Trace metal limitation not only affects the biological function of organisms, but also the health of ecosystems and the global cycling of elements. The enzymatic machinery of microbes helps to drive critical biogeochemical cycles at the macroscale, and in many cases, the function of metalloenzyme-mediated processes may be limited by the scarcity of essential trace metals. In response to these nutrient limitations, some organisms employ a strategy of exuding metallophores, biogenic ligands that facilitate the uptake of metal ions. For example, bacterial, fungal, and graminaceous plant species are known to use Fe(III)-binding siderophores for nutrient acquisition, providing the best known and most thoroughly studied example of metallophores. However, recent breakthroughs have suggested or established the role of metallophores in the uptake of several other metallic nutrients. Furthermore, these metallophores may influence environmental trace metal fate and transport beyond nutrient acquisition. These discoveries have resulted in a deeper understanding of trace metal geochemistry and its relationship to the cycling of carbon and nitrogen in natural systems. In this review, we provide an overview of the current state of knowledge on the biogeochemistry of metallophores in trace metal acquisition, and explore established and potential metallophore systems.Electronic supplementary material The online version of this article (

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Sediments of Coeur d'Alene Lake, ID, are heavily contaminated with mine tailings that contain high levels of iron, lead, zinc, arsenic, and other trace elements. These tailings originate from the Silver Valley mining district drained by the South Fork of the Coeur d'Alene River. The possibilities that either lake eutrophication or the develop ment of a seasonally anoxic hypolimnion could mobilize trace elements from sediments into overlying waters led us to evaluate their phase associations. Analysis of ∼0.5 m gravity cores reveals these sediments to be highly reduced, and the trace elements therein predominantly associated with an operationally defined sulfidic phase. Vertical patterns of metal distribution suggest that Fe, Mn, and As have mobilized toward the sediment−water interface; these patterns are consistent with diagenetic solubilization. This is not the case for Zn, Pb, and other trace elements whose maximum abundance is generally found in deeper sediments. We postulate that metal sulfide formation and metal binding with organic material restricts mobilization of most trace elements. The abundance of redox-active elements such as As, Fe, and Mn is highly correlated by depth. The abundance of less redox-sensitive elements such as Pb and Zn is also highly correlated; however, the two groups correlate poorly with one other.

Minerals are inorganic compounds that are essential to the support of a variety of biological functions. Understanding the range and variability of the content of these minerals in biological samples can provide insight into the relationships between mineral content and the health of individuals. In particular, abnormal mineral content may serve as an indicator of illness. The development of robust, reliable analytical methods for the determination of the mineral content of biological samples is essential to developing biological models for understanding the relationship between minerals and illnesses. This manuscript describes a method for the analysis of the mineral content of small volumes of serum and whole blood samples from healthy individuals. Interday and intraday precision for the mineral content of the blood (250 μl) and serum (250 μl) samples was measured for eight essential minerals, sodium (Na), calcium (Ca), magnesium (Mg), potassium (K), iron (Fe), zinc (Zn), copper (Cu), and selenium (Se) by plasma spectrometric methods and ranged from 0.635 – 10.1% relative standard deviation (RSD) for serum and 0.348 – 5.98% for whole blood. A comparison of the determined ranges for ten serum samples and six whole blood samples provided good agreement with literature reference ranges. The results demonstrate that the digestion and analysis methods can be used to reliably measure the content of these minerals, and potentially to add other minerals.

Sediments of Coeur d'Alene Lake, ID, are heavily contaminated with mine tailings that contain high levels of arsenic, iron, lead, and other trace elements. Maximal abundance of redox-active elements such as As and Fe is generally found close to the sediment-water interface, whereas peak abundance of less redox-active elements such as Pb is found at >25 cm. The suggestion that As is mobile within reduced sediments led us to characterize the sediment microbiota with regard to organisms whose activities favor As mobilization. Most probable number (MPN) estimates reveal that the densities of cultivable sulfate-, iron-, and arsenate-reducing bacteria approach 10 6 , 10 5 , and 10 4 cells g -1 wet weight sediment, respectively. Because As is considered more mobile in environments that produce As(III), we measured aqueous As(III) generation within As(V)-amended sediment microcosms. In organic acidstimulated microcosms, >50% of a 10mM As(V) amendment is transformed to As(III), compared to 30% and 5% in unstimulated microcosms and abiotic controls, respectively. In microcosms amended with an inhibitor of SRB metabolism (molybdate), As(V) reduction was in some cases diminished, suggesting that SRB may contribute to As(V) reduction. The capacity for biotic As(V) reduction clearly exists in CDAL sediments, and the profile of As abundance may be partly attributed to metal(loid)-transforming bacteria.

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Cadmium is a naturally-occurring element, and humans are exposed from cigarettes, food, and industrial sources. Following exposure, cadmium accumulates in the kidney and is slowly released into the urine, usually proportionally to the levels found in the kidneys. Cadmium levels in a single spot urine sample have been considered indicative of long-term exposure to cadmium; however, such a potentially exceptional biomarker requires careful scrutiny. In this review, we report good to excellent temporal stability of urinary cadmium (intraclass correlation coefficient 0.66–0.81) regardless of spot urine or first morning void sampling. Factors such as changes in smoking habits and diseases characterized by increased excretion of proteins may produce short-term changes in urinary cadmium levels. We recommend that epidemiologists use this powerful biomarker in prospective studies stratified by smoking status, along with thoughtful consideration of additional factors that can influence renal physiology and cadmium excretion.

The viability of iron(III/II) reduction as the initial step in the in vivo release of iron from its thermodynamically stable siderophore complex is explored.