Purification and characterization of exo-β-agarase from an endophytic marine bacterium and its catalytic potential in bioconversion of red algal cell wall polysaccharides into galactans

An extracellular exo-β-agarase was characterized from an endophytic bacterial strain Pseudomonas sp. isolated from the red alga Gracilaria dura. The enzyme was purified to homogeneity with a recovery of 28.2% and a purity fold of 8.33. The purified enzyme was composed of single polypeptide with a molecular mass of about 66 kDa. The enzyme exhibited a maximum activity of 81.74 U mL−1 and a specific activity of 615.5 U mg−1. The optimal pH and temperature for its maximum activity were 9.0 and 35 °C respectively. The enzyme stabilized its activity in alkaline pH 7–11 and high salt concentration up to 4 mol dm−3. The enzymatic hydrolyzed product of agar was characterized as neoagarobiose while the bacterium when incubated with G. dura biomass yielded galactose 20% on dry wt basis. The agarolytic ability of the former was further confirmed by release of protoplasts from G. dura tissue through digestion of cell wall polysaccharides. The bacterium investigated in this study could possibly be used for bioconversion of marine red algal polysaccharides into energy feedstock and the purified enzyme for preparation of compounds having pharmaceutical importance.

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► Characterized β-agarase has catalytic activity at broad pH and salt concentrations.
► Catalytic conversion of agar into neoagarobiose of medical importance in one step.
► DNA protective effect of neoagarobiose against the damage induced by free radicals.
► Bioconversion of red algal biomass into fermentable sugar (galactose).
► These novel properties signified its role as a prospective industrial enzyme.