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 degrees 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 K-m and V-max 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-alpha/beta-D-galactopyranoside revealed that strain NTa agarase was a beta-agarase that degraded agarose into neoagarobiose, neoagarotetraose and neoagarohexaose as the predominant products, as well as a small amount of 3,6-anhydro-alpha-L-galactose. This is the first to present evidence of agarolytic activity in strain from genus Stenotrophomonas. (C) 2016 Published by Elsevier B.V.