Gene cloning, expression and characterisation of a new β-agarase, AgWH50C, producing neoagarobiose from Agarivorans gilvus WH0801.

agWH50C, a novel β-agarase gene, was cloned from Agarivorans gilvus WH0801 by degenerate PCR and nested PCR. The gene agWH50C comprized a 2,223-bp, encoding a protein of 740 amino acids. Sequencing results demonstrated that AgWH50C shared 45 % sequence identity with a well characterized β-agarase, Aga50D, from Saccharophagus degradans 2-40. The mature agarase was expressed in Escherichia coli and purified by affinity chromatography. The optimum pH and temperature for AgWH50C activity were 6.0 and 30 °C. The K m and V max values for agarose were 12.55 mg/ml and 1.17 U/mg. Analysis of the hydrolysis products using linear ion trap mass spectrometry, Fourier transform-nuclear magnetic resonance spectrometry and thin-layer chromatography confirmed that the reaction product of AgWH50c was α-neoagarobiose alone. Therefore, our novel agarase has the potential for industrial applications to produce neoagarobiose as well as provides a key β-agarase for fermentation of agar biomass.