Abstract:[Background] Undaria pinnatifida, a species of edible brown algae, is considered as an excellent raw material for the preparation of alginate oligosaccharides (AOSs) due to the high content of intracellular alginate. Alginate lyases (EC 4.2.2.-) can depolymerize alginate into AOSs. However, the low catalytic efficiency makes it difficult to produce AOSs from brown algae by directly enzymatic degradation. [Objective] To mine and screen alginate lyases from the marine bacterium Photobacterium gaetbulicola for degrading U. pinnatifida in the production of AOSs. [Methods] Alginate lyases with high activities were screened from P. gaetbulicola Gung47 by sequence analysis, transcriptional analysis, recombinant expression, and enzymatic characterization. The degrading conditions for U. pinnatifida were optimized, and the final products were identified. [Results] Three alginate lyases (AlgPg1, AlgPg2, and AlgPg3) were identified from P. gaetbulicola Gung47. Both the transcription level and the specific activity of AlgPg1 were higher than those of AlgPg2 and AlgPg3. The specific activity of AlgPg1 was enhanced by NaCl, reaching up to 466 U/mg. AlgPg1 degraded the powder and blades of U. pinnatifida, producing reducing sugar at a yield of (26.2±1.6) mg/mL, i.e., AOSs conversion ratio of 32.5%. The degradation products were a mixture of AOSs with the degree of polymerization (DP) ranging from 1 to 6, in which DP3 had the highest content. [Conclusion] The alginate lyase AlgPg1 showed a remarkable ability of producing AOSs from U. pinnatifida, demonstrating the potential of serving as a novel tool for the utilization of U. pinnatifida.
