Cadmium in the hyperaccumulating mushroom Thelephora penicillata: Intracellular speciation and isotopic composition

Rhizobiome diversity of field-collected hyperaccumulating Noccaea sp

Hyperaccumulating plants are able to (hyper)accumulate high concentrations of metal(loid)s in their above-ground tissues without any signs of toxicity. Studies on the root-associated microbiome have been previously conducted in relation to hyperaccumulators, yet much remains unknown about the interactions between hyperaccumulating hosts and their microbiomes, as well as the dynamics within these microbial communities. Here, we assess the impact of the plant host on shaping microbial communities of three naturally occurring populations of Noccaea species in Slovenia: Noccaea praecox and co-occurring N. caerulescens from the non-metalliferous site and N. praecox from the metalliferous site. We investigated the effect of metal enrichment on microbial communities and explored the interactions within microbial groups and their environment. The abundance of bacterial phyla was more homogeneous than fungal classes across all three Noccaea populations and across the three root-associated compartments (roots, rhizosphere, and bulk soil). While most fungal and bacterial Operational Taxonomic Units (OTUs) were found at both sites, the metalliferous site comprised more unique OTUs in the root and rhizosphere compartments than the non-metalliferous site. In contrast to fungi, bacteria exhibited differentially significant abundance between the metalliferous and non-metalliferous sites as well as statistically significant correlations with most of the soil parameters. Results revealed N. caerulescens had the highest number of negative correlations between the bacterial phyla, whereas the population from the metalliferous site had the fewest. This decrease was accompanied by a big perturbation in the bacterial community at the metalliferous site, indicating increased selection between the bacterial taxa and the formation of potentially less stable rhizobiomes. These findings provide fundamentals for future research on the dynamics between hyperaccumulators and their associated microbiome.

Precise Determination of Cd Isotope Ratios at 3-10 ng Level by Thermal Ionization Mass Spectrometry Using a Molybdenum Silicide Emitter

Thermal ionization mass spectrometry (TIMS) combined with the double spike technique has excellent analytical precision for Cd isotopic ratio analysis. However, because of the low ionization efficiency of Cd by TIMS, it is still not possible to obtain high precision Cd isotope ratios for small sample size (<100 ng) due to the lack of a highly sensitive emitter for Cd. A new loading method using molybdenum silicide (MoSi2) emitter has been developed for Cd isotope ratio measurements. This emitter produces a significant enhancement in the ionization efficiency of Cd and thus significantly reduces the required sample size to the 3-10 ng level. Analyses of δ114/110Cd for the NIST SRM 3108 using 108Cd-116Cd double spike method show excellent reproducibility (2 SD) that reaches ±0.032‰, ±0.042‰, and ±0.051‰ for 10, 5, and 3 ng of Cd, respectively. This method was further verified with a suite of geological reference materials. Replicate digestions and analyses (n = 8, 2 SD) of δ114/110Cd for NIST SRM 2711a, NOD A-1, and GBW08401 demonstrated good external reproducibility with results of 0.596 ± 0.024‰ for NIST SRM 2711a, 0.150 ± 0.036‰ for NOD A-1, and -0.665 ± 0.084‰ for GBW08401. These data clearly indicate that MoSi2 is an excellent alternative for traditional silica gel to Cd isotopic measurements, especially for samples with a low content of Cd.

Stable isotopic signature of cadmium in tracing the source, fate, and translocation of cadmium in soil: A review

Cadmium (Cd), one of the most severe environmental pollutants in soil, poses a great threat to food safety and human health. Understanding the potential sources, fate, and translocation of Cd in soil-plant systems can provide valuable information on Cd contamination and its environmental impacts. Stable Cd isotopic ratios (δ114/110Cd) can provide "fingerprint" information on the sources and fate of Cd in the soil environment. Here, we review the application of Cd isotopes in soil, including (i) the Cd isotopic signature of soil and anthropogenic sources, (ii) the interactions of Cd with soil constituents and associated Cd isotopic fractionation, and (iii) the translocation of Cd at soil-plant interfaces and inside plant bodies, which aims to provide an in-depth understanding of Cd transport and migration in soil and soil-plant systems. This review would help to improve the understanding and application of Cd isotopic techniques for tracing the potential sources and (bio-)geochemical cycling of Cd in soil environment.

Metal Content in Caps and Stalks of Edible Mushrooms: Health Benefits and Risk Evaluation

Mushrooms are a good source of protein and phenolic compounds which provides health benefits for humans. The purpose of this study was to compare the content of eight metals, protein, and total phenolics (TPC) of 5 different species (Agaricus bisporus-white and brown mushrooms, Agaricus cupreobrunneus, Auricularia cornea, Hypsizgus tesselatus, and Pleurotus eryngii species-complex) of edible mushrooms available on the Romanian market. Agaricus bisporus and Agaricus cupreobrunneus were purchased and cultivated in Romania and the other species were cultivated in other countries (Turkey and China). The metal content determined by graphite atomic absorption spectrometry (GTAAS) varied in the order Cu > Pb > Ni > Fe > Cr > Mn > Co > Cd. Almost all the samples contained a greater quantity of metals in the stalk than in the cap. In addition, the levels of toxic metals were low. The protein content of analyzed samples ranged from 0.0926 to 0.2743%, the highest value being observed in Pleurotus eryngii species-complex mushroom. TPC of extracts increased over time but there was a variability in the concentration for each mushroom species (0.25-12.25 mg GAE/g). The investigated mushroom species possess no health risk and may be potential nutritional supplements for human diets due to their phenolic compounds, protein, and mineral content.

