Wastewater Treatment: Role of Microbial Biofilm and Their Biotechnological Advances

Microbial Biofilm

A microbial biofilm is a group of surface-associated microbial cells enclosed in an extracellular matrix containing polymeric substances (Ghannoum and O’Toole, 2004). Extracellular polymeric substances (EPS) are primary matrix material that accounts for 50 to 90% of the entire organic carbon of a biofilm (Flemming et al., 2000). EPS is composed of polysaccharides but may vary chemically and physically. The polysaccharides are neutral or anionic, such as EPS of gram-negative bacteria is consisted of uronic acids (D-glucuronic, D-galacturonic, and mannuronic acids) which provides anionic characteristics to the biofilm (Sutherland, 2001). The anionic nature of EPS attracts divalent cations (magnesium and calcium) which makes cross-link structures with the polymer that provides larger binding force to a biofilm (Flemming et al., 2000). However, EPS of some gram-positive bacteria is cationic, for example, Staphylococci. On the other hand, the amount of EPS production differs among the organisms and it increases as biofilm grows (Leriche, 2000); however, several factors like nutrient status of the medium, accessible carbon and limited nitrogen or phosphate sources affect EPS production (Sutherland, 2001).