In situ production of human β defensin‐3 in lager yeasts provides bactericidal activity against beer‐spoiling bacteria under fermentation conditions

Abstract Aims To examine the use of a natural antimicrobial peptide, human β ‐defensin‐3 ( HBD 3), as a means of preventing spoilage from bacterial contamination in brewery fermentations and in bottled beer. Methods and Results A chemically synthesised HBD 3 peptide was tested for bactericidal activity against common G ram‐positive and G ram‐negative beer‐spoiling bacteria, including species of L actobacillus, P ediococcus and P ectinatus . The peptide was effective at the μ mol l −1 range in vitro , reducing bacterial counts by 95%. A gene construct encoding a secretable form of HBD 3 was integrated into the genome of the lager yeast Saccharomyces pastorianus strain CMBS ‐33. The integrated gene was expressed under fermentation conditions and was secreted from the cell into the medium, but a significant amount remains associated with yeast cell surface. We demonstrate that under pilot‐scale fermentation conditions, secreted HBD 3 possesses bactericidal activity against beer‐spoiling bacteria. Furthermore, when added to bottled beer, a synthetic form of HBD 3 reduces the growth of beer‐spoiling bacteria. Conclusions Defensins provide prophylactic protection against beer‐spoiling bacteria under brewing conditions and also in bottled beer. Significance and Impact of the study The results have direct application to the brewing industry where beer spoilage due to bacterial contamination continues to be a major problem in breweries around the world.