Streptocidins A-D, novel cyclic decapeptide antibiotics produced by Streptomyces sp. Tü 6071. II. Structure elucidation.

The structures of the new antibiotics streptocidins A approximately D were elucidated as cyclic decapeptides cyclo[L-Val1-L-Orn2-L-Leu3-D-Phe4-L-Pro5-L-Leu6-X7-L-Asn8-L-Gln9-X10] with X7=D-Trp (A, B, C) or D-Phe (D) and X10=L-Tyr (A), L-Trp (B, D), or D-Trp (C). The amino acid composition (including the configuration) of the substances was determined by chiral-phase GC-MS of the hydrolysates. The sequences were established by EDMAN degradation following linearisation of the cyclic peptides upon treatment with LiAlH4. NMR spectroscopic studies of streptocidins C and D confirmed the proposed sequences and provided conformational data which indicate a molecular topology of streptocidins C and D similar to those of tyrocidine A and gramicidin S.

Characterization of reutericyclin produced by Lactobacillus reuteri LTH2584.

Lactobacillus reuteri LTH2584 exhibits antimicrobial activity that can be attributed neither to bacteriocins nor to the production of reuterin or organic acids. We have purified the active compound, named reutericyclin, to homogeneity and characterized its antimicrobial activity. Reutericyclin exhibited a broad inhibitory spectrum including Lactobacillus spp., Bacillus subtilis, B. cereus, Enterococcus faecalis, Staphylococcus aureus, and Listeria innocua. It did not affect the growth of gram-negative bacteria; however, the growth of lipopolysaccharide mutant strains of Escherichia coli was inhibited. Reutericyclin exhibited a bactericidal mode of action against Lactobacillus sanfranciscensis, Staphylococcus aureus, and B. subtilis and triggered the lysis of cells of L. sanfranciscensis in a dose-dependent manner. Germination of spores of B. subtilis was inhibited, but the spores remained unaffected under conditions that do not permit germination. The fatty acid supply of the growth media had a strong effect on reutericyclin production and its distribution between producer cells and the culture supernatant. Reutericyclin was purified from cell extracts and culture supernatant of L. reuteri LTH2584 cultures grown in mMRS by solvent extraction, gel filtration, RP-C(8) chromatography, and anion-exchange chromatography, followed by rechromatography by reversed-phase high-pressure liquid chromatography. Reutericyclin was characterized as a negatively charged, highly hydrophobic molecule with a molecular mass of 349 Da. Structural characterization (A. Höltzel, M. G. Gänzle, G. J. Nicholson, W. P. Hammes, and G. Jung, Angew. Chem. Int. Ed. 39:2766-2768, 2000) revealed that reutericyclin is a novel tetramic acid derivative. The inhibitory activity of culture supernatant of L. reuteri LTH2584 corresponded to that of purified as well as synthetic reutericyclin.

The macrocyclic peptide antibiotic micrococcin P(1) is secreted by the food-borne bacterium Staphylococcus equorum WS 2733 and inhibits Listeria monocytogenes on soft cheese.

Staphylococcus equorum WS 2733 was found to produce a substance exhibiting a bacteriostatic effect on a variety of gram-positive bacteria. The metabolite was purified to homogeneity by ammonium sulfate precipitation and semipreparative reversed-phase high-performance liquid chromatography. Electrospray mass spectrometry confirmed the high purity of the compound and revealed a molecular mass of 1,143 Da. By two-dimensional nuclear magnetic resonance spectroscopy the substance was identified as micrococcin P(1) which is a macrocyclic peptide antibiotic that has not yet been reported for the genus Staphylococcus. A total of 95 out of 95 Listeria strains and 130 out of 135 other gram-positive bacteria were inhibited by this substance, while none of 37 gram-negative bacteria were affected. The antilisterial potential of this food-grade strain as a protective starter culture was evaluated by its in situ application in cheese-ripening experiments under laboratory conditions. A remarkable growth reduction of Listeria monocytogenes could be achieved compared to control cheese ripened with a nonbacteriocinogenic type strain of Staphylococcus equorum. In order to prove that inhibition was due to micrococcin P(1), a micrococcin-deficient mutant was constructed which did not inhibit L. monocytogenes in cheese-ripening experiments.

Spirofungin, a new antifungal antibiotic from Streptomyces violaceusniger Tü 4113.

A new secondary metabolite was detected in the culture filtrate and extracts of Streptomyces violaceusniger Tü 4113 by HPLC-diode-array and HPLC-electrospray-mass-spectrometry screening. The compound named spirofungin has a polyketide-spiroketal structure and shows various antifungal activities, particularly against yeasts.