title: Identification of an osmo-dependent and an osmo-independent choline transporter in Acinetobacter baylyi: implications in osmostress protection and metabolic adaptation.
abstract: Members of the genus Acinetobacter are well known for their metabolic versatility that allows them to adapt to different ecological niches. In previous studies, we have demonstrated that Acinetobacter baylyi ADP1 can cope with high salinities by uptake and accumulation of the well-known compatible solute glycine betaine. Here, we demonstrate that addition of choline restores growth at high salinities. We further show that choline was actively taken up by the cells and converted to glycine betaine. Uptake of choline was induced by high salinity and the presence of choline in the growth medium. At high salinities, glycine betaine was accumulated in the cells whereas in the absence of osmotic stress it was exported. Inspection of the genome sequence followed by mutant studies led to the identification of two genes encoding secondary transporters (BetT1 and BetT2) of the betaine-choline-carnitine transporter (BCCT) family. The BetT1 transporter lacks an extended C-terminal domain usually found in osmoregulated choline BCCTs. BetT1 was found to facilitate osmolarity-independent choline transport most likely by a uniport mechanism. We propose that BetT1 does not primarily function in osmoadaptation but might play a role in metabolic adaptation to choline-rich environments.
authors.affiliation: Molecular Microbiology & Bioenergetics, Institute of Molecular Biosciences, Johann Wolfgang Goethe University Frankfurt, Max-von-Laue-Str. 9, 60438, Frankfurt am Main, Germany.
authors.forename: Miriam
authors.initials: M
authors.lastname: Sand
authors.forename: Julia
authors.initials: J
authors.lastname: Stahl
authors.forename: Izabela
authors.initials: I
authors.lastname: Waclawska
authors.forename: Christine
authors.initials: C
authors.lastname: Ziegler
authors.forename: Beate
authors.initials: B
authors.lastname: Averhoff
mesh_terms: D000150:Acinetobacter / Q000235:genetics / Q000378:metabolism*; D000222:Adaptation, Physiological; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001622:Betaine / Q000378:metabolism; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D002794:Choline / Q000378:metabolism*; D017124:Conserved Sequence; D050485:GABA Plasma Membrane Transport Proteins; D005798:Genes, Bacterial; D007700:Kinetics; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009997:Osmotic Pressure; D010084:Oxidation-Reduction; D054712:Salinity; D055049:Salt Tolerance; D012964:Sodium / Q000378:metabolism; D014882:Water-Electrolyte Balance
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D050485:GABA Plasma Membrane Transport Proteins; D026901:Membrane Transport Proteins; C065637:choline transporter; C072207:betaine plasma membrane transport proteins; D001622:Betaine; D012964:Sodium; D002794:Choline