What are Bacterial Extracellular Polymeric Substances?

Abstract

The vast majority of microorganisms live and grow in aggregated forms such as biofilms and flocs (“planktonic biofilms”). This mode of existence is lumped in the somewhat inexact but generally accepted expression “biofilm”. The common feature of all these phenomena is that the microorganisms are embedded in a matrix of extracellular polymeric substances (EPS). The production of EPS is a general property of microorganisms in natural environments and has been shown to occur both in prokaryotic (Bacteria, Archaea) and in eukaryotic (algae, fungi) microorganisms. Biofilms containing mixed populations of these organisms are ubiquitously distributed in natural soil and aquatic environments, on tissues of plants, animals and man as well as in technical systems such as filters and other porous materials, reservoirs, plumbing systems, pipelines, ship hulls, heat exchangers, separation membranes, etc. (Costerton et al. 1987; 1995; Flemming and Schaule 1996). Biofilms develop adherent to a solid surface (substratum) at solid-water interfaces, but can also be found at water-oil, water-air and solid-air interfaces. Biofilms are accumulations of microorganisms (prokaryotic and eukaryotic unicellular organisms), EPS, multivalent cations, biogenic and inorganic particles as well as colloidal and dissolved compounds. EPS are mainly responsible for the structural and functional integrity of biofilms and are considered as the key components that determine the physicochemical and biological properties of biofilms.