title: The ectD gene, which is involved in the synthesis of the compatible solute hydroxyectoine, is essential for thermoprotection of the halophilic bacterium Chromohalobacter salexigens.
abstract: The halophilic bacterium Chromohalobacter salexigens synthesizes and accumulates compatible solutes in response to salt and temperature stress. (13)C-nuclear magnetic resonance analysis of cells grown in minimal medium at the limiting temperature of 45 degrees C revealed the presence of hydroxyectoine, ectoine, glutamate, trehalose (not present in cells grown at 37 degrees C), and the ectoine precursor, Ngamma-acetyldiaminobutyric acid. High-performance liquid chromatography analyses showed that the levels of ectoine and hydroxyectoine were maximal during the stationary phase of growth. Accumulation of hydroxyectoine was up-regulated by salinity and temperature, whereas accumulation of ectoine was up-regulated by salinity and down-regulated by temperature. The ectD gene, which is involved in the conversion of ectoine to hydroxyectoine, was isolated as part of a DNA region that also contains a gene whose product belongs to the AraC-XylS family of transcriptional activators. Orthologs of ectD were found within the sequenced genomes of members of the proteobacteria, firmicutes, and actinobacteria, and their products were grouped into the ectoine hydroxylase subfamily, which was shown to belong to the superfamily of Fe(II)- and 2-oxoglutarate-dependent oxygenases. Analysis of the ectoine and hydroxyectoine contents of an ectABC ectD mutant strain fed with 1 mM ectoine or hydroxyectoine demonstrated that ectD is required for the main ectoine hydroxylase activity in C. salexigens. Although in minimal medium at 37 degrees C the wild-type strain grew with 0.5 to 3.0 M NaCl, with optimal growth at 1.5 M NaCl, at 45 degrees C it could not cope with the lowest (0.75 M NaCl) or the highest (3.0 M NaCl) salinity, and it grew optimally at 2.5 M NaCl. The ectD mutation caused a growth defect at 45 degrees C in minimal medium with 1.5 to 2.5 M NaCl, but it did not affect growth at 37 degrees C at any salinity tested. With 2.5 M NaCl, the ectD mutant synthesized 38% (at 37 degrees C) and 15% (at 45 degrees C) of the hydroxyectoine produced by the wild-type strain. All of these data reveal that hydroxyectoine synthesis mediated by the ectD gene is thermoregulated and essential for thermoprotection of C. salexigens.
authors.affiliation: Department of Microbiology and Parasitology, Faculty of Pharmacy, University of Seville, c/ Profesor García González 2, 41012 Seville, Spain.
authors.forename: Raúl
authors.initials: R
authors.lastname: García-Estepa
authors.forename: Montserrat
authors.initials: M
authors.lastname: Argandoña
authors.forename: Mercedes
authors.initials: M
authors.lastname: Reina-Bueno
authors.forename: Nieves
authors.initials: N
authors.lastname: Capote
authors.forename: Fernando
authors.initials: F
authors.lastname: Iglesias-Guerra
authors.forename: Joaquín J
authors.initials: JJ
authors.lastname: Nieto
authors.forename: Carmen
authors.initials: C
authors.lastname: Vargas
mesh_terms: D000222:Adaptation, Physiological; D000595:Amino Acid Sequence; D000599:Amino Acids, Diamino / Q000378:metabolism*; D002874:Chromosome Mapping; D017124:Conserved Sequence; D004269:DNA, Bacterial / Q000235:genetics / Q000302:isolation & purification; D044129:Halomonadaceae / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D006358:Hot Temperature; D006836:Hydro-Lyases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D008969:Molecular Sequence Data; D010957:Plasmids; D016415:Sequence Alignment; D017385:Sequence Homology; D012965:Sodium Chloride / Q000494:pharmacology; D013696:Temperature
chemical_list: D000599:Amino Acids, Diamino; D004269:DNA, Bacterial; C121557:hydroxyectoine; D012965:Sodium Chloride; C045628:ectoine; D006836:Hydro-Lyases; C106231:ectoine synthase