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

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 11.3mg/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.