I've seen almost the same question here, but it was like Can a microorganism reproduce so fast, to be used as fuel?. Then, I was inspired and new question came up. Does some real microorganism in some laboratory environment can be forced to reproduce so fast that it can be used as weapon?
Weapon logic: I have some grenade where that microorganism is hibernated. Then, when I activate it, some reaction happens and environment mentioned in question comes up. Microorganism starts to reproduce and in some seconds fills the room, as cement mortar or polyurethane foam, and people inside buried alive.
P.S: Real scenario might be fundamentally different, but I think the main idea is clear.