Analysis of ATP-citrate lyase and malic enzyme mutants of Yarrowia lipolytica points out the importance of mannitol metabolism in fatty acid synthesis

AbstractThe role of the two key enzymes of fatty acid (FA) synthesis, ATP-citrate lyase (Acl) and malic enzyme (Mae), was analyzed in the oleaginous yeast Yarrowia lipolytica. In most oleaginous yeasts, Acl and Mae are proposed to provide, respectively, acetyl-CoA and NADPH for FA synthesis. Acl was mainly studied at the biochemical level but no strain depleted for this enzyme was analyzed in oleaginous microorganisms. On the other hand the role of Mae in FA synthesis in Y. lipolytica remains unclear since it was proposed to be a mitochondrial NAD(H)-dependent enzyme and not a cytosolic NADP(H)-dependent enzyme. In this study, we analyzed for the first time strains inactivated for corresponding genes. Inactivation of ACL1 decreases FA synthesis by 60 to 80%, confirming its essential role in FA synthesis in Y. lipolytica. Conversely, inactivation of MAE1 has no effects on FA synthesis, except in a FA overaccumulating strain where it improves FA synthesis by 35%. This result definitively excludes Mae as a major key enzyme for FA synthesis in Y. lipolytica. During the analysis of both mutants, we observed a negative correlation between FA and mannitol level. As mannitol and FA pathways may compete for carbon storage, we inactivated YlSDR, encoding a mannitol dehydrogenase converting fructose and NADPH into mannitol and NADP+. The FA content of the resulting mutant was improved by 60% during growth on fructose, demonstrating that mannitol metabolism may modulate FA synthesis in Y. lipolytica

Unraveling fatty acid transport and activation mechanisms in Yarrowia lipolytica

AbstractFatty acid (FA) transport and activation have been extensively studied in the model yeast species Saccharomyces cerevisiae but have rarely been examined in oleaginous yeasts, such as Yarrowia lipolytica. Because the latter begins to be used in biodiesel production, understanding its FA transport and activation mechanisms is essential. We found that Y. lipolytica has FA transport and activation proteins similar to those of S. cerevisiae (Faa1p, Pxa1p, Pxa2p, Ant1p) but mechanism of FA peroxisomal transport and activation differs greatly with that of S. cerevisiae. While the ScPxa1p/ScPxa2p heterodimer is essential for growth on long-chain FAs, ΔYlpxa1 ΔYlpxa2 is not impaired for growth on FAs. Meanwhile, ScAnt1p and YlAnt1p are both essential for yeast growth on medium-chain FAs, suggesting they function similarly. Interestingly, we found that the ΔYlpxa1 ΔYlpxa2 ΔYlant1 mutant was unable to grow on short-, medium-, or long-chain FAs, suggesting that YlPxa1p, YlPxa2p, and YlAnt1p belong to two different FA degradation pathways. We also found that YlFaa1p is involved in FA storage in lipid bodies and that FA remobilization largely depended on YlFat1p, YlPxa1p and YlPxa2p. This study is the first to comprehensively examine FA intracellular transport and activation in oleaginous yeast

Etude des mécanismes de l'extrême tolérance aux radiations de la bactérie Deinococcus deserti par une approche de génomique fonctionnelle

Le génome de Deinococcus deserti, une bactérie très radiotolérante, a été analysé et comparé à ceux de D. radiodurans et D. geothermalis. Environ 230 protéines sont spécifiquement conservées chez ces 3 espèces, dont IrrE, un régulateur essentiel pour la radiotolérance. D. deserti possède plusieurs gènes supplémentaires liés à la réparation de l ADN, dont imuY et dnaE2 (ADN polymérases translesionnelles). En plus, D. deserti a 3 recA qui codent pour 2 protéines RecA différentes (RecAC et RecAP). Pour étudier ces gènes, des outils génétiques ont été mis au point. Différents résultats suggèrent qu IrrE, nécessaire pour l induction de plusieurs gènes après irradiation, a une activité peptidase. Les 2 RecA sont fonctionnelles pour la réparation de l ADN. D. deserti est mutable par UV, ce qui nécessite ImuY, DnaE2 et RecAC, mais pas RecAPThe genome of Deinococcus deserti, a highly radiation-tolerant bacterium, was analyzed and compared to those of D. radiodurans and D. geothermalis. About 230 proteins are specifically conserved in these 3 species, including IrrE, a regulator protein essential for radiotolerance. D.deserti has several supplementary DNA repair genes, like imuY and dnaE2 (translesion DNA polymerases). Moreover, D. deserti has 3 recA that code for 2 different RecA proteins (RecAC et RecAP). To study these genes, genetic tools were developed for D. deserti. Different results suggest that IrrE, required for the induction of several genes after irradiation, has peptidase activity. The 2 RecA proteins are functional for DNA repair. D. deserti is mutable by UV, which requires ImuY, DnaE2 and RecAC, but not RecAPAIX-MARSEILLE2-BU Sci.Luminy (130552106) / SudocSudocFranceF

