Study On Screening And Selecting An Effectively Alginase-producing Strain, Its Optimal Cultivation And Characteristics Of Alginase

With the purposes of screening and selecting an effectively alginase-producing strain, studying the biological effect and characteristics of alginase and using alginase to produce alginate oligosaccharides, several strains have been isolated with alginase activity from the decaying parts of Laminaria japonica. Among these strains, the strain s4 showed the highest alginase activity during the second screening and demonstrates a good stability, so it was chosen to investigate the fermentation condition and some properties of alginase produced by strain s4.There are many factors that influence the alginase production. It was found that the strain can not produce alginase without sodium alginate. The different carbon sources tests also showed that the alginase of strain s4 was an induced enzyme. In one-factor-at-a-time methodology experiment, the optimal conditions of strain s4 to produce algniase were studied. The optimal fermentation medium of strain s4 contained sodium alginate 1.2%; NH4Cl 0.9%; NaCl 1.5% initial pH 7.5. The optimal temperature and time of fermentation conditions for s4 to produce alginase were 25℃and 48h, respectively.Under the condition,the strain s4 would produce the highest amount of alginase.Alginase produced by strain s4 was an inducible and secreting extracellar enzyme. The alginase produced by the strain s4 was purified to an apparent homogeneity identified by SDS-PAGE through ammonium sulfate precipitation (20-80% saturation), CM-Sepharose Fast Flow chromatography, and Sephacryl S-100 gel filtration. Molecular weights of the enzymes were estimated to be 29 kDa. Alginase activity was stable in the pH range of 6.0-9.0 and under 45℃,and the optimal pH value and temperature of alginase were 7.5 and 40℃. The enzyme activity was significantly inhibited by Hg2+and slightly activated by Mg2+,Na+ and K+ at ion concentration being 5mmoL/L.By hydrolyzing sodium alginate, the components of hydrolytic product was mainly poly(M).