Identification of a Green Algal Strain Collected from the Sarno River Mouth (Gulf of Naples, Italy) and Its Exploitation for Heavy Metal Remediation

Heavy metals (HMs) can induce both chronic and acute harmful effects on marine and freshwater biota. The environmental impact of HMs in freshwater, seawater, soil, and wastewater can be limited using microbes, including microalgae, that are able to remove metals from environmental matrices. Indeed, they can passively adsorb and actively accumulate these persistent pollutants within their organelles, limiting their detrimental effects on cellular metabolism. The Sarno River is a 30 km long freshwater stream located in Southern Italy, polluted by partially untreated municipal, agricultural, and industrial wastewaters. In spite of this, microalgal cultures from Sarno River or Sarno River Mouth have never been established. In the present study, we isolated a green algal strain from the Sarno River Mouth and determined its ability to grow in polluted seawater containing different concentrations of cadmium, lead, or zinc. This strain was found to be able to accumulate these elements within its biomass in a dose-dependent manner. Growth inhibition experiments confirm the relatively low toxicity of Cd and Pb below 50 µM, while algal growth was seriously affected in Zn-amended media. To the best of our knowledge, this is the first study focused on the ability of microalgae from Sarno River Mouth to tolerate and uptake HMs.

Effects of nitrogen and phosphorus availability on cadmium tolerance in the marine diatom Phaeodactylum tricornutum

Although the influence of major nutrients on metal toxicity in marine phytoplankton has been widely explored, the mechanisms involving the cell surface are poorly understood. Here, the model marine diatom Phaeodactylum tricornutum was cultured under different nitrogen (N), and phosphorus (P) availabilities from the f/2 to the f/20 level in the laboratory; the diatom's accumulation of cadmium (Cd) and the effects of the physical and chemical properties of the cell wall were investigated at the single-cell level. Under higher N and/or P supply at the f/2 level, both the adsorption and uptake of Cd were enhanced in the P. tricornutum cells. The N and P increased the ion-binding sites on the cell surface, causing more negative surface potential and less depolarization of the diatoms' cell walls. Up-regulated transporter genes were detected in those cells with enriched nutrient supply, which could be attributed to the higher Cd uptake. These results strongly indicate that N and P are critical nutrients for frustule-mediated metal accumulation and tolerance in marine diatoms. Our study provides new clues on the nutrient-dependent cell-surface physical and chemical mechanisms involved in metal toxicity in marine diatoms.

Tuning the Biological Activity of Camphorimine Complexes through Metal Selection

The cytotoxic activity of four sets of camphorimine complexes based on the Cu(I), Cu(II), Ag(I), and Au(I) metal sites were assessed against the cisplatin-sensitive A2780 and OVCAR3 ovarian cancer cells. The results showed that the gold complexes were ca. one order of magnitude more active than the silver complexes, which in turn were ca. one order of magnitude more active than the copper complexes. An important finding was that the cytotoxic activity of the Ag(I) and Au(I) camphorimine complexes was higher than that of cisplatin. Another relevant aspect was that the camphorimine complexes did not interact significantly with DNA, in contrast with cisplatin. The cytotoxic activity of the camphorimine complexes displayed a direct relationship with the cellular uptake by OVCAR3 cells, as ascertained by PIXE (particle-induced X-ray emission). The levels of ROS (reactive oxygen species) formation exhibited an inverse relationship with the reduction potentials for the complexes with the same metal, as assessed by cyclic voltammetry. In order to gain insight into the toxicity of the complexes, their cytotoxicity toward nontumoral cells (HDF and V79 fibroblasts) was evaluated. The in vivo cytotoxicity of complex 5 using the nematode Caenorhabditis elegans was also assessed. The silver camphorimine complexes displayed the highest selectivity coefficients (activity vs. toxicity).

