Extensive use and inadequate disposal of chloroethenes have led to prevalent groundwater contamination worldwide. The occurrence of the lesser chlorinated ethenes [i.e. vinyl chloride (VC) and cis-1,2-dichloroethene (cDCE)] in groundwater is primarily a consequence of incomplete anaerobic reductive dechlorination of the more highly chlorinated ethenes (tetrachloroethene and trichloroethene). VC and cDCE are toxic and VC is a known human carcinogen. Therefore, their presence in groundwater is undesirable. In situ cleanup of VC- and cDCE-contaminated groundwater via oxidation by aerobic microorganisms is an attractive and potentially cost-effective alternative to physical and chemical approaches. Of particular interest are aerobic bacteria that use VC or cDCE as growth substrates (known as the VC- and cDCE-assimilating bacteria). Bacteria that grow on VC are readily isolated from contaminated and uncontaminated environments, suggesting that they are widespread and influential in aerobic natural attenuation of VC. In contrast, only one cDCE-assimilating strain has been isolated, suggesting that their environmental occurrence is rare. In this review, we will summarize the current knowledge of the physiology, biodegradation pathways, genetics, ecology, and evolution of VC- and cDCE-assimilating bacteria. Techniques (e.g. PCR, proteomics, and compound-specific isotope analysis) that aim to determine the presence, numbers, and activity of these bacteria in the environment will also be discussed.

The increasing likelihood of silver nanoparticle (AgNP) releases to the environment highlights the importance of understanding AgNP interactions with plants, which are cornerstones of most ecosystems. In this study, poplars (Populus deltoides × nigra) and Arabidopsis thaliana were exposed hydroponically to nanoparticles of different sizes (PEG-coated 5 and 10 nm AgNPs, and carbon-coated 25 nm AgNPs) or silver ions (Ag(+), added as AgNO₃) at a wide range of concentrations (0.01 to 100 mg/L). Whereas all forms of silver were phytotoxic above a specific concentration, a stimulatory effect was observed on root elongation, fresh weight, and evapotranspiration of both plants at a narrow range of sublethal concentrations (e.g., 1 mg/L of 25 nm AgNPs for poplar). Plants were most susceptible to the toxic effects of Ag(+) (1 mg/L for poplar, 0.05 mg/L for Arabidopsis), but AgNPs also showed some toxicity at higher concentrations (e.g., 100 mg/L of 25 nm AgNPs for poplar, 1 mg/L of 5 nm AgNPs for Arabidopsis) and this susceptibility increased with decreasing AgNP size. Both poplars and Arabidopsis accumulated silver, but silver distribution in shoot organs varied between plant species. Arabidopsis accumulated silver primarily in leaves (at 10-fold higher concentrations than in the stem or flower tissues), whereas poplars accumulated silver at similar concentrations in leaves and stems. Within the particle subinhibitory concentration range, silver accumulation in poplar tissues increased with exposure concentration and with smaller AgNP size. However, compared to larger AgNPs, the faster silver uptake associated with smaller AgNPs was offset by their toxic effect on evapotranspiration, which was exerted at lower concentrations (e.g., 1 mg/L of 5 nm AgNPs for poplar). Overall, the observed phytostimulatory effects preclude generalizations about the phytotoxicity of AgNPs and encourage further mechanistic research.

Polaromonas sp. strain JS666 can grow on cis-1,2-dichloroethene (cDCE) as a sole carbon and energy source and may be useful for bioremediation of chlorinated solvent-contaminated sites. Analysis of the genome sequence of JS666 (5.9 Mb) shows a bacterium well adapted to pollution that carries many genes likely to be involved in hydrocarbon and xenobiotic catabolism and metal resistance. Clusters of genes coding for haloalkane, haloalkanoate, n-alkane, alicyclic acid, cyclic alcohol, and aromatic catabolism were analyzed in detail, and growth on acetate, catechol, chloroacetate, cyclohexane carboxylate, cyclohexanol, ferulate, heptane, 3-hydroxybenzoate, hydroxyquinol, gentisate, octane, protocatechuate, and salicylate was confirmed experimentally. Strain JS666 also harbors diverse putative mobile genetic elements, including retrons, inteins, a miniature inverted-repeat transposable element, insertion sequence transposases from 14 families, eight genomic islands, a Mu family bacteriophage, and two large (338-and 360-kb) plasmids. Both plasmids are likely to be self-transferable and carry genes for alkane, alcohol, aromatic, and haloacid metabolism. Overall, the JS666 genome sequence provides insights into the evolution of pollutant-degrading bacteria and provides a toolbox of catabolic genes with utility for biotechnology.

Silver nanoparticles have traditionally been synthesised using physical and chemical methods, often requiring expensive equipment and reagents that pose risks to the environment. This work provides a green method for the biosynthesis of silver nanoparticles using leaf extracts from upland cress: Barbarea verna. Natural reducing agents within the leaf extracts of upland cress reduce silver ions from silver nitrates, resulting in the formation of silver nanoparticles. The silver nanoparticles were purified using centrifugation and extraction using Triton X-114. The resulting nanoparticles were characterised using UV-Vis spectroscopy, dynamic light scattering, atomic force microscopy, and scanning electron microscopy. Silver nanoparticles were shown to have a diameter of 30-40 nm with a characteristic UV-Vis absorption peak at 420 nm. Antimicrobial properties of the synthesised silver nanoparticles were also confirmed using S. epidermis and E. coli bacteria.

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