A comparative study of cellulase and hemicellulase activities of brackish water clam Corbicula japonica with those of other marine Veneroida bivalves

Abstract

Corbicula japonica is a typical brackish water bivalve species belonging to the order Veneroida, and it is the most important inland fishery resource in Japan. Corbicula japonica has been suggested to assimilate organic matter from terrestrial plants, unlike Ruditapes philippinarum and Mactra veneriformis, which selectively assimilate organic matter of marine origin. This led us to hypothesize that C. japonica, despite being a suspension feeder, could assimilate cellulosic materials derived from terrestrial plants. In the present study, we measured cellulase and hemicellulase activities in the crystalline styles of C. japonica and other commercially important Veneroida bivalve species in Japan: Ruditapes philippinarum, Meretrix lamarckii and Meretrix lusoria. Corbicula japonica demonstrated notably higher cellulase, xylanase and beta-mannanase activities than the other marine bivalves, suggesting that this species possesses a far greater biochemical capacity to break down the structural polysaccharides of plant cell walls than the other species. In contrast, the beta-1,3-glucanase and pectinase activities of C. japonica were similar to or even lower than those of the others. This is possibly due to the presence of these polysaccharides in the cell walls of diatoms, a principal food of most marine bivalves. Although direct evidence is lacking, the high cellulase, xylanase and beta-mannanase activities of C. japonica may result from adaptation to an upstream estuarine environment where phytoplankton and diatoms are scarce, but plant-derived substances are abundant.