Study on fermentation process of Sargassum by a composite microbial consortium based on enzymatic pretreatment

Sargassum, a type of brown algae rich in bioactive polysaccharides and other functional components, faces limitations in high-value utilization due to its dense cellular structure. Thus, we developed an integrated enzymatic hydrolysis-fermentation process to achieve efficient degradation. After 24 hours of pretreatment with a composite enzyme (5% cellulase + 5% xylanase), the release of reducing sugars reached 7.16 mg·mL⁻¹, showing a 6.24-fold increase compared with the initial reducing sugar content, which created the necessary conditions for subsequent fermentation. Subsequent microbial fermentation further increased the reducing sugar content to 9.87 mg·mL⁻¹, while significantly reducing heavy metal levels (Pb, As, etc.) and enhancing nutrient components (Fe, \textV_\textB_\text6 , etc.) by 1.83–4.64 times. Metagenomic analysis reveals that the microbial consortium was dominated by halotolerant genera (e.g., Halomonas, Jeotgalibacillus). The microflora detected 177 carbohydrate-active enzymes (CAZymes) in the community. Through comparison with the NCBI and CAZy databases, 40 enzyme proteins related to the degradation of seaweed polysaccharides were identified. Among these, 12, 9, 12, and 7 enzyme proteins were associated with the degradation of alginate, laminarin, cellulose, and fucoidan, respectively. The study shows that the combined enzymatic hydrolysis-fermentation technology can effectively break down the dense cell walls of Sargassum, significantly improving the yield of reducing sugars and the value of products, thus providing theoretical basis and technical support for the high-value utilization of Sargassum.