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Fungi possess the biochemical and ecological capacity to degrade environmental organic chemicals and to decrease the risk associated with metals, metalloids and radionuclides, either by chemical modification or by influencing chemical bioavailability. Furthermore, the ability of these fungi to form extended mycelial networks, the low specificity of their catabolic enzymes and their independence from using pollutants as a growth substrate make these fungi well suited for bioremediation processes. However, despite dominating the living biomass in soil and being abundant in aqueous systems, fungi have not been exploited for the bioremediation of such environments. In this Review, we describe the metabolic and ecological features that make fungi suited for use in bioremediation and waste treatment processes, and discuss their potential for applications on the basis of these strengths.

The capacity of fungi to serve as vectors for the dispersion of pollutant-degrading bacteria was analyzed in laboratory model systems mimicking water-saturated (agar surfaces) and unsaturated soil environments (glass-bead-filled columns). Two common soil fungi (Fusarium oxysporum and Rhexocercosporidium sp.) forming hydrophilic and hydrophobic mycelia, respectively, and three polycyclic aromatic hydrocarbon degrading bacteria (Achromobacter sp. SK1, Mycobacterium frederiksbergense LB501TG, and Sphingomonas sp. L138) were selected based on the absence of mutual antagonistic effects. It was shown that fungal hyphae act as vectors for bacterial transport with mobilization strongly depending on the specific microorganisms chosen: The motile strain Achromobacter sp. SK1 was most efficiently spread along hyphae of hydrophilic F. oxysporum in both model systems with transport velocities of up to 1 cm d(-1), whereas no dispersion of the two nonmotile strains was observed in the presence of F. oxysporum. By contrast, none of the bacteria was mobilized along the hydrophobic mycelia of Rhexocercosporidium sp. growing on agar surfaces. In column experiments however, strain SK1 was mobilized by Rhexocercosporidium sp. It is hypothesized that bacteria may move by their intrinsic motilitythrough continuous (physiological) liquid films forming around fungal hyphae. The results of this study suggest that the specific stimulation of indigenous fungi may be a strategy to mobilize pollutant-degrading bacteria leading to their homogenization in polluted soil thereby improving bioremediation.

Fungi and bacteria are found living together in a wide variety of environments. Their interactions are significant drivers of many ecosystem functions and are important for the health of plants and animals. A large number of fungal and bacterial families engage in complex interactions that lead to critical behavioural shifts of the microorganisms ranging from mutualism to antagonism. The importance of bacterial-fungal interactions (BFI) in environmental science, medicine and biotechnology has led to the emergence of a dynamic and multidisciplinary research field that combines highly diverse approaches including molecular biology, genomics, geochemistry, chemical and microbial ecology, biophysics and ecological modelling. In this review, we discuss recent advances that underscore the roles of BFI across relevant habitats and ecosystems. A particular focus is placed on the understanding of BFI within complex microbial communities and in regard of the metaorganism concept. We also discuss recent discoveries that clarify the (molecular) mechanisms involved in bacterial-fungal relationships, and the contribution of new technologies to decipher generic principles of BFI in terms of physical associations and molecular dialogues. Finally, we discuss future directions for research in order to stimulate synergy within the BFI research area and to resolve outstanding questions.

Viability measurements of individual bacteria are applied in various scopes of research and industry using approaches where propidium iodide (PI) serves as dead cell indicator. The reliability of PI uptake as a cell viability indicator for dead (PI permeable) and viable (PI impermeable) bacteria was tested using two soil bacteria, the gram 2 Sphingomonas sp. LB126 and the gram 1 Mycobacterium frederiksbergense LB501T. Bacterial proliferation activities observed via DAPI and Hoechst 33342 staining were linked to the energy charge and the proportion of dead cells as obtained by diOC 6 (3)-staining and PI-uptake, respectively. Calibration and verification experiments were performed using batch cultures grown on different substrates. PI uptake depended on the physiological state of the bacterial cells. Unexpectedly, up to 40% of both strains were stained by PI during early exponential growth on glucose when compared to 2-5% of cells in the early stationary phase of growth. The results question the utility of PI as a universal indicator for the viability of (environmental) bacteria. It rather appears that in addition to nonviable cells, PI also stains growing cells of Sphingomonas sp. and M. frederiksbergense during a short period of their life cycle. ' 2007 International Society for Analytical Cytology

ABSTRACTAmong the adaptive responses of bacteria to rapid changes in environmental conditions, those of the cell envelope are known to be the most crucial. Therefore, several mechanisms with which bacteria change their cell surface and membranes in the presence of different environmental stresses have been elucidated. Among these mechanisms, the release of outer membrane vesicles (MV) in Gram-negative bacteria has attracted particular research interest because of its involvement in pathogenic processes, such as that ofPseudomonas aeruginosabiofilm formation in cystic fibrosis lungs. In this study, we investigated the role of MV formation as an adaptive response ofPseudomonas putidaDOT-T1E to several environmental stress factors and correlated it to the formation of biofilms. In the presence of toxic concentrations of long-chain alcohols, under osmotic stress caused by NaCl, in the presence of EDTA, and after heat shock, cells of this strain released MV within 10 min in the presence of a stressor. The MV formed showed similar size and charge properties, as well as comparable compositions of proteins and fatty acids. MV release caused a significant increase in cell surface hydrophobicity, and an enhanced tendency to form biofilms was demonstrated in this study. Therefore, the release of MV as a stress response could be put in a physiological context.

Background: Tau aggregation is a multistep process. The identity of Tau species compromising cell viability remains largely unknown. Results: Analysis of Tau aggregation dynamic identifies oligomeric Tau aggregates as toxic species that impair viability. Conclusion: Membrane leakage induced by oligomeric Tau is a mechanism for toxicity. Significance: Tau belongs to the class of amyloidogenic proteins that share a common toxicity-mediating mechanism.

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