Chromosomal integration and expression of two bacterial alfa-acetolactate decarboxylase genes in brewer's yeast

A bacterial gene encoding a-acetolactate decarboxylase, isolated from Klebsiella ternigena or Enterobacter
aerogenes, was expressed in brewer's yeast. The genes were expressed under either the yeast phosphoglycerokinase
(PGKI) or the alcohol dehydrogenase (ADHI) promoter and were integrated by gene replacement by
using cotransformation into the PGKI or ADHI locus, respectively, of a brewer's yeast. The expression level
of the aL-acetolactate decarboxylase gene of the PGKI integrant strains was higher than that of the ADHI
integrants. Under pilot-scale brewing conditions, the a-acetolactate decarboxylase activity of the PGKI
integrant strains was sufficient to reduce the formation of diacetyl below the taste threshold value, and no
lagering was needed. The brewing properties of the recombinant yeast strains were otherwise unaltered, and
the quality (most importantly, the flavor) of the trial beers produced was as good as that of the control beer.