Intracellular alginolytic enzymes of the marine bacterium Pseudoalteromonas citrea KMM 3297

The marine bacterium Pseudoalteromonas citrea KMM 3297 is an associate of the holothurian Apostichopus japonicus. When grown in a medium containing glucose, the strain produces two intracellular alginolytic enzymes, AII and AIII. Fucoidan from the brown alga Fucus evanescens induces synthesis of one more alginolytic enzyme, AIIII. These enzymes were separated using anion-exchange chromatography. The alginate lyase AII completely retains its activity at 35degreesC, AIII and AIIII being stable at 45degreesC. The alginate lyases exhibit maximal activities in the range of pH 7-8. The molecular weights of AII, AIII, and AIIII determined by gel filtration are 25, 79, and 61 kD, respectively. All the investigated enzymes are endo-type alginate lyases. They catalyze degradation Of polyguluronate (poly-G) and polymannuronate (poly-M) yielding oligosaccharides of the polymerization degree of 5 greater than or equal to n greater than or equal to 3 with the unsaturated bond between the C4 and C5 atoms of the non-reducing terminus. A mixture of these three enzymes exhibits synergism while acting on the polymeric substrate. The K., values of the alginate lyase AII for poly-G and poly-M are 24 and 34 mug/ml, respectively. Alginate lyase AIIII exhibits less affinity to poly-M (K-m = 130.0 mug/ml) than to poly-G (K-m = 40.0 mug/ml). NaCl (0.2 M), MgCl2 and MgSO4 (0.01 M) activate all three enzymes more than twofold. The presence of several alginolytic enzymes of different specificity provides efficient destruction of alginic acids of brown algae by the strain P. citrea KMM 3297.