A derivative of the menaquinone precursor 1,4-dihydroxy-2-naphthoate is involved in the reductive transformation of carbon tetrachloride by aerobically grown Shewanella oneidensis MR-1
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Transformation of carbon tetrachloride (CT) by Shewanella oneidensis MR-1 has been proposed to involve the anaerobic respiratory-chain component menaquinone. To investigate this hypothesis a series of menaquinone mutants were constructed. The menF mutant is blocked at the start of the menaquinone biosynthetic pathway. The menB, menA and menG mutants are all blocked towards the end of the pathway, being unable to produce 1,4-dihydroxy-2-naphthoic acid (DHNA), demethyl-menaquinone and menaquinone , respectively. Aerobically grown mutants unable to produce the menaquinone precursor DHNA (menF and menB mutants) showed a distinctly different CT transformation profile than mutants able to produce DHNA but unable to produce menaquinone (menA and menG mutants). While DHNA did not reduce CT in an abiotic assay, the addition of DHNA to the menF and menB mutants restored normal CT transformation activity. We conclude that a derivative of DHNA, that is distinct from menaquinone, is involved in the reduction of CT by aerobically grown S. oneidensis MR-1. When cells were grown anaerobically with trimethylamine-N-oxide as the terminal electron acceptor, all the menaquinone mutants showed wild-type levels of CT reduction. We conclude that S. oneidensis MR-1 produces two different factors capable of dehalogenating CT. The factor produced under anaerobic growth conditions is not a product of the menaquinone biosynthetic pathway.
KeywordsCarbon Tetrachloride Shewanella TMAO Menaquinone menE Gene
Preliminary sequence data was obtained from The Institute for Genomic Research website at http://www.tigr.org. Sequencing of Shewanella oneidensis MR-1 was accomplished with support from the Department of Energy's Microbial Genome Program. This work was funded by NIEHS grant no. 2 P42 ES04911–12 through the NIEHS Superfund Basic Research program of the Institute for Environmental Toxicology at Michigan State University. CHJY was funded by a subsidy from an undergraduate Research Fund from the Department of Civil and Environmental Engineering, Stanford University. Since this manuscript has not been reviewed by these agencies, no endorsement should be inferred. All experiments conducted in this paper comply with current United States law.
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