Alternating magnetic fields enhance growth and co-production of cellulase and protease in Bacillus velezensis fermentation.

Bacillus velezensis is a safety-grade probiotic with wide applications in agricultural, food and industrial biotechnology. Improving its growth and extracellular enzyme production is critical for enhancing process efficiency and reducing production costs. This study evaluated the potential of alternating magnetic fields (AMFs) to enhance the growth and extracellular enzyme production in B. velezensis. A preliminary comparison with static magnetic fields (SMFs) demonstrated that AMFs exerted a stronger stimulatory effect, therefore AMFs were selected for subsequent investigation. Under the optimal AMF conditions (3 mT, 18 h), biomass increased by 63.59% relative to the untreated control, while cellulase and protease activities were enhanced by 142.93% and 130.5%, respectively. Moreover, AMF treatment significantly improved enzyme stability, for example, cellulase produced under AMF-assisted fermentation retained 72.15% of its initial activity after 24 h at 37 °C when incubated under a 3 mT AMF, whereas only 19.05% activity remained under non-AMF incubation. A similar stabilization trend was observed for enzymes produced under non-AMF fermentation conditions. Scanning electron microscopy revealed that AMF treatment induced notable changes in cell surfaces, including increased roughness, pronounced folding, and depressions, potentially enhancing membrane permeability. Transcriptomic profiling further indicated significant upregulation of key metabolic pathways, specifically branched-chain amino acid biosynthesis, acetyl-CoA metabolism, and secondary metabolite biosynthesis. These results demonstrate that AMF represents a promising non-invasive strategy for enhancing microbial bioprocess performance.