Rainbow trout (Salmo gairdneri) were exposed to 3.6 and 6.4 μg Cd/L for periods up to 178 d. Transitory changes in plasma calcium and magnesium were observed in fish exposed to 3.6 μg Cd/L although the differences were not significant. Exposure to 6.4 μg Cd/L, however, resulted in significantly lowered plasma sodium, potassium, calcium, and chloride and elevated magnesium concentrations. Analyses of urine indicated that the rate of urine production, osmolality, and sodium, potassium, chloride, magnesium, calcium, and protein concentrations were unaffected by exposure to 3.6 μg Cd/L although slight changes were observed in the first week of exposure. Urine production rate and urinary concentrations of potassium and chloride were unaffected in trout exposed to 6.4 μg Cd/L but sodium, protein, and osmolality were elevated and calcium and magnesium concentrations reduced in these fish. The results demonstrate that the majority of the cadmium-induced electrolyte imbalances do not result from impairment of renal function.

Genetically encoding the synthesis of functional nanomaterials such as magnetic nanoparticles enables sensitive and non-invasive biological sensing and control. Via directed evolution of the natural iron-sequestering ferritin protein, we discovered key mutations that lead to significantly enhanced cellular magnetism, resulting in increased physical attraction of ferritin-expressing cells to magnets and increased contrast for cellular magnetic resonance imaging (MRI). The magnetic mutants further demonstrate increased iron biomineralization measured by a novel fluorescent genetic sensor for intracellular free iron. In addition, we engineered Escherichia coli cells with multiple genomic knockouts to increase cellular accumulation of various metals. Lastly to explore further protein candidates for biomagnetism, we characterized members of the DUF892 family using the iron sensor and magnetic columns, confirming their intracellular iron sequestration that results in increased cellular magnetization.

Adult rainbow trout, Salmo gairdneri, were exposed to 3.6 and 6.4 μg Cd/L for 178 d. Cadmium accumulated most rapidly in gill tissue which became saturated at levels 100-fold higher than controls within 24 and 52 d in the high- and low-metal exposures, respectively. Liver cadmium increased 250- to 400-fold over the test period but accumulation exhibited a plateau between 52 and 129 d followed by a rapid rise by 178 d. Kidney cadmium increased consistently throughout the test period to levels approximately 50- to 100-fold higher than control values. Cadmium in the gut and skin increased 10- and 5-fold, respectively, while no increase was recorded in white muscle. A maximum of 2.1% of the cadmium available in a commercial diet (0.2 μg Cd/g dry food} was accumulated in control fish. Although cadmium was not detected in the urine, urinary zinc excretion was elevated in trout exposed to 6.4 μg Cd/L such that 7 mol of zinc was excreted per 1 mol of cadmium accumulated during the initial 24 d of exposure. The whole-body burden of cadmium increased linearly with time in both treatments with a time constant of 0.366 and 0.554%/d for trout exposed to 3.6 and 6.4 μg Cd/L, respectively.

The dose-dependent relationships of several physiological responses to acid were examined in rainbow trout (Salmo gairdneri) exposed for 22 d to water at pH 4.2–6.0. Significant increases in ventilatory and cardiac rates occurred at pHw < 4.9. Hematocrit and hemoglobin concentration increased progressively with acid stress at pHw < 5.5. Plasma calcium, magnesium, sodium, and chloride concentrations were reduced and plasma phosphate elevated in acid-exposed fish. Seasonal differences were observed in the quantitative responses to acid exposure in the relationship between hematocrit and hemoglobin concentration and in the plasma concentrations of calcium and magnesium. The fractional contribution of sodium and chloride to plasma osmolality decreased linearly with increasing hydrogen ion concentration, and the change in plasma sodium, chloride, and osmolality per unit change in pHw was 35.2 mmol/L, 39.7 mmol/L, and 47.4 mosmol/kg, respectively, in the pH range of 4.5–5.2. We concluded that the discrepancy between the reduction in plasma osmotic pressure and the combined reduction in the major plasma electrolytes is a result of the elevation in concentration of an unidentified plasma solute which offsets 40–45% of the expected reduction in osmotic pressure.

Poison frogs acquire chemical defenses from the environment for protection against potential predators. These defensive chemicals are lipophilic alkaloids that are sequestered by poison frogs from dietary arthropods and stored in skin glands. Despite decades of research focusing on identifying poison frog alkaloids, we know relatively little about how environmental variation and subsequent arthropod availability impacts alkaloid loads in poison frogs. We investigated how seasonal environmental variation influences poison frog chemical profiles through changes in the diet of the Climbing Mantella (Mantella laevigata). We collected M. laevigata females on the Nosy Mangabe island reserve in Madagascar during the wet and dry seasons and tested the hypothesis that seasonal differences in rainfall is associated with changes in diet composition and skin alkaloid profiles of M. laevigata. The arthropod diet of each frog was characterized into five groups (i.e. ants, termites, mites, insect larvae, or ‘other’) using visual identification and cytochrome oxidase 1 DNA barcoding. We found that frog diet differed between the wet and dry seasons, where frogs had a more diverse diet in the wet season and consumed a higher percentage of ants in the dry season. To determine if seasonality was associated with variation in frog defensive chemical composition, we used gas chromatography / mass spectrometry to quantify alkaloids from individual skin samples. Although the assortment of identified alkaloids was similar across seasons, we detected significant differences in the abundance of certain alkaloids, which we hypothesize reflects seasonal variation in the diet of M. laevigata. We suggest that these variations could originate from seasonal changes in either arthropod leaf litter composition or changes in frog behavioral patterns. Although additional studies are needed to understand the consequences of long-term environmental shifts, this work suggests that alkaloid profiles are relatively robust against short-term environmental perturbations.