Screening and phylogenetic analysis of cellulolytic <i>Bacillus</i> spp. isolated from fermented brown algae (<i>Sargassum</i> sp.)

Sargassum sp., a type of brown algae, is rich in bioactive compounds that offer significant health benefits. However, the presence of cellulose-rich cell walls limits their availability, highlighting the need for efficient cellulolytic bacteria. Fermentation of brown algae, including Sargassum sp., offers a sustainable strategy to enhance the extraction of these compounds by breaking down the cellulose barrier. The present study aimed to isolate and characterize cellulase-producing bacteria from fermented Sargassum sp., evaluate their enzyme activity, and identify potential strains suitable for fermentation starter applications. Fresh Sargassum was fermented under anaerobic conditions for 12 days, both with and without pH adjustment. Bacterial isolates were obtained using CMC and MRS agar, followed by screening for cellulase activity through clear zone formation on Congo red-stained plates and quantitative assays using the DNS method. Of the 22 isolates obtained, 12 exhibited cellulase activity, with cellulase activity values ranging from 0.063 to 0.32 U/mL. Among the isolates, SF4 (Bacillus subtilis) exhibited the highest cellulase activity (0.32 U/mL). However, its ß-hemolytic activity raises potential safety concerns, limiting its applicability in food fermentation. In contrast, isolate F6 (Bacillus amyloliquefaciens) demonstrated moderate cellulase activity and was non-hemolytic, making it a safer and more promising candidate for use as a microbial starter culture. These results underscore the potential of Bacillus -derived cellulolytic enzymes to enhance the functional properties of fermented Sargassum, and support the application of B. amyloliquefaciens F6 in the development of safe, bioactive-rich fermented food products.