A Review about the Mycoremediation of Soil Impacted by War-like Activities: Challenges and Gaps

(1) Background: The frequency and intensity of war-like activities (war, military training, and shooting ranges) worldwide cause soil pollution by metals, metalloids, explosives, radionuclides, and herbicides. Despite this environmentally worrying scenario, soil decontamination in former war zones almost always involves incineration. Nevertheless, this practice is expensive, and its efficiency is suitable only for organic pollutants. Therefore, treating soils polluted by wars requires efficient and economically viable alternatives. In this sense, this manuscript reviews the status and knowledge gaps of mycoremediation. (2) Methods: The literature review consisted of searches on ScienceDirect and Web of Science for articles (1980 to 2023) on the mycoremediation of soils containing pollutants derived from war-like activities. (3) Results: This review highlighted that mycoremediation has many successful applications for removing all pollutants of war-like activities. However, the mycoremediation of soils in former war zones and those impacted by military training and shooting ranges is still very incipient, with most applications emphasizing explosives. (4) Conclusion: The mycoremediation of soils from conflict zones is an entirely open field of research, and the main challenge is to optimize experimental conditions on a field scale.

Cadmium accumulation and isotope fractionation in typical protozoa Tetrahymena: A new perspective on remediation of Cd pollution in wastewater

Cadmium (Cd) pollution threatens water safety and human health, which has raised serious public concern. Tetrahymena is a model protozoan, possessing the potential to remediate Cd contaminated water given the rapid expression of thiols. However, the mechanism of Cd accumulation in Tetrahymena has not been well understood, which hinders its application in environmental remediation. This study elucidated the pathway of Cd accumulation in Tetrahymena using Cd isotope fractionation. Our results showed that Tetrahymena preferentially absorb light Cd isotopes, with Δ^114/110Cd_{Tetrahymena-solution} = -0.20 ± 0.02‰ ∼ - 0.29 ± 0.02‰, which implies that the intracellular Cd is probably in the form of Cd-S. The fractionation generated by Cd complexation with thiols is constant (Δ^114/110Cd_{Tetrahymena-remaining solution} ∼ -0.28 ± 0.02‰), which is not affected by the concentrations of Cd in intracellular and culture medium, nor by the physiological changes in cells. Furthermore, the detoxification process of Tetrahymena results in an increase in cellular Cd accumulation from 11.7% to 23.3% with the elevated Cd concentrations in batch Cd stress culture experiments. This study highlights the promising application of Cd isotope fractionation in Tetrahymena for the remediation of heavy metal pollution in water.

Translocation of elements and fractionation of Mg, Cu, Zn, and Cd stable isotopes in a penny bun mushroom (Boletus edulis) from western Czech Republic

Boletus edulis mushroom behaved as an accumulating biosystem with respect to Ag, Rb, Zn, and K. The mushroom was not an efficient accumulator of toxic As, Pb, and Cr, but Se and Cd displayed much higher concentrations in the mushroom than in the substrate samples. Other elements were bioexclusive. Different elements had different within-mushroom mobilities. The highest mobilities were displayed by Zn and Ag, and the lowest by Ti. The mushroom's fruiting body preferentially took up lighter Mg, Cu, and Cd isotopes (Δ26MgFB-soil =  -0.75‰; Δ65CuFB-soil =  -0.96‰; Δ114CdFB-soil =  -0.63‰), and the heavier 66Zn isotope (Δ66ZnFB-soil = 0.92‰). Positive within-mushroom Zn isotope fractionation resulted in accumulation of the heavier 66Zn (Δ66Zncap-stipe = 0.12‰) in the mushroom's upper parts. Cadmium displayed virtually no within-mushroom isotope fractionation. Different parts of the fruiting body fractionated Mg and Cu isotopes differently. The middle part of the stipe (3-6 cm) was strongly depleted in the heavier 26 Mg with respect to the 0-3 cm (Δ26Mgstipe(3-6)-stipe(0-3) =  -0.73‰) and 6-9 cm (Δ26Mgstipe(6-9)-stipe(3-6) = 0.28‰) sections. The same stipe part was strongly enriched in the heavier 65Cu with respect to the 0-3 cm (Δ65Custipe(3-6)-stipe(0-3) = 0.63‰) and 6-9 cm (Δ65Custipe(6-9)-stipe(3-6) =  -0.42‰) sections. An overall tendency for the upper mushroom's parts to accumulate heavier isotopes was noted for Mg (Δ26Mgcap-stipe = 0.20‰), Zn (Δ66Zncap-stipe = 0.12‰), and Cd (Δ114Cdcap-stipe = 0.04‰), whereas Cu showed the opposite trend (Δ65Cucap-stipe =  -0.08‰).