Screening of Alginate Lyase-Producing Strains and Optimization of Fermentation and Enzymatic Hydrolysis Processes

Alginate lyase, as a tool enzyme capable of efficiently degrading alginate, plays a significant role in the industrial production of alginate oligosaccharides. In this study, using sodium alginate as the sole carbon source, a bacterial strain with high sodium alginate degradation efficiency was isolated and purified from decaying Ecklonia maxima. Based on morphological, physiological, biochemical characteristics, and 16S rRNA gene sequencing, the strain was identified as Klebsiella pneumoniae and designated as SW06. Through optimization of enzyme production and enzymatic hydrolysis conditions, the enzyme activity of the strain was significantly enhanced. The optimal medium composition for strain SW06 was as follows: sodium alginate 5 g/L, (NH₄)₂SO₄ 5 g/L, MgSO₄·7H₂O 6 mmol/L, NaCl 120 mmol/L, K₂HPO₄ 15 mmol/L, and FeSO₄·7H₂O 0.04 mmol/L. The optimized culture conditions were as follows: inoculum size 1%, medium volume 90 mL (in a 250 mL conical flask), shaking speed 180 r/min, and initial medium pH 6.0. After optimization, the maximum activity of alginate lyase reached 311 U/mL, representing a 395% increase compared to the pre-optimization level. Enzymatic property experiments revealed that the optimal temperature for enzymatic hydrolysis was 40 °C, with good pH stability at this temperature; the enzyme remained stable within the pH range of 6.0–9.0. The addition of β-mercaptoethanol and NaCl significantly enhanced enzyme activity (≥50% increase). Analysis of enzymatic hydrolysis products indicated that the main products were alginate disaccharide, trisaccharide, and tetrasaccharide. This study successfully isolated a high-activity alginate lyase-producing strain from Ecklonia maxima, demonstrating potential application prospects and providing a new alternative for the industrial production of alginate oligosaccharides.