Comparative study of two plasmids, pRH45 and pRH 20690, isolated from beer-spoilage Lactobacillus brevis ABBC45 and L. lindneri DSM20690

Southern blot analysis with beer-spoilage Lactobacillus lindneri DSM 20690(T) showed the presence of the homologue of horA, a hop-resistance gene originally identified in L. brevis ABBC45. The horA homologue found in L. lindneri DSM 20690(T) was carried by a plasmid designated pRH20690. This plasmid is similar in size to pRH45, a plasmid harboring horA gene in L. brevis ABBC45. The full sequencing analysis of pRH20690 revealed that this 13.0-kb plasmid is remarkably similar in the organization of the open reading frames (ORFs) to that of pRH45. The putative replication origin re.-ions and the ORFs encoding a putative rep gene were found to be 99.0 and 100.0% identical, respectively, between the two beer-spoilage strains, indicating that these two plasmids share the same origin. It was further shown that the 6.9-kb DNA portions of the plasmids containing, six putative ORFs are 99.4% identical in nucleotide sequence. suggesting that the hop-resistant Lactobacillus strains acquired horA by plasmid-mediated horizontal gene transfer. This hypothesis potentially provides brewers with a theoretical basis for applying trans-species genetic markers. such as horA, to complement the traditional species-specific approaches.