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Mercury operon regulation by the merR gene of the organomercurial resistance system of plasmid pDU1358.

ABSTRACT: The structural basis for induction of the mercury resistance operon with inorganic mercury and with the organomercurial compound phenylmercuric acetate was addressed by DNA sequencing analysis and by lac fusion transcription experiments regulated by merR in trans from broad-spectrum-resistance plasmid pDU1358 (Hg2+ and phenylmercury responding). The lac fusion results were compared with those from a narrow-spectrum-resistance (Hg2+ responding but not phenylmercuric responding) operon and the pDU1358 merR deleted at the 3' end. The nucleotide sequence of the beginning region of the broad-spectrum mer operon of plasmid pDU1358 was determined, including that of the merR gene, the operator-promoter region, the merT and merP genes, and the first 60% of the merA gene. Comparison of this sequence with DNA sequences of narrow-spectrum mer operons from transposon Tn501 and plasmid R100 showed that a major difference occurred in the 3' 29 base pairs of the merR gene, resulting in unrelated C-terminal 10 amino acids. A hybrid mer operon consisting of the merR gene from pDU1358, a hybrid merA gene (determining mercuric reductase enzyme), and lacking the merB gene (determining phenylmercury lyase activity) was inducible by both phenylmercury and inorganic Hg2+. This shows that organomercurial lyase is not needed for induction by organomercurial compounds. A mutant form of pDU1358 merR missing the C-terminal 17 amino acids responded to inorganic Hg2+ but not to phenylmercury. Thus, the C-terminal region of the MerR protein of the pDU1358 mer operon is involved in the recognition of phenylmercury.

SUBMITTER: Nucifora G

PROVIDER: S-EPMC210196 | biostudies-other | 1989 Aug

REPOSITORIES: biostudies-other

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Mercury operon regulation by the merR gene of the organomercurial resistance system of plasmid pDU1358.

Nucifora G G Chu L L Silver S S Misra T K TK

Journal of bacteriology 19890801 8

The structural basis for induction of the mercury resistance operon with inorganic mercury and with the organomercurial compound phenylmercuric acetate was addressed by DNA sequencing analysis and by lac fusion transcription experiments regulated by merR in trans from broad-spectrum-resistance plasmid pDU1358 (Hg2+ and phenylmercury responding). The lac fusion results were compared with those from a narrow-spectrum-resistance (Hg2+ responding but not phenylmercuric responding) operon and the pDU ...[more]

PMID: 2666393

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Project description:Mercuric mercury (Hg[II]) is a highly toxic and mobile element that is likely to have had a pronounced and adverse effect on biology since Earth's oxygenation ∼2.4 billion years ago due to its high affinity for protein sulfhydryl groups, which upon binding destabilize protein structure and decrease enzyme activity, resulting in a decreased organismal fitness. The central enzyme in the microbial mercury detoxification system is the mercuric reductase (MerA) protein, which catalyzes the reduction of Hg(II) to volatile Hg(0). In addition to MerA, mer operons encode for proteins involved in regulation, Hg binding, and organomercury degradation. Mer-mediated approaches have had broad applications in the bioremediation of mercury-contaminated environments and industrial waste streams. Here, we examine the composition of 272 individual mer operons and quantitatively map the distribution of mer-encoded functions on both taxonomic SSU rRNA gene and MerA phylogenies. The results indicate an origin and early evolution of MerA among thermophilic bacteria and an overall increase in the complexity of mer operons through evolutionary time, suggesting continual gene recruitment and evolution leading to an improved efficiency and functional potential of the Mer detoxification system. Consistent with a positive relationship between the evolutionary history and topology of MerA and SSU rRNA gene phylogenies (Mantel R = 0.81, p < 0.01), the distribution of the majority of mer functions, when mapped on these phylograms, indicates an overall tendency to inherit mer-encoded functions through vertical descent. However, individual mer functions display evidence of a variable degree of vertical inheritance, with several genes exhibiting strong evidence for acquisition via lateral gene transfer and/or gene loss. Collectively, these data suggest that (i) mer has evolved from a simple system in geothermal environments to a widely distributed and more complex and efficient detoxification system, and (ii) merA is a suitable biomarker for examining the functional diversity of Hg detoxification and for predicting the composition of mer operons in natural environments.

Dataset Information

Mercury operon regulation by the merR gene of the organomercurial resistance system of plasmid pDU1358.

Publications

Mercury operon regulation by the merR gene of the organomercurial resistance system of plasmid pDU1358.

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