Heterogeneity of Natural Biofilm Communities

Scanning confocal laser microscopy (SCLM) studies have shown that microbial biofilms consist of a spatially heterogeneous arrangement of bacterial cells, biogenic extracellular material, and void space. Biofilm architecture is dominated by the presence of cell aggregates interspersed by channels, the arrangement of which varies for different hydrodynamic regimes, ages, species composition, or nutrient status. This organization may regulate the flux of nutrients and oxygen, creating chemical microenvironments (Eh, pH) facilitating the growth of aerobic heterotrophs and anaerobes. The presence of microenvironments has been confirmed using laser microscopy and environmentally sensitive fluorescent probes. In addition, changes in cell number and growth rate with depth and location have also been documented. Elegant methods using fluorescent rRNA probes and reporter gene systems have allowed in situ visualization of high genetic diversity and the regulation of genes in microbial biofilms. Through the use of scanning confocal laser microscopy (SCLM) and fluorescent probes, both qualitative and quantitative analyses of many aspects of the ecology of biofilms may be studied