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The role of rhizobia in alleviating cadmium (Cd) stress in woody legumes is still unclear. Therefore, two types of black locust (Robinia pseudoacacia L.) with high and low Cd accumulation abilities were selected from 11 genotypes in China, and the effects of rhizobium (Mesorhizobium huakuii GP1T11) inoculation on the growth, CO 2 and H 2 O gas exchange parameters, Cd accumulation, and the absorption of mineral elements of the high (SX) and low Cd-accumulator (HB) were compared. The results showed that rhizobium-inoculation significantly increased biomass, shoot Cd contents, Cd accumulation, root-to-shoot translocation factor (TF) and the absorption and accumulation of mineral elements in both SX and HB. Rhizobium-inoculation increased chlorophyll a and carotenoid contents, and the intercellular carbon dioxide concentrations in HB plants. Under Cd exposure, the high-accumulator SX exhibited a significant decrease in photosynthetic CO 2 fixation (Pn) and an enhanced accumulation of Cd in leaves, but coped with Cd exposure by increasing chlorophyll synthesis, regulating stomatal aperture (Gs), controlling transpiration (Tr), and increasing the absorption and accumulation of mineral elements. In contrast, the low-accumulator HB was more sensitive to Cd exposure despite preferential accumulation of Cd in roots, with decreased chlorophyll and carotenoid contents, but significantly increased root biomass. Compared to the low-accumulator HB, non-inoculated Cd-exposed SX plants had higher chlorophyll contents, and rhizobium-inoculated Cd-exposed SX plants had higher Pn , Tr , and Gs as well as higher levels of P, K, Fe, Ca, Zn, and Cu. In conclusion, the high- and low-Cd-accumulator exhibited different physiological responses to Cd exposure. Overall, rhizobium-inoculation of black locust promoted the growth and heavy metal absorption, providing an effective strategy for the phytoremediation of heavy metal-contaminated soils by this woody legume. [Display omitted] • The presence of rhizobia significantly enhanced Cd accumulation. • Rhizobium inoculation increased Cd root-to-shoot TF. • Rhizobium inoculation promoted mineral element absorption. • Rhizobium inoculation enhanced the tolerance of low-Cd accumulator to Cd. • Black locust can be a potential woody plant in phytoremediation. [ABSTRACT FROM AUTHOR]

Rice consumption is an essential cause of mercury (Hg) exposure for humans in Asia. However, the mechanism of Hg transport and accumulation in rice plants (Oryza sativa L.) remains unclear. Here, rice genotypes with contrasting Hg uptake and translocation abilities, i.e. H655 (high Hg-accumulator) and H767 (low Hg-accumulator), were selected from 261 genotypes. Through comparative physiological and transcriptome analyses, we investigated the processes responsible for the relationship between Hg accumulation, transport and tolerance. The results showed significant stimulation of antioxidative metabolism, particularly glutathione (GSH) accumulation, and up-regulated expression of regulatory genes of glutathione metabolism for H655, but not for H767. In addition, up-regulated expression of GSH S-transferase (GST) and OsPCS1 in H655 that catalyzes the binding of Hg and GSH, enhances the Hg detoxification capacity, while high-level expression of YSL2 in H655 enhances the transport ability for Hg. Conclusively, Hg accumulation in rice is a consequence of enhanced expression of genes related to Hg binding with GSH and Hg transport. With these results, the present study contributes to the selection of rice genotypes with limited Hg accumulation and to the mitigation of Hg migration in food chains thereby enhancing nutritional safety of Hg-polluted rice fields. [Display omitted] • High and low Hg-accumulators (H655 and H767) were screened from 261 rice genotypes. • Antioxidant capacity of H655 in response to Hg stress was stronger than H767. • Glutathione metabolism responded more exclusively to Hg stress in H655. • Transporter contributed to Hg accumulation difference between H655 and H767. [ABSTRACT FROM AUTHOR]

Anaerobic activated sludge is rich in humic substances and water, leading to significant differences in the stability of metagenomic DNA and metatranscriptomic RNA. Thus, it is of great difficulty to exact high-quality and high-yield DNA and RNA from them, especially those cultured at a wide range of temperatures. Here, we established fast and effective DNA and RNA extraction methods based on current commercial kits. The modified methods combined liquid nitrogen grinding with kits, achieving notable improvements in concentrations, yields, purity and integrities for both DNA and RNA. The ratios of OD260/280 of the metagenomic DNA were between 1.81 ± 0.03 and 1.83 ± 0.02, while OD260/280 and OD260/230 of the metatranscriptomic RNA ranged from 1.96 ± 0.01 to 2.13 ± 0.03 and from 1.94 ± 0.02 to 2.30 ± 0.03 respectively. Metagenomic DNA and metatranscriptomic RNA obtained by the modified methods perfectly met the requirements of second- and third-generation sequencing, providing valuable reference for extracting high-quality metagenomic DNA and metatranscriptomic RNA from environmental samples of high water content and humic substances under temperatures ranging from 18 °C to 52 °C. • Liquid nitrogen grinding combined with kits generated high-quality DNA/RNA. • DNA/RNA extracted improved greatly in concentration, yield, purity and integrity. • The methods are suitable for sludge at a wide range of temperatures. [ABSTRACT FROM AUTHOR]

