Nucleotide sequence identities of horA homologues and adjacent DNA regions identified in three species of beer-spoilage lactic acid bacteria

The horA homologues and adjacent DNA regions identified in beer-spoilage Lactobacilus lindneri DSM 20690(T) and L. paracollinoides DSM 15502(T) were examined and compared with the corresponding DNA region of beer-spoilage L. brevis ABBC45, a strain in which the hop-resistance gene horA was originally identified. The PCR analysis suggests ORFB1-B5 regions Surrounding horA are conserved in all of the strains. The nucleotide sequence comparison of the conserved DNA regions revealed extremely high levels of identities among the three beer-spoilage strains that are not typical for distinct species. The PCR methods using printers specific to the adjacent ORFs were found to be able to differentiate beer-spoilage Lactobacillus strains from non-spoilers, indicating these ORFs are also useful genetic markers for determining the beer-spoilage ability of lactobacilli The presence or absence of the adjacent ORFs in 92 bacterial strains was completely identical with that of horA homologues, indicating the ORFB1-B5 regions are generally conserved in beer-spoilage Lactobacillus strains. Taken together, these results suggest the ORFB1-B5 regions have been acquired by beer-spoilage lactobacilli through horizontal gene transfer and provide a theoretical basis for applying a trans-species genetic marker such as horA to deal with unencountered species of beer-spoilage lactobacilli.