Solubilization of insoluble inorganic zinc compounds by ericoid mycorrhizal fungi derived from heavy metal polluted sites

Ericoid mycorrhizal fungi increase the ability of their host plants to colonize soils polluted with toxic metals, although the underlying mechanisms are not clearly understood. Two mycorrhizal strains of Oidiodendron maius isolated from contaminated soil were previously shown to tolerate high concentrations of toxic metals. We investigated further the biological mechanisms that may explain metal tolerance, focussing on the interactions between insoluble metal species and extracellular fungal metabolites. In particular, we demonstrate that fungal strains derived from polluted and unpolluted soils mobilize insoluble inorganic zinc compounds to different extents. Strains from polluted soils showed in fact little ability to solubilize Zn from both ZnO and Zn₃(PO₄)₂, whereas strains from unpolluted soils showed a higher solubilization potential. This different behaviour was confirmed when the solubilization abilities of a wider range of fungal strains (25 isolates) was examined. Induction of organic acids (malate and citrate) by the metal compounds was at least in part responsible for metal solubilization. Our results suggest that ericoid mycorrhizal strains from polluted and unpolluted soils may interact differently with metal compounds. We speculate that this may reflect specific strategies to maintain homeostasis of essential metals under different soil conditions.     

Epidemiological aspects of viral haemorrhagic septicaemia virus genotype II isolated from Baltic herring, Clupea harengus membras L

This study was carried out to clarify the role of wild fish, especially Baltic herring, Clupea harengus membras L., in the epidemiology of viral haemorrhagic septicaemia virus (VHSV) in brackish water in Finland. Baltic herring with no visible signs of disease were collected from the Archipelago Sea, the Gulf of Bothnia and the eastern Gulf of Finland. In total, 7580 herring were examined by virus isolation as 758 pooled samples and 3029 wild salmonid broodfish as pooled samples during 2004-2006. VHSV was isolated from 51 pooled herring samples in bluegill fibroblast-2 cells, but not in epithelioma papulosum cyprini cells. The majority of isolations were from the coastal archipelago and from fish caught during the spawning season. Based on glycoprotein (G) gene sequences, the virus was classified as a member of genotype II of VHSV. Pairwise comparisons of the G gene regions of herring isolates revealed that all the isolates were closely related, with 98.8-100% nucleotide homology. Phylogenetic analyses revealed that they were closely related to the strains isolated previously from herring and sprat, Sprattus sprattus (L.), in Gotland and to the VHSV isolates from European river lamprey, Lampetra fluviatilis (L.), in the rivers that flow into the Bothnian Bay. The infection in Baltic herring is likely to be independent of the VHSV Id epidemic in farmed rainbow trout, Oncorhynchus mykiss (Walbaum).