Volatilization of metal mercury from Organomercurials by highly mercury-resistant Acidithiobacillus ferrooxidans MON-1.
ABSTRACT The iron-oxidizing bacterium Acidithiobacillus ferrooxidans MON-1 is highly resistant not only to mercuric chloride (HgCl(2)) but also to organomercurials such as methylmercury chloride (MMC). We have found that cytochrome c oxidase, purified from strain MON-1, reduces Hg(2+) to volatilizable metal mercury (Hg(0)) with reduced mammalian cytochrome c or Fe(2+) as an electron donor. In this study we found that cytochrome c oxidase can volatilize Hg(0) from MMC as well as from Hg(2+) with reduced mammalian cytochrome c or c-type cytochrome purified from strain MON-1 as an electron donor. We also found that MMC-Hg(0) volatilization activity is present in the MON-1 plasma membrane but not in the cytosol. These activities were strongly inhibited by sodium cyanide (NaCN) and the antibody produced against purified MON-1 cytochrome c oxidase. This is the first report to indicate that cytochrome c oxidase is involved in the degradation of organomercurials in microorganisms.
- SourceAvailable from: pnas.org[show abstract] [hide abstract]
ABSTRACT: The broad-spectrum mercurial-resistance plasmid pDU1358 was analyzed by cloning the resistance determinants and preparing a physical and genetic map of a 45-kilobase (kb) region of the plasmid that contains two separate mercurial-resistance operons that mapped about 20 kb apart. One encoded narrow-spectrum mercurial resistance to Hg2+ and a few organomercurials; the other specified broad-spectrum resistance to phenylmercury and additional organomercurials. Each determinant governed mercurial transport functions. Southern DNA X DNA hybridization experiments using gene-specific probes from the plasmid R100 mer operon indicated close homology with the R100 determinant. The 2153 base pairs of the promoter-distal part of the broad-spectrum Hg2+-resistance operon of pDU1358 were sequenced. This region included the 3'-terminal part of the merA gene, merD, unidentified reading frame URF1, and a part of URF2 homologous to previously sequenced determinants of plasmid R100. Between the merA and merD genes, an open reading frame encoding a 212 amino acid polypeptide was identified as the merB gene that determines the enzyme organomercurial lyase that cleaves the C--Hg bond of phenylmercury.Proceedings of the National Academy of Sciences 06/1987; 84(10):3112-6. · 9.74 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: During iron oxidation,Thiobacillus ferrooxidans (Ferrobacillus ferrooxidans) was able to tolerate high concentrations of Zn, Ni, Cu, Co, Mn and Al (more than 10 g/litre). Silver and anions of tellurium, arsenic and selenium were toxic in concentrations of 50–100 mg/litre. Molybdenum (as molybdate), at concentrations above 5 mg/litre, was lethal toT. ferrooxidans.During thiosulphate oxidation, the tolerance to Zn, Ni and Co was greatly reduced, cobalt now being at least 2000 times more toxic, and the inhibitory levels of Zn and Ni being 600 mg Zn/litre and 150 mg Ni/litre.During sulphur oxidation, the tolerance to heavy metals extended to concentrations above 5 g/litre.Adaptation to Zn, Ni or Cu during iron oxidation was found to result in increased tolerance to some of the other metals also.Antonie van Leeuwenhoek 11/1971; 37(1):489-496. · 2.07 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: The chromosomal mercury resistance (mer) region of the acidophilic bacterium Thiobacillus T3.2 was cloned, characterized, and compared to reported homologous sequences. The Thiobacillus T3.2 mer resistance system is organized as an operon that transcribes into a polycistronic mRNA encoding the Hg2+ ion transport MerT and MerP proteins and the mercuric reductase MerA. In contrast to the Thiobacillus ferrooxidans mer determinant, no merC gene was detected. Transcription of structural genes is regulated by the product of the regulatory merR gene. On the basis of sequence data and expression experiments in E. coli, both merTPA and merR transcription units could be located close to each other and in different strands, with their promoters (PTPA and PR, respectively) overlapping the putative MerR binding site in the intergenic operator/promoter (O/P) region. Amino acid sequences of mer gene products were compared to their homologs. Some sequence features, such as the number and position of cysteine residues, are unique for the Mer proteins of this bacterium. Similarities (-10 and -35 boxes are 19bp apart in both PR and PTPA promoters) and differences (inverted repeats in the Thiobacillus T3.2 MerR-binding site are 2bp shorter than in Thiobacillus ferrooxidans) exist between the O/P intergenic regions of both Thiobacilli. In vivo experiments showed inducible expression of mercury resistance in E. coli cells transformed with the entire Thiobacillus T3.2 mer genetic determinant (structural plus regulatory genes), and little or no expression in clones containing only the structural merT, merP, and merA genes.Extremophiles 02/1999; 3(1):35-43. · 2.20 Impact Factor