Study of transcription factors involved in lipid accumulation induced by nitrogen stress in the microalgae Isochrysis affinis galbana

Chez tout organisme, l’évolution et l’acclimatation aux changements du milieu de vie sont orchestrés par de nombreux acteurs moléculaires. Parmi eux, les facteurs de transcription (FTs) jouent un rôle clé en régulant l’expression des gènes. Identifier les FTs impliqués dans la production de composés d’intérêt est donc une étape importante dans un contexte biotechnologique. Le laboratoire dispose d’une souche mutante de la microalgue haptophyte Tisochrysis lutea produisant deux fois plus de lipides de réserve que la souche sauvage en condition de privation azotée. Compte tenu du rôle clé des FTs dans l’établissement du phénotype, cette thèse vise à identifier les FTs impliqués dans la mise en place de ce phénotype mutant.Un pipeline bio-informatique d’identification et classification des FTs présents dans le génome de T. lutea a été élaboré. Le manque de donnée chez les haptophytes constituant un vide dans l’étude de l’histoire évolutive des microalgues, une étude comparative des FTs présents dans le génome d’algues de différentes lignées a été réalisée. Celle-ci révèle que l’étude des FTs aide à comprendre et illustrer l’histoire évolutive des microalgues par la mise en évidence de présences/absences de familles de FTs spécifiques de lignée.Afin de comprendre l’établissement du phénotype de la souche mutante de T. lutea, des données transcriptomiques ont permis la construction de réseaux de co-expression et de régulation des gènes chez les deux souches. Leur analyse croisée a identifié sept FTs candidats potentiellement liés au phénotype mutant. Une approche de p-RT-PCR a confirmé l’implication de deux FTs dans la remobilisation de l’'azote en condition de stress azoté.In every organism, evolution and acclimation to environmental changes are orchestrated by numerous molecular players. Among them, transcription factors (TFs) play a crucial role by regulating gene expression. Therefore, identify TFs involved in the production of high value products is a significant step in a biotechnological context. The laboratory has at its disposal a mutant strain of the haptophyte microalga Tisochrysis lutea producing twice more storage lipids than the wild type strain when exposed to nitrogen deprivation. Given the key role of TFs in phenotype establishment, this PhD aim at identify the TFs involved in that of the mutant phenotype of T. lutea.A TFs identification and classification pipeline was elaborated and applied to T. lutea’s genome. Since the lack of data in haptophytes constitutes a limit in studies on microalgae evolutionary history, a comparative study of TFs identified in the genome of microalgae belonging to different lineages was carried out. This study reveals that TFs could be used to understand and illustrate microalgae evolutionary history through the highlight of lineage specific presence/absence of TF families.Aiming at understanding T. lutea’s mutant strain phenotype establishment, transcriptomic data were used to build gene co-expression networks and gene regulatory networks for both strains. Their comparative analysis identified seven TFs potentially liked to the mutant phenotype. A q-RT-PCR approach confirmed the involvement of two TFs in nitrogen recycling under nitrogen deprivation

Etude des facteurs de transcription impliqués dans l'accumulation lipidique en condition de stress azoté chez la microalgue haptophyte Isochrysis affinis galbana

