Proteins that cannot form biofilm? I am trying to build a machine learning training set for bacterial protein sequences that form biofilm, and that cannot. I collected the positive sequences from the GO ontology website but for negative sequences I am not sure which sequences to incorporate into my training set.

Can anyone point me to resources for proteins sequences that are known to be not capable of forming biofilms?
One option is to treat all proteins that are not explicitly known to form a biofilm as proteins that are incapable of doing so, but this will likely result in many false negatives.

You could take a look at one-class classification and positive-unlabeled (PU) learning. Both are techniques specifically designed for these kind of problems where only one of the two classes is known. (In this case: only biofilm forming proteins are known.)