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)

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

White-rot fungi and their enzymes for the treatment of industrial dye effluents.

White-rot fungi produce various isoforms of extracellular oxidases including laccase, Mn peroxidase and lignin peroxidase (LiP), which are involved in the degradation of lignin in their natural lignocellulosic substrates. This ligninolytic system of white-rot fungi (WRF) is directly involved in the degradation of various xenobiotic compounds and dyes. This review summarizes the state of the art in the research and prospective use of WRF and their enzymes (lignin-modifying enzymes, LME) for the treatment of industrial effluents, particularly dye containing effluents. The textile industry, by far the most avid user of synthetic dyes, is in need of ecoefficient solutions for its colored effluents. The decolorization and detoxification potential of WRF can be harnessed thanks to emerging knowledge of the physiology of these organisms as well as of the biocatalysis and stability characteristics of their enzymes. This knowledge will need to be transformed into reliable and robust waste treatment processes

Degradation of dye-containing textile effluent by the agaric white-rot fungus Clitocybula dusenii

Raw mixed-dye wastewater from a textile dye-producing plant was partly decolorized by the agaric white-rot fungus, Clitocybula dusenii. The fungus had higher Mn peroxidase (MnP) and laccase activities when grown with dye effluent than in control cultures. The activity of MnP increased commensurately with the proportion of the raw dye wastewater in the medium (control: 20 U l(-1); 10% v/v effluent: 67 U l(-1); 25% v/v effluent: 130 U l(-1); and 33% v/v effluent: 180 U l(-1)). Maximal decolorization rates were achieved over 20 d at 28 degreesC using four-fold diluted dye-containing effluent on a 5 d pre-grown mycelium

TolC Is Involved in Enterobactin Efflux across the Outer Membrane of Escherichia coli

Escherichia coli excretes the catecholate siderophore enterobactin in response to iron deprivation. While the mechanisms underlying enterobactin biosynthesis and ferric enterobactin uptake and utilization are widely understood, nearly nothing is known about how enterobactin is exported from the cell. Mutant and high-performance liquid chromatography analyses demonstrated that the outer membrane channel tunnel protein TolC but none of the respective seven resistance nodulation cell division (RND) proteins CusA, AcrB, AcrD, AcrF, MdtF (YhiV), or the twin RND MdtBC (YegNO) was essential for enterobactin export across the outer membrane. Mutant E. coli strains with additional deletion of tolC or the major facilitator entS were growth deficient in iron-depleted medium. Strains with deletion of tolC or entS, but not with deletion of genes encoding RND transporters, excreted very little enterobactin into the growth medium. Enterobactin excretion in E. coli is thus probably a two-step process involving the major facilitator EntS and the outer membrane channel tunnel protein TolC. Quantitative reverse transcription-PCR analysis of gene-specific transcripts showed no significant changes in tolC expression upon iron depletion. However, iron starvation led to increased expression of the RND gene mdtF and a decrease in acrD