title: The hydroxyectoine gene cluster of the non-halophilic acidophile Acidiphilium cryptum.
abstract: Acidiphilium cryptum is an acidophilic, heterotrophic α-Proteobacterium which thrives in acidic, metal-rich environments (e.g. acid mine drainage). Recently, an ectABCDask gene cluster for biosynthesis of the compatible solutes ectoine and hydroxyectoine was detected in the genome sequence of A. cryptum JF-5. We were able to demonstrate that the type strain A. cryptum DSM 2389(T) is capable of synthesizing the compatible solute hydroxyectoine in response to moderate osmotic stress caused by sodium chloride and aluminium sulphate, respectively. Furthermore, we used the A. cryptum JF-5 sequence to amplify the ectABCDask gene cluster from strain DSM 2389(T) and achieved heterologous expression of the gene cluster in Escherichia coli. Hence, we could for the first time prove metabolic functionality of the genes responsible for hydroxyectoine biosynthesis in the acidophile A. cryptum. In addition, we present information on specific enzyme activity of A. cryptum DSM 2389(T) ectoine synthase (EctC) in vitro. In contrast to EctCs from halophilic microorganisms, the A. cryptum enzyme exhibits a higher isoelectric point, thus a lower acidity, and has maximum specific activity in the absence of sodium chloride.
authors.affiliation: Institut für Mikrobiologie und Biotechnologie, Rheinische Friedrich-Wilhelms-Universität Bonn, Meckenheimer Allee 168, 53115, Bonn, Germany, kmoritz1@uni-bonn.de.
authors.forename: Katharina D
authors.initials: KD
authors.lastname: Moritz
authors.forename: Birgit
authors.initials: B
authors.lastname: Amendt
authors.forename: Elisabeth M H J
authors.initials: EM
authors.lastname: Witt
authors.forename: Erwin A
authors.initials: EA
authors.lastname: Galinski
mesh_terms: D041801:Acidiphilium / Q000235:genetics*; D000534:Alum Compounds / Q000737:chemistry; D000599:Amino Acids, Diamino / Q000096:biosynthesis*; D019295:Computational Biology; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D005822:Genetic Vectors; D006836:Hydro-Lyases / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007526:Isoelectric Point; D005810:Multigene Family; D009997:Osmotic Pressure; D012965:Sodium Chloride / Q000737:chemistry
chemical_list: D000534:Alum Compounds; D000599:Amino Acids, Diamino; C121557:hydroxyectoine; C041524:aluminum sulfate; D012965:Sodium Chloride; C045628:ectoine; D006836:Hydro-Lyases; C106231:ectoine synthase