In every organism, evolution and acclimation to environmental changes are orchestrated by numerous molecular players. Among them, transcription factors (TFs) play a crucial role by regulating gene expression. Therefore, identify TFs involved in the production of high value products is a significant step in a biotechnological context. The laboratory has at its disposal a mutant strain of the haptophyte microalga Tisochrysis lutea producing twice more storage lipids than the wild type strain when exposed to nitrogen deprivation. Given the key role of TFs in phenotype establishment, this PhD aim at identify the TFs involved in that of the mutant phenotype of T. lutea.A TFs identification and classification pipeline was elaborated and applied to T. lutea’s genome. Since the lack of data in haptophytes constitutes a limit in studies on microalgae evolutionary history, a comparative study of TFs identified in the genome of microalgae belonging to different lineages was carried out. This study reveals that TFs could be used to understand and illustrate microalgae evolutionary history through the highlight of lineage specific presence/absence of TF families.Aiming at understanding T. lutea’s mutant strain phenotype establishment, transcriptomic data were used to build gene co-expression networks and gene regulatory networks for both strains. Their comparative analysis identified seven TFs potentially liked to the mutant phenotype. A q-RT-PCR approach confirmed the involvement of two TFs in nitrogen recycling under nitrogen deprivation.Chez tout organisme, l’évolution et l’acclimatation aux changements du milieu de vie sont orchestrés par de nombreux acteurs moléculaires. Parmi eux, les facteurs de transcription (FTs) jouent un rôle clé en régulant l’expression des gènes. Identifier les FTs impliqués dans la production de composés d’intérêt est donc une étape importante dans un contexte biotechnologique. Le laboratoire dispose d’une souche mutante de la microalgue haptophyte Tisochrysis lutea produisant deux fois plus de lipides de réserve que la souche sauvage en condition de privation azotée. Compte tenu du rôle clé des FTs dans l’établissement du phénotype, cette thèse vise à identifier les FTs impliqués dans la mise en place de ce phénotype mutant.Un pipeline bio-informatique d’identification et classification des FTs présents dans le génome de T. lutea a été élaboré. Le manque de donnée chez les haptophytes constituant un vide dans l’étude de l’histoire évolutive des microalgues, une étude comparative des FTs présents dans le génome d’algues de différentes lignées a été réalisée. Celle-ci révèle que l’étude des FTs aide à comprendre et illustrer l’histoire évolutive des microalgues par la mise en évidence de présences/absences de familles de FTs spécifiques de lignée.Afin de comprendre l’établissement du phénotype de la souche mutante de T. lutea, des données transcriptomiques ont permis la construction de réseaux de co-expression et de régulation des gènes chez les deux souches. Leur analyse croisée a identifié sept FTs candidats potentiellement liés au phénotype mutant. Une approche de p-RT-PCR a confirmé l’implication de deux FTs dans la remobilisation de l’'azote en condition de stress azoté

Intermittent antibiotic treatment of bacterial biofilms favors the rapid evolution of resistance

International audienceBacterial antibiotic resistance is a global health concern of increasing importance and intensive study. Although biofilms are a common source of infections in clinical settings, little is known about the development of antibiotic resistance within biofilms. Here, we use experimental evolution to compare selection of resistance mutations in planktonic and biofilm Escherichia coli populations exposed to clinically relevant cycles of lethal treatment with the aminoglycoside amikacin. Consistently, mutations in sbmA , encoding an inner membrane peptide transporter, and fusA , encoding the essential elongation factor G, are rapidly selected in biofilms, but not in planktonic cells. This is due to a combination of enhanced mutation rate, increased adhesion capacity and protective biofilm-associated tolerance. These results show that the biofilm environment favors rapid evolution of resistance and provide new insights into the dynamic evolution of antibiotic resistance in biofilms

Selection for nonspecific adhesion is a driver of FimH evolution increasing Escherichia coli biofilm capacity

International audienceBacterial interactions with surfaces rely on the coordinated expression of a vast repertoire of surface-exposed adhesins. However, how bacteria dynamically modulate their adhesion potential to achieve successful surface colonization is not yet well understood. Here, we investigated changes in adhesion capacity of an initially poorly adherent Escherichia coli strain using experimental evolution and positive selection for mutations improving adhesion and biofilm formation on abiotic surfaces. We showed that all identified evolved populations and clones acquired mutations located almost exclusively in the lectin domain of fimH, the gene coding for the α-d-mannose-specific tip adhesin of type 1 fimbriae, a key E. coli virulence factor. While most of these fimH mutants showed reduced mannose-binding ability, they all displayed enhanced binding to abiotic surfaces, indicating a trade-off between FimH-mediated specific and nonspecific adhesion properties. Several of the identified mutations were already reported in the FimH lectin domain of pathogenic and environmental E. coli, suggesting that, beyond pathoadaptation, FimH microevolution favoring nonspecific surface adhesion could constitute a selective advantage for natural E. coli isolates. Consistently, although E. coli deleted for the fim operon still evolves an increased adhesion capacity, mutants selected in the ∆fim background are outcompeted by fimH mutants revealing clonal interference for adhesion. Our study therefore provides insights into the plasticity of E. coli adhesion potential and shows that evolution of type 1 fimbriae is a major driver of the adaptation of natural E. coli to colonization

The Transition Toward Nitrogen Deprivation in Diatoms Requires Chloroplast Stand-By and Deep Metabolic Reshuffling

