Isolation and identification of potential beer-spoilage Pediococcus inopinatus and beer-spoilage Lactobacillus backi strains carrying the horA and horC gene clusters

Four beer-spoilage strains, LA20, LA21, LA22 and LA23, were isolated from brewery environments. Based on the 16S rRNA gene sequence, LA20 was identified as Pediococcus inopinatus and the remaining three were identified as Lactobacillus back[. The homologs of horA and horC, the hop resistance genes originally identified in L. brevis ABBC45, were detected simultaneously in LA22 and LA23, while only a horA homolog and a horC homolog were found in LA20 and LA21 respectively. The 5.6 kb DNA regions containing the horA homolog in LA20 and LA22 were almost 99% identical with the corresponding region of ABBC45. Similarly the 8.2 kb regions containing the horC homolog in LA21 and LA22 were more than 99% identical with that of ABBC45. Interestingly the horA-containing 5.6 kb regions in LA20 and LA22 were found to be completely identical despite the distinct genus status. Coupled with the fact that LA20 and LA22 were isolated from the same sampling site, these results, taken collectively, reinforce our hypothesis that horA and horC genes were acquired by beer-spoilage species through horizontal gene transfer and confirm the usefulness of horA and horC as genetic markers for the species-independent determination of beer-spoilage ability in lactic acid bacteria.