Analysis of plasmids encoding the histidine decarboxylase gene in Tetragenococcus muriaticus isolated from Japanese fermented seafoods

In order to analyze the genes related to histamine production in halophilic lactic acid bacteria, 16 strains of histamine-producing bacteria were isolated from three fermented seafoods produced in the Hokuriku region of Japan. Phenotypic and 16S rRNA gene sequence analyses identified all of the strains as those of Tetragenococcus muriaticus. Pyruvoyl-dependent histidine decarboxylase gene (hdcA) was determined from all strains using the PCR method with an hdcA-specific detection primer set. Genetic analyses (Southern blot and restriction fragment length polymorphism analysis) of hdcA and genes related to histamine production (the hdc cluster) confirmed that all of the strains harbored 21-23 kbp plasmids encoding a single copy of hdcA. The four representative strains were selected based on isolation source and genetic analysis, and subsequently full sequences of plasmids harbored in these strains were determined. hdc cluster sequences from the plasmids showed very high similarity (> 99 %) to known hdc clusters of T. halophilus, Lactobacillus hilgardii 0006, and other lactic acid bacteria. The structures of the plasmids, the replication region, the hdc cluster, and the plasmid maintenance system were conserved between the plasmids present in new isolates and the T. halophilus strains. These results indicate that plasmids encoding hdcA are widely distributed among T. halophilus and T. muriaticus and function in both species.