Cloning, Expression and Characterization of β-agarase Gene from a Marine Bacterium, Pseudoalteromonas sp. JT-6

A gene (agaA6) encoding an extracellular agarase from a marine bacterium, Pseudoalteromonas sp. JT-6, was cloned, sequenced and expressed in Escherichia coli. It comprised an open reading frame of 1338 base pairs and encodes a protein of 445 amino acids with a predicted molecular weight of 50,150 daltons. The entire amino acid sequence of this agarase gene showed 99% identity with the agaA gene from Janthinobacterium sp. SY12. It consists of a signal peptide, a glycoside hydrolase family 16 β-agarase domain and a carbohydrate-binding domain. The recombinant agarase was overexpressed and purified to homogeneity. Enzyme activity analysis revealed that the optimum temperature and pH for the purified recombinant enzyme were around 40℃ and 9.0. The enzyme was an endo-type β-agarase and hydrolyzed agarose to several oligosaccharides.