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Iron plaque is a strong adsorbent on rice roots, acting as a barrier to prevent metal uptake by rice. However, the role of root iron plaque microbes in governing metal redox cycling and metal bioavailability is unknown. In this study, the microbial community structure on the iron plaque of rice roots from an arsenic-contaminated paddy soil was explored using high-throughput next-generation sequencing. The microbial composition and diversity of the root iron plaque were significantly different from those of the bulk and rhizosphere soils. Using the aoxB gene as an identifying marker, we determined that the arsenite-oxidizing microbiota on the iron plaque was dominated by Acidovorax and Hydrogenophaga -affiliated bacteria. More importantly, the abundance of arsenite-oxidizing bacteria (AsOB) on the root iron plaque was significantly negatively correlated with the arsenic concentration in the rice root, straw and grain, indicating that the microbes on the iron plaque, particularly the AsOB, were actively catalyzing arsenic transformation and greatly influencing metal uptake by rice. This exploratory research represents a preliminary examination of the microbial community structure of the root iron plaque formed under arsenic pollution and emphasizes the importance of the root iron plaque environment in arsenic biogeochemical cycling compared with the soil-rhizosphere biotope.

Antimony (Sb) contamination released from mine tailings represents a global threat to natural ecosystems and human health. The geochemical conditions of Sb tailings, which are oligotrophic and replete in sulfur (S) and Sb, may promote the coupled metabolism of Sb and S. In this study, multiple lines of evidence indicate that a novel biogeochemical process, S oxidation coupled to Sb(V) reduction, is enzymatically mediated by Desulfurivibrio spp. The distribution of Desulfurivibrio covaried with S and Sb concentrations, showing a high relative abundance in Sb mine tailings but not in samples from surrounding sites (i.e., soils, paddies, and river sediments). Further, the metabolic potential to couple S oxidation to Sb(V) reduction, encoded by a non-canonical, oxidative sulfite reductase ( dsr ) and arsenate reductase ( arrA ) or antimonate reductase ( anrA ), respectively, was found to be common in Desulfurivibrio genomes retrieved from metal-contaminated sites in southern China. Elucidation of enzymatically-catalyzed S oxidation coupled to Sb(V) reduction expands the fundamental understanding of Sb biogeochemical cycling, which may be harnessed to improve remediation strategies for Sb mine tailings.

Background Genes associated with arsenite uptake and transport in rice plants (i.e., OsLsi1 , OsLsi2 , OsLsi3 , OsLsi6 and OsABCC1 ) have been identified to date. However, their expression over time during the whole growth period of rice under arsenite stress conditions is still poorly understood. In this study, the dynamics of gene expression associated with arsenite transport and arsenic concentrations in different organs of rice were investigated to determine the critical period(s) of arsenite uptake and translocation regulated by gene expression during the whole growth period. Results The relative expression of OsLsi2 and OsLsi1 in the roots was upregulated and reached its highest value (2 -∆∆Ct  = 4.04 and 1.19, respectively) at the jointing stage (9 weeks after transplantation), in which the arsenic concentration in roots also was the highest at 144 mg/kg. A range from 45.1 to 61.2% of total arsenic accumulated in the roots during seedling to heading stages (3–16 weeks), which was mainly associated with the relatively high expression of OsABCC1 (1.50–7.68), resulting in arsenic located in the vacuoles of roots. Subsequently, the As translocation factor from root to shoot increased over time from heading to milky ripe (16–20 weeks), and 74.3% of the arsenic accumulated in shoots at the milk stage. Such an increase in arsenic accumulation in shoots was likely related to the findings that (i) OsABCC1 expression in roots was suppressed to 0.14–0.75 in 18–20 weeks; (ii) OsLsi3 and OsABCC1 expression in nodes I, II, and III was upregulated to 4.01–25.8 and 1.59–2.36, respectively, in 16–20 weeks; and (iii)  OsLsi6 and OsABCC1 expression in leaves and husks was significantly upregulated to 2.03–5.26 at 18 weeks. Conclusions The jointing stage is the key period for the expression of arsenite-transporting genes in roots, and the heading to milky ripe stages are the key period for the expression of arsenite-transporting genes in shoots, both of which should be considered for regulation during safe rice production in arsenic-contaminated paddy soil. Graphical abstract

