[Show abstract][Hide abstract] ABSTRACT: Lactobacillus gasseri LA39 and L. reuteri LA6 isolated from feces of the same human infant were found to produce similar cyclic bacteriocins (named gassericin A and
reutericin 6, respectively) that cannot be distinguished by molecular weights or primary amino acid sequences. However, reutericin
6 has a narrower spectrum than gassericin A. In this study, gassericin A inhibited the growth of L. reuteri LA6, but reutericin 6 did not inhibit the growth of L. gasseri LA39. Both bacteriocins caused potassium ion efflux from indicator cells and liposomes, but the amounts of efflux and patterns
of action were different. Although circular dichroism spectra of purified bacteriocins revealed that both antibacterial peptides
are composed mainly of α-helices, the spectra of the bacteriocins did not coincide. The results of d- and l-amino acid composition analysis showed that two residues and one residue of d-Ala were detected among 18 Ala residues of gassericin A and reutericin 6, respectively. These findings suggest that the different
d-alanine contents of the bacteriocins may cause the differences in modes of action, amounts of potassium ion efflux, and secondary
structures. This is the first report that characteristics of native bacteriocins produced by wild lactobacillus strains having
the same structural genes are influenced by a difference in d-amino acid contents in the molecules.
[Show abstract][Hide abstract] ABSTRACT: ABSTRACT Gassericin A, a bacteriocin produced by Lactobacillus gasseri LA39, has a cyclic structure linking N- and C-terminal amino acids. Gassericin A was expressed in Escherichia coli JM109 as a biotinylated fusion protein on the basis of the DNA sequence of mature bacteriocin. A positive clone accumulated the bacteriocin, with no activity, as a soluble fusion protein in the cytoplasm. After release of an N-terminal tag with factor Xa protease, gassericin A was converted into an active peptide having N- and C-termini. The total amount of purified bacteriocins (expressed and native) was 480 µg/L and 370 µg/L, respectively. However, the specific activity of expressed gassericin A was 15 AU/mg lower than that of native bacteriocin (2600 AU/mg). Although the actual Mr (molecular weight) of the expressed bacteriocin should be 5666, the peptide showed the same mobility (Mr 3800) in sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) as native cyclic gassericin A, suggesting that the expressed peptide retains compact folding of the molecule similar to that of native gassericin A.
[Show abstract][Hide abstract] ABSTRACT: 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 fromLactobacillus 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.
[Show abstract][Hide abstract] ABSTRACT: The effect of an extracellular neutral- and phosphopolysaccharide produced by Lactobacillus delbrueckii ssp. bulgaricus OLL 1073R-1 on macrophage functions was examined in short-term studies. The total number of peritoneal macrophages elicited by an intraperitoneal injection of 100 mg kg−1of the polysaccharide was three fold greater than that by PBS. The macrophage phagocytosis was augmented by the phosphopolysaccharide in vivo and in vitro, but not or less by the neutral polysaccharide. The cytostatic activity of thioglycolate-induced macrophages against tumour cell lines (Sarcoma-180 or P388) was significantly augmented by a 6-h treatment of the phosphopolysaccharide at a concentration of 10–100 μg ml−1, while only at 100 μg ml−1of the neutral polysaccharide. The phosphopolysaccharide purified by high performance liquid chromatography also had a substantial effect on macrophage cytostatic activity. The partial hydrolysis by trifluoroacetic acid treatment and dephosphorylation by hydrofluoric acid degradation of phosphopolysaccharides reduced the cytostatic activity in macrophages. The phosphopolysaccharide produced byLactobacillus delbrueckii ssp. bulgaricus 1073R-1 is a potent enhancer of macrophage functions in which the conformational structure or phosphate group may play an important role.