EPS-Then and Now

Abstract

"Slime" played a brief and spectacular role in the 19th century founded by the theory of primordial slime by Ernst Haeckel. However, that substance was never found and eventually abandoned. Further scientific attention slowly began in the 1930s referring to slime as a microbial product and then was inspired by "How bacteria stick" by Costerton et al. in 1978, and the matrix material was considered to be polysaccharides. Later, it turned out that proteins, nucleic acids and lipids were major other constituents of the extracellular polymeric substances (EPS), an acronym which was highly discussed. The role of the EPS matrix turns out to be fundamental for biofilms, in terms of keeping cells in proximity and allowing for extended interaction, resource capture, mechanical strength and other properties, which emerge from the life of biofilm organisms, including enhanced tolerance to antimicrobials and other stress. The EPS components are extremely complex and dynamic and fulfil many functional roles, turning biofilms into the most ubiquitous and successful form of life on Earth.

Keywords: EPS; biofilms; emergent properties; nutrient acquisition; resistance; tolerance.

Figure 1

Bathybius Haeckelii. Figure 1 on Table 17 in Ernst Haeckels Article, Beiträge zur Plastidentheorie (1870) (Image in public domain).

Figure 2

Resource caption and retention by and in biofilms. The biofilm is a sponge-like system that provides surfaces for the sorption of a diverse range of molecules that can be sequestered from the environment. This confers several benefits to the biofilm, such as nutrient acquisition and matrix stabilization. Similarly, the physicochemical properties of the matrix enable biofilms to retain and stabilize extracellular digestive enzymes produced by biofilm cells, turning the matrix into an external digestive system. Surface-attached biofilms are not only able to take up nutrients from the water phase but can also digest biodegradable components from the substratum, which is exposed to enzymes in the matrix (after [19], with permission).

Figure 3

Fluorescent staining of a biofilm. Colour allocation: Nucleic acid stain (SybrGreen) = green; lectin stain (AAL-Alexa568) = red; autofluorescence of algae (chlorophyll A) = blue; autofluoresence of cyanobacteria = purple/white. Image dimensions: 246 × 246 μm (from [34], with permission, source: [35]).

Figure 4

Properties of biofilms emerging from life in the EPS matrix (after [19], with permission).

Figure 5

Control of biofilm formation by c-di-Guanidinemonophosphate (c-di-GMP). Concentration of c-di-GMP is regulated by DGC (Diguanylate cyclase; GGDEF domain: diguanylate cyclase), PDE 1 (Phosphodiesterase; EAL domain: diguanylate phosphodiesterase, linearizes c-di-GMP to 5′-pGpG), PDE (nonspecific cellular PDEs, further degrading 5′-pGpG to GMP), and PDE 2 (Phosphodiesterase; HD-GYP domain, metal dependent, unrelated to the EAL domain, linearizes c-di-GMP to 5′-pGpG, degrades 5′-pGpG further to GMP). pGpG—5′ phosphoguanylyl(3′,5′)guanosine; GMP—Guanosine-5-phosphate (from Krauss, G.-J., Nies, D. (Eds.): Ecological Biochemistry-Environmental and Interspecies Interactions today, VCH Weinheim, 2014, with permission).

Figure 6

The dammned polymer matrix (J.C. Bryers, Univ. Washington, with permission).