Total Biosynthesis of Circular Bacteriocins by Merging the Genetic Engineering and Enzymatic Catalysis

Circular bacteriocins are known for their structural stability and effective antimicrobial properties, positioning them as potential natural food preservatives. However, their widespread application is impeded by restricted availability. This research developed a total biosynthesis platform for circular bacteriocins, with a focus on AS-48 by involving recombinant production of the linear precursor in <i>Escherichia coli</i>, followed by enzymatic cyclization of the precursor into cyclic AS-48 using the ligase butelase-1 <i>in vitro</i>. An important discovery is that, aside from fusion tags, the C-terminal motif LE and LEKKK also could affect the expression yield of the precursor. This biosynthesis platform is both versatile and high-yielding, achieving yields of 10-20 mg/L of AS-48. Importantly, the biosynthetic AS-48 exhibited a secondary structure and antimicrobial activities comparable to those of the native molecules. As such, this work proposes an effective synthetic approach for circular bacteriocins, facilitating their advancement and application in the food industry.