Measurement of polysaccharides and proteins in biofilm extracellular polymers

Abstract

The structure of biofilm extracellular polymers (ECPs) was studied by measuring their polysaccharide and protein spatial distributions along biofilm depth. Biofilm was collected from two aerobic heterotrophic biofilm reactors, which were seeded with Sphingomonas sp. and Sphingomonas sp. plus mixed liquor, respectively, and operated under toxic organic (in this case, azo dye) degrading conditions. Complete mixing conditions in the two reactors were verified by measuring water content, and polysaccharide and protein quantities from three vertical sampling positions over time. Experimental results showed that: (1) the biofilm water content of either reactor did not change with sample position or biofilm age, with an average biofilm water content in both reactors of 97%; (2) polysaccharides and proteins in the ECPs did not change with sample position; (3) the profiles of polysaccharides and proteins along the biofilm depth showed a stratified biofilm structure, with their ratio (proteins/polysaccharides) being relatively stable over the depth. Oxygen and substrate transport and interactions among species were considered to be the main reasons for producing such a non-uniform biofilm structure; and (4) Sphingomonas sp. could not compete well with microorganisms derived from the mixed liquor of a wastewater treatment plant aeration basin.