title: The Rhizobium etli opt operon is required for symbiosis and stress resistance.
abstract: Rhizobium etli is a Gram-negative root-colonizing soil bacterium capable of fixing nitrogen while living in symbiosis with its leguminous host Phaseolus vulgaris. A genome-wide screening for R. etli symbiotic mutants revealed a R. etli operon encoding an oligopeptide ABC-transporter (Opt), two redA homologous genes and one redB gene. Expression analysis showed this opt operon to be transcribed both under free-living and symbiotic conditions and expression levels were demonstrated to be growth-phase-dependent. Plants nodulated by R. etli opt mutants showed a reduced symbiotic nitrogen fixation activity (approximately 50% reduction). Growth experiments with opt mutants in the presence of oligopeptides as the sole nitrogen source confirmed the involvement of the opt genes in oligopeptide uptake. Further phenotypic analysis of the opt mutants revealed them to display an enhanced resistance to the oligopeptide antibiotic bacitracin, an increased susceptibility to the beta-lactam antibiotic ampicillin and a decreased osmotolerance. In conclusion, our results demonstrate that the opt operon plays a crucial role during symbiosis and stress resistance.
authors.affiliation: Centre of Microbial and Plant Genetics, Katholieke Universiteit Leuven, 3001 Heverlee, Belgium.
authors.forename: K
authors.initials: K
authors.lastname: Vos
authors.forename: K
authors.initials: K
authors.lastname: Braeken
authors.forename: M
authors.initials: M
authors.lastname: Fauvart
authors.forename: M
authors.initials: M
authors.lastname: Ndayizeye
authors.forename: J
authors.initials: J
authors.lastname: Verhaert
authors.forename: S
authors.initials: S
authors.lastname: Zachurzok
authors.forename: I
authors.initials: I
authors.lastname: Lambrichts
authors.forename: J
authors.initials: J
authors.lastname: Michiels
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics* / Q000378:metabolism; D000667:Ampicillin / Q000633:toxicity; D001414:Bacitracin / Q000633:toxicity; D001483:Base Sequence; D017931:DNA Primers / Q000235:genetics; D040461:Gene Components; D015964:Gene Expression Regulation, Bacterial; D005966:Glucuronidase / Q000378:metabolism; D046529:Microscopy, Electron, Transmission; D008969:Molecular Sequence Data; D009586:Nitrogen Fixation; D009842:Oligopeptides / Q000378:metabolism; D009876:Operon / Q000235:genetics* / Q000502:physiology; D027805:Phaseolus / Q000382:microbiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D042163:Rhizobium etli / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development / Q000648:ultrastructure; D017422:Sequence Analysis, DNA; D013559:Symbiosis
chemical_list: D018528:ATP-Binding Cassette Transporters; D017931:DNA Primers; D009842:Oligopeptides; D001414:Bacitracin; D000667:Ampicillin; D005966:Glucuronidase