title: Polychlorinated biphenyl rhizoremediation by Pseudomonas fluorescens F113 derivatives, using a Sinorhizobium meliloti nod system to drive bph gene expression.
abstract: Rhizoremediation of organic chemicals requires high-level expression of biodegradation genes in bacterial strains that are excellent rhizosphere colonizers. Pseudomonas fluorescens F113 is a biocontrol strain that was shown to be an excellent colonizer of numerous plant rhizospheres, including alfalfa. Although a derivative of F113 expressing polychlorinated biphenyl (PCB) biodegradation genes (F113pcb) has been reported previously, this strain shows a low level of bph gene expression, limiting its rhizoremediation potential. Here, a high-level expression system was designed from rhizobial nod gene regulatory relays. Nod promoters were tested in strain F113 by using beta-galactosidase transcriptional fusions. This analysis showed that nodbox 4 from Sinorhizobium meliloti has a high level of expression in F113 that is dependent on an intact nodD1 gene. A transcriptional fusion of a nodbox cassette containing the nodD1 gene and nodbox 4 fused to a gfp gene was expressed in the alfalfa rhizosphere. The bph operon from Burkholderia sp. strain LB400 was cloned under the control of the nodbox cassette and was inserted as a single copy into the genome of F113, generating strain F113L::1180. This new genetically modified strain has a high level of BphC activity and grows on biphenyl as a sole carbon and energy source at a growth rate that is more than three times higher than that of F113pcb. Degradation of PCBs 3, 4, 5, 17, and 25 was also much faster in F113L::1180 than in F113pcb. Finally, the modified strain cometabolized PCB congeners present in Delor103 better than strain LB400, the donor of the bph genes used.
authors.affiliation: Departamento de Biología, Facultad de Ciencias, Universidad Autónoma de Madrid, E-28049 Madrid, Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: Villacieros
authors.forename: Clare
authors.initials: C
authors.lastname: Whelan
authors.forename: Martina
authors.initials: M
authors.lastname: Mackova
authors.forename: Jesper
authors.initials: J
authors.lastname: Molgaard
authors.forename: María
authors.initials: M
authors.lastname: Sánchez-Contreras
authors.forename: Javier
authors.initials: J
authors.lastname: Lloret
authors.forename: Daniel
authors.initials: D
authors.lastname: Aguirre de Cárcer
authors.forename: Roke I
authors.initials: RI
authors.lastname: Oruezábal
authors.forename: Luis
authors.initials: L
authors.lastname: Bolaños
authors.forename: Thomas
authors.initials: T
authors.lastname: Macek
authors.forename: Ulrich
authors.initials: U
authors.lastname: Karlson
authors.forename: David N
authors.initials: DN
authors.lastname: Dowling
authors.forename: Marta
authors.initials: M
authors.lastname: Martín
authors.forename: Rafael
authors.initials: R
authors.lastname: Rivilla
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics*; D001673:Biodegradation, Environmental; D004268:DNA-Binding Proteins / Q000235:genetics*; D009876:Operon; D011078:Polychlorinated Biphenyls / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011551:Pseudomonas fluorescens / Q000254:growth & development / Q000378:metabolism*; D016962:Sinorhizobium meliloti / Q000235:genetics*; D012989:Soil Pollutants / Q000378:metabolism*; D015534:Trans-Activators / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D012989:Soil Pollutants; D015534:Trans-Activators; D011078:Polychlorinated Biphenyls