Biosynthesis and regulation of alterins expression, an antibiotic peptide family produced by marine Pseudoalteromonas bacteria

• Main Author: Cuny, Héléna
• Other Authors: Laboratoire de Biotechnologie et Chimie Marines (LBCM), Université de Bretagne Sud (UBS)-Université de Brest (UBO)-Institut Universitaire Européen de la Mer (IUEM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Université de Bretagne occidentale - Brest, Yannick Fleury, Alexis Bazire
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2021
• Subjects: Alterins; Antibiotics; NRPS; AMP; Pseudoalteromonas; Altérines; Antibiotiques; PAM; [SDV.BIO]Life Sciences [q-bio]/Biotechnology; Crassostrea gigas
• Online Access: https://theses.hal.science/tel-04416403; https://theses.hal.science/tel-04416403/document; https://theses.hal.science/tel-04416403/file/These-2021-SML-Biotechnologies-CUNY_Helena.pdf

The exploration of antibacterial properties from hemolymph of marins animals leaded to the isolation of several Pseudoalteromonas strains. Two of them were isolated from Crassostrea gigas hemolymph, called hCg-6 and hCg-42 and produce an antibacterial peptide family called alterins. These alterins are composed of a cationic heptapeptidic cycle with uncommon residues and a fatty acyl chain.As part of this PhD, the work focused on alterins chemodiversity characterization and their biosynthesis mechanism.We led a study through UPLC-MS method on alterins produced by the 2 strains hCg-6 and hCg-42 and also3 other Pseudoalteromonas strains isolated from Ostrea edulis hemolymph, called hOe-66, hOe-124 and hOe-125. It revealed a family of at least 37 isoforms with modifications on specific residues and the fatty acyl chain. The genomic analysis of the 5 strains allowed the identification of a new Pseudoalteromonas species for the 3 hOe strains, called Pseudoalteromonas ostreae.In order to elucidate the alterins biosynthesis pathway and the regulation mechanisms, we combined genomic, transcriptomic and culturomic methods. The biosynthesis pathway of alterins is a non-ribosomal pathway and involve a 30 kb BGC composed of (i) 2 genes coding Non Ribosomal Peptide Synthetase(NRPS), (ii) genes coding a peptide cyclic transporter and enzymes for the biosynthesis of non proteogenic residues and (iii) genes sharing homologies with genes involved in the polymyxins resistance. The transcriptomic study revealed that the alterin production depends on the availability of unusual residues.This thesis opens research perspectives on strain immunity to their own alterins. L’exploration des propriétés anti-bactériennes du microbiote hémolymphatique des animaux marins a conduit à l’isolement de différentes souches de Pseudaolteromonas. Deux d’entre elles, isolées de l’hémolymphe d’huître creuse et nommée hCg-6 et hCg-42, produisent une famille de peptides antibactériens nommés altérines. Les altérines sont composées d’un cycle ...