Evaluation of Genotypic Diversity in Hop Resistance of Beer Spoilage Bacteria

Abstract:

To evaluate the accuracy of genetic markers of horA and horC genesto rapidly detect the spoilage ability of beer spoilage bacteria，the genotypes and phenotypes of 53 spoilage bacteria strains which were isolated from 5 Chinese breweries were compared in this study. The physiological features studied included M13-PCR fingerprint，horA and horC genes，beer spoilage ability and hop resistance ability. The clustering analysisof M13-PCR fingerprint indicated that the similaritycoefficient was less than 70% between different species and the similarity between strains in the same specie also varied greatly. Hence，the genotypes of 53 strains were different from each other. Phenotype analysis showed that almost all strains with strong spoilage ability or hop resistance ability contained horA or horC genes，which confirmedthe good accuracy of these genetic markers. However，some non-spoilage or weak hop-resistant strains also contained horA or horC genes，leading to a highfalse positive rate of 78.6%. A few weak spoilage strains did not contain horA or horC genes，which led to a false negative rate of 28%. Two strong hop-resistant strains did not contain horA or horC genes and they were supposed to have other mechanism of hop resistance. It is interesting that horA and horC geneswere found to be conserved in L. plantarum species. These results indicated that horA or horC genesare not suitable to be used as genetic markers for rapidly detectionof the spoilage ability and hop resistance of all beerspoilage bacteria.