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High concentrations of toxic cadmium (Cd) in soils are problematic as the element accumulates in food crops such as rice and cacao. A mitigation strategy to minimise Cd accumulation is to enhance the competitive uptake of plant-essential metals. Theobroma cacao seedlings were grown hydroponically with added Cd. Eight different treatments were used, which included/excluded hydroponic or foliar zinc (Zn) and/or iron (Fe) for the final growth period. Analyses of Cd concentrations and natural stable isotope compositions by multiple collector ICP-MS were conducted. Cadmium uptake and translocation decreased when Fe was removed from the hydroponic solutions, while the application of foliar Zn-EDTA may enhance Cd translocation. No significant differences in isotope fractionation during uptake were found between treatments. Data from all treatments fit a single Cd isotope fractionation model associated with sequestration (seq) of isotopically light Cd in roots and unidirectional mobilisation (mob) of isotopically heavier Cd to the leaves (ε 114 Cd seq-mob = -0.13‱). This result is in excellent agreement with data from an investigation of 19 genetically diverse cacao clones. The different Cd dynamics exhibited by the clones and seen in response to different Fe availability may be linked to similar physiological processes, such as the regulation of specific transporter proteins.

Soil particle size may significantly affect metal distribution and stable isotopic behavior. Here, two soils were separated into four particle size fractions, namely fine sand, silt, fine silt, and colloidal particles and used to determine cadmium (Cd) and zinc (Zn) concentrations and isotope compositions. Concentrations of Cd and Zn were generally enriched in the finer particles and positively correlated with the iron (Fe) and manganese (Mn) oxide contents. However, Cd concentration in the fine sand was higher than in the silt fraction due to the higher soil organic matter contents in the former particle fraction. The maximum δ 114/110 Cd value was found in the colloidal particles (-0.02 and 0.01‰) of both soils while the minimum was in the silt particles (-0.12 and 0.06‰). Incorporation into the mineral lattice of Fe and Mn oxides is suggested to explain the slight enrichment of heavy Cd isotopes in the colloidal fraction. The similar δ 66 Zn values of the four particle fractions (0.20-0.29‰ with a mean of 0.25‰) indicate similar Zn sources in different particle sizes. Metal isotopic fingerprint of different soil particle size fractions provides further insight into the underlying metal retention mechanisms within soil micro-zones and helps in tracing metal sources and biogeochemical processes., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

Antimicrobial resistance (AMR) is one of the major challenges humans are facing this century. Understanding the mechanisms behind the rise of AMR is therefore crucial to tackling this global threat. The presence of transition metals is one of the growth-limiting factors for both environmental and pathogenic bacteria, and the mechanisms that bacteria use to adapt to and survive under transition metal toxicity resemble those correlated with the rise of AMR. A deeper understanding of transition metal toxicity and its potential as an antimicrobial agent will expand our knowledge of AMR and assist the development of therapeutic strategies. In this study, we investigate the antimicrobial effect of two transition metal ions, namely cobalt (Co 2+ ) and nickel (Ni 2+ ), on the non-tuberculous environmental mycobacterium and the opportunistic human pathogen Mycobacterium abscessus . The minimum inhibitory concentrations of Co 2+ and Ni 2+ on M. abscessus were first quantified and their impact on the bacterial intracellular metallome was investigated. A multi-omics strategy that combines transcriptomics, bioenergetics, metabolomics, and phenotypic assays was designed to further investigate the mechanisms behind the effects of transition metals. We show that transition metals induced growth defect and changes in transcriptome and carbon metabolism in M. abscessus , while the induction of the glyoxylate shunt and the WhiB7 regulon in response to metal stresses could be the key response that led to higher AMR levels. Meanwhile, transition metal treatment alters the bacterial response to clinically relevant antibiotics and enhances the uptake of clarithromycin into bacterial cells, leading to increased efficacy. This work provides insights into the tolerance mechanisms of M. abscessus to transition metal toxicity and demonstrates the possibility of using transition metals to adjuvant the efficacy of currently using antimicrobials against M. abscessus infections., Competing Interests: Competing interestsThe authors declare no competing interests., (© The Author(s) 2024.)

This study employs stable isotope analysis to investigate the mechanisms of cadmium (Cd) and zinc (Zn) interaction in the metal hyperaccumulating plant species Sedum plumbizincicola . To this end, the Cd and Zn isotope compositions of root, stem, leaf, and xylem sap samples were determined during metal uptake and translocation at different Cd and Zn concentrations. The enrichment of light isotopes of both elements in plants during uptake was less pronounced at low metal supply levels, likely reflecting the switch from a low-affinity to a high-affinity transport system at lower levels of external metal supply. The lower δ 114/110 Cd values of xylem sap when treated with a metabolic inhibitor decreasing the active Cd uptake further supports the preference of heavier Cd isotopes during high-affinity transport. The Δ 66 Zn plant-initial solution or Δ 66 Zn plant-final solution values were similar at different Cd concentrations, indicating negligible interaction of Cd in the Zn uptake process. However, decreasing Zn supply levels significantly increased the enrichment of light Cd isotopes in plants (Δ 114/110 Cd = -0.08‰) in low-Cd treatments but reduced the enrichment of light Cd isotopes in plants (Δ 114/110 Cd = 0.08‰) under high Cd conditions. A systematic enrichment of heavy Cd and light Zn isotopes was found in root-to-shoot translocation of the metals. The Cd concentrations of the growth solutions thereby had no significant impact on Zn isotope fractionation during root-to-shoot translocation. However, the Δ 114/110 Cd translocation values hint at possible competition between Cd and Zn for transporters during root-to-shoot transfer and this may impact the transport pathway of Cd. The stable isotope data demonstrate that the interactions between the two metals influenced the uptake and transport mechanisms of Cd in S. plumbizincicola but had little effect on those of Zn.

