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Particulate cadmium (Cd) and zinc (Zn) are ubiquitous in agricultural soils of Pb–Zn mining regions. Water management serves as an important agronomic measure altering the bioavailability of Zn and Cd in soils, but how this affects particulate Cd and Zn and the underlying mechanisms remain largely unknown. Microcosm soil incubation combined with spectroscopic and microscopic characterization was conducted. During a two-year-long incubation period we observed that the concentrations of soil CaCl 2 -extractable Zn and Cd increased 3–10 times in sphalerite-spiked soils and 1–2 times in smithsonite-spiked soils under periodic flooding conditions due to the long-term dissolution of sphalerite (SP) and smithsonite (SM). However, the increase in the concentration of CaCl 2 -extractable metals (Zn: from 0.607 mg kg−1 to 1.051 mg kg−1 and Cd: from 0.047 mg kg−1 to 0.119 mg kg−1) was found only in SP-treatment under continuous flooding conditions, indicating the mobilization of metals. Ultrafiltration analysis shows that the nanoparticulate fraction of Zn and Cd in soil pore water increased 5 and 7 times in SP-treatments under continuous flooding conditions, suggesting the increment of metal pools in soil pore water. HRTEM-EDX-SAED further reveals that these nanoparticles were mainly crystalline ZnS and Zn-bearing sulfate nanoparticles in the SP-treatment and amorphous ZnCO 3 and ZnS nanoparticles in the SM-treatment. Therefore, the formation of the stable crystalline Zn-bearing nanoparticles in the SP-treatment may explain the elevation of the concentration of soil CaCl 2 -extractable Zn and Cd under continuous flooding. The potential mobility of particulate metals should therefore be expected in scenarios of continuous flooding such as paddy soils and wetland systems. • CaCl 2 -extractable Cd and Zn increased in SP-spiked soils under continuous flooding. • Formation of Cd- and Zn-bearing nano-colloids enhanced the extractability of Cd and Zn in soils. • More stable metal-bearing nano-crystals were abundant in SP- than in SM-spiked soil pore water. [ABSTRACT FROM AUTHOR]

Two phylogenetically distantly-related IncF plasmids, F and pED208, serve as important models for mechanistic and structural studies of F-like type IV secretion systems (T4SS F s) and F pili. Here, we present the pED208 sequence and compare it to F and pUMNF18, the closest match to pED208 in the NCBI database. As expected, gene content of the three cargo regions varies extensively, although the maintenance/leading regions (MLRs) and transfer (Tra) regions also carry novel genes or motifs with predicted modulatory effects on plasmid stability, dissemination and host range. By use of a Cre recombinase assay for translocation (CRAfT), we recently reported that pED208-carrying donors translocate several products of the MLR (ParA, ParB1, ParB2, SSB, PsiB, PsiA) intercellularly through the T4SS F. Here, we extend these findings by reporting that pED208-carrying donors translocate 10 additional MLR proteins during conjugation. In contrast, two F plasmid-encoded toxin components of toxin-antitoxin (TA) modules, CcdB and SrnB, were not translocated at detectable levels through the T4SS F. Remarkably, most or all of the pED208-encoded MLR proteins and CcdB and SrnB were translocated through heterologous T4SSs encoded by IncN and IncP plasmids pKM101 and RP4, respectively. Together, our sequence analyses underscore the genomic diversity of the F plasmid superfamily, and our experimental data demonstrate the promiscuous nature of conjugation machines for protein translocation. Our findings raise intriguing questions about the nature of T4SS translocation signals and of the biological and evolutionary consequences of conjugative protein transfer. • pED208 genome comparisons underscores mosaicism of F plasmids • Diversification of conjugation systems influences plasmid transfer and host range • Leading region proteins are co-translocated with the F plasmid during conjugation • Leading region proteins are translocated through heterologous conjugation systems • Conjugation systems translocate a large repertoire of proteins substrates [ABSTRACT FROM AUTHOR]

