Optimized recombinant production of the bacteriocin garvicin Q by .

Bacteriocins are antimicrobial peptides applied in food preservation and are interesting candidates as alternatives to conventional antibiotics or as microbiome modulators. Recently, we established as a suitable production host for various bacteriocins including garvicin Q (GarQ). Here, we establish secretion of GarQ by via the Sec translocon achieving GarQ titers of about 7 mg L in initial fermentations. At neutral pH, the cationic peptide is efficiently adsorbed to the negatively charged envelope of producer bacteria limiting availability of the bacteriocin in culture supernatants. A combination of CaCl and Tween 80 efficiently reduces GarQ adsorption to . Moreover, cultivation in minimal medium supplemented with CaCl and Tween 80 improves GarQ production by to about 15 mg L but Tween 80 resulted in reduced GarQ activity at later timepoints. Using a reporter strain and proteomic analyses, we identified HtrA, a protease associated with secretion stress, as another potential factor limiting GarQ production. Transferring production to HtrA-deficient K9 improves GarQ titers to close to 40 mg L. Applying conditions of low aeration prevented loss in activity at later timepoints and improved GarQ titers to about 100 mg L. This is about 50-fold higher than previously shown with a strain employing the native GarQ transporter GarCD for secretion and in the range of levels observed with the native producer B1726. Additionally, we tested several synthetic variants of GarQ and were able to show that exchange of the methionine in position 5 to a phenylalanine (GarQ) results in markedly increased activity against and . In summary, our findings shed light on several aspects of recombinant GarQ production that may also be of relevance for production with natural producers and other bacteriocins.