Can the protein/carbohydrate (P/C) ratio of exopolymeric substances (EPS) be used as a proxy for their 'stickiness' and aggregation propensity?

Microbially secreted exopolymeric substances (EPS), rich in polysaccharides and proteins, make up an important part of natural organic matter in the ocean, especially marine snow. While the attention in the oceanographic literature is focused more on the role of polysaccharides and less of proteins in EPS functions, the role of proteins, especially the role of the protein/carbohydrate (P/C) ratio of particles and colloids (macromolecular fraction) remains to be explored. EPS associated with particles forms a biofilm, where proteins are not only involved in cell surface attachment, but also in the stabilization of the biofilm matrix, and the development of a three-dimensional biofilm architecture. Here, we provide a perspective based on the most recent literature on EPS, marine oil spills and waste water treatment to describe the relationship between the P/C ratio of EPS and a number of biophysical properties related to biopolymer aggregation propensity, e.g., relative hydrophobicity, surface activity and surface tension, attachment efficiency, light-induced chemical crosslinking, and sedimentation efficiency of marine snow in marine environments.