Magnetic immobilization of Bacillus subtilis natto cells for menaquinone-7 fermentation. 
Production of menaquinone-7 (MK-7) by Bacillus subtilis natto is associated with major drawbacks.  To address the current challenges in MK-7 fermentation, studying the effect of magnetic nanoparticles on the bacterial cells can open up a new domain for intensified bioprocesses.  This article introduces the new concept of application of iron oxide nanoparticles (IONs) as a pioneer tool for MK-7 process intensification.  In this order, IONs with the average size of 11 nm were successfully fabricated and characterized for possible in situ removal of target substances from the fermentation media.  The prepared particles were used for decoration and immobilization of B. subtilis natto cells.  Presence of iron oxide nanoparticles significantly enhanced the MK-7 specific yield (15 %) as compared to the control samples.  In addition, fabricated IONs showed a promising ability for in situ recovery of bacterial cells from the fermentation media with more than 95 % capture efficiency.  Based on the results, IONs can be implemented successfully as a novel tool for MK-7 production.  This study provides a considerable interest for industrial application of magnetic nanoparticles and their future role in designing an intensified biological process.