Permeabilized whole cells containing co‐expressed cyclomaltodextrinase and maltooligosyltrehalose synthase facilitate the synthesis of nonreducing maltoheptaose (N‐G7) from β‐cyclodextrin

BACKGROUND Maltodextrin is an important bulk ingredient in food and other industries; however, drawbacks such as uneven polymerization and high reducibility limit its utilization. Nonreducing maltoheptaose (N‐G7) is a good substitute for maltodextrin owing to its single degree of polymerization and its nonreducing properties. In this study, in vitro cell factory biotransformation of β‐cyclodextrin (β‐CD) to N‐G7 is demonstrated using coexpressed cyclomaltodextrinase (CDase, EC 3.2.1.54) and maltooligosyltrehalose synthase (MTSase, EC 5.4.99.15). However, the cell membrane prevents β‐CD from entering the cell owing to its large diameter. RESULTS The amylase‐deficient permeabilized host ΔycjM‐ΔmalS‐ΔlpxM is utilized for the coexpression of recombinant CDase and MTSase. Deletion of lpxM effectively allows the entry of β‐cyclodextrin into the cell, despite its large diameter, without requiring any relevant cell membrane permeability‐promoting reagent. This results in a 28.44% increase in the efficiency of β‐CD entry into the cell, thus enabling intracellular N‐G7 synthesis without the extracellular secretion of recombinant CDase and MTSase. After reacting for 5.5 h, the highest purity of N‐G7 (65.50%) is obtained. However, hydrolysis decreases the purity of N‐G7 to 49.30%, thus resulting in a conversion rate of 40.16% for N‐G7 when the reaction lasts 6 h. Precise control of reaction time is crucial for obtaining high‐purity N‐G7. CONCLUSION Whole‐cell catalysis avoids cell fragmentation and facilitates the creation of an eco‐friendly, energy‐efficient biotransformation system; thus, it is a promising approach for N‐G7 synthesis. © 2023 Society of Chemical Industry.