title: Ectoine and hydroxyectoine as protectants against osmotic and cold stress: uptake through the SigB-controlled betaine-choline- carnitine transporter-type carrier EctT from Virgibacillus pantothenticus.
abstract: Virgibacillus pantothenticus has been shown to synthesize the compatible solute ectoine in response to high salinity or low growth temperature. We found that exogenously provided ectoine and hydroxyectoine also serve as protectants against these challenges. Transport studies with [(14)C]ectoine revealed that both types of stress induced a high-affinity ectoine uptake activity in V. pantothenticus. By using an Escherichia coli mutant defective in osmoprotectant uptake systems, a functional complementation approach for osmostress resistance in the presence of ectoine was employed to retrieve a gene encoding an ectoine transporter from V. pantothenticus. The cloned gene (ectT) encodes a protein (EctT) that is a member of the BCCT (betaine-choline-carnitine-transporter) family of carriers. Osmoprotection assays demonstrated that the EctT carrier mediates the preferential import of ectoine and hydroxyectoine but also possesses minor uptake activities for the compatible solutes proline and glycine betaine. Northern blot analysis with RNA isolated from V. pantothenticus revealed that a rise in the external osmolality or a reduction in growth temperature strongly increased the transcription of the ectT gene. Primer extension analysis demonstrated that ectT was transcribed under these conditions from a SigB-type promoter. SigB is the master regulator of the general stress regulon of bacilli and provides protection to cells against various challenges, including high salinity and low temperature. Both the synthesis of ectoine and the EctT-mediated uptake of ectoine and hydroxyectoine are triggered by the same environmental cues, high salinity and cold stress, and thereby provide, in a concerted fashion, the protection of V. pantothenticus against these challenges.
authors.affiliation: Philipps-University Marburg, Department of Biology, Laboratory for Microbiology, Karl-von-Frisch-Str. 8, D-35032 Marburg, Germany.
authors.forename: Anne U
authors.initials: AU
authors.lastname: Kuhlmann
authors.forename: Tamara
authors.initials: T
authors.lastname: Hoffmann
authors.forename: Jan
authors.initials: J
authors.lastname: Bursy
authors.forename: Mohamed
authors.initials: M
authors.lastname: Jebbar
authors.forename: Erhard
authors.initials: E
authors.lastname: Bremer
mesh_terms: D000599:Amino Acids, Diamino / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism*; D015152:Blotting, Northern; D002250:Carbon Radioisotopes / Q000378:metabolism; D058639:Cold-Shock Response; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D005816:Genetic Complementation Test; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009997:Osmotic Pressure; D017422:Sequence Analysis, DNA; D012808:Sigma Factor / Q000378:metabolism*; D013194:Staining and Labeling / Q000379:methods; D013312:Stress, Physiological; D013379:Substrate Specificity; D024363:Transcription Initiation Site; D058679:Virgibacillus / Q000235:genetics / Q000378:metabolism / Q000502:physiology*
chemical_list: D000599:Amino Acids, Diamino; D001426:Bacterial Proteins; D002250:Carbon Radioisotopes; D004269:DNA, Bacterial; D026901:Membrane Transport Proteins; C079011:SigB protein, Bacteria; D012808:Sigma Factor; C121557:hydroxyectoine; C045628:ectoine