Function of EPS

Abstract

The production of extracellular polymeric substances (EPS) involves a significant investment of carbon and energy by microorganisms. Considering the tendency in nature to conserve rather than to waste, this expenditure of energy (in some cases more than 70% — see Harder and Dijkhuizen 1983) is likely to hold benefits to the producers of EPS, as well as those organisms associated with them. Bacteria are very efficient in converting nutrients into EPS; it has been calculated (Underwood et al. 1995) that a single Azotobacter cell can produce enough EPS to coat more than 500 particles with a 0.4 µm diameter per day. The size of a single cell is typically 1–2 µm by 0.5 µm, and often much smaller, and therefore this number is impressive. The importance of EPS has long been recognized and a variety of functions have been attributed to EPS as far as the benefits they provide to cells, either living as single organisms, in binary associations, or in heterogeneous communities. However, Christensen and Characklis (1990) implied that there is a lack of knowledge of the properties of EPS in biofilms, as well as their role in biofilm ecology. The aim of this chapter is to provide an overview of some of the progress that has been made in recent years to elucidate the functional role of EPS.