Interactions of toxic metals with fungi have long been of importance since metal toxicity still is the basis of many fungicidal preparations while in an environmental context, accelerating pollution of the natural environment has led to increased interest because of the sometimes dominant presence of fungi in metal-polluted habitats, the translocation of toxic metals and radionuclides to fruit bodies of edible higher fungi, and the significance of mycorrhizal fungi in the amelioration of metal phytotoxicity (Colpaert and Van Assche, 1987). Furthermore, the use of fungal (and other microbial) biomass for the detoxification of metal/radionuclide-containing industrial effluents is of biotechnological potential (Gadd, 1990, 1992a).

Interactions of fungip with toxic metals

A wealth of chemical, spectroscopic and structural data attest to the uniqueness of the metallothioneins as a group of novel bioinorganic structures. Their earmarking feature is the arrangement of “soft” metal ions in complexes with cysteine side chains to form discrete metal-thiolate clusters. In this review an account is given of the chemical characteristics of the 52 metallothioneins whose primary structures are now known completely or in part. Also included is an up-to-date summary of the spectroscopic properties and of the spatial structure models derived from X-ray diffraction crystallographic analysis and from two-dimensional nuclear magnetic resonance spectroscopy.

Chemistry and biochemistry of metallothionein.

Whole genome sequencing (WGS) promises to be transformative for the practice of clinical microbiology, and the rapidly falling cost and turnaround time mean that this will become a viable technology in diagnostic and reference laboratories in the near future. The objective of this article is to consider at a very practical level where, in the context of a modern diagnostic microbiology laboratory, WGS might be cost-effective compared to current alternatives. We propose that molecular epidemiology performed for surveillance and outbreak investigation and genotypic antimicrobial susceptibility testing for microbes that are difficult to grow represent the most immediate areas for application of WGS, and discuss the technical and infrastructure requirements for this to be implemented.

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Routine Use of Microbial Whole Genome Sequencing in Diagnostic and Public Health Microbiology

S. cerevisiae encodes an essential protein homologous in sequence and function to mammalian BiP

Copper is both an essential micronutrient and a toxic heavy metal for most living cells. The presence of high concentrations of cupric ions in the environment promotes the selection of microorganisms possessing genetic determinants for copper resistance. Several examples of chromosomal and plasmid copper-resistance systems in bacteria have been reported, and the mechanisms of resistance have started to be understood at the molecular level. Bacterial mechanisms of copper resistance are related to reduced copper transport, enhanced effiux of cupric ions, or copper complexation by cell components. Copper tolerance in fungi has also been ascribed to diverse mechanisms involving trapping of the metal by cell-wall components, altered uptake of copper, extracellular chelation or precipitation by secreted metabolites, and intracellular complexing by metallothioneins and phytochelatins; only the metallothionein chelation mechanism has been approached with molecular detail.

Copper resistance mechanisms in bacteria and fungi

Addition of copper to yeast cells leads to the induction of a low molecular weight, cysteine-rich protein that binds copper. This protein, termed copper chelatin or thionein, is related to the metallothionein family of proteins that are induced in response to cadmium and zinc in vertebrate cells. We have determined the structure of the yeast copper-binding protein by DNA sequence analysis of the gene. Although the 6573-dalton yeast protein is substantially divergent from vertebrate metallothioneins, the arrangement of 12 cysteine residues, which is a hallmark of metal-binding proteins, is partially conserved. We analyzed the regulatory DNA sequence of the gene by fusing it with the Escherichia coli galactokinase gene and assaying the levels of enzyme activity in yeast in response to copper. The transcriptional activation has a specific requirement for copper. Zinc, cadmium, and gold were unable to regulate the galactokinase activity. The yeast copper metallothionein regulatory sequences represent a previously unreported class of yeast promoter that is regulated by copper.

https://www.pnas.org/content/pnas/81/11/3332.full.pdf

Copper metallothionein of yeast, structure of the gene, and regulation of expression

The millions of deaths from cholera during the past 200 y, coupled with the morbidity and mortality of cholera in Haiti since October 2010, are grim reminders that Vibrio cholerae, the etiologic agent of cholera, remains a scourge. We report the isolation of both V. cholerae O1 and non-O1/O139 early in the Haiti cholera epidemic from samples collected from victims in 18 towns across eight Arrondissements of Haiti. The results showed two distinct populations of V. cholerae coexisted in Haiti early in the epidemic. As non-O1/O139 V. cholerae was the sole pathogen isolated from 21% of the clinical specimens, its role in this epidemic, either alone or in concert with V. cholerae O1, cannot be dismissed. A genomic approach was used to examine similarities and differences among the Haitian V. cholerae O1 and V. cholerae non-O1/O139 strains. A total of 47 V. cholerae O1 and 29 V. cholerae non-O1/O139 isolates from patients and the environment were sequenced. Comparative genome analyses of the 76 genomes and eight reference strains of V. cholerae isolated in concurrent epidemics outside Haiti and 27 V. cholerae genomes available in the public database demonstrated substantial diversity of V. cholerae and ongoing flux within its genome.

https://www.pnas.org/content/pnas/109/29/E2010.full.pdf

Genomic diversity of 2010 Haitian cholera outbreak strains

We report the autochthonous existence of Vibrio cholerae in coastal waters of Iceland, a geothermally active country where cholera is absent and has never been reported. Seawater, mussel, and macroalgae samples were collected close to and distant from sites where geothermal activity causes a significant increase in water temperature during low tides. V. cholerae was detected only at geothermal-influenced sites during low-tides. None of the V. cholerae isolates encoded cholera toxin (ctxAB) and all were non-O1/non-O139 serogroups. However, all isolates encoded other virulence factors that are associated with cholera as well as extra-intestinal V. cholerae infections. The virulence factors were functional at temperatures of coastal waters of Iceland, suggesting an ecological role. It is noteworthy that V. cholerae was isolated from samples collected at sites distant from anthropogenic influence, supporting the conclusion that V. cholerae is autochthonous to the aquatic environment of Iceland.

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Philip Clark

Papers

Copper metallothionein of yeast, structure of the gene, and regulation of expression

Genomic diversity of 2010 Haitian cholera outbreak strains

Vibrio cholerae in a historically cholera-free country