The release of silver nanoparticles (AgNPs) in the environment has raised concerns about their effects on living organisms, including plants. In this study, changes in gene expression in Arabidopsis thaliana exposed to polyvinylpyrrolidone-coated AgNPs and silver ions (Ag(+)) were analyzed using Affymetrix expression microarrays. Exposure to 5 mg/L AgNPs (20 nm) for 10 days resulted in upregulation of 286 genes and downregulation of 81 genes by reference to nonexposed plants. Exposure to 5 mg/L Ag(+) for 10 days resulted in upregulation of 84 genes and downregulation of 53 genes by reference to nonexposed plants. Many genes differentially expressed by AgNPs and Ag(+) were found to be involved in the response of plants to various stresses: upregulated genes were primarily associated with the response to metals and oxidative stress (e.g., vacuolar cation/proton exchanger, superoxide dismutase, cytochrome P450-dependent oxidase, and peroxidase), while downregulated genes were more associated with response to pathogens and hormonal stimuli [e.g., auxin-regulated gene involved in organ size (ARGOS), ethylene signaling pathway, and systemic acquired resistance (SAR) against fungi and bacteria]. A significant overlap was observed between genes differentially expressed in response to AgNPs and Ag(+) (13 and 21% of total up- and downregulated genes, respectively), suggesting that AgNP-induced stress originates partly from silver toxicity and partly from nanoparticle-specific effects. Three highly upregulated genes in the presence of AgNPs, but not Ag(+), belong to the thalianol biosynthetic pathway, which is thought to be involved in the plant defense system. Results from this study provide insights into the molecular mechanisms of the response of plants to AgNPs and Ag(+).

Transgenic plants and associated bacteria constitute a new generation of genetically modified organisms for efficient and environmental-friendly treatment of soil and water contaminated with polychlorinated biphenyls (PCBs). This review focuses on recent advances in phytoremediation for the treatment of PCBs, including the development of transgenic plants and associated bacteria. Phytoremediation, or the use of higher plants for rehabilitation of soil and groundwater, is a promising strategy for cost-effective treatment of sites contaminated by toxic compounds, including toxic PCBs. Plants can help mitigate environmental pollution by PCBs through a range of mechanisms: besides uptake from soil (phytoextraction), plants are capable of enzymatic transformation of PCBs (phytotransformation); by releasing a variety of secondary metabolites, plants also enhance the microbial activity in the root zone, improving biodegradation of PCBs (rhizoremediation). However, because of their hydrophobicity and chemical stability, PCBs are only slowly taken up and degraded by plants and associated bacteria, resulting in incomplete treatment and potential release of toxic metabolites into the environment. Moreover, naturally occurring plant-associated bacteria may not possess the enzymatic machinery necessary for PCB degradation. In order to overcome these limitations, bacterial genes involved in the metabolism of PCBs, such as biphenyl dioxygenases, have been introduced into higher plants, following a strategy similar to the development of transgenic crops. Similarly, bacteria have then been genetically modified that exhibit improved biodegradation capabilities and are able to maintain stable relationships with plants. Transgenic plants and associated bacteria bring hope for a broader and more efficient application of phytoremediation for the treatment of PCBs.

A pink-pigmented symbiotic bacterium was isolated from hybrid poplar tissues (Populus deltoides ؋ nigra DN34). The bacterium was identified by 16S and 16S-23S intergenic spacer ribosomal DNA analysis as a Methylobacterium sp. (strain BJ001). The isolated bacterium was able to use methanol as the sole source of carbon and energy, which is a specific attribute of the genus Methylobacterium. The bacterium in pure culture was shown to degrade the toxic explosives 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazene (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5-tetrazocine (HMX

