Biofilms are a mixture of microorganisms, layered together and usually adhered to a surface. The advantages of a biofilm include resistance to environmental stresses, antibiotics, and the ability to more easily obtain nutrients.  PhoB is used to enhance biofilm formation in environments where Pi is not in sufficient supply. This has been shown in multiple microbes including Pseudomonas, V. cholera, and E. coli. This is not always the effect of the Pho regulon as for other species in different environments it is more advantageous to not be in biofilm when Pi is low. In these cases PhoB represses biofilm formation.