In situ production of human [beta] defensin-3 in lager yeasts provides bactericidal activity against beer-spoiling bacteria under fermentation conditions

Aims To examine the use of a natural antimicrobial peptide, human [beta]-defensin-3 (HBD3), as a means of preventing spoilage from bacterial contamination in brewery fermentations and in bottled beer. Methods and Results A chemically synthesised HBD3 peptide was tested for bactericidal activity against common Gram-positive and Gram-negative beer-spoiling bacteria, including species of Lactobacillus, Pediococcus and Pectinatus. The peptide was effective at the µmol l-1 range in vitro, reducing bacterial counts by 95%. A gene construct encoding a secretable form of HBD3 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 HBD3 possesses bactericidal activity against beer-spoiling bacteria. Furthermore, when added to bottled beer, a synthetic form of HBD3 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. [PUBLICATION ABSTRACT]