Directed Evolution of an Alginate Lyase from Flammeovirgasp. for Seaweed Fertilizer Production from the Brown Seaweed Laminaria japonica

An alginate lyase (FsAly7) from Flammeovirgasp. was engineered by directed evolution to improve its optimum temperature and thermostability. The optimum temperature of the positive mutant mFsAly7 (FsAly7-Ser43Pro) was increased by 5 °C, and the thermal inactivation half-lives at 40 and 45 °C were 4.4 and 5.6 times higher than those of FsAly7, respectively. mFsAly7 was expressed in high levels in Pichia pastoriswith the highest yield of 3125.5 U·mL–1. On the property-improved enzyme, a bioconversion strategy was developed to prepare the Laminaria japonicahydrolysate, and the highest AOS yield (29.5 mg·mL–1) was 1.5 times higher than that of FsAly7. Moreover, the application potential of the L. japonicahydrolysate as an organic fertilizer was evaluated. The addition of L. japonicahydrolysate improved the sprouting rate, fresh mass, seedling height, and stem diameter of the buckwheat sprouts. Therefore, mFsAly7 may be a good candidate for the production of seaweed fertilizers from L. japonica.