In situ analysis of bacterial extracellular polymeric substances from a Pseudomonas fluorescens biofilm by combined vibrational and single molecule force spectroscopies.

Extracellular polymeric substances (EPS) play an important role in biofilm cohesion and adhesion to surfaces. EPS of a P. fluorescens biofilm were characterized through their vibrational spectra (infrared and Raman) and their conformational properties using single molecule force spectroscopy with specific probes for glucose, galactose, and N-acetyl glucosamine-rich EPS. Vibrational spectra evidenced the overproduction of glycogen and other carbohydrates in the biofilm. The conformational analysis was performed from both the freely jointed chain (FJC) and worm like chain (WLC) models. The results of the FJC fittings showed highly ramified and/or folded structures for all the detected EPS with molecular elongations up to 1000-2500 nm, and typical Kuhn lengths of glycogen macromolecules. The characteristics of galactose-rich EPS have been found to be significantly different from those of glucose- and N-acetyl glucosamine-rich EPS. On the basis of the theoretical fittings with the WLC model, our results suggested that carbohydrates may be associated with peptide domains.