Therapeutic potential of vanadium complexes with 1,10-phenanthroline ligands, quo vadis? Fate of complexes in cell media and cancer cells

V^IVO-complexes formulated as [V^IVO(OSO₃)(phen)₂] (1) (phen = 1,10-phenanthroline), [V^IVO(OSO₃)(Me₂phen)₂] (2) (Me₂phen = 4,7-dimethyl-1,10-phenanthroline) and [V^IVO(OSO₃)(amphen)₂] (3) (amphen = 5-amino-1,10-phenanthroline) were prepared and stability in cell incubation media evaluated. Their cytotoxicity was determined against the A2780 (ovarian), MCF7 (breast) and PC3 (prostate) human cancer cells at different incubation times. While at 3 and 24 h the cytotoxicity differs for complexes and corresponding free ligands, at 72 h incubation all compounds are equally active presenting low IC₅₀ values. Upon incubation of A2780 cells with 1-3, cellular distribution of vanadium in cytosol, membranes, nucleus and cytoskeleton, indicate that the uptake of V is low, particularly for 1, and that the uptake pattern depends on the ligand. Nuclear microscopic techniques are used for imaging and elemental quantification in whole PC3 cells incubated with 1. Once complexes are added to cell culture media, they decompose, and with time most V^IV oxidizes to V^V-species. Modeling of speciation when [V^IVO(OSO₃)(phen)₂] (1) is added to cell media is presented. At lower concentrations of 1, V^IVO- and phen-containing species are mainly bound to bovine serum albumin, while at higher concentrations [V^IVO(phen)_n]²⁺-complexes become relevant, being predicted that the species taken up and mechanisms of action operating depend on the total concentration of complex. This study emphasizes that for these V^IVO-systems, and probably for many others involving oxidovanadium or other labile metal complexes, it is not possible to identify active species or propose mechanisms of cytotoxic action without evaluating speciation occurring in cell media.

The roles of silicon in combating cadmium challenge in the Marine diatom Phaeodactylum tricornutum

Marine phytoplankton possess a sophisticated homeostatic network to counteract metal toxicity. Changes in environmental conditions such as ambient nutrient concentrations can significantly impact their intrinsic metal sensitivity. In this study, we evaluated the role of silicon (Si) in counteracting cadmium (Cd) toxicity in the marine diatom Phaeodactylum tricornutum. We first demonstrated that Si enrichment dramatically enhanced Cd tolerance and changed the Cd accumulation in the diatom. Our modeling suggested that Si-enriched cells adsorbed more Cd but had a higher Cd elimination rate than the Si-starved cells. Examinations by atomic force microscopy and X-ray photoelectron spectroscopy revealed that the Si-enriched cells had better silification and more SiO^- in the cell walls, which markedly lowered the surface potential of the diatom cells and allowed them to attract more Cd. Although the Si-enriched cells tended to have a high Cd burden when facing Cd stress, they suppressed the increase of intracellular Cd by both down-regulating the influx transporter ZIP and up-regulating the efflux transporter ATPase5-1B. Our study shows the significant roles Si plays in maintaining metal homeostasis and combating Cd challenge in marine diatoms.

Salinity-dependent nanostructures and composition of cell surface and its relation to Cd toxicity in an estuarine diatom

The interactions between metal and phytoplankton are affected by salinity in estuarine environments. While water chemistry is an important factor regulating the metal bioavailability in phytoplankton, the physiological adaptation of the algae cells may also change their intrinsic response to metals. In this work, we tried to interpret the salinity-dependent Cd toxicity in a pennate diatom Nitzchia closterium from a biological side. As with many studies, we observed Cd toxicity to the diatom increased with decreasing salinity. However, changing free Cd ion concentrations may be partly responsible for the enhanced Cd toxicity. Multiple evidences showed that diatom cells acclimated at low salinity had stronger intrinsic Cd adsorption capacity. Salinity significantly affected not only the nanostructures but also the biochemical composition in the cell surface of the diatom. Diatom cells grown at lower salinity had a lower surface potential, higher specific surface area, and more sulfur-containing groups in the cell wall, leading to stronger Cd binding capacity in the cells. Meanwhile, more Si was present as poly-silicic acid when the salinity decreased. The change of Si content and speciation in the cell wall are also considered a major reason for the variations of Cd surface binding. Our study provided new clues for the salinity-dependent metal toxicity in marine diatoms.

