From PCBs to highly toxic metabolites by the biphenyl pathway.
The degradation of polychlorobiphenyls (PCBs) by diverse bacteria, including Burkholderia sp. LB400, is incomplete with a concomitant accumulation of metabolic intermediates. In this study, the toxicity of diverse (chloro)biphenyls and of their biotransformation into the first two metabolic intermediates of the biphenyl pathway, were determined for the model bacterium Escherichia coli. Recombinant E. coli strains expressing different subsets of bph genes of strain LB400 accumulated metabolic intermediates from (chloro)biphenyls. During biotransformation of these compounds into metabolic intermediates, the viability and metabolic kinetics were determined. The toxicity of biotransformation of (chloro)biphenyls into different metabolic intermediates of (chloro)biphenyls varied. Dihydrodiols and dihydroxybiphenyls are very toxic metabolites for bacteria even after short incubation times, affecting the cell viability much more than (chloro)biphenyls. When bacteria transformed 2-CB into dihydrodiol or dihydroxybiphenyl, a great decrease of intact cells and abundant cell lysis was observed by transmission electronic microscopy. Cell viability of Burkholderia sp. LB400 and of E. coli exposed directly to 2,3-dihydroxybiphenyl decreased also drastically. The toxicity of metabolites generated during oxidation of PCBs may partly explain the recalcitrance to biodegradation of these pollutants. Conversion of less toxic compounds into products with increased toxicity resembles the bioactivation of xenobiotics in higher organisms.
Cámara
Beatriz
B
Laboratorio de Microbiología Molecular y Biotecnología Ambiental, Departamento de Química, Universidad Técnica Federico Santa María, Avenida España 1680, Valparaíso, Chile.
Herrera
Cristina
C
González
Myriam
M
Couve
Eduardo
E
Hofer
Bernd
B
Seeger
Michael
M
D001673:Biodegradation, Environmental; D001711:Biotransformation; D001713:Biphenyl Compounds / Q000378:metabolism / Q000633:toxicity*; D019117:Burkholderia / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism*; D002396:Catechols / Q000378:metabolism / Q000633:toxicity*; D003001:Cloning, Molecular; D015169:Colony Count, Microbial; D004785:Environmental Pollutants; D004926:Escherichia coli / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism* / Q000648:ultrastructure; D005798:Genes, Bacterial / Q000235:genetics / Q000502:physiology; D007506:Iron-Sulfur Proteins / Q000235:genetics / Q000378:metabolism; D010105:Oxygenases / Q000235:genetics / Q000378:metabolism; D011078:Polychlorinated Biphenyls / Q000378:metabolism* / Q000633:toxicity; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism
D001713:Biphenyl Compounds; D002396:Catechols; D004785:Environmental Pollutants; D007506:Iron-Sulfur Proteins; D011994:Recombinant Proteins; C454813:2,3-dihydroxybiphenyl; D011078:Polychlorinated Biphenyls; D010105:Oxygenases; C074161:biphenyl-2,3-dioxygenase