Role of Pex11p in Lipid Homeostasis in Yarrowia lipolytica

Peroxisomes are essential organelles in the cells of most eukaryotes, from yeasts to mammals. Their role in beta-oxidation is particularly essential in yeasts; for example, in Saccharomyces cerevisiae, fatty acid oxidation takes place solely in peroxisomes. In this species, peroxisome biogenesis occurs when lipids are present in the culture medium, and it involves the Pex11p protein family: ScPex11p, ScPex25p, ScPex27p, and ScPex34p. Yarrowia lipolytica has three Pex11p homologues, which are YALI0C04092p (YlPex11p), YALI0C04565p (YlPex11C), and YALI0D25498p (Pex11/25p). We found that these genes are regulated by oleic acid, and as has been observed in other organisms, YlPEX11 deletion generated giant peroxisomes when mutant yeast were grown in oleic acid medium. Moreover, Delta Ylpex11 was unable to grow on fatty acid medium and showed extreme dose-dependent sensitivity to oleic acid. Indeed, when the strain was grown in minimum medium with 0.5% glucose and 3% oleic acid, lipid body lysis and cell death were observed. Cell death and lipid body lysis may be partially explained by an imbalance in the expression of the genes involved in lipid storage, namely, DGA1, DGA2, and LRO1, as well as that of TGL4, which is involved in lipid remobilization. TGL4 deletion and DGA2 overexpression resulted in decreased oleic acid sensitivity and delayed cell death of Delta Ylpex11, which probably stemmed from the release of free fatty acids into the cytoplasm. All these results show that YlPex11p plays an important role in lipid homeostasis in Y. lipolytica

Yarrowia lipolytica AAL genes are involved in peroxisomal fatty acid activation

In yeast, beta-oxidation of fatty acids (FAs) essentially takes place in peroxisomes, and FA activation must precede FA oxidation. In Saccharomyces cerevisiae, a single fatty-acyl-CoA-synthetase, ScFaa2p, mediates peroxisomal FA activation. We have previously shown that this reaction also exists in the oleaginous yeast Yarrowia lipolytica; however, the protein involved in this process remains unknown. Here, we found that proteins, named Aal proteins (Acyl/Aryl-CoA-ligases), resembling the 4-coumarate-CoA-ligase-like enzymes found in plants are involved in peroxisomal FA activation in Y. lipolytica; Y. lipolytica has 10 AAL genes, eight of which are upregulated by oleate. All the Aal proteins contain a PTS1-type peroxisomal targeting sequence (A/SILL), suggesting a peroxisomal localization. The function of the Aal proteins was analyzed using the faa1 Delta ant1 Delta, mutant strain, which demonstrates neither cytoplasmic FA activation (direct result of FAA1 deletion) nor peroxisomal FA activation (indirect result of ANT1 deletion, a gene coding an ATP transporter). This strain is thus highly sensitive to external FA levels and unable to store external FAs in lipid bodies (LBs). Whereas the overexpression of (cytoplasmic) AAL1 Delta PTS1 was able to partially complement the growth defect observed in the faa1 Delta ant1 Delta mutant on short-, medium- and long-chain FA media, the presence of Aal2p to Aal10p only allowed growth on the short-chain FA medium. Additionally, partial LB formation was observed in the oleate medium for strains overexpressing Aal1 Delta PTS1p, Aal4 Delta PTS1p, Aal7 Delta PTS1p, and Aal8 Delta PTS1p. Finally, an analysis of the FA content of cells grown in the oleate medium suggested that Aal4p and Aal6p present substrate specificity for C16:1 and/or C18:0

Radiation response in D einococcus deserti : IrrE is a metalloprotease that cleaves repressor protein DdrO

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Identification of new genes contributing to the extreme radioresistance of Deinococcus radiodurans using a Tn5-based transposon mutant library.

Here, we have developed an extremely efficient in vivo Tn5-based mutagenesis procedure to construct a Deinococcus radiodurans insertion mutant library subsequently screened for sensitivity to genotoxic agents such as γ and UV radiations or mitomycin C. The genes inactivated in radiosensitive mutants belong to various functional categories, including DNA repair functions, stress responses, signal transduction, membrane transport, several metabolic pathways, and genes of unknown function. Interestingly, preliminary characterization of previously undescribed radiosensitive mutants suggests the contribution of cyclic di-AMP signaling in the recovery of D. radiodurans cells from genotoxic stresses, probably by modulating several pathways involved in the overall cell response. Our analyses also point out a new transcriptional regulator belonging to the GntR family, encoded by DR0265, and a predicted RNase belonging to the newly described Y family, both contributing to the extreme radioresistance of D. radiodurans. Altogether, this work has revealed new cell responses involved either directly or indirectly in repair of various cell damage and confirmed that D. radiodurans extreme radiation resistance is determined by a multiplicity of pathways acting as a complex network

The abundant and essential HU proteins in Deinococcus deserti and Deinococcus radiodurans are translated from leaderless mRNA.

International audienceHU proteins have an important architectural role in nucleoid organization in bacteria. Compared with HU of many bacteria, HU proteins from Deinococcus species possess an N-terminal lysine-rich extension similar to the eukaryotic histone H1 C-terminal domain involved in DNA compaction. The single HU gene in Deinococcus radiodurans, encoding DrHU, is required for nucleoid compaction and cell viability. Deinococcus deserti contains three expressed HU genes, encoding DdHU1, DdHU2 and DdHU3. Here, we show that either DdHU1 or DdHU2 is essential in D. deserti. DdHU1 and DdHU2, but not DdHU3, can substitute for DrHU in D. radiodurans, indicating that DdHU3 may have a non-essential function different from DdHU1, DdHU2 and DrHU. Interestingly, the highly abundant DrHU and DdHU1 proteins, and also the less expressed DdHU2, are translated in Deinococcus from leaderless mRNAs, which lack a 5'-untranslated region and, hence, the Shine-Dalgarno sequence. Unexpectedly, cloning the DrHU or DdHU1 gene under control of a strong promoter in an expression plasmid, which results in leadered transcripts, strongly reduced the DrHU and DdHU1 protein level in D. radiodurans compared with that obtained from the natural leaderless gene. We also show that the start codon position for DrHU and DdHU1 should be reannotated, resulting in proteins that are 15 and 4 aa residues shorter than initially reported. The expression level and start codon correction were crucial for functional characterization of HU in Deinococcus