Phytoplankton community-level bio-optical assessment in a naturally mercury contaminated Antarctic ecosystem (Deception Island)

Mercury naturally contaminated environments, like Deception Island (Antarctica), are field labs to study the physiological consequences of chronic Hg-exposure at the community level. Deception Island volcanic vents lead to a continuous chronic exposure of the phytoplanktonic communities to potentially toxic Hg concentrations. Comparing Hg-contaminated areas (Fumarolas Bay - FB, Gabriel de Castilla station - GdC station), no significant differences in chlorophyll a concentrations were detected, indicating that biomass production was not impaired by Hg-exposure despite the high Hg levels found in the cells. Moreover, the electron transport energy, responsible for energy production, also presented rather similar values in phytoplankton from both locations. Regarding FB communities, although the cells absorbed and trapped lower amounts of energy, the effect of Hg was not relevant in the photochemical work produced by the electronic transport chain. This might be due to the activation of alternative internal electron donors, as counteractive measure to the energy accumulated inside the cells. In fact, this alternative electron pathway, may have allowed FB communities to have similar electron transport energy fluxes without using respiration as photoprotective measure towards excessive energy. Hg-exposed cells also showed a shift from the energy flux towards the PS I (photosystem I), alleviating the excessive energy accumulation at the PS II (photosystem II) and preventing an oxidative burst. Our findings suggest a higher energy use efficiency in the communities exposed to volcanic Hg, which is not observable in cultured phytoplankton species grown under Hg exposure. This may constitute a metabolic adaptation, driven from chronic exposure allowing the maintenance of high levels of primary productivity under the assumingly unfavourable conditions of Deception Island.

A freshwater diatom challenged by Zn: Biochemical, physiological and metabolomic responses of Tabellaria flocculosa(Roth) Kützing

Freshwater ecosystems are under threatening anthropogenic pressures worldwide, namely by metals. Diatoms are used as water quality indicators, but the influence of micronutrients such as Zn and its impacts are poorly understood. Thus, our study aimed to elucidate the tolerance level, the cellular targets and the responses to counteract Zn toxicity of freshwater diatoms by exposing Tabellaria flocculosa, isolated from a Zn contaminated stream. Biochemical, physiological and metabolomic approaches were used. It was demonstrated that Zn is toxic to T. flocculosa at concentrations occurring in contaminated environments. At low stress (30 μg Zn/L) few alterations in the metabolome were observed, but the enzymatic (SOD, CAT) and molecular (GSH, GSSG) antioxidant systems were induced, protecting cells from oxidative stress. At moderate stress (500 μg Zn/L) the main changes occurred in the metabolome (increases in fatty acids, amino acids, terpenoids, glycerol and phosphate, decreases in sucrose and lumichrome) with a moderate increase in cell damage (LPO and PC). The concerted action of all these mechanisms resulted in a non-significant decrease of growth, explaining the survival of this T. flocculosa strain in an environment with this Zn concentration. At the highest stress level (1000 μg Zn/L) the metabolome was identical to 500 μg Zn/L, and the induction of antioxidant systems and extracellular ion chelation (exopolysaccharides, frustulins) were the main responses to the increase of Zn toxicity. However, these mechanisms were unable to effectively abrogate cellular damage and growth reduction was observed. Moreover, the decrease in sucrose and especially in lumichrome should be tested as new specific markers of Zn toxicity. The information obtained in this study can assist in environmental risk assessment policies, support the prediction of diatom behaviour in highly impacted Zn environments, such as mining scenarios, and may help develop new indices, which include alterations induced by metals.

3D map distribution of metallic nanoparticles in whole cells using MeV ion microscopy

In this work, a new tool was developed, the MORIA program that readily translates Rutherford backscattering spectrometry (RBS) output data into visual information, creating a display of the distribution of elements in a true three-dimensional (3D) environment. The program methodology is illustrated with the analysis of yeast Saccharomyces cerevisiae cells, exposed to copper oxide nanoparticles (CuO-NP) and HeLa cells in the presence of gold nanoparticles (Au-NP), using different beam species, energies and nuclear microscopy systems. Results demonstrate that for both cell types, the NP internalization can be clearly perceived. The 3D models of the distribution of CuO-NP in S. cerevisiae cells indicate the nonuniform distribution of NP in the cellular environment and a relevant confinement of CuO-NP to the cell wall. This suggests the impenetrability of certain cellular organelles or compartments for NP. By contrast, using a high-resolution ion beam system, discretized agglomerates of Au-NP were visualized inside the HeLa cell. This is consistent with the mechanism of entry of these NPs in the cellular space by endocytosis enclosed in endosomal vesicles. This approach shows RBS to be a powerful imaging technique assigning to nuclear microscopy unparalleled potential to assess nanoparticle distribution inside the cellular volume.

Iron incorporation in biosilica of the marine diatom Stephanopyxis turris: dispersed or clustered?

