Figure 1. Transitional episodes in biofilm development by Pseudomonas aeruginosa strain PAO1 examined by transmitted light microscopy. Each panel represents a distinct episode in biofilm development. (a) Reversible attachment. Initial event in biofilm development, bacteria are attached to substratum at cells pole (arrow). (b) Irreversible attachment. Cells were cemented to the substratum and formed nascent cell clusters (arrow) with all cells in contact with the substratum. (c) Maturation-1. Cell clusters matured (arrow) and were several cells thick, embedded in the EPS matrix. (d) Maturation-2. Cell clusters reached maximum thickness, approximately 100 m. (e and f) Dispersion. Cells evacuated interior portions of cell clusters (arrow), forming void spaces (figure supplied by D. Davies, Binghamton University). Reproduced with permission from Sauer et al. (2002).

Figure 2. Scanning electron micrograph of a biofilm of Pseudomonas putida on a mineral surface. EPS (dehydrated for SEM sample preparation) are surrounding the cells, keeping them together and on the surface.

Figure 3. Structures of quorum-sensing signals and their derivatives. Letter designations for the Gram-positive peptide signals indicate amino acids. For the Lactobacillus lactis signal nisin, the structural abbreviations were Bu, dehydroxybutyrine with a lanthionine bridge; Ha, dehydroalanine; Hb, dehydrobutirine (from Horswill et al., 2007, with kind permission of Springer Science and Business Media; figure supplied by Alexander R. Horswill, University of Iowa and Matthew R Parsek, University of Washington).

Figure 4. Artist's view of biofilm architecture and processes. Reproduced by permission of P Dirckx, Center for Biofilm Engineering, MSU, Bozeman.