Abstract: Phosphate is ubiquitous in the environment. However, its impact on sorption of hydrophobic organic compounds in soils has received little attention. Some effects of phosphate on phenanthrene sorption were investigated in this study using two Chinese soils with contrasting properties. The presence of phosphate significantly decreased the capacity and increased the nonlinearity of phenanthrene sorption in the soils, and this sorption-inhibiting effect was more significant at high phosphate concentration. The influence of phosphate on phenanthrene sorption in the soils was governed by the release of dissolved organic carbon (DOC), particularly higher-molecular-weight and highly aromatic DOC, which tended to be enhanced in the presence of phosphate (p <0.01) as evidenced by size exclusion chromatography and specific UV absorbance analysis. Atomic force microscopy and ζ potential analysis reveal that the ringed microaggregates of DOC were disrupted into larger condensed microaggregates and the solid interfaces tended to be more hydrophilic in the presence of phosphate which also inhibited the accumulation of phenanthrene in the soils. This study for the first time points to an important role of phosphate in the sorption of phenanthrene in soils and provides substantial evidence for the mechanisms involved using a combination of microscopic and chromatographic techniques. [ABSTRACT FROM AUTHOR]

Cold plasma seed treatment can promote plant growth and enhance the resistance of agricultural crops to adverse stress. However, the effects of plasma seed treatment on the growth and phytoextraction response of plants to cadmium (Cd) remain poorly documented. Here, we have investigated the feasibility of using plasma seed treatment to enhance the biomass and Cd accumulation of three Cd-tolerant species, namely Bidens pilosa L, Solanum nigrum L. and Trifolium repens L, under different plasma treatment conditions. Possible enhancement mechanisms are also proposed according to the levels of organic acids in the roots and the Cd fractions in rhizosphere soil following different plasma treatment conditions. The optimum plasma power was 100 W (B. pilosa) or 500 W (S. nigrum and T. repens). The optimum plasma exposure time for all three species was 60 s. Plasma seed treatment under the optimum treatment conditions enhanced plant dry biomass by ~17.3–45.0% and Cd accumulation by 8.8–54.4% across all three species compared to the controls. Furthermore, the phytoremediation efficiencies, bioaccumulation factors and transfer factors of the three species also increased significantly after seed plasma treatment. The promotion of plasma treatment on the biomass and Cd accumulation of three species might be due to increased exudation of organic acids from the roots into the rhizosphere soil, thus increasing the concentrations of acid-soluble Cd to form Cd-organic acid complexes that facilitated the uptake and translocation of Cd by the plants. Results of this study revealed that cold plasma seed treatment is an environmentally friendly, economical and efficient means to develop the application of phytoremediation for Cd-contaminated soils. [Display omitted] • Cold plasma seed treatment enhanced plant biomass and Cd accumulation. • Optimum plasma power level was 100 W (B. pilosa) or 500 W (S. nigrum and T. repens). • Optimum plasma exposure time was 60 s for seeds of the three plant species. • Plasma treatment altered organic acid levels and Cd fractions in rhizosphere soils. [ABSTRACT FROM AUTHOR]

The Agrobacterium tumefaciens VirB/D4 type IV secretion system (T4SS) translocates DNA and protein substrates across the bacterial cell envelope. Six presumptive channel subunits of this T4SS (VirD4, VirB11, VirB6, VirB8, VirB2, and VirB9) form close contacts with the VirD2-T-strand transfer intermediate during export, as shown recently by a novel transfer DNA immunoprecipitation (TrIP) assay. Here, we characterize the contribution of the hydrophobic channel component VirB6 to substrate translocation. Results of reporter protein fusion and cysteine accessibility studies support a model for VirB6 as a polytopic membrane protein with a periplasmic N terminus, five transmembrane segments, and a cytoplasmic C terminus. TrIP studies aimed at characterizing the effects of VirB6 insertion and deletion mutations on substrate translocation identified several VirB6 functional domains: (i) a central region composed of a large periplasmic loop (P2) (residues 84 to 165) mediates the interaction of VirB6 with the exiting T-strand; (ii) a multi-membrane-spanning region carboxyl-terminal to loop P2 (residues 165 to 245) is required for substrate transfer from VirB6 to the bitopic membrane subunit VirB8; and (iii) the two terminal regions (residues 1 to 64 and 245 to 290) are required for substrate transfer to the periplasmic and outer membrane-associated VirB2 and VirB9 subunits. Our findings support a model whereby the periplasmic loop P2 comprises a portion of the secretion channel and distinct domains of VirB6 participate in channel subunit interactions required for substrate passage to the cell exterior. [Copyright &y& Elsevier]

