Effet de la limitation en fer selon le mode de vie et étude des mécanismes moléculaires de l'acquisition du fer chez Marinobacter hydrocarbonoclasticus

Effect of iron limitation according to the growth mode and study of molecular mechanisms of iron acquisition in Marinobacter hydrocarbonoclasticus

• Auteur / Autrice : Kilian Ducos
• Direction : Régis Grimaud, Sophie Nolivos
• Type : Thèse de doctorat
• Discipline(s) : Aspects moléculaires
• Date : Soutenance le 09/12/2022
• Etablissement(s) : Pau
• Ecole(s) doctorale(s) : École doctorale sciences exactes et leurs applications (Pau, Pyrénées Atlantiques ; 1995-)
• Partenaire(s) de recherche : Laboratoire : Institut des sciences analytiques et de Physico-chimie pour l'Environnement et les Matériaux - Institut des sciences analytiques et de physico-chimie pour l'environnement et les materiaux
• Jury : Président / Présidente : Ryszard Łobiński
• Jury : Examinateurs / Examinatrices : Ryszard Łobiński, Virginie Chapon, Isabelle Schalk, Laurent Ouerdane, Johann Far
• Jury : Rapporteurs / Rapporteuses : Virginie Chapon, Isabelle Schalk

Mots clés

Mots clés contrôlés

Aspect environnemental

Sidérophores

Mots clés libres

Sidérophore

Environnement

Fer

Bactérie

Siderophore

Environment

Iron

Bacteria

Résumé

Le fer est indispensable pour la croissance de tous les organismes. Dans les environnements marins, le fer est généralement présent à très faible concentration et lié à de la matière organique, ce qui le rend peu biodisponible pour les cellules. Une stratégie mise en place par les microorganismes est la production de molécules, les sidérophores, capables de se lier à un atome de fer. C'est le cas de Marinobacter hydrocarbonoclasticus, une bactérie marine hétérotrophe qui produit un sidérophore connu, la pétrobactine. Cet organisme est capable de se développer sous forme planctonique et biofilm. Les principaux objectifs de ma thèse sont d'étudier la dépendance vis à vis du fer en fonction du mode de croissance ainsi que le rôle de la pétrobactine dans l'acquisition du fer chez Marinobacter hydrocarbonoclasticus.

Iron is an essential element for most living organisms because it is present in prosthetic groups of many enzymes, especially those of the respiratory chain. Marine microorganisms must extract iron directly from seawater, where its concentration is particularly low (less than 1 nmol.L-1) and where it is mostly bound to organic molecules. The iron is consequently poorly available for the growth of microorganisms and therefore, it controls indirectly essential microbial activities for the biogeochemical cycles of major elements such as carbon and nitrogen for example. The use of siderophores, molecules with high affinity for iron, has been recognized for several years as an effective way for marine bacteria to recover poorly available iron. However, only few studies have focused on the effect of iron limitation on the physiology of the cell according to its mode of growth: planktonic, where the cells are free or in biofilm, where the cells adhere to a substrate.To determine the importance of iron on the lifestyle of bacteria, we used as a model Marinobacter hydrocarbonoclasticus SP17, a heterotrophic marine bacterium that grows as a planktonic population when the carbon source is soluble, like acetate, or as a biofilm when the carbon source is insoluble, such as alkanes or triglycerides. We observed that planktonic growth requires more iron than biofilm growth and that alkane growth requires more iron than triglyceride growth. This variability according to the growth mode and the carbon source can be explained by differences in iron requirements and/or in the efficiency of iron acquisition.To measure the importance of siderophore production and biofilm formation, genetic and chemical analyses techniques were used. A standard of the siderophore produced by M. hydrocarbonoclasticus, the petrobactin, was obtained. It allowed to quantify by mass spectrometry the petrobactin in the extracellular medium under different growth conditions. The results obtained showed an overproduction of the siderophore at low iron concentration, suggesting a more important role in this condition. To confirm the petrobactin involvement and to understand what are the other mechanisms involved in iron acquisition, mutants of the biosynthesis pathway of petrobactin and of the potential transport of Fe3+ ions were constructed. Although the study of the phenotypes of all simple and double mutants constructed could not be completed during this work, the results obtained suggest the presence of two main iron acquisition pathways, one petrobactin dependent, and another dependent on the periplasmic protein FbpA. The double mutation seems to be lethal, but the study of the conditional mutant constructed will allow confirmation of these results and will give a better understanding of the iron acquisition pathways involved in the different growth modes.