Back in high school in the late 1970s I had a book of short stories we had to read in English class, and one story has stayed with me every since. It was a sci-fi story that was called, I think, "Green Mold", about a space ship that landed on Mars that was slowly being consumed by a form of green mold that was growing on the surfaces of everything and, eventually, the astronauts themselves.
The green mold or fungus starts growing on the outside of the ship and compromising the skin of the spacecraft. It spreads to the inside of the ship when brought in on the boots of the explorers, tiny green specks that are a form of intelligent life itself. When the equipment starts failing they discover it has spread behind the instrument panels, starting with the softer wiring and rubber insulation and soon spreading to the metal itself. As a result all of their instruments no longer work. Eventually, the structure of the ship becomes unsound and the crew has to evacuate to the surface of the planet and find shelter with no means of leaving, no way to contact anyone, and limited supplies to keep them alive. Eventually the story ends when they discover one day that the mold has now begun growing on themselves and they will eventually disappear with no trace in a slow, painful way. It certainly doesn't end on a happy note, and seems to be science fiction horror.
I think the author may have been Russian, but I don't know if it was written in the 50s, 60s, or 70s. Some of the other stories in the book might have been written by Russian authors, but I don't know if that applies to this story or not.