Assessment of the potential of Nostoc strains from the Pasteur Culture Collection for the production of polysaccharides of applied interest

Abstract

The exocellular polysaccharides released during thephotoautotrophic growth by 25 Nostoc strainsbelonging to the Pasteur Culture Collection (PCC) wereinvestigated with regard to their chemical andrheological properties in order to assess theirpotential for the production of polysaccharides ofindustrial interest.All the released polysaccharides (RPSs) were complexanionic heteropolymers, composed of a number ofmonosaccharides ranging from six to nine, alwaysincluding glucose and fucose, and most frequentlygalactose. Ribose, rarely reported to be present incyanobacterial RPSs, was found in seven polymers. TheRPSs were shown to possess an anionic charge due tothe presence of uronic acids and in most cases also ofpyruvil and sulphate groups. Moreover, a large numberof polymers showed the presence of significant amountsof constituents such as acetyl groups, peptidicmoieties and deoxysugars, that may contribute to thehydrophobicity of the macromolecules. The viscositydependence on the shear rate of aqueous solutions ofthe RPSs was, in three cases, comparable with that ofxanthan gum, and one RPS showed a very satisfactorystability of the viscosity over a wide range of pH,temperature and salinity values. The most promisingPCC Nostoc strains for the production of RPSsfor specific applications were thus singled out, basedon the characteristics of their polymers.