Lactobacillus reuteri LA6 and Lactobacillus gasseri LA39 isolated from faeces of the same human infant produce identical cyclic bacteriocin

Reutericin 6, a bacteriocin produced by Lactobacillus reuteri LA6 that was isolated from the faeces of a human infant at 2 months of age, was purified to homogeneity from broth culture-supernatant by reverse-phase chromatography. Molecular weight (5652) by mass spectrometry and primary structure of reutericin 6 were identical to that of gassericin A produced by Lactobacillus gasseri LA39 which was isolated from the faeces of the same human infant at 4 months old. Reutericin 6 was shown to be a class II and cyclic bacteriocin. PCR amplification on the chromosome DNA of L reuteri LA6 as a template with the primers based on the DNA sequences cloned (gassericin A and acidocin B from Lactobacillus acidophilus M46) and sequencing revealed that L. reuteri LA6 has the structural gene for gassericin A with no variations among those primers. These results indicate that a bacteriocin of the same structure has been produced by different lactobacilli species isolated from the same infant.