Methylobacterium populi sp. nov., a novel aerobic, pink-pigmented, facultatively methylotrophic, methane-utilizing bacterium isolated from poplar trees (Populus deltoides6nigra DN34) Species of the genus Methylobacterium are strictly aerobic, facultatively methylotrophic, Gram-negative, rod-shaped bacteria that are able to grow on one-carbon compounds (e.g. methanol or methylamine), as well as on a variety of C 2 , C 3 and C 4 substrates (Green, 1992). Only the type species, Methylobacterium organophilum, has been shown to use methane as the sole source of carbon and energy (Patt et al., 1976). The genus Methylobacterium belongs to the a2 subclass of the Proteobacteria and currently consists of 14 species with validly published names (Heumann, 1962;Ito & Iizuka, 1971;Kouno & Ozaki, 1975;Patt et al., 1976;Rock et al., 1976;Austin & Goodfellow, 1979;Urakami & Komagata, 1984;Bousfield & Green, 1985;Green et al., 1988;Urakami et al., 1993; Wood et al., 1998; Doronina et al., 2000 Doronina et al., , 2002 McDonald et al., 2001;Sy et al., 2001). Members of the genus Methylobacterium are distributed in a wide variety of natural and man-made environments, including soil, air, dust, freshand marine water and sediments, water supplies, bathrooms, air-conditioning systems and masonry (Hiraishi et al., 1995;Trotsenko et al., 2001). Some species have been described as opportunistic human pathogens (Truant et al., 1998; Hornei et al., 1999). In addition, methylotrophic bacteria are frequently associated with terrestrial and aquatic plants, where they colonize roots and leaf surfaces (Austin et al., 1978;Yoshimura, 1982;Corpe & Rheem, 1989;Trotsenko et al., 2001;Lidstrom & Chistoserdova, 2002). The association of Methylobacterium species with plants seems to rely on a symbiotic relationship between the bacterium and the plant host. Plants produce methanol The GenBank/EMBL/DDBJ accession number for the 16S and 16S-23S IGS rDNA sequence of strain BJ001 T is AY251818.Tissue culture images, photomicrographs, 16S and 16S-23S IGS rDNA sequences of BJ001 T , sequence similarity matrices, carbon-and nitrogen-source utilization data and enzymic reactions of BJ001 T are available as supplementary material in IJSEM Online.Abbreviations: IGS, intergenic spacer; SEM, scanning electron microscope.

Hydroxylated polychlorinated biphenyls (OH-PCBs) are produced in the environment by the oxidation of PCBs through a variety of mechanisms, including metabolic transformation in living organisms and abiotic reactions with hydroxyl radicals. As a consequence, OH-PCBs have been detected in a wide range of environmental samples, including animal tissues, water, and sediments. OH-PCBs have recently raised serious environmental concerns because they exert a variety of toxic effects at lower doses than the parent PCBs and they are disruptors of the endocrine system. Although evidence has accumulated about the widespread dispersion of OH-PCBs in various compartments of the ecosystem, little is currently known about their biodegradation and behavior in the environment. OH-PCBs are today increasingly considered as a new class of environmental contaminants that possess specific chemical, physical, and biological properties not shared with the parent PCBs. This article reviews recent findings regarding the sources, fate, and toxicities of OH-PCBs in the environment.

In view of compliance with increasingly stringent environmental legislation imposed by regional, national, and supranational (e.g., European Union) authorities, innovative environmental technologies for the treatment of dye-contaminated effluents are necessary in the color industry. In this study, effluents of an industrial dye producer were subjected to distinct treatment trains following an initial qualitative characterization. The effectiveness of ozonation and a treatment using white rot fungi (WRF) and their enzymes were compared with respect to parameters such as residual color, toxicity on human cells, and genotoxicity. A combined ozonation/WRF process was also investigated. The effluent exhibited significant toxicity that was reduced by only 10% through ozonation, whereas the fungal treatment achieved a 35% reduction. A combined treatment (ozone/WRF) caused an abatement of the toxicity by more than 70%. In addition, the initial genotoxicity of the effluent was still present after the ozone treatment, while it was completely removed through the fungal treatment.

Poplar tissue cultures and leaf crude extracts (Populus deltoides x nigra DN-34) were exposed to [U-14C]hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and incubated under light and in the dark. Poplar tissue cultures were able to partially reduce RDX to hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX) and hexahydro-1,3-dinitroso-5-nitro-1,3,5-triazine (DNX), regardless of the presence or absence of light. However, further transformation of RDX, MNX, and DNX required exposure to light and resulted in the formation of formaldehyde (CH2O), methanol (CH3OH), and carbon dioxide (CO2). Similarly, transformation of RDX by poplar leaf crude extracts required exposure to light. Neither reduction of RDX to MNX and DNX nor mineralization into CO2 were recorded in crude extracts, even when exposed to light, suggesting that both processes were light-independent and required intact plant cells. Control experiments without plant material showed that RDX was partially transformed abiotically, by the sole action of light, but to a lesser extent than in the presence of plant crude extracts, suggesting the intervention of plant subcellular structures through a light-mediated mechanism. Poplar tissue cultures were also shown to mineralize 14CH2O and 14CH3OH, regardless of the presence or absence of light. These results suggest that transformation of [U-14C]RDX by plant tissue cultures may occur through a three-step process, involving (i) a light-independent reduction of RDX to MNX and DNX by intact plant cells; (ii) a plant/light-mediated breakdown of the heterocyclic ring of RDX, MNX, or DNX into C1-labeled metabolites (CH2O and CH3OH); and (iii) a further light-independent mineralization of C1-labeled metabolites by intact plant cells. This is the first time that a significant mineralization of RDX into CO2 by light-exposed plant tissue cultures is reported.

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