Scanning electron micrographs of the wild-type and the two mutants grown in 1% maltose or 1% glucose. The wild-type formed a well-organized, multilayered biofilm in all growth conditions. The transposon mutant formed biofilm only in maltose while the triple deletion mutant exhibited a well-formed biofilm in glucose. Maltose induced the formation of amorphous material covering the cells. Biofilm in glucose and maltose was different: wild-type bacteria grown in glucose showed small aggregates on the cell surface and these aggregates became larger and less regular when bacteria were grown in maltose. These larger aggregates where also present on the surface of the transposon mutant when grown in maltose and on the deletion mutant grown in glucose.