title: Extracytoplasmic storage as the nickel resistance mechanism in a natural isolate of Pseudomonas putida S4.
abstract: Metal resistances in microbes are important to study not only to understand metal homeostasis but also to use such organisms further in environmental bioremediation. Nickel (Ni2+) is an important micronutrient, which at higher concentration becomes toxic. Many Ni2+-resistant organisms are known, which resist metal by active efflux. Pseudomonas putida S4, a natural isolate from India, is reported to show a multi-metal resistance profile. In the present study, the Ni2+-resistance mechanism in strain S4 was examined. Wild-type cells gradually accumulated Ni2+ but kept it preferentially in the periplasmic space in a bound form. In Ni2+-sensitive mutants, periplasmic storage was disturbed and more metal accumulated cytoplasmically, producing toxicity. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis analysis of periplasmic proteins revealed a band of approximately 18 kDa, which appeared only in Ni2+-exposed wild-type cells, and which was absent from cells not exposed to Ni2+ as well as from Ni2+-sensitive mutants. On the basis of these observations, we propose a Ni2+-resistance mechanism in P. putida S4 based on sequestration of metal in the periplasmic space. This is the first study of sequestration-based Ni2+ resistance.
authors.affiliation: Department of Genetics, University of New Delhi, South Campus, New Delhi 110021, India.
authors.forename: V N
authors.initials: VN
authors.lastname: Tripathi
authors.forename: S
authors.initials: S
authors.lastname: Srivastava
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D003300:Copper / Q000378:metabolism / Q000494:pharmacology; D024881:Drug Resistance, Bacterial / Q000235:genetics; D004591:Electrophoresis, Polyacrylamide Gel; D005838:Genotype; D009154:Mutation; D009532:Nickel / Q000378:metabolism / Q000494:pharmacology*; D019897:Periplasm / Q000187:drug effects / Q000378:metabolism; D016958:Pseudomonas putida / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D013997:Time Factors; D015032:Zinc / Q000378:metabolism / Q000494:pharmacology
chemical_list: D001426:Bacterial Proteins; D003300:Copper; D009532:Nickel; D015032:Zinc