most humans don’t really realize how interdependent we are to other organisms. Bacteria, fungi, viruses, bugs—there is still this binary thinking of these organisms as good or bad, as clean or dirty, which really obscures the reality.
E. coli can congregate as long as their microbial tongues taste the amino acid serine. It just so happens that in the normal course of its metabolism, E. coli casts off serine in its waste.