A novel hydroxamic acid-containing antibiotic produced by a Saharan soil-living Streptomyces strain.

During screening for potentially antimicrobial actinobacteria, a highly antagonistic strain, designated WAB9, was isolated from a Saharan soil of Algeria. A polyphasic approach characterized the strain taxonomically as a member of the genus Streptomyces. The strain WAB9 exhibited a broad spectrum of antimicrobial activity toward various multidrug-resistant micro-organisms. A PCR-based assay of genomic potential for producing bioactive metabolites revealed the presence of PKS-II gene. After 6 days of strain fermentation, one bioactive compound was extracted from the remaining aqueous phase and then purified by HPLC. The chemical structure of the compound was determined by spectroscopic (UV-visible, and (1)H and (13)C NMR) and spectrometric analysis. The compound was identified to be 2-amino-N-(2-amino-3-phenylpropanoyl)-N-hydroxy-3-phenylpropanamide, a novel hydroxamic acid-containing molecule. The pure molecule showed appreciable minimum inhibitory concentration values against a selection of drug-resistant bacteria, filamentous fungi and yeasts. Significance and impact of the study: This study presents the isolation of a Streptomyces strain, named WAB9, from a Saharan soil in Algeria. This strain was found to produce a new hydroxamic acid-containing molecule with interesting antimicrobial activities towards various multidrug-resistant micro-organisms. Although hydroxamic acid-containing molecules are known to exhibit low toxicities in general, only real evaluations of the toxicity levels could decide on the applications for which this new molecule is potentially most appropriate. Thus, this article provides a new framework of research.

[Antimicrobial activity of a Saharan Streptomyces spp. PAL111 strain against various clinical and toxinogenic microorganisms resistant to antibiotics]. / Activité antimicrobienne de Streptomyces sp. PAL111 d'origine saharienne contre divers microorganismes cliniques et toxinogènes résistants aux antibiotiques.

OBJECTIVE: Study of the taxonomy and the biological activity of the actinomycete strain PAL111 against several pathogenic and toxigenic microorganisms for humans, and resistant to many antibiotics. MATERIALS AND METHODS: The taxonomic study of isolate PAL111 is carried out on the basis of phenotypic and molecular characteristics. The tests against the pathogenic microorganisms are realized on ISP-2 and Bennett media. The kinetics of antibiotic production was investigated on ISP-2 medium. The antibiotic is highlighted by bioautography and chemical revelations, and then purified by chromatography on thick layer of silica gel and Sephadex LH20 column. The minimum inhibitory concentrations (MIC) were determined against pathogenic microorganisms. RESULTS: The phenotypic and molecular studies showed that the isolate PAL111 is closely related to the type strain of Streptomyces ambofaciens. It showed a strong activity against Candida albicans, filamentous fungi, and Gram-positive and Gram-negative bacteria. The optimal antibiotic production was observed at the end of the exponential phase of growth and at the beginning of the decline phase. The bioautography tests showed the presence of an antibiotic with both antibacterial and antifungal activities. This antibiotic is a hydrophilic amino-glycoside compound. The MIC were observed between 2 and 20µg/mL for yeasts, 10 and 50µg/mL for filamentous fungi, 2 and 10µg/mL for Gram-positive bacteria, and 20 and 75µg/mL for Gram-negative bacteria. CONCLUSION: The strong activity of isolate PAL111 against the pathogenic microorganisms and the polar characteristic of the produced antibiotic could encourage further studies on this bioactive molecule.