Summary:
Seaweed biomass is an underutilized resource that is rich in polysaccharides, including xylan. Seaweed polysaccharides could be used as a feedstock in industrial microbiology and and for production of prebiotic oligosaccharides and rare monosaccharides – processes that would benefit from the availability of robust enzymes that break down the seaweed polysaccharides. The present study aimed to identify genes encoding endo-xylanases in bacterial genomes and metagenomes sourced from marine thermal environments, and to characterize the respective enzymes. Twelve endo-xylanases were studied which displayed 59 % median maximal sequence similarity to characterized GH10 or GH11 enzymes. Overall, most of the enzymes functioned optimally at high temperatures, in the presence of salt, and at circumneutral pH. Eight enzymes functioned optimally at temperatures of 50°C or higher, and in the most extreme cases at 85°C to 95°C. Six enzymes retained activity after three-hour incubation at 60°C or higher. Ten enzymes displayed improved catalytic function in the presence of salt, and several retained high catalytic function at 10 % NaCl concentration. All the enzymes hydrolyzed xylan from diverse sources, including crude biomass. The study contributes to an increased understanding of the structural diversity of xylanases; it expands the availability of thermostable xylanases of marine origin; and contributes to increased valorization of seaweed biomass.