Recombinant production of antimicrobial proteins in bacterial expression systems: Escherichia coli vs. lactic acid...

The development of antimicrobial treatments as alternatives to antibiotics to combat antimicrobial-resistant (AMR) bacteria is a global priority. Antimicrobial peptides and proteins such as Host Defense Peptides (HDPs) and endolysins are one of the alternatives that are being explored. HDPs are small, cationic, and amphiphilic antimicrobial peptides derived from the innate immune system exhibiting a broad-spectrum antimicrobial activity. On the other hand, endolysins are enzymes produced by bacteriophages to hydrolyze the bacterial peptidoglycan layer, offering more specific antimicrobial activity than HDPs. While short peptides can be chemically synthesized, this approach presents several limitations, and recombinant production is also being used. Escherichia coli is the most used bacterial expression system for protein production. Alternative systems based on Generally Recognized as Safe (GRAS) microorganisms such as Lactic Acid Bacteria (LAB) have also been employed. However, so far, no comparative studies have evaluated the production and activity of antimicrobial proteins expressed in E. coli versus LAB and this study aims to address that gap.

To evaluate potential differences in the production of antimicrobial proteins using E. coli and two LAB (Lactococcus lactis and Lactiplantibacillus plantarum) hosts, various proteins were evaluated. These included two HDPs fused to a GFP, two multidomain HDP-based proteins and one endolysin. The results revealed a clear influence of the expression system on the quality of HDP-based protein, including both GFP fusions and multidomain constructs. Protein yield was higher in E. coli and all HDP-based proteins exhibited higher antimicrobial activity when expressed in E. coli compared to L. lactis and L. plantarum. In contrast, endolysin activity was comparable when produced in E. coli and L. lactis.

These results demonstrate that the choice of bacterial expression host significantly affects not only the yield but, more importantly, the antimicrobial activity of HDP-based proteins. For these proteins, the antimicrobial activity was consistently higher when produced in E. coli. In contrast, endolysins exhibited similar characteristics regardless of whether they were expressed in E. coli or in L. lactis.