Iron incorporation into diatom biosilica was investigated for the species Stephanopyxis turris. It is known that several "foreign" elements (e.g., germanium, titanium, aluminum, zinc, iron) can be incorporated into the siliceous cell walls of diatoms in addition to silicon dioxide (SiO₂). In order to examine the amount and form of iron incorporation, the iron content in the growth medium was varied during cultivation. Fe:Si ratios of isolated cell walls were measured by ICP-OES. SEM studies were performed to examine of a possible influence of excess iron during diatom growth upon cell wall formation. The chemical state of biosilica-attached iron was characterized by a combination of infrared, ²⁹Si MAS NMR, and EPR spectroscopy. For comparison, synthetic silicagels of variable iron content were studied. Our investigations show that iron incorporation in biosilica is limited. More than 95% of biosilica-attached iron is found in the form of iron clusters/nanoparticles. In contrast, iron is preferentially dispersedly incorporated within the silica framework in synthetic silicagels leading to Si-O-Fe bond formation.

Genotoxic and mutagenic evaluation of water samples from a river under the influence of different anthropogenic activities

Pollution of aquatic ecosystems is associated with the discharge of mostly industrial and urban effluents, which may cause loss of biodiversity and damage to public health. This study aims to evaluate the toxicity and mutagenicity of water samples collected in the Corrente River, a major waterway in the river basin district of Pedro II, Piauí (Brazil). This river is exposed to intense anthropogenic influence from urban, automotive mechanical and family farm waste, and it is used as the main source of water supply by the population. Water samples were collected during the rainy and dry seasons, at four sites in the Corrente River, and evaluated by physicochemical, microbiological and inorganic elements analyses. The samples were evaluated for mutagenicity using the Allium cepa test (toxicity, chromosomal aberration and micronucleus tests) and fish (Tilapia rendalli and Hoplias malabaricus). The physicochemical, microbiological and inorganic results show a large contribution to the pollution loads at collection points in the town of Pedro II, demonstrating the influence of urban pollution. The Al, Si, Ti, Cr, Ni and Cu contents were determined by PIXE. These same Corrente River water samples demonstrated mutagenic effect for A. cepa and fish, as well as toxicity in the A. cepa test. The observations of mutagenic effect may suggest that the complex mixture of agents is comprised of both clastogenic and aneugenic agents. This study also showed the need for constant monitoring in places with environmental degradation caused by urban sewage discharges.

Where is it and how much? Mapping and quantifying elements in single cells

The biological function of a chemical element in cells not only requires the determination of its intracellular quantity, but also the spatial distribution of its concentration. Different strategies can be employed to quantify and map the intracellular concentration of elements in single cells. The assessment of the intracellular elemental concentration, which is the relevant information, requires the measurement of cell volume. This challenging and demanding task requires combining different techniques allowing gathering of both morphological and compositional information on the same cell. Moreover, the need to analyse samples more similar to their natural state requires complex hardware equipment, and supplementary efforts in preparation protocols. Nevertheless, the response to the question: "where is it and how much?" is worth all these efforts. This review aims at providing an insight into the recent and most advanced techniques and strategies for quantifying and mapping chemical elements in single cells. We describe and discuss indirect detection techniques (label based) which make use of fluorescent dyes, and direct ones (label free), such as particle induced X-ray emission, proton backscattering spectrometry, scanning transmission ion spectrometry, nano-secondary ion mass spectrometry, X-ray fluorescence microscopy, complemented by X-ray imaging.

Elemental mapping inventory of the fish Liza aurata brain: a biomarker of metal pollution vulnerability

The elemental distributions in optic tectum of brains of wild Liza aurata a teleost fish captured in polluted and reference coastal areas were assessed quantitatively by nuclear microscopy providing insights into brain vulnerability to metal pollution. Elemental maps enabled us to visualize optic tectum layers and identify cellular arrangements. Whereas Cl, K and Ca contents identify meninges, the Ca, Fe and Zn concentrations distinguish the underneath grey matter, white matter and inner cellular layers. Exposed animals showed significantly decreased P concentrations and increased contents of Cu, Zn and Ni in all brain structures. These changes highlight homeostasis modification, altered permeability of the blood-brain barrier and suggest risk for neurological toxicity. Our study initiated for the first time an inventory of physiological measures containing images and elemental compositions of brain regions of fish exposed to different environmental conditions. This will help defining total and local brain vulnerability to metals and pollution levels.