Penetrating into every single corner of the station, they showed an enormous appetite and demonstrated their capacity to eat up even highly durable materials. A vivid example of the bacteria's' "outrage" is illustrated by what happened to the window of a transportation spacecraft that docked to Mir when piloted by its last crew. Some time after docking, the cosmonauts' attention was drawn to the rapidly deteriorating window glass. It was covered by a strange film, spreading "as quickly as in the horror movies," and became absolutely non-transparent.
The test results raised the researchers' eyebrows. It turned out the quartz glass and the titan, which framed it, were damaged by a large colony of bacteria. As experts explained later, these microorganisms exuded a metabolism product--an acid so strong that it could easily corrode the window the creatures had settled on.
Besides this case, which rightfully belongs in the microbiology textbooks, the little angry bacteria more than once ate up the metallic casing and destroyed the equipment on board the station. Their next victim was the control panel of a communication device, in which the parasites devoured the whole insulation. When the astronauts Anatoly Solovyev and Pavel Vinogradov sent the device down to the earth, one could see that it was entirely green inside!
http://www.anomalist.com/reports/mir.html