It is increasingly evident that biofilms growing in a diverse range of medical, industrial and natural environments form a similarly diverse range of complex structures (Stoodley et al., 1999a). These structures often contain water channels which can increase the supply of nutrients to cells in the biofilm (deBeer & Stoodley, 1995) and prompted Costerton et al. (1995) to propose that the water channels may serve as a rudimentary circulatory system of benefit to the biofilm as a whole. This concept suggests that biofilm structure may be controlled, to some extent, by the organisms themselves and may be optimized for a certain set of environmental conditions. To date, most of the research on biofilm structure has been focused on the influence of external environmental factors such as surface chemistry and roughness, physical forces (that is, hydrodynamic shear) or nutrient conditions and the chemistry of the aqueous environment. However, there has been a recent increase in the number of researchers using molecular techniques to study the genetic regulation of biofilm formation and development. Davies et al. (1998) demonstrated that the structure of a Pseudomonas aeruginosa biofilm could be controlled through production of the cell signal (or pheromone) N-(3-oxododecanoyl)-L-homoserine lactone (OdDHL). In this paper, we will examine some of the research that has been conducted in our laboratories and those of others on the relative contribution of hydrodynamics, nutrients and cell signalling to the structure and behaviour of bacterial biofilms.
The hydrodynamic conditions of an aquatic environment will determine the transport rate of nutrients and planktonic cells to a surface, the shear stress acting on the biofilm and the rate of erosion of cells from the biofilm.