Forget the danger of heavy-weight debris raining down from space when Russia sends the Mir orbiter to a watery grave this month — the real threat could be mutant fungi, a researcher said on Tuesday. Yuri Karash, an expert on the Russian space program, said there was a possibility that micro-organisms, which have spent the last 15 years mutating in isolation aboard Mir, could present a threat if they survived the fall to Earth.