Résumé
Various bacteria use non-ribosomal peptide synthesis (NRPS) to produce peptides or other small molecules. These molecules exhibit broad structural diversity and display biological activities that range from adaptation to unfavorable environments, communication or competition with other microorganisms in their natural habitat, or even to action as virulence factors. Conserved features within the NRPS machinery allow the type, and sometimes even the structure, of the synthesized polypeptide to be predicted. Thus, bacterial genome mining via in siIico analyses of NRPS genes offers an attractive opportunity to uncover new bioactive non-ribosomally synthesized peptides. To date, the only known small molecule synthesized by NRPS in the genus Xanthomonas is albicidin produced by Xanthomonas albilineans, a xylem-invading pathogen that causes leaf scald-a lethal disease of sugarcane. In silica analysis of available genomic sequences of Xanthomonas strains led to the discovery of a novel NRPS gene cluster called META-B which doesn't resemble to any gene cluster de- scribed to date. This NRPS gene cluster occurs in (i) X. albilineans, (ii) two pathovars of Xanthomonas oryzae which are the causal agents of two agronomically important diseases of rice (bacterial leaf blight caused by X. oryzae pv. oryzae and bacterial leaf streak caused by X. oryzae pv. oryzicola), and (iii) Xanthomonas translucens , the causal agent of the bacterial leaf streak of wheat. Interestingly, the NRPS gene cluster META-B seems to be specific to strains of Xanthomonas associated with monocotyledonous plants, suggesting a putative involvement in plant-bacteria interactions. (Résumé d'auteur)