Phosphate Starvation Triggers Production and Secretion of an Extracellular Lipoprotein in Caulobacter crescentus

Life in oligotrophic environments necessitates quick adaptive responses to a sudden lack of nutrients. Secretion of specific degradative enzymes into the extracellular medium is a means to mobilize the required nutrient from nearby sources. The aquatic bacterium Caulobacter crescentus must often face changes in its environment such as phosphate limitation. Evidence reported in this paper indicates that under phosphate starvation, C. crescentus produces a membrane surface-anchored lipoprotein named ElpS subsequently released into the extracellular medium. A complete set of 12 genes encoding a type II secretion system (T2SS) is located adjacent to the elpS locus in the C. crescentus genome. Deletion of this T2SS impairs release of ElpS in the environment, which surprisingly remains present at the cell surface, indicating that the T2SS is not involved in the translocation of ElpS to the outer membrane but rather in its release. Accordingly, treatment with protease inhibitors prevents release of ElpS in the extracellular medium suggesting that ElpS secretion relies on a T2SS-secreted protease. Finally, secretion of ElpS is associated with an increase in alkaline phosphatase activity in culture supernatants, suggesting a role of the secreted protein in inorganic phosphate mobilization. In conlusion, we have shown that upon phosphate starvation, C. crescentus produces an outer membrane bound lipoprotein, ElpS, which is further cleaved and released in the extracellular medium in a T2SS-dependent manner. Our data suggest that ElpS is associated with an alkaline phosphatase activity, thereby allowing the bacterium to gather inorganic phosphates from a poor environment

Etude de la réponse à différents stress environnementaux chez Caulobacter crescentus

Caulobacter crescentus triggers the secretion of various proteins to adapt to stressful or changing environment. In particular, C. crescentus secretes an extracellular lipoprotein, ElpS, in response to phosphate starvation. Our results demonstrate that ElpS is partially released in the environment dependently on type II secretion system and activates an external alkaline phosphatase activity. Nevertheless, the exact role of ElpS in phosphate mobilization remains unclear. Interestingly, PcoAcc, encoding an putative protein involved in copper resistance, modulates the expression of elpS but physiological relevance of this interaction is still unknown. PcoAcc is encoded on C. crescentus chromosome in operon with a second gene, pcoBcc, which also contains several predicted copper binding domains. Although the exact mechanism is not still entirely described, PcoAcc et PcoBcc are both essential for C. crescentus survival in medium containing copper. Preliminary results suggest that PcoAcc is exported in cell surface and facilitate copper efllux. Deletion of pcoAcc and/or pcoBcc in C. crescentus results in enhanced copper accumulation in bacteria leading to cell death. Reciprocally, mutant strains for pcoAcc are able to remove high amount of copper from contaminated aqueous solutions and can be consequently be used as biosorbents in water treatment.La sécrétion de protéines chez Caulobacter crescentus est primordiale dans la réponse à différents stress environnementaux. C. crescentus module ainsi la production et la sécrétion d’une lipoprotéine de surface, ElpS, en réponse à une carence en phosphate inorganique dans son milieu de culture. Différents résultats montrent qu’ElpS est partiellement relarguée dans l’espace extracellulaire de manière dépendante du système de sécrétion de type II où elle stimule une activité phosphatase alcaline externe. Le rôle exact d’ElpS dans la mobilisation du phosphate extracellulaire reste néanmoins à déterminer. De manière intéressante, PcoAcc, annotée en tant qu’oxydase capable de fixer du cuivre, influence la transcription d’elpS sans que les détails physiologiques de cette régulation ne soient élucidés. De manière intéressante, PcoAcc est encodée sur le chromosome de C. crescentus sous forme d’opéron avec un second gène, pcoBcc, qui possède également plusieurs domaines putatifs de liaison au cuivre. Bien que les fonctions exactes de PcoAcc et PcoBcc restent à élucider, les deux protéines sont essentielles simultanément à la survie de C. crescentus en présence de cuivre. Des résultats préliminaires indiquent que PcoAcc serait exportée en surface bactérienne et pourrait ainsi faciliter l’export d’ions métalliques hors de la cellule. La délétion de pcoAcc et/ou de pcoBcc chez C. crescentus conduit à une accumulation importante de cuivre dans les cellules qui induit une mort cellulaire importante. Réciproquement, des souches mutantes pour pcoAcc sont capables d’absorber de grandes quantités de cuivre depuis des échantillons liquides et peuvent par conséquent être utilisées en bioremédiation des métaux pour le traitement d’effluents contaminés. Nos premières analyses indiquent également que ces souches peuvent être régénérées après absorption de cuivre par incubation dans du milieu frais sont ainsi potentiellement ré-utilisables.(DOCSC03) -- FUNDP, 201

Repression of ergosterol level during oxidative stress by fission yeast F-box protein Pof14 independently of SCF.

peer reviewe

Involvement of Escherichia coli DNA Polymerase IV in Tolerance of Cytotoxic Alkylating DNA Lesions in Vivo

Escherichia coli PolIV, a DNA polymerase capable of catalyzing synthesis past replication-blocking DNA lesions, belongs to the most ubiquitous branch of Y-family DNA polymerases. The goal of this study is to identify spontaneous DNA damage that is bypassed specifically and accurately by PolIV in vivo. We increased the amount of spontaneous DNA lesions using mutants deficient for different DNA repair pathways and measured mutation frequency in PolIV-proficient and -deficient backgrounds. We found that PolIV performs an error-free bypass of DNA damage that accumulates in the alkA tag genetic background. This result indicates that PolIV is involved in the error-free bypass of cytotoxic alkylating DNA lesions. When the amount of cytotoxic alkylating DNA lesions is increased by the treatment with chemical alkylating agents, PolIV is required for survival in an alkA tag-proficient genetic background as well. Our study, together with the reported involvement of the mammalian PolIV homolog, Polκ, in similar activity, indicates that Y-family DNA polymerases from the DinB branch can be added to the list of evolutionarily conserved molecular mechanisms that counteract cytotoxic effects of DNA alkylation. This activity is of major biological relevance because alkylating agents are continuously produced endogenously in all living cells and are also present in the environment

Repression of ergosterol level during oxidative stress by fission yeast F-box protein Pof14 independently of SCF

We describe a new member of the F-box family, Pof14, which forms a canonical, F-box dependent SCF (Skp1, Cullin, F-box protein) ubiquitin ligase complex. The Pof14 protein has intrinsic instability that is abolished by inactivation of its Skp1 interaction motif (the F-box), Skp1 or the proteasome, indicating that Pof14 stability is controlled by an autocatalytic mechanism. Pof14 interacts with the squalene synthase Erg9, a key enzyme in ergosterol metabolism, in a membrane-bound complex that does not contain the core SCF components. pof14 transcription is induced by hydrogen peroxide and requires the Pap1 transcription factor and the Sty1 MAP kinase. Pof14 binds to and decreases Erg9 activity in vitro and a pof14 deletion strain quickly loses viability in the presence of hydrogen peroxide due to its inability to repress ergosterol synthesis. A pof14 mutant lacking the F-box and an skp1-3 ts mutant behave as wild type in the presence of oxidant showing that Pof14 function is independent of SCF. This indicates that modulation of ergosterol level plays a key role in adaptation to oxidative stress