The extracellular beta-agarase LSL-1 produced by an agar-liquefying, soil bacterium Acinetobacter sp., AG LSL-1 was purified to homogeneity by combination of ion-exchange and size exclusion chromatography with final yield of 44%. The enzyme has a specific activity of 397 U mg(-1) protein and with a molecular mass of 100 kDa. The agarase was active in the pH range of 5.0-9.0, optimally at pH 6.0 and temperature between 25 degrees C and 55 degrees C and optimal at 40 degrees C. The enzyme retained 63% of native activity at 50 degrees C suggesting it is a thermostable. The activity of the agarase was completely inhibited by metal ions, Hg(2+), Ag(+) and Cu(2+), whereas 25-40% of native activity was retained in the presence of Zn(2+), Sn(2+) and SDS. Neoagarobiose was the final product of hydrolysis of both agarose and neoagarohexaose by the purified agarase LSL-1. Based on the molecular mass and final products of agarose hydrolysis, the beta-agarase LSL-1 may be further grouped under group III beta-agarases and may be a member of GH-50 family. This is the first report on the purification and biochemical characterization of beta-agarase from an agar-liquefying Acinetobacter species. (C) 2009 Elsevier Ltd. All rights reserved.