Relevance of microbial extracellular polymeric substances (EPSs) - Part I:Structural and ecological aspects

Extracellular polymeric substances are the construction materials for micro bial aggregates such as biofilms, fiocs ("planktonic biofilms") and sludge. Their major components are not only polysaccharides but also proteins and in some cases lipids, with minor contents of nucleic acids and other biopol ymers. In the EPS, biofilm organisms can establish stable arrangements and function multicellularly as synergistic microconsortia. The matrix facilita tes the retention of exoenzymes, cellular debris and genetic material; it c an be considered as a microbial recycling yard. Gradients can develop due t o the physiological activity and the fact that diffusive mass transport pre vails over convective transport in the matrix. Biofilm cells tolerate highe r concentrations of many biocides. The EPS matrix sequesters nutrients from the water phase. In photosynthetic communities, EPS molecules can function as light transmitters and provide photons to organisms located deeper in a microbial mat. The EPS matrix is a dynamic system, constructed by the orga nisms and responding to environmental changes. It enables the cells to func tion in a manner similar to multicellular organisms.