Genetic Characterization of Hop-Sensitive Variants Obtained from Beer-Spoilage <i>Lactobacillus Brevis</i>

Abstract

Hop-sensitive variants were isolated from six different beer-spoilage strains of Lactobacillus brevis after the 15th subculture at 37°C. All the variants lost beer-spoilage ability, indicating that the loss of hop resistance is primarily responsible for the loss of beer-spoilage ability of the variants. The polymerase chain reaction and Southern blot analysis revealed that all variants lost the homologs of horA, a hop resistance gene originally identified in beer-spoilage L. brevis ABBC45. When the wild-type L. brevis strains were subcultured at 37°C with 200 μM hop compounds, the isolates obtained from the 15th subculture exhibited a higher level of hop-resistance ability than did the hop-sensitive variants. The horA homologs were also detected in the strains subcultured under these conditions. Further subcultures at 37°C with hop compounds did not cause the loss of hop resistance and horA homologs in any of the L. brevis strains, indicating that the loss of the horA homologs are at least partly responsible for the loss of hop resistance observed with the variants. It is also suggested that the horA homologs are carried as part of plasmids, accounting for the relatively unstable nature of hop-resistance ability of beer-spoilage L. brevis strains found in our study.