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AIMS: To characterize genes involved in maintaining homeostatic levels of zinc in the cyanobacterium Nostoc punctiforme. METHODS AND RESULTS: Metal efflux transporters play a central role in maintaining homeostatic levels of trace elements such as zinc. Sequence analyses of the N. punctiforme genome identified two potential cation diffusion facilitator (CDF) metal efflux transporters, Npun_F0707 (Cdf31) and Npun_F1794 (Cdf33). Deletion of either Cdf31or Cdf33 resulted in increased zinc retention over 3 h. Interestingly, Cdf31(-) and Cdf33(-) mutants showed no change in sensitivity to zinc exposure in comparison with the wild type, suggesting some compensatory capacity for the loss of each other. Using qRT-PCR, a possible interaction was observed between the two cdf's, where the Cdf31(-) mutant had a more profound effect on cdf33 expression than Cdf33(-) did on cdf31. Over-expression of Cdf31 and Cdf33 in ZntA(-) - and ZitB(-) -deficient Escherichia coli revealed function similarities between the ZntA and ZitB of E. coli and the cyanobacterial transporters. CONCLUSIONS: The data presented shed light on the function of two important transporters that regulate zinc homeostasis in N. punctiforme. SIGNIFICANCE AND IMPACT OF THE STUDY: This study shows for the first time the functional characterization of two cyanobacterial zinc efflux proteins belonging to the CDF family.

A wide variety of enzymatic pathways that produce specialized metabolites in bacteria, fungi and plants are known to be encoded in biosynthetic gene clusters. Information about these clusters, pathways and metabolites is currently dispersed throughout the literature, making it difficult to exploit. To facilitate consistent and systematic deposition and retrieval of data on biosynthetic gene clusters, we propose the Minimum Information about a Biosynthetic Gene cluster (MIBiG) data standard.

Seven acidophilic/acid-tolerant fungal strains were characterised from the process waters at the Ranger U mine in the Northern Territory, Australia. Process waters were typically very acidic with pH values of 1.7-1.8 and contained high concentrations of total dissolved/colloidal salts of about 80-100 g/l. The strains obtained were T1 (Teratosphaeria acidotherma), T2 (Teratosphaeriaceae species), FRL (Coniochaeta-Lecythophora sp.), BS (Coniochaeta-Lecythophora sp.), NFR (Coniochaeta-Lecythophora sp.), FoF (Teratosphaeria acidotherma) and YoF (Coniochaeta-Lecythophora sp.). Fungal cultures were grown in raffinate and Mackintosh medium followed by enrichment in Mackintosh medium with glucose and yeast extract additions. Strains were isolated in potato dextrose agar at pH 3.0 and their characteristics examined in a synthetic medium similar in composition to their source environment. Toxicity tests showed that growth of the isolates T1, T2 and FRL occurred at all the U concentrations tested. Qualitative evaluation of growth showed no observable differences between controls without U and 0.1 and 0.2 mM U cultures across all strains. Strains T1 and FRL showed slightly reduced growth at concentrations at and above 0.5 mM U, but even at 2.5 mM U growth could still be considered as good. The results of ICP analyses showed variable U biosorption capacity. In solutions containing 0.1 and 0.2 mM U, the T1 and FRL cultures showed significant U removal from the supernatant with 24.73% and 16.83% U removal for T1, and 58.73% and 39.79% U removal for FRL. The lack of significant removal of U by T2 may be explained by the low biomass density of the cultures. The potential role of the fungi in the hydrometallurgical extraction of U is discussed., Seven acidophilic/acid-tolerant fungal strains were characterised from the process waters at the Ranger U mine in the Northern Territory, Australia. Process waters were typically very acidic with pH values of 1.7-1.8 and contained high concentrations of total dissolved/colloidal salts of about 80-100 g/l. The strains obtained were T1 (Teratosphaeria acidotherma), T2 (Teratosphaeriaceae species), FRL (Coniochaeta-Lecythophora sp.), BS (Coniochaeta-Lecythophora sp.), NFR (Coniochaeta-Lecythophora sp.), FoF (Teratosphaeria acidotherma) and YoF (Coniochaeta-Lecythophora sp.). Fungal cultures were grown in raffinate and Mackintosh medium followed by enrichment in Mackintosh medium with glucose and yeast extract additions. Strains were isolated in potato dextrose agar at pH 3.0 and their characteristics examined in a synthetic medium similar in composition to their source environment. Toxicity tests showed that growth of the isolates T1, T2 and FRL occurred at all the U concentrations tested. Qualitative evaluation of growth showed no observable differences between controls without U and 0.1 and 0.2 mM U cultures across all strains. Strains T1 and FRL showed slightly reduced growth at concentrations at and above 0.5 mM U, but even at 2.5 mM U growth could still be considered as good. The results of ICP analyses showed variable U biosorption capacity. In solutions containing 0.1 and 0.2 mM U, the T1 and FRL cultures showed significant U removal from the supernatant with 24.73% and 16.83% U removal for T1, and 58.73% and 39.79% U removal for FRL. The lack of significant removal of U by T2 may be explained by the low biomass density of the cultures. The potential role of the fungi in the hydrometallurgical extraction of U is discussed.

Microcystis, cyanobacteria, Daphnia, microviridin, NMR, microcystin, environmental toxins

Udgivelsesdato: November 2001, Daphnia.

Salt-tolerant autotrophic and mixotrophic Fe-oxidising bacteria were isolated from Sydney Harbour sediment as part of a programme to develop remedial technologies for harbour sediments. The leaching potential of the bacteria was assessed using heavy metal-contaminated sediments and mineral ores. Leaching of metals from sediment by autotrophic isolates was evaluated in shake flasks and in stirred reactors in media containing 0-5% NaCl. At 15% pulp density and 2% NaCl, the removal of Cu, Zn and Cd after 3 days was sufficient to meet regulatory requirements for disposal. The ability of three mixotrophic Fe-oxidising bacteria to oxidise FeSO4 and leach ores was tested. Leaching of pyrite, arsenopyrite and mixed base metal sulphides was observed at 0.5-4% NaCl. Pyrite oxidation was maximum at 0.5-1% NaCl and declined with higher concentrations. Fe(III) oxidation was fastest at 1% NaCl and cell doubling was three times slower at 4% NaCl., Salt-tolerant autotrophic and mixotrophic Fe-oxidising bacteria were isolated from Sydney Harbour sediment as part of a programme to develop remedial technologies for harbour sediments. The leaching potential of the bacteria was assessed using heavy metal-contaminated sediments and mineral ores. Leaching of metals from sediment by autotrophic isolates was evaluated in shake flasks and in stirred reactors in media containing 0-5% NaCl. At 15% pulp density and 2% NaCl, the removal of Cu, Zn and Cd after 3 days was sufficient to meet regulatory requirements for disposal. The ability of three mixotrophic Fe-oxidising bacteria to oxidise FeSO4 and leach ores was tested. Leaching of pyrite, arsenopyrite and mixed base metal sulphides was observed at 0.5-4% NaCl. Pyrite oxidation was maximum at 0.5-1% NaCl and declined with higher concentrations. Fe(III) oxidation was fastest at 1% NaCl and cell doubling was three times slower at 4% NaCl.