Bioelectrochemistry system (BES) provides a new strategy for the improvement of low temperature anaerobic digestion (AD) for methane production. In this study, the BES with carbon brushes as electrodes was operated at 15 °C to analyze the changes of microbial abundance and functional genes. The microbial community structure showed that the application of voltage had no effect to type and relative abundance of bacteria based on 16S-rRNA sequencing. Metatranscriptomic analyses revealed that significantly enhanced the abundance of fermentation bacteria in the fluid activated sludge, and the relative abundance of biosynthesis of other secondary metabolites (61.56%) was also highly expressed. More than that, the abundance of electricigens (Pseudomonas , Syntrophomonas) was also enriched in the BES system. These electricigens could interact with methanogens to promote electron transfer by direct interspecies electron transfer (DIET). The expression level of functional enzyme related to electron transport was increased at the anode (30.60%), but decreased at the cathode (−33.84%). Analysis of methanogens found that the application of voltage decreased the relative abundance of Methanosarcina and promoted the enrichment of Methanothrix. At 15 ℃, acetoclastic was the mainly methanogenic pathway. What's more, the application of voltage could enhance the acetoclastic and inhibited the hydrogenotrophic and the methylotrophic pathway. Further, the acetoclastic pathway was changed from acetate kinase (EC: 2.7.2.1) and phosphate acetyltransferase (EC: 2.3.1.8) to acetate-CoA ligase (EC: 6.2.1.1) by applied voltage. These results are conducive to the further development of low-temperature AD treatment technology. [Display omitted] • Methahnosarcina and Methanothrix were dominated in DNC and SC reactor, respectively. • The applied voltage increased the abundance of electroactive microorganisms. • The application of voltage promoted the acetoclastic pathway at low temperature. • The SC reactor achieved acetate to acetyl-CoA by acetate-CoA ligase. • The DNC reactor was through acetate kinase and phosphate acetyltransferase. [ABSTRACT FROM AUTHOR]

[Display omitted] • Acetoclastic pathway was most important in low-temperature MES. • Methahnosarcina and Methanothrix were enriched in DC and SC reactor, respectively. • Electroactive bacteria Syntrophomonas , Pseudomonas and Bacteroides were dominated. • The single-chamber MES achieve acetate to acetyl-CoA by acetate-CoA ligase. • The dual-chamber MES was by acetate kinase and phosphate acetyltransferase. In this study, single-chamber and dual-chamber Microbial electrosynthesis (MES) with carbon fiber brushes as electrodes were operated at 15°C to compare and analyze the difference in methanogenic performance. Metatranscriptomic analysis showed that the relative abundance of electroactive microorganisms Syntrophomonas , Pseudomonas and Bacteroides in each group exceeded 90%, while the abundance of Geobacter was less than 4%. Acetoclastic methanogens Methahnosarcina was more enriched in dual-chamber MES (61.74%~70.42%), and Methanothrix showed higher abundance in single-chamber MES (33.44%~51.71%). Methahnosarcina and Methanothrix could interact with electroactive microorganisms to improve the electron transfer efficiency through direct interspecies electron transfer (DIET). Analysis of the methane metabolic pathways of low-temperature MES found acetoclastic pathway was domination, and single-chamber MES achieved acetate to acetyl-CoA through acetate-CoA ligase (EC: 6.2.1.1), whereas dual-chamber MES was by acetate kinase (EC: 2.7.2.1) and phosphate acetyltransferase (EC: 2.3.1.8). These results are beneficial to further research on the treatment of low-temperature wastewater. [ABSTRACT FROM AUTHOR]

[Display omitted] • Methylators were dominating in rice rhizosphere, rather than the bulk soil. • Hg-promoted methylators are key taxa in the rhizosphere at the flowering stage. • In planta demethylation and methylation in rice roots are possible. • Desulfovibrionaceae may play an important role in Hg detoxification of rice. The plant microbiota can affect plant health and fitness by promoting methylmercury (MeHg) production in paddy soil. Although most well-known mercury (Hg) methylators are observed in the soil, it remains unclear how rice rhizosphere assemblages alter MeHg production. Here, we used network analyses of microbial diversity to identify bulk soil (BS), rhizosphere (RS) and root bacterial networks during rice development at Hg gradients. Hg gradients greatly impacted the niche-sharing of taxa significantly relating to MeHg/THg, while plant development had little effect. In RS networks, Hg gradients increased the proportion of MeHg-related nodes in total nodes from 37.88% to 45.76%, but plant development enhanced from 48.59% to 50.41%. The module hub and connector in RS networks included taxa positively (Nitrososphaeracea, Vicinamibacteraceae and Oxalobacteraceae) and negatively (Gracilibacteraceae) correlating with MeHg/THg at the blooming stage. In BS networks, Deinococcaceae and Paludibacteraceae were positively related to MeHg/THg, and constituted the connector at the reviving stage and the module hub at the blooming stage. Soil with an Hg concentration of 30 mg kg−1 increased the complexity and connectivity of root microbial networks, although microbial community structure in roots was less affected by Hg gradients and plant development. As most frequent connector in root microbial networks, Desulfovibrionaceae did not significantly correlate with MeHg/THg, but was likely to play an important role in the response to Hg stress. [ABSTRACT FROM AUTHOR]

