Copper oxide nanoparticles induce oxidative stress, DNA strand breaks and laccase activity in aquatic fungi

This work was supported by the DAAD-FCT-2010-2011 project (Micro)analysis of nanoparticles on aquatic fungi and A. Pradhan received the FCT grant SFRH/BD/45614/2008

Responses of freshwater microbial decomposers to copper oxide nanoparticles

Intensive use of nano metals increases the chance of their release into natural watercourses and may pose at risk aquatic biota and their ecological functions. In streams, microbial decomposers, predominantly aquatic fungi, play a crucial role in organic matter turnover. We investigated the impact of nano CuO on stream-dwelling microbial decomposers of leaf litter by examining i) structure and functions of fungal and bacterial communities retrieved from a non-polluted stream, and ii) the physiological and cellular responses of fungal populations isolated from metal-polluted and non-polluted streams. Results were compared to those obtained after exposure to Cu2+. The exposure to nano CuO (≤500 ppm, 4 levels) and Cu2+ (≤30 ppm, 4 levels) significantly reduced leaf decomposition, bacterial and fungal biomass, fungal reproduction and diversity. Cluster analysis of DGGE based on DNA fingerprints showed that both forms of copper induced shifts in community structure. However, impacts were stronger for bacteria than fungi. At the cellular level, increased nano CuO concentrations (≤200 ppm, 5 levels) induced activity of laccase by single fungal populations. Fungal populations from non-polluted streams were more affected by nano CuO than those from polluted streams, as shown by stronger inhibition of biomass production, accumulation of reactive oxygen species (ROS), plasma membrane disruption and DNA strand breaks. Results showed that nano forms are less toxic than ionic forms, and further suggest that the toxicity of nano CuO to freshwater microbial decomposers may occur due to induction of oxidative stress.FEDER-POFC-COMPETE and FCT supported this study (PEst-C/BIA/UI4050/2011, PTDC/AAC- AMB/121650/2010 and FCT-DAAD: 2010-2011) and AP (SFRH/BD/45614/2008)

Effects of nano CuO on aquatic decomposers: from community to cellular responses

ntensive use of metal nanoparticles increases the chance of their release into freshwaters that may pose risk to biota and associated ecological processes. In streams, microbes play a key role in detritus foodwebs transferring carbon and energy from plant litter to invertebrate shredders. Here, we investigated the effects of nano CuO (<50 nm, nanopowder, Sigma) on aquatic detritus foodwebs by examining i) leaf-litter decomposition by bacterial and fungal communities, ii) cellular damage and physiological responses of fungal populations collected from non-polluted and metal-polluted streams, and iii) survival, growth and leaf consumption by an invertebrate shredder. Results were compared with those obtained with ionic copper. Stream-dwelling microbial communities were obtained by immersion of leaves in a non- polluted stream (Portugal). Microbial communities were exposed in microcosms to nano CuO (≤ 500 mg L-1) and Cu2+ (≤ 30 mg L-1). Leaf decomposition decreased with increasing concentrations of nano and ionic copper. Both copper forms reduced biomass of bacteria and fungi, and fungal reproduction. Cu2+ had stronger effects than nano CuO. Exposure to Cu2+ and nano CuO led to a decrease in fungal diversity and to shifts in species dominance. Increased concentrations of nano CuO (≤ 100 mg L–1) stimulated extracellular laccase activity by fungi. Populations from non-polluted streams were more affected by nano CuO than those from polluted streams, as shown by a stronger inhibition of biomass production, higher Cu adsorption, higher levels of reactive oxygen species and DNA strand breaks. Acute lethality tests suggested low toxicity of nano CuO to the shredder Allogamus ligonifer. However, sublethal concentrations of nano CuO (≤ 75 mg L–1) strongly reduced leaf consumption and invertebrate growth under aqueous and dietary exposure. Concentration of leached Cu2+ in the stream water increased with increasing nano CuO concentration. Exposure to 75 mg L–1 of nano CuO via water or food led to higher Cu adsorption and accumulation in larvae. Moreover, leached Cu2+ appeared to have a role in inducing toxicity of nano CuO.Acknowledgement: FEDER-POFC-COMPETE, DAAD and FCT supported this work (PEst-C/BIA/UI4050/2011, FCT-DAAD-2010-2011, NANOECOTOX-PTDC/AAC-AMB/121650/2010) and A. Pradhan (SFRH/BD/45614/2008)

Evidence for Lignocellulose-Decomposing Enzymes in the Genome and Transcriptome of the Aquatic Hyphomycete Clavariopsis aquatica

