The gene of agaG1 from Alteromonas sp. GNUM1 encoding a P-agarase (AgaG1) was heterologously expressed in E. coli BL21 (DE3). The recombinant strain was cultured at 37 degrees C and then AgaG1 was expressed at 25 degrees C and 0.5 mM IPTG. The optimum conditions for AgaG1 to hydrolyze agarose were pH 7.0 and 40 degrees C. The main products of agarose hydrolysis by AgaG1 were confirmed to be neoagarobiose and neoagarotetraose. A new agarose hydrolysis process using AgaG1 was developed, in which the reaction temperature was adjusted stepwise to avoid gelation problem with no chemical pretreatment step. The enzyme AgaG1 was found to be very effective and highly selective. When 10.0 g/L agarose was hydrolyzed, 98% of the agarose added was converted to 3.8 and 6.4 g/L of neoagarobiose and neoagarotetraose, respectively. (C) 2014 Published by Elsevier Ltd.