Evolving perspectives of biofilm structure

The application of confocal scanning laser microscopy (CSLM) to biofilm research has provided detailed new information on the structural complexity of fully hydrated living biofilms. Biofilms studied by CSLM are widely reported to be heterogeneous and consist of micro-colonies or cell clusters (aggregates of microbial cells in an extracellular polysaccharide matrix) separated by interstitial voids and channels. CSLM combined with molecular probing can identify the distribution of individual species within biofilms, while CSLM combined with microelectrodes and particle tracking has demonstrated the significance of structural heterogeneity on mass transfer in biofilms. In this review the contribution that CSLM has made towards the development of conceptual and mathematical biofilm models over the last decade is discussed. The significance of biofilm structural heterogeneity to understanding of mass transfer processes in biofilm systems and the fundamental significance of hydrodynamics in shaping biofilm structure are also discussed. Finally, some of the recent findings which suggest that biofilm structure may be controlled in part by cell signalling, quorum sensing mechanisms, are briefly discussed.