Mining restoration is a key in ecological sustainable development. Ecological stoichiometry and homeostasis in the plant-litter-soil system remain largely unknown but are vital for developing guidelines for vegetation restoration in mining subsidence areas in arid northwest China. Six re-vegetation types comprising stands of Amorpha fruticosa , Hippophae rhamnoides , Xanthoceras sorbifolium , Cerasus humilis , Cerasus szechuanica and Pinus sylvestris were selected for study. We investigated changes in the contents and stoichiometry of C, N and P in roots, stems, leaves, litter and soil in order to understand stoichiometric homeostasis and the factors driving nutrient cycling. The stoichiometry of the plant-soil system varied markedly with different re-vegetation types. The coupling of plant and soil N:P ratios indicates that the concentrations of C, N and P are usually equilibrated. Leave N:P ratios in all re-vegetation types studies indicate that plant growth was N-limited. 1/H only in H. rhamnoides and A. fruticosa (nitrogen-fixing plants) was simultaneously categorized as 'homeostatic' and this might mitigate the N-limitation. Soil easily-extractable glomalin, hyphal density and available phosphorus were key factors shifting the ecological stoichiometry. The study demonstrates that nitrogen-fixing re-vegetation species can promote stoichiometric homeostasis and the results contribute to guidance for vegetation restoration practices in mining subsidence areas. • Re-vegetation types had significant effects on the stoichiometry of the plant-litter-soil system and soil properties. • Nitrogen-fixing re-vegetation with a significantly higher N:P ratio mitigated N-limitation. • Mycorrhizal fungi may help to elucidate the allocation of ecological stoichiometry and stoichiometric homeostasis. [ABSTRACT FROM AUTHOR]

Blending waste biomass for co-pyrolysis is generally regarded as a promising method for reduced-volume, value-added, and hazard-free treatment of sewage sludge. Hence, a comparison was made of the co-pyrolysis of sewage sludge with rice husk and with bamboo sawdust (1:1, w/w) at 400 and 700 °C and the properties and behaviors of selected metals in the corresponding biochars. Biochar produced by co-pyrolysis with both biomass wastes had larger (5 × 5 rectangle) aromatic clusters than did the sewage sludge biochar (4 × 4 rectangle) using the rectangle-like model on the basis of biochar molar H/C ratio, indicating increased aromaticity of the co-pyrolyzed biochars. Moreover, the molar O/C ratio of the sewage sludge-bamboo biochar was much lower than that of the sewage sludge-husk biochar, especially after pyrolysis at 700 °C (0.02 vs 0.27), suggesting greater recalcitrance to ageing. Co-pyrolysis of sewage sludge with husk invariably resulted in a higher percentage of metals studied in the residual fraction than co-pyrolysis with sawdust at the same temperature, leading to a lower risk index (14.2) because of the maximum metal encapsulation in the sewage sludge-husk biochar at 700 °C. Overall, co-pyrolysis of sewage sludge with husk provided higher metal immobilization but apparently lower biochar stability than co-pyrolysis with sawdust. These results provide an alternatively practical strategy for the safe disposal of sewage sludge and biomass wastes. • Co-pyrolysis of sewage sludge with rice husk or bamboo sawdust was assessed. • Co-pyrolysis of sewage sludge with sawdust was preferable for biochar aromaticity. • Co-pyrolysis of sewage sludge and husk was preferable for metal immobilization. • Biochar aromaticity and metal stabilization was achieved by co-pyrolysis at 700 °C. [ABSTRACT FROM AUTHOR]