Some thiols, such as cysteine (CYS) at moderate concentrations (10–500 µM), can enhance methylmercury (MeHg) formation by Geobacter sulfurreducens PCA, whereas others such as dithiol 2,3-dimercaptopropanesulfonate (DMPS) and 2,3-dimercaptosuccinic acid (DMSA) abolish mercury [Hg(II)] methylation. Little is known, however, about whether Hg(II) methylation could be enhanced or inhibited by the presence of mixed thiol ligands at low concentrations observed in the environment. Surprisingly we found that mixing CYS (1 µM) with DMPS (0.025–0.5 µM) or DMSA (0.025–1 µM) substantially increased MeHg production by 1.5–3.5-fold, compared to the no-thiol control, whereas complexation with a single DMPS, or DMSA, or CYS (1 µM) strongly inhibited Hg(II) methylation. Pre-equilibration between Hg(II) and thiols before the addition of cells was necessary to observe enhanced methylation. Spectroscopic analyses indicated the formation of mixed or heteroleptic coordinated Hg(II)-S 3 /S 4 complexes, which likely facilitated exchange of Hg(II) with cells and its uptake and internal transfer to the HgcAB proteins required for methylation. These results suggest that the effects of thiols on Hg(II) methylation were more complex than previously thought (using a single thiol) and thus underscore the importance of understanding how mixed thiols and their interactions with Hg(II) may ultimately influence MeHg production in the natural environment. [ABSTRACT FROM AUTHOR]

Lead (Pb) is a widespread highly toxic and persistent environmental pollutant. Plant leaves play a key role in accumulating atmospheric Pb, but its distribution in different cells and subcellular structures and the factors affecting it have been little studied. Here, Tillandsia usneoides , an indicator plant for atmospheric heavy metals, was treated with an aerosol generation device to analyze Pb contents in different cells (three types of cells in leaf surface scales, epidermal cells, mesophyll cells, vascular bundle cells), subcellular structures (cell wall, cell membrane, vacuoles, and organelles) and cell wall components (pectin, hemicellulose 1 and 2, and cellulose). Results show the different cells of T. usneoides leaves play distinct roles in the process of Pb retention. The outermost wing cells are structures that capture external pollutants, while mesophyll cells, as the aggregation site after material transport, ring cells, disc cells, epidermal cells, and vascular cells are material transporters. Pb was only detected in the cell wall and pectin, indicating the cell wall was the dominant subcellular structure for Pb retention, while pectin was the main component affecting Pb retention. FTIR analysis of cell wall components indicated the esterified carboxyl (C O) functional group in pectin may function in absorbing Pb. Pb entered leaf cells mainly in the form of low toxicity and activity to enhance its resistance. [Display omitted] • Plant leaves are important atmospheric Pb sinks. • Different types of cells play different roles in Pb retention. • Cell wall is the main subcellular structure affecting atmospheric Pb retention. • Pectin is the main component affecting Pb retention in cell wall. • C O functional group is the main component affecting Pb retention in pectin. [ABSTRACT FROM AUTHOR]

To strengthen mass heat transfer in dry fermentation and avoid the high shear forces breaking microbial flora. A reactor is designed to rotate itself instead of mechanical stirring. Its performance was verified by comparing it with the common stirring of dry digestion and wet digestion. The results showed that the designed reactor could effectively overcome the existing problems of stirring dry digestion. The total solids removal rate was up to 68.74%, which was 18% higher than that of wet digestion. Acetic acid and propionic acid were the main volatile fatty acids in dry digestion, and acetic acid and butyric acid were higher in wet digestion. The high diversity of fermentation bacteria integrated with hydrotrophic methanogens in the designed dry reactor resulted in its better performance. The information provided will be useful to research the anaerobic treatment of solid municipal waste. • A reactor used rotating instead of stirring was designed for dry fermentation. • The designed reactor performed well in the dry fermentation of kitchen waste. • More functional bacteria and hydrotrophic methanogens lead to good fermentation. • Methahnosarcina dominated in both designed dry reactor and common wet reactor. • Proteiniphilum and Enterococcus dominated in the designed reactor. [ABSTRACT FROM AUTHOR]