45 Philippine Journal of Science 142 (1): 45-54, June 2013 ISSN 0031 - 7683 Date Received: ?? Feb 20?? Key Words: κ-carrageenan, κ-carrageenase, carrageenan-degrading bacteria, Kappaphycus alvarezii *Corresponding author: aolluisma@gmail.com Crimson C. Tayco 1 , Francis A. Tablizo 1 , Raymond S. Regalia 2 and Arturo O. Lluisma 1* 1 The Marine Science Institute, University of the Philippines Diliman, Quezon City, Philippines 1101 2 Center for Marine Bio-Innovation, School of Biotechnology and Biomolecular Sciences, Faculty of Science, The University of New South Wales, Sydney, Australia 2052 Carrageenases are glycoside hydrolases that specifically degrade carrageenan, a highly anionic polysaccharide found in the cell wall of many red algal species. To date, only a few of these enzymes have been characterized, and identifying additional sources is important considering the role of carrageenases in production of carrageenan derivatives. In this paper, we report the characterization of a marine bacterial strain that produces κ-carrageenase. The strain, which we designate as ALAB-001, was isolated from diseased thallus fragments of the red alga Kappaphycus alvarezii, a commercially important source of carrageenan. Genotypic and phenotypic data suggest that the isolate belongs to a relatively poorly-characterized group of bacteria in Alteromonadaceae (Alteromonadales) and is closely related to Marinimicrobium and Microbulbifer. Significant κ-carrageenase activity (175 U/mL) was evident when the isolate was grown in the presence of κ-carrageenan. Activity against starch was also high (180 U/mL), but activity against agar, alginate, cellulose, ι-carrageenan, and λ-carrageenan was significantly lower (25-50 U/mL). Laboratory-scale production of the enzyme using batch cultures of the isolate was achieved by optimizing culture medium, length of culture time and degree temperature. Optimal growth was observed at 25°C, though the isolate survived at 30°C. An in-house developed seawater-based medium containing equal concentrations of yeast extract and tryptone (YETS) yielded the highest cell growth based on total protein concentration (~ 3000 μg/mL) and enzyme activity (~ 45 U/mL). Characterization of a κ-Carrageenase-producing Marine Bacterium, Isolate ALAB-001 INTRODUCTION κ-carrageenases are enzymes that catalyze the hydrolysis of κ-carrageenan, a highly sulfated polysaccharide and a major component of the cell wall matrix in many red algal species. κ-carrageenases are members of the Family 16 glycoside hydrolases based on their overall and catalytic domain structure (Michel et al. 1999). Studies have already demonstrated the structural similarity of κ-carrageenases with other Family 16 glycoside hydrolases such as β-agarase, laminarase, lichenase and xyloglucan transglycosylases (Lemos et al. 1985). Only a handful of published reports describe the isolation of κ-carrageenase-producing marine bacteria and demonstrate their ability to produce carrageenase in culture. Bacterial species reported in the scientific literature include Pseudomonas carrageenovora (Weigl and Yaphe 1966), Cytophaga strain 1k-C783 (Sarwar