Chemical and structural characterization of exopolymers produced by Pseudomonas sp. NCIMB 2021 in continuous culture

The growth of marine Pseudomonas sp. NCIMB 2021 as continuous cultures in the presence of surfaces of AISI 316 stainless steel allowed the isolation and partial chemical characterization of exopolymers released into the culture medium (free exopolymers), as well as capsular and biofilm exopolymers. Fourier-transform infrared (FTIR) spectroscopy demonstrated the presence of O- and N-acetylation within the carbohydrate moieties and a predominant 310-helical structure of the protein component, highly resistant to hydrogen/deuterium exchange. Differences between the exopolymers were apparent. Relatively less uronic acid residues were detected in the capsular exopolymers compared to either the biofilm or free exopolymers. O- and N-acetylation were greatest in the biofilm exopolymer. SDS-PAGE protein profiles confirmed differences between exopolymers. The secondary structures of proteins determined using FTIR spectroscopy indicated that the capsular exopolymer had reduced helical content and an increased aggregated strand content compared to the biofilm exopolymer. However, the free exopolymer had an increased β-sheet component and a reduced unordered component when compared to the biofilm and capsular exopolymers. These data suggest that exopolymer chemistry varies with cellular mode of growth.