of foodstuff grains currently
being utilized for alcohol (fuel) production. However, the
yields of these compounds were lower than those found on
the oatmeal-based medium, probably because the digestion
of cellulose is rate limiting. Increases in the yields of these
products may be enhanced by new developments in
fermentation technology, membrane technologies and
genetic manipulation (Danner & Braun, 1999).
"The fungus can even make these diesel compounds from cellulose," says Professor Gary Strobel from Montana State University, which incidentally has patented the fungus. My guess, and that's all it can be, is that the answer lies in the genetic make up of the fungus (do they have genomes?). Unless the fungus is particularly fast growing, yields might be higher from modified microbes?