Concurrent methylation and demethylation of arsenic by fungi and their differential expression in the protoplasm proteome

Metal-Binding Protein TaGlo1 Improves Fungal Resistance to Arsenite (AsIII) and Methylarsenite (MAsIII) in Paddy Soil

Trivalent arsenicals such as arsenite (AsIII) and methylarsenite (MAsIII) are thought to be ubiquitous in flooded paddy soils and have higher toxicity than pentavalent forms. Fungi are widely prevalent in the rice rhizosphere, and the latter is considered a hotspot for As uptake. However, few studies have focused on alleviating As toxicity in paddy soils using fungi. In this study, we investigated the mechanism by which the protein TaGlo1, derived from the As-resistant fungal strain Trichoderma asperellum SM-12F1, mitigates AsIII and MAsIII toxicity in paddy soils. Taglo1 gene expression in Escherichia coli BL21 conferred strong resistance to AsIII and MAsIII, while purified TaGlo1 showed a high affinity for AsIII and MAsIII. Three cysteine residues (Cys13, Cys18, and Cys71) play crucial roles in binding with AsIII, while only two (Cys13 and Cys18) play crucial roles for MAsIII binding. TaGlo1 had a stronger binding strength for MAsIII than AsIII. Importantly, up to 90.2% of the homologous TaGlo1 proteins originate from fungi by GenBank searching. In the rhizospheres of 14 Chinese paddy soils, Taglo1 was widely distributed and its gene abundance increased with porewater As. This study highlights the potential of fungi to mitigate As toxicity and availability in the soil-rice continuum and suggests future microbial strategies for bioremediation.

The role of microbial partners in heavy metal metabolism in plants: a review

Heavy metal pollution threatens plant growth and development as well as ecological stability. Here, we synthesize current research on the interplay between plants and their microbial symbionts under heavy metal stress, highlighting the mechanisms employed by microbes to enhance plant tolerance and resilience. Several key strategies such as bioavailability alteration, chelation, detoxification, induced systemic tolerance, horizontal gene transfer, and methylation and demethylation, are examined, alongside the genetic and molecular basis governing these plant-microbe interactions. However, the complexity of plant-microbe interactions, coupled with our limited understanding of the associated mechanisms, presents challenges in their practical application. Thus, this review underscores the necessity of a more detailed understanding of how plants and microbes interact and the importance of using a combined approach from different scientific fields to maximize the benefits of these microbial processes. By advancing our knowledge of plant-microbe synergies in the metabolism of heavy metals, we can develop more effective bioremediation strategies to combat the contamination of soil by heavy metals.

Influence of environmental factors on arsenite transformation and fate in the Hydrilla verticillata (L.f.) royle - Medium system

Hydrilla verticillata (L.f.) Royle has a great ability to accumulate large amounts of arsenic (As). We studied the influence of phosphorus (P), nitrogen (N), pH, and arsenite (As(III)) on As transformation and fate in the H. verticillata - medium system via orthogonal experimental design. The results showed highest plant growth was under intermediate As(III) in the medium, with Chlorophyll a and Chlorophyll b contents in plant diminishing after 96 h treatment. Exposure to high N, high As(III), intermediate P, and low pH in the medium, the highest total arsenic uptake by plants were 169.1 ± 5.5 μg g^-1 dry weight, with As(III) as the predominant speciation (49.1 ± 4.8% to 88.5 ± 0.2%) in plants. Meanwhile, trace As (mainly arsenate (As(V))) was adsorbed on the surface of H. verticillata, and the adsorption amounts of As(V) increased with increasing As(III) concentrations in the medium. The dominant As species was As(V) in the medium although plant was supplied with As(III), and highest As(III) oxidation proportion in the medium would occur when low N and pH associated with high P and As(III). Collectively, As(III) uptake and transformation by H. verticillata cannot be overlooked in the biogeochemical cycling of As in aquatic environment.

Functionalized Mesoporous Silicon Nanomaterials in Inorganic Soil Pollution Research: Opportunities for Soil Protection and Advanced Chemical Imaging

"Innovative actions towards a pollution free-planet" is a goal of the United Nations Environment Assembly (UNEA). Aided by both the Food and Agricultural Organisation (FAO) and its Global Soil Partnership under the 3rd UNEA resolution, a consensus from > 170 countries have agreed a need for accelerated action and collaboration to combat soil pollution. This initiative has been tasked to find new and improved solutions to prevent and reduce soil pollution, and it is in this context that this review provides an updated perspective on an emerging technology platform that has already provided demonstrable utility for measurement, mapping, and monitoring of toxic trace elements (TTEs) in soils, in addition to the entrapment, removal, and remediation of pollutant sources. In this article, the development and characteristics of functionalized mesoporous silica nanomaterials (FMSN) will be discussed and compared with other common metal scavenging materials. The chemistries of the common functionalizations will be reviewed, in addition to providing an outlook on some of the future directions/applications of FMSN. The use of FMSN in soil will be considered with some specific case studies focusing on Hg and As. Finally, the advantages and developments of FMSN in the widely used diffusive gradients-in-thin films (DGT) technique will be discussed, in particular, its advantages as a DGT substrate for integration with oxygen planar optodes in multilayer systems that provide 2D mapping of metal pollutant fluxes at submillimeter resolution, which can be used to measure detailed sediment-water fluxes as well as soil-root interactions, to predict plant uptake and bioavailability.

Transportation and Transformation of Arsenic Species at the Intertidal Sediment-Water Interface of Bohai Bay, China

Arsenic species including arsenite As(III), arsenate As(V), monomethylarsenate (MMA), dimethylarsenate (DMA), and some diagenetic constituents (Fe, Mn, and S2−) in porewaters along with the unstable arsenic species in sediments collected from a typical intertidal zone of Bohai Bay in China were measured. Their vertical distributions were subsequently obtained to reveal the transportation and transformation characteristics of arsenic at the intertidal sediment-water interface (SWI). Results show that the reduction of As(V) by microorganisms occurred in sediments, but the methylation of arsenic by microorganisms was weak in the intertidal zone. The distribution of As(V) was mainly controlled by Mn, whereas As(III) appeared to be more likely controlled by Fe. Arsenic in sediments mainly existed in a stable state, so that only little arsenic could be released from sediments when the environmental conditions at the SWI are changed. As(III) diffused from porewaters to the overlying water while the opposite was true for As(V) at that time when the samples were collected. The total diffusion direction for arsenic across the SWI was from porewaters to the overlying water with a total diffusive flux estimated at 1.23 mg·m−2·a−1.