Purpose The aim of this study was to evaluate the roles of aluminum-based minerals, especially their surface Lewis acid sites (LASs), on the transformation and fate of chloroacetanilide herbicide contaminants when nucleophilic reagents are present. Materials and methods Batch experiments were used to study propachlor transformation processes under different reaction conditions. The surface bonding of aluminas before and after interacting with propachlor and dithionite were characterized by Fourier transform infrared (FTIR) spectra. The LASs on different aluminas, acting as the key role for accelerating the propachlor transformation, were analyzed by pyridine adsorption/FTIR spectroscopic technique. Results and discussion Rates of dithionite-initiated propachlor dechlorination were increased in the presence of aluminas. Transformation efficiencies of propachlor on different aluminas were found to be as γ-Al 2 O 3  > γ-AlOOH > α-Al 2 O 3 . A higher reaction temperature, higher pH, and higher alumina dosage can further increase the propachlor dechlorination rate. The addition of citric acid may block the active sites on alumina and reduce propachlor transformation by dithionite. FTIR and pyridine adsorption/diffuse reflectance Fourier transform infrared spectroscopy indicated that Al–S and Al–O bonds on the LASs of alumna play a key role in accelerating propachlor transformation. Conclusions LASs on alumina surfaces can effectively accelerate the propachlor transformation by dithionite. The strong electron accepting ability of LASs gives dithionite a favorable affinity to form surface sulfur compounds, which are stronger reductants and nucleophilic reagents for propachlor dechlorination. The intensities of LASs on alumina surfaces can be used to control the rate of propachlor transformation by dithionite.

The extensive application of graphene nanosheets (GNSs) has raised concerns over risks to sensitive species in the aquatic environment. The humic acid (HA) corona is traditionally considered to reduce GNSs toxicity. Here, we evaluate the effect of sorbed HA (GNSs-HA) on the toxicity of GNSs to Gram positive Bacillus tropicus . Contrary to previous data, GNSs-HA exhibits greater toxicity compared to GNSs. Multi-omics combined with sensitive bioassays and electrochemical methods reveals GNSs disrupt oxidative phosphorylation by causing physical membrane damage. This leads to the accumulation of intracellular reactive oxygen species and inhibition of ATP production, subsequently suppressing synthetic and metabolic processes and ultimately causing bacterial death. Conversely, GNSs-HA directly extracts electrons from bacteria and oxidized biomolecules due to HA-improved electron transfer. This finding suggests that the HA corona does not always mitigate the toxicity of nanoparticles, thereby introducing uncertainty over the interaction between environmental corona and nanoparticles during ecological risk evaluation. Wide use of graphene nanosheets has raised concerns about the potential for environmental toxicity. Here, the authors explore the use of humic acid, traditionally considered to reduce graphene nanosheet toxicity, and show the coating has increased toxicity to model bacteria.

The rhizosphere is a critical hotspot for metabolic activities involving arsenic (As). While recent studies indicate many functions for soil viruses, much remains overlooked regarding their quantitative impact on rhizosphere processes. Here, we analyze time-series metagenomes of rice ( Oryza sativa L.)rhizosphere and bulk soil to explore how viruses mediate rhizosphere As biogeochemistry. We observe the rhizosphere favors lysogeny in viruses associated with As-oxidizing microbes, with a positive correlation between As oxidation and the prevalence of these microbial hosts. Moreover, results demonstrate these lysogenic viruses enrich both As oxidation and phosphorus co-metabolism genes and mediated horizontal gene transfers (HGTs) of As oxidases. In silico simulation with genome-scale metabolic models (GEMs) and in vitro validation with experiments estimate that rhizosphere lysogenic viruses contribute up to 25% of microbial As oxidation. These findings enhance our comprehension of the plant-microbiome-virome interplay and highlight the potential of rhizosphere viruses for improving soil health in sustainable agriculture. Rhizosphere viruses mediate arsenic (As) biogeochemistry by promoting lysogeny in As-oxidizing microbes. Metagenomics, metabolic modeling, and in vitro experiments estimate rhizosphere lysogenic viruses contribute to up to 25% of microbial As oxidation.