Fungi are ecologically outstanding decomposers of lignocellulose. Fungal lignocellulose degradation is prominent in saprotrophic Ascomycota and Basidiomycota of the subkingdom Dikarya. Despite ascomycetes dominating the Dikarya inventory of aquatic environments, genome and transcriptome data relating to enzymes involved in lignocellulose decay remain limited to terrestrial representatives of these phyla. We sequenced the genome of an exclusively aquatic ascomycete (the aquatic hyphomycete Clavariopsis aquatica), documented the presence of genes for the modification of lignocellulose and its constituents, and compared differential gene expression between C. aquatica cultivated on lignocellulosic and sugar-rich substrates. We identified potential peroxidases, laccases, and cytochrome P450 monooxygenases, several of which were differentially expressed when experimentally grown on different substrates. Additionally, we found indications for the regulation of pathways for cellulose and hemicellulose degradation. Our results suggest that C. aquatica is able to modify lignin to some extent, detoxify aromatic lignin constituents, or both. Such characteristics would be expected to facilitate the use of carbohydrate components of lignocellulose as carbon and energy sources

Application of the aquatic fungus Phoma sp. (DSM22425) in bioreactors for the treatment of textile dye model effluents

Background: Textile dyes are hardly removed from effluents by conventional wastewater treatment but can be degraded by a number of physicochemical processes nevertheless having specific limitations. The development of bioremediation processes may provide a viable alternative. Results: Resting cells of three aquatic fungal strains, Alternaria sp. (Tt-S1), Coniothyrium sp. (Kl-S5) and Phoma sp. (DSM22425), were evaluated for their ability to decolorize model effluents of different dye application classes. Phoma sp., who decolorized all four applied model wastewaters (MWW), was immobilized on a polyester-based fleece material originally designed for the use as cooker-hood filters, and applied in internal loop airlift and bubble column reactors in repeated batch mode under sterile and nonsterile conditions. Depending on the applied MWW and bioreactor setup, a decolorization by more than 90 % was achieved in three consecutive treatment cycles and a total operation time of 16 days. In an upscaled reactor (10 L), Phoma sp. decolorized a MWW for acid dyes by 61 %. Chemical oxygen demand of the MWW was reduced by 36 %. Conclusion: The presented results underline the potential of aquatic fungi for the development of textile dyeing effluent treatment processes

Cosmogenic 26Al in the atmosphere and the prospect of a 26Al/10Be chronometer to date old ice

Cosmogenic radionuclides in the one-million-year half-life range offer unique possibilities for age determinations in geophysics. In measurements where the radioactive decay is being utilized as a clock, uncertainties in age determinations may be reduced if the ratio of two radioisotopes with different half-lives can be used as a chronometer. In this work we investigate the atomic ratio of atmospheric 26Al (t1/2= 0.717 Ma) to 10Be (t1/2=1.386 Ma) measured with accelerator mass spectrometry (AMS), and its potential as a chronometer for dating old ice. The 26Al/10Be ratio decreases with an effective half-life of t1/2(26Al/10Be)= 1.49 Ma. For its application as a chronometer, the atmospheric 26Al/10Be ratio has to be well characterized. However, the properties of atmospheric 26Al have been understood only poorly so far. At the VERA AMS facility of the University of Vienna, a first systematic study of the global variations of the 26Al/10Be ratio in the atmosphere and in surface firn has been carried out, and pilot measurements of the 26Al/10Be ratio in deep Antarctic ice have been performed. Our results indicate that this ratio is globally constant to within 5% in the atmosphere and in surface firn with a mean value of 1.89×10−3. The data also suggest that non-atmospheric sources of 26Al, such as extraterrestrial, in situ produced or re-suspended 26Al, do not contribute significantly to the observed 26Al/10Beratio. In addition, atmospheric mixing seems to exert only aminor influence. In a first application of the method,26Al/10Be ratios were measured in chips collected in connection with the drilling of the lowest part of an ice core (2250 to 2760 m) in Dronning Maud Land,Antarctica. Surprisingly, variable 26Al/10Be ratios ranging between0.5 and up to 2 times the atmospheric ratio were found at different locations in this deep ice core. While the cause for the ratios higher than atmospheric remains unexplained so far, the ratios lower than atmospheric may be caused by radioactive decay, allowing a first dating attempt using the 26Al/10Be ratio. Thus, at an ice depthof 2760 m an approximate date of (6.7±2.6)×105years was established