Enzyme activities of marine bacteria involved in Laminaria-thallus decomposition and the resulting sugar release

The extracellular decomposing enzyme activities of marine bacteria, including 60 and 16 strains of Laminaria-thallus decomposing bacteria (LDB) and non-LDB, respectively, were determined against several algal polysaccharides. A number of LDB decomposed alginate, fucoidan, and cellulose, but not laminarin. Clear decomposing activity was not observed in the culture supernatant from nutrient broth, but was detected in that from a Laminaria-thallus medium, suggesting that decomposing enzymes were induced. During the incubation of LDB in Laminaria-thallus medium, depolymerized sugar materials with a wide range of molecular size were released into the culture fluid. Total sugars released into the culture fluid after 4 d of incubation amounted to a maximum of 95% of the initial content in the thallus tissues. These findings suggest that microbial decomposition of Laminaria thallus in sea water could be a good source of carbohydrates which may support the heterotrophic growth of marine organisms.