Résumé
Albicidin is a toxin and an antibiotic produced by the slow-growing bacterium Xanthomonas albilineans, the causal agent of sugarcane leaf scald. Albicidin is involved in the pathogenicity of X. albilineans and inhibits the replication of chloroplastic DNA. It also inhibits DNA replication in Escherichia coli at nanomolar concentrations, whereas mammalian cells are unaffected at 8 ?g/ml. Albicidin targets DNA gyrase with features of inhibition that differ from those of other known antibiotics. It is synthesized by a unique hybrid polyketide synthase-nonribosomal peptide synthetase (PKS-NRPS) pathway that does not resemble any other pathway described to date. The antibiotic activity of albicidin against a wide range of gram-positive and gram-negative pathogenic bacteria (Enterobacter aerogenes, E. coli, Haemophilus influenzae, Klebsiella pneumoniae, Shigella sonnei, and Staphylococcus aureus) is of interest for the development of new antibacterial drugs. Low yields of albicidin production in slow-growing X. albilineans have slowed studies of its chemical structure and potential therapeutic applications. Therefore, we have developed a heterologous system for albicidin overproduction using a Xanthomonas axonopodis pv. vesicatoria strain transformed with two plasmids harbouring the complete albicidin biosynthetic gene set. A sixty-fold increase in albicidin production was obtained when compared to albicidin production by the native host, X. albilineans. Heterologous production of albicidin was confirmed by FTICR-MS (high resolving Fournier Transform Ion Cyclotron Resonance Mass Spectrometry). (Texte intégral)