This study aims to establish whether zinc (Zn) and cadmium (Cd) share similar physiological mechanisms for uptake and translocation in cacao plants (Theobroma cacao L.). Multiple-collector ICP-MS was used to determine the Zn stable isotope compositions in the roots, stems and leaves of 19 diverse cacao genotypes grown in hydroponics with 20 µmol L -1 CdCl 2 . Additional plants of one genotype were grown in hydroponic solutions containing lower Cd concentrations (0 and 5 µmol L -1 added CdCl 2 ). Regardless of the Cd concentration used in the exposures, the Zn stable isotope compositions show the same systematic patterns in plant organs, with δ 66 Zn root  > δ 66 Zn stem  > δ 66 Zn leaf (δ 66 Zn denotes relative differences in 66 Zn/ 64 Zn ratios in parts per thousand). The mean Zn stable isotope fractionation between the plants and the hydroponic solutions was ε 66 Zn uptake  = -1.15 ± 0.36‰ (2SD), indicating preferential uptake of isotopically light Zn by plants from the hydroponic solution. The mean  stable isotope fractionation factor associated with translocation of Zn from roots to shoots, ε 66 Zn seq-mob  =  + 0.52 ± 0.36‰ (2SD), shows that isotopically heavy Zn is preferentially sequestered in the cacao roots, whilst isotopically light Zn is mobilised to the leaves. A comparison with the Cd stable isotope compositions of the same plants shows that both isotopically light Zn and Cd are preferentially taken up by cacao plants. In contrast to Zn, however, the cacao roots retain isotopically light Cd and transfer isotopically heavy Cd to the leaves., (© 2023. The Author(s).)

In the last 20 years, the application of high-precision isotopic analysis of essential mineral elements (Mg, K, Ca, Fe, Cu, and Zn) to biomedicine (sometimes referred to as isotope metallomics) has revealed that their stable isotopic compositions are altered by the metal dysregulation that is fundamental to the pathogenesis of many cancers and other diseases. Despite many published works showing the diagnostic and prognostic potential of this approach, a number of factors that may influence the stable isotopic composition of these essential mineral elements in healthy individuals remain unstudied. In this perspective article, we summarize the available evidence from trophic level studies, animal models, and ancient and modern humans, relating to physiological and lifestyle factors that appear likely (there is evidence indicating their influence) or unlikely (there is evidence indicating their lack of influence) to require controlling for when investigating variations in essential mineral element isotopic compositions in human subjects. We also discuss factors that require additional data to properly assess. There is evidence that sex, menopausal status, age, diet, vitamin and metal supplementation, genetic variation, and obesity influence the isotopic composition of at least one essential mineral element in the human body. The task of investigating potential influences on essential mineral element isotopic compositions in the human body is sizeable, but presents an exciting research opportunity, with each incremental advance helping to improve the quality of research output in the context of isotope metallomics., (© The Author(s) 2023. Published by Oxford University Press.)

This work critically reviews stable isotope fractionation of essential (B, Mg, K, Ca, Fe, Ni, Cu, Zn, Mo), beneficial (Si), and non-essential (Cd, Tl) metals and metalloids in plants. The review (i) provides basic principles and methodologies for non-traditional isotope analyses, (ii) compiles isotope fractionation for uptake and translocation for each element and connects them to physiological processes, and (iii) interlinks knowledge from different elements to identify common and contrasting drivers of isotope fractionation. Different biological and physico-chemical processes drive isotope fractionation in plants. During uptake, Ca and Mg fractionate through root apoplast adsorption, Si through diffusion during membrane passage, Fe and Cu through reduction prior to membrane transport in strategy I plants, and Zn, Cu, and Cd through membrane transport. During translocation and utilization, isotopes fractionate through precipitation into insoluble forms, such as phytoliths (Si) or oxalate (Ca), structural binding to cell walls (Ca), and membrane transport and binding to soluble organic ligands (Zn, Cd). These processes can lead to similar (Cu, Fe) and opposing (Ca vs. Mg, Zn vs. Cd) isotope fractionation patterns of chemically similar elements in plants. Isotope fractionation in plants is influenced by biotic factors, such as phenological stages and plant genetics, as well as abiotic factors. Different nutrient supply induced shifts in isotope fractionation patterns for Mg, Cu, and Zn, suggesting that isotope process tracing can be used as a tool to detect and quantify different uptake pathways in response to abiotic stresses. However, the interpretation of isotope fractionation in plants is challenging because many isotope fractionation factors associated with specific processes are unknown and experiments are often exploratory. To overcome these limitations, fundamental geochemical research should expand the database of isotope fractionation factors and disentangle kinetic and equilibrium fractionation. In addition, plant growth studies should further shift toward hypothesis-driven experiments, for example, by integrating contrasting nutrient supplies, using established model plants, genetic approaches, and by combining isotope analyses with complementary speciation techniques. To fully exploit the potential of isotope process tracing in plants, the interdisciplinary expertise of plant and isotope geochemical scientists is required., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Wiggenhauser, Moore, Wang, Bienert, Laursen and Blotevogel.)