Capsular polysaccharides of cultured phototrophic biofilms

Abstract

Phototrophic biofilm samples from an Italian wastewater treatment plant were studied in microcosm experiments under varying irradiances, temperatures and flow regimes to assess the effects of environmental variables and phototrophic biomass on capsular exopolysaccharides (CPS). The results, obtained from circular dichroism spectroscopy and High Performance Liquid Chromatography, suggest that CPS have a stable spatial conformation and a complex monosaccharide composition. The total amount present was positively correlated with the biomass of cyanobacteria and diatoms, and negatively with the biovolume of green algae. The proportion of uronic acids showed the same correlation with these taxon groups, indicating a potential role of cyanobacteria and diatoms in the removal of residual nutrients and noxious cations in wastewater treatment. While overall biofilm growth was limited by low irradiance, high temperature (30°C) and low flow velocity (25 l h⁻¹) yielded the highest phototrophic biomass, the largest amount of CPS produced, and the highest proportion of carboxylic acids present.

Keywords:

• phototrophic biofilms
• capsular exopolysaccharides
• microcosm
• circular dichroism
• HPLC

Acknowledgements

The authors gratefully acknowledge Dr NTW Ellwood for constructive criticism of the manuscript. This research was partly conducted within the framework of EU project PHOBIA (QLK3-CT2002-01938). A. Bohn acknowledges support by the Fundação para a Ciência e a Tecnologia (Portugal) through fellowship SFRH/BPD/25967/2005.