Identification of novel horA-harbouring bacteria capable of spoiling beer.

An ATP-binding cassette (ABC) multi-drug resistance (MDR) gene was found in 4 Gram-positive bacterial isolates of environmental origin and found capable of spoiling beer. The bacteria isolated were Bacillus cereus, Bacillus licheniformis, Paenibacillus humicus, and Staphylococcus epidermidis; all of which were previously unappreciated as beer-spoilage bacteria. The MDR gene found in these bacteria has less than 37% similarity to known ABC MDR proteins described for Bacillus and Staphylococcus, and this is the first finding of an ABC MDR gene in the genus Paenibacillus. The sequenced region of the gene was translated and compared phylogenetically with the closest GenBank matches of the respective species and the closest GenBank matches overall. The ABC MDR proteins from these isolates were found to cluster among known sequences of HorA, sharing 99.5% identity within the sequenced region. In the beer-spoilage-associated genera Lactobacillus and Pediococcus, the presence of the MDR gene horA correlates with the ability to grow in beer. As the unique horA-harbouring isolates described here are capable of growing in beer, it is likely that the presence of the horA gene likewise confers hop resistance to these organisms.