Immobilization of Alginate Microbeads With Whole‐Cells Expressing Nitrilase for Continuous Nicotinic Acid Production in Chip Millireactor

ABSTRACT

The biocatalytic production of nicotinic acid using nitrilases has emerged as a promising alternative to conventional chemical synthesis, offering improved selectivity and environmental sustainability. In this study, we developed a continuous‐flow millireactor system employing Escherichia coli cells expressing a nitrilase from Paraburkholderia phymatum (Nit _Phym ) for the continuous production of nicotinic acid. To enhance catalytic efficiency and stability, whole cells were immobilized using two different strategies: covalent attachment to the reactor walls and encapsulation in alginate microbeads. The performance of these immobilization techniques was evaluated in millireactors with two different geometries: pillar and zigzag configurations. Encapsulation of Nit _Phym ‐expressing E. coli cells in alginate microbeads was achieved through a centrifuge‐assisted microencapsulation method, yielding beads with diameters of up to 350 µm. Continuous‐flow reactions demonstrated that the microencapsulated cells maintained their activity over at least 7 days, achieving stable conversion rates of approximately 30% in both pillar and zigzag millireactors. Compared to direct covalent immobilization, microencapsulation significantly reduced cell leaching and contamination of the reaction product. These findings highlight the potential of whole‐cell microencapsulation for enhancing the stability and efficiency of biocatalytic processes in continuous‐flow millireactors.