Glycoside hydrolase DisH from Desulfovibrio vulgaris degrades the N-acetylgalactosamine component of diverse biofilms

Biofilms of sulfate-reducing bacteria (SRB) produce H₂S, which contributes to corrosion. Although bacterial cells in biofilms are cemented together, they often dissolve their own biofilm to allow the cells to disperse. Using Desulfovibrio vulgaris as a model SRB, we sought polysaccharide-degrading enzymes that disperse its biofilm. Using a whole-genome approach, we identified eight enzymes as putative extracellular glycoside hydrolases including DisH (DVU2239, dispersal hexosaminidase), an enzyme that we demonstrated here, by utilizing various p-nitrooligosaccharide substrates, to be an N-acetyl-β-D-hexosaminidase. For N-acetyl-β-D-galactosamine (GalNAc), V_max was 3.6 µmol of p-nitrophenyl/min (mg protein)⁻¹ and K_m was 0.8 mM; the specific activity for N-acetyl β-D-glucosamine (GlcNAc) was 7.8 µmol of p-nitrophenyl/min (mg protein)⁻¹. Since GalNAc is one of the three exopolysaccharide matrix components of D. vulgaris, purified DisH was found to disperse 63 ± 2% biofilm as well as inhibit biofilm formation up to 47 ± 4%. The temperature and pH optima are 60°C and pH 6, respectively; DisH is also inhibited by copper and is secreted. In addition, since polymers of GalNAc and GlcNAc are found in the matrix of diverse bacteria, DisH dispersed biofilms of Pseudomonas aeruginosa, Escherichia coli and Bacillus subtilis. Therefore, DisH has the potential to inhibit and disperse a wide-range of biofilms.