Characterization of an alkaline β-agarase from Stenotrophomonas sp. NTa and the enzymatic hydrolysates

• This is the first to present evidence of agarolytic activity in strain from genus Stenotrophomonas. We purified an extracellular β-agarase from marine bacterium Stenotrophomonas sp. NTa. This alkaline agarase exhibited stricking stability across a wide pH range. It also had a relatively good resistance against some detected inhibitors, detergents and urea denaturant. We identified the enzymatic hydrolysates and their antioxidant activities.

An extracellular agarase from marine bacterium Stenotrophomonas sp. NTa was purified to homogeneity. By size exclusion chromatography and SDS-PAGE analysis, the enzyme was determined to be a homodimer with monomeric molecular mass of 89.0 kDa. The optimal temperature and pH of strain NTa agarase were 40 °C and 10.0, respectively. It exhibited striking stability across a wide pH range of 5.0–11.0. Agarase from Stenotrophomonas sp. NTa had a relatively good resistance against the detected inhibitors, detergents and urea denaturant. The Km and Vmax for agar were 11.3 mg/ml and 25.4 U/mg, respectively. Thin layer chromatography analysis, mass spectrometry, and enzyme assay using p-nitrophenyl-α/β-d-galactopyranoside revealed that strain NTa agarase was a β-agarase that degraded agarose into neoagarobiose, neoagarotetraose and neoagarohexaose as the predominant products, as well as a small amount of 3,6-anhydro-α-l-galactose. This is the first to present evidence of agarolytic activity in strain from genus Stenotrophomonas.