title: Extracellular zinc competitively inhibits manganese uptake and compromises oxidative stress management in Streptococcus pneumoniae.
abstract: Streptococcus pneumoniae requires manganese for colonization of the human host, but the underlying molecular basis for this requirement has not been elucidated. Recently, it was shown that zinc could compromise manganese uptake and that zinc levels increased during infection by S. pneumoniae in all the niches that it colonized. Here we show, by quantitative means, that extracellular zinc acts in a dose dependent manner to competitively inhibit manganese uptake by S. pneumoniae, with an EC50 of 30.2 µM for zinc in cation-defined media. By exploiting the ability to directly manipulate S. pneumoniae accumulation of manganese, we analyzed the connection between manganese and superoxide dismutase (SodA), a primary source of protection for S. pneumoniae against oxidative stress. We show that manganese starvation led to a decrease in sodA transcription indicating that expression of sodA was regulated through an unknown manganese responsive pathway. Intriguingly, examination of recombinant SodA revealed that the enzyme was potentially a cambialistic superoxide dismutase with an iron/manganese cofactor. SodA was also shown to provide the majority of protection against oxidative stress as a S. pneumoniae ΔsodA mutant strain was found to be hypersensitive to oxidative stress, despite having wild-type manganese levels, indicating that the metal ion alone was not sufficiently protective. Collectively, these results provide a quantitative assessment of the competitive effect of zinc upon manganese uptake and provide a molecular basis for how extracellular zinc exerts a 'toxic' effect on bacterial pathogens, such as S. pneumoniae.
authors.affiliation: Research Centre for Infectious Diseases, School of Molecular and Biomedical Science, University of Adelaide, South Australia, Australia.
authors.forename: Bart A
authors.initials: BA
authors.lastname: Eijkelkamp
authors.affiliation: Research Centre for Infectious Diseases, School of Molecular and Biomedical Science, University of Adelaide, South Australia, Australia.
authors.forename: Jacqueline R
authors.initials: JR
authors.lastname: Morey
authors.affiliation: Research Centre for Infectious Diseases, School of Molecular and Biomedical Science, University of Adelaide, South Australia, Australia.
authors.forename: Miranda P
authors.initials: MP
authors.lastname: Ween
authors.affiliation: School of Chemistry and Molecular Biosciences, Australian Infectious Diseases Research Centre and Institute for Molecular Bioscience, University of Queensland, Brisbane, Australia.
authors.forename: Cheryl-lynn Y
authors.initials: CL
authors.lastname: Ong
authors.affiliation: School of Chemistry and Molecular Biosciences, Australian Infectious Diseases Research Centre and Institute for Molecular Bioscience, University of Queensland, Brisbane, Australia.
authors.forename: Alastair G
authors.initials: AG
authors.lastname: McEwan
authors.affiliation: Research Centre for Infectious Diseases, School of Molecular and Biomedical Science, University of Adelaide, South Australia, Australia.
authors.forename: James C
authors.initials: JC
authors.lastname: Paton
authors.affiliation: Research Centre for Infectious Diseases, School of Molecular and Biomedical Science, University of Adelaide, South Australia, Australia.
authors.forename: Christopher A
authors.initials: CA
authors.lastname: McDevitt
mesh_terms: D001667:Binding, Competitive / Q000502:physiology; D017931:DNA Primers / Q000235:genetics; D005110:Extracellular Space / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D008345:Manganese / Q000378:metabolism*; D018384:Oxidative Stress / Q000502:physiology*; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D013296:Streptococcus pneumoniae / Q000378:metabolism / Q000502:physiology*; D013482:Superoxide Dismutase / Q000378:metabolism; D015032:Zinc / Q000378:metabolism*
chemical_list: D017931:DNA Primers; D008345:Manganese; D013482:Superoxide Dismutase; D015032:Zinc