Although c -type cytochromes ( c -Cyts) mediating metal reduction have been mainly investigated with in vitro purified proteins of dissimilatory metal reducing bacteria, the in vivo behavior of c -Cyts is still unclear given the difficulty in measuring the proteins of intact cells. Here, c -Cyts in living Shewanella putrefaciens 200 (SP200) was successfully quantified using diffuse-transmission UV/Vis spectroscopy due to the strong absorbance of hemes, and the in situ spectral kinetics of Cr(VI) reduction by c -Cyts were examined over time. The reduced product Cr(III) observed on the cell surface may play a role in inhibiting the Cr(VI) reduction and reducing the cell numbers with high concentrations (>200 μM) of Cr(VI) evidenced by the 16S rRNA analysis. A brief kinetic model was established with two predominant reactions, redox transformation of c -Cyts and Cr(VI) reduction by reduced c -Cyts, but the fitting curves were not well-matched with c -Cyts data. The Cr(III)-induced inhibitory effect to the cellular function of redox transformation of c -Cyts was then added to the model, resulting in substantially improved the model fitting. This study provides a case of directly examining the reaction properties of outer-membrane enzyme during microbial metal reduction processes under physiological conditions.

With the rapid expansion of nuclear power facilitating humanity’s shift towards a low-carbon energy society, proper management of nuclear waste generated by nuclear plants has become crucial for minimizing environmental impacts and alleviating public concerns. Assessing the impacts of radiation on various organisms to understand the toxicity mechanisms, potential health effects, and dose-response relationships related to radionuclide exposure can help assess the potential consequences of radionuclide leakage and providing information for decision making in risk management. [3] synthesize an amine-linked COF, namely TABN-COF, which shows a strong affinity for iodine, with an adsorption capacity of up to 365 mg/g for I3− in the aqueous phase. Besides the COF materials, Zhao et al.

Soil secondary minerals are important scavengers of rare earth elements (REEs) in soils and thus affect geochemical behavior and occurrence of REEs. The fractionation of REEs is a common geochemical phenomenon in soils but has received little attention, especially fractionation induced by secondary minerals. In this study, REEs (La to Lu and Y) associated with soil-abundant secondary minerals Fe-, Al-, and Mn-oxides in 196 soil samples were investigated to explore the fractionation and anomalies of REEs related to the minerals. The results show right-inclined chondrite-normalized REE patterns for La–Lu in soils subjected to total soil digestion and partial soil extraction. Light REEs (LREEs) enrichment features were negatively correlated with a Eu anomaly and positively correlated with a Ce anomaly. The fractionation between LREEs and heavy REEs (HREEs) was attributed to the high adsorption affinity of LREEs to secondary minerals and the preferred activation/leaching of HREEs. The substantial fractions of REEs in soils extracted by oxalate and Dithionite-Citrate-Bicarbonate buffer solutions were labile (10 %–30 %), which were similar to the mass fraction of Fe (10 %–20 %). Furthermore, Eu was found to be more mobile than the other REEs in the soils, whereas Ce was less mobile. These results add to our understanding of the distribution and geochemical behavior of REEs in soils, and also help to deduce the conditions of soil formation from REE fractionation.

Arsenic (As) and antimony (Sb) are known carcinogens and are present as contaminants in paddy soils. However, the complicated dynamics of the mobility of these metalloids have not been well understood due to changing redox conditions in paddy soils. Herein, the kinetics of dissolved As and Sb, and functional bacteria/genes were examined in a paddy soil cultured under aerobic and anaerobic conditions. Under aerobic condition, dissolved As(V) and Sb(V) increased constantly due to sulfide oxidation by O2 and bound As and Sb were released. Under anaerobic condition, the reduction of As(V) and Sb(V) occurred, and the mobility of As and Sb were affected by soil redox processes. The bacteria with functional genes aioA and arrA were responsible for the direct As/Sb transformation, while Fe- and N-related bacteria had an indirect effect on the fate of As/Sb via coupling with the redox processes of Fe and N. These findings improve understanding of the mobility of As and Sb in paddy soil systems under different redox conditions.