The roles of Pseudomonas aeruginosa extracellular polysaccharides in biofouling of reverse osmosis membranes and nitric oxide induced dispersal

The roles of Pseudomonas aeruginosa polysaccharides (Pel, Psl, alginate) in reverse osmosis (RO) membrane biofouling and nitric oxide (NO) induced dispersal were investigated. While mutants deficient in Psl formed significantly lower biofilm (total cell and polysaccharide) biovolumes than the PAO1 wild-type on glass surfaces, total cell biovolumes were similar during fouling of RO membranes. However, biofilms of the Psl deficient mutants exhibited a striated pattern, leaving large areas of membrane unfouled and contained up to 70% less polysaccharide and 24% less protein than the wild-type. Membranes fouled by the psl mutants exhibited a 69% reduction in the rate of biofouling (pressure rise over a given period), while the pel and alginate mutants were similar to the wild-type, suggesting functional differences in the polysaccharides. Overproduction of alginate by a PDO300 mutant increased the biofouling rate (59%) relative to wild-type, highlighting the ability of this polysaccharide to promote biofilm adherence and increase hydraulic resistance to permeate flow in an RO system. These results emphasize the importance of attachment specific polysaccharides for bacteria when fouling industrial RO membranes. When exposed to NO, dispersal of the PDO300 mutant biofilm was 25% lower than the wild-type, whilst dispersal of the alginate deficient mutant was 11% greater. Alginate thus appears to play an important role in NO induced dispersal of PAO1 biofilms.