Microalgae have adapted to face abiotic stresses by accumulating energy storage molecules such as lipids, which are also of interest to industries. Unfortunately, the impairment in cell division during the accumulation of these molecules constitutes a major bottleneck for the development of efficient microalgae-based biotechnology processes. To address the bottleneck, a multidisciplinary approach was used to study the mechanisms involved in the transition from nitrogen repletion to nitrogen starvation conditions in the marine diatom Phaeodactylum tricornutum that was cultured in a turbidostat. Combining data demonstrate that the different steps of nitrogen deficiency clustered together in a single state in which cells are in equilibrium with their environment. The switch between the nitrogen-replete and the nitrogen-deficient equilibrium is driven by intracellular nitrogen availability. The switch induces a major gene expression change, which is reflected in the reorientation of the carbon metabolism toward an energy storage mode while still operating as a metabolic flywheel. Although the photosynthetic activity is reduced, the chloroplast is kept in a stand-by mode allowing a fast resuming upon nitrogen repletion. Altogether, these results contribute to the understanding of the intricate response of diatoms under stress

Politiques d\u2019integration et mediation interculturelle: \ue9tude comparative et un exemple en Italie

International audienceBackground: Studying transcription factors, which are some of the key players in gene expression, is of outstanding interest for the investigation of the evolutionary history of organisms through lineage-specific features. In this study we performed the first genome-wide TF identification and comparison between haptophytes and other algal lineages.Results: For TF identification and classification, we created a comprehensive pipeline using a combination of BLAST, HMMER and InterProScan software. The accuracy evaluation of the pipeline shows its applicability for every alga, plant and cyanobacterium, with very good PPV and sensitivity. This pipeline allowed us to identify and classified the transcription factor complement of the three haptophytes Tisochrysis lutea, Emiliania huxleyi and Pavlova sp.; the two stramenopiles Phaeodactylum tricornutum and Nannochloropsis gaditana; the chlorophyte Chlamydomonas reinhardtii and the rhodophyte Porphyridium purpureum. By using T. lutea and Porphyridium purpureum, this work extends the variety of species included in such comparative studies, allowing the detection and detailed study of lineage-specific features, such as the presence of TF families specific to the green lineage in Porphyridium purpureum, haptophytes and stramenopiles. Our comprehensive pipeline also allowed us to identify fungal and cyanobacterial TF families in the algal nuclear genomes.Conclusions: This study provides examples illustrating the complex evolutionary history of algae, some of which support the involvement of a green alga in haptophyte and stramenopile evolution

Characterization of Pseudomonas aeruginosa L,D-transpeptidases and evaluation of their role in peptidoglycan adaptation to biofilm growth

International audiencePeptidoglycan is an essential component of the bacterial cell envelope that sustains the turgor pressure of the cytoplasm, determines cell shape, and acts as a scaffold for the anchoring of envelope polymers such as lipoproteins. The final cross-linking step of peptidoglycan polymerization is performed by classical d,d-transpeptidases belonging to the penicillin-binding protein (PBP) family and by l,d-transpeptidases (LDTs), which are dispensable for growth in most bacterial species and whose physiological functions remain elusive. In this study, we investigated the contribution of LDTs to cell envelope synthesis in Pseudomonas aeruginosa grown in planktonic and biofilm conditions. We first assigned a function to each of the three P. aeruginosa LDTs by gene inactivation in P. aeruginosa, heterospecific gene expression in Escherichia coli, and, for one of them, direct determination of its enzymatic activity. We found that the three P. aeruginosa LDTs catalyze peptidoglycan cross-linking (LdtPae1), the anchoring of lipoprotein OprI to the peptidoglycan (LdtPae2), and the hydrolysis of the resulting peptidoglycan-OprI amide bond (LdtPae3). Construction of a phylogram revealed that LDTs performing each of these three functions in various species cannot be assigned to distinct evolutionary lineages, in contrast to what has been observed with PBPs. We showed that biofilm, but not planktonic bacteria, displayed an increase proportion of peptidoglycan cross-links formed by LdtPae1 and a greater extent of OprI anchoring to peptidoglycan, which is controlled by LdtPae2 and LdtPae3. Consistently, deletion of each of the ldt genes impaired biofilm formation and potentiated the bactericidal activity of EDTA. These results indicate that LDTs contribute to the stabilization of the bacterial cell envelope and to the adaptation of peptidoglycan metabolism to growth in biofilm. IMPORTANCE Active-site cysteine LDTs form a functionally heterologous family of enzymes that contribute to the biogenesis of the bacterial cell envelope through formation of peptidoglycan cross-links and through the dynamic anchoring of lipoproteins to peptidoglycan. Here, we report the role of three P. aeruginosa LDTs that had not been previously characterized. We show that these enzymes contribute to resistance to the bactericidal activity of EDTA and to the adaptation of cell envelope polymers to conditions that prevail in biofilms. These results indicate that LDTs should be considered putative targets in the development of drug-EDTA associations for the control of biofilm-related infections