title: Phosphate starvation triggers production and secretion of an extracellular lipoprotein in Caulobacter crescentus.
abstract: 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 conclusion, 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.
authors.affiliation: Unité de Recherche en Biologie Moléculaire, University of Namur, Namur, Belgium.
authors.forename: Sophie
authors.initials: S
authors.lastname: Le Blastier
authors.forename: Aurore
authors.initials: A
authors.lastname: Hamels
authors.forename: Matthew
authors.initials: M
authors.lastname: Cabeen
authors.forename: Lionel
authors.initials: L
authors.lastname: Schille
authors.forename: Françoise
authors.initials: F
authors.lastname: Tilquin
authors.forename: Marc
authors.initials: M
authors.lastname: Dieu
authors.forename: Martine
authors.initials: M
authors.lastname: Raes
authors.forename: Jean-Yves
authors.initials: JY
authors.lastname: Matroule
mesh_terms: D000469:Alkaline Phosphatase / Q000737:chemistry; D016935:Caulobacter crescentus / Q000378:metabolism*; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D016680:Genome, Bacterial; D008074:Lipoproteins / Q000737:chemistry*; D008957:Models, Genetic; D019308:Palmitic Acid / Q000494:pharmacology; D010710:Phosphates / Q000737:chemistry* / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012835:Silver Nitrate / Q000494:pharmacology; D013347:Subcellular Fractions / Q000378:metabolism; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D008074:Lipoproteins; D010710:Phosphates; D012333:RNA, Messenger; D019308:Palmitic Acid; D012835:Silver Nitrate; D000469:Alkaline Phosphatase; D001616:beta-Galactosidase