Biotechnology and Bioprocess Engineering 2019; 24(5): 799-809  
Characterization of Two Thermostable β-agarases from a Newly Isolated Marine Agarolytic Bacterium, Vibrio sp. S1
Won-Jae Chi1, Ju Won Seo2, and Soon-Kwang Hong2,*
1Biological and Genetic Resource Assessment Division, National Institute of Biological Resource, Incheon 22689, Korea
2Department of Bioscience and Bioinformatics, Myongji University, Yongin 17058, Korea
Correspondence to: Soon-Kwang Hong
Department of Bioscience and Bioinformatics, Myongji University, Yongin 17058, Korea
Tel: +82-31-330-6198; Fax: +82-31-335-8249
E-mail: skhong@mju.ac.kr
Received: May 14, 2019; Revised: July 12, 2019; Accepted: July 17, 2019; Published online: October 31, 2019.
© The Korean Society for Biotechnology and Bioengineering. All rights reserved.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
An agar-degrading bacterium, strain S1, was isolated from the coastal seawater of Jeju Island, Korea, and identified as a novel species of the genus Vibrio. The isolate, Vibrio sp. S1, produced at least five kinds of extracellular agarases in artificial sea water broth containing yeast extract and bacto peptone, and two of them were purified to homogeneity. Both agarases, AgaA33 and AgaA29, with apparent molecular weights of 33 kDa and 29 kDa, respectively, exhibited an optimum temperature and pH of 45°C and 7.0, respectively. AgaA33 and AgaA29 showed acidophilic properties and maintained 93% and 87% of the maximum agarase activity at 50°C, respectively, displaying their thermostability. Moreover, more than 80% activity was retained after heat treatment at 45°C for 1 h. Their agarase activities were inhibited by the presence of EDTA and remarkably stimulated by the presence of Mn2+ in a concentration-dependent manner, indicating that both agarases required the Mn2+ ion as a cofactor. The AgaA33 enzyme exhibited Km and Vmax values of 4.02 mg/mL and 27 U/mg, respectively. AgaA29 exhibited Km and Vmax values of 3.26 mg/mL and 200 U/mg, respectively. The instrumental analysis demonstrated that both are new β-agarases that can hydrolyze agarose and agaro-oligomers into neoagarotetraose and neoagarohexaose. In addition, AgaA33 coproduced neoagarooctaose as the major final product. Both thermostable enzymes are expected to be useful for the industrial application of agar.
Keywords: Vibrio sp. S1, beta-agarase, thermostable agarase, agar


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