Proteomic analysis of chromate-induced modifications in Pseudokirchneriella subcapitata

Physiological and proteomic responses of Chlamydomonas reinhardtii to arsenate and lead mixtures

Arsenic (As) and lead (Pb) are frequently emitted from various sources into environment, but microbial responses to their combined toxicity have not been systematically investigated. In this study, Chlamydomonas reinhardtii was exposed to two levels of arsenate (As (V), 50, 500 μg/L), Pb (II) (500, 5000 μg/L) and their mixture (50 μg/L As (V) + 500 μg/L Pb (II); 500 μg/L As (V) + 5000 μg/L Pb (II)). The growth of C. reinhardtii was inhibited more remarkably by As (V) than by Pb (II). The As stress was alleviated by Pb in the 50 μg/L As (V) + 500 μg/L Pb (II) treatment, but was enhanced upon the 500 μg/L As (V) + 5000 μg/L Pb (II) exposure, with more pronounced changes in a number of physiological parameters of the algal cells. Proteomic results showed that 71 differently expressed proteins (DEPs) in the treatment of 50 μg/L As (V) + 500 μg/L Pb (II), and 167 DEPs were identified in that of 500 μg/L As (V) + 5000 μg/L Pb (II). These proteins were involved in energy metabolism, photosynthetic carbon fixation, reactive oxygen scavenging and defense, and amino acid synthesis. Taken together, these physiological and proteomic data demonstrated that C. reinhardtii could resist the As (V) and Pb (II) combined treatments through extracellular complexation and intracellular pathways.

Intraspecific variability in membrane proteome, cell growth, and morphometry of the invasive marine neurotoxic dinoflagellate Alexandrium pacificum grown in metal-contaminated conditions

Over the past decades, the occurrence, distribution and intensity of harmful algal blooms involving the dinoflagellate Alexandrium pacificum have increased in marine coastal areas disturbed by anthropogenic inputs. This invasive species produces saxitoxin, which causes the paralytic shellfish poisoning syndrome in humans upon consumption of contaminated seafood. Blooms of A. pacificum have been reported in metal-contaminated coastal ecosystems, suggesting some ability of these microorganisms to adapt to and/or resist in metal stress conditions. This study seeks to characterize the modifications in membrane proteomes (by 2-D electrophoresis coupled to LC-MS/MS), cell growth and morphometry (measured with an inverted microscope), in response to metal stress (addition of Zn²⁺, Pb²⁺, Cu²⁺ and Cd²⁺), in two Mediterranean A. pacificum strains: SG C10-3 and TAR C5-4F, respectively isolated from the Santa Giusta Lagoon (Sardinia, Italy) and from the Tarragona seaport (Spain), both metal-contaminated ecosystems. In the SG C10-3 cultures grown in a metal cocktail, cell growth was significantly delayed, and cell size increased (22% of 37.5 μm cells after 25 days of growth). Conversely, no substantial change was observed for cell growth or cell size in the TAR C5-4F cultures grown in a metal cocktail (P > 0.10), thus indicating intraspecific variability in the responses of A. pacificum strains to metal contamination. Regardless of the conditions tested, the total number of proteins constituting the membrane proteome was significantly higher for TAR C5-4F than for SG C10-3, which may help TAR C5-4F to thrive better in contaminated conditions. For both strains, the total number of proteins constituting the membrane proteomes was significantly lower in response to metal stress (29% decrease in the SG C10-3 proteome: 82 ± 12 proteins for controls, and 58 ± 12 in metal-contaminated cultures; 17% decrease in the TAR C5-4F proteome: 101 ± 8 proteins for controls, and 84 ± 5 in metal-contaminated cultures). Moreover, regardless of the strain, proteins with significantly modified expression in response to stress were mainly down-regulated (representing 45% of the proteome for SG C10-3 and 38% for TAR C5-4F), clearly showing the harmful effects of the metals. Protein down-regulation may affect cell transport (actin and phospholipid scramblase in SG C10-3), photosynthesis (RUBISCO in SG C10-3, light-harvesting protein in TAR C5-4F, and high-CO₂-inducing periplasmic protein in both strains), and finally energy metabolism (ATP synthase in both strains). However, other modifications in protein expression may confer to these A. pacificum strains a capacity for adaptation and/or resistance to metal stress conditions, for example by (i) limiting the metal entry through the plasma membrane of the SG C10-3 cells (via the down-regulation of scramblase) and/or (ii) reducing the oxidative stress generated by metals in SG C10-3 and TAR C5-4F cells (due to down-regulation of ATP-synthase).

Toxicity of functionalized fullerene and fullerene synthesis chemicals

Fullerene is one of the most studied carbon-based nanoparticles due to its unique structure and potential for diverse applications. This study focuses on toxicological effects of two fullerene nanomaterials, contributing to ecological as well as human risk assessment strategies. The biological responses from two basic fullerene materials, aqueous-nanoC₆₀ and alkaline-synthesized fullerenol, were examined using four model organisms. Bioassays were conducted on bacteria (Pseudomonas aeruginosa and Staphylococcus aureus) to determine population impacts and to assess mechanisms of cellular effects for both Gram-negative and Gram-positive species. LC₅₀ of aqu-nC₆₀ stirred for 28 days for P. aeruginosa was estimated to be 1336 mg/L; however, toxicity of the same aqu-nC₆₀ preparation for S. aureus was insignificant. Freshwater green algae Raphidocelus subcapitata and invertebrate Ceriodaphnia dubia were exposed to 28-day stirred aqu-nC₆₀ with no significant toxicological impact. Aqu-nC₆₀ stirred for 14 days bore no toxicity within two orders of magnitude greater than the highest concentration administered. LC₅₀ for organisms exposed to alkaline-synthesized fullerenol prepared in the laboratory was 2409 mg/L for P. aeruginosa with no determinable toxicity to S. aureus, and 1462 mg/L and 45.2 mg/L for R. subcapitata and C. dubia, respectively. Toxicity thresholds for commercially-prepared fullerenol were lower for all species, an impact attributed to the presence of impurities. Mechanistic analysis of membrane damage on bacteria by laboratory-prepared fullerenol indicated necrotic and apoptotic responses with and without photoactivation. Toxicological responses from fullerenol synthesis by-products were only determinable for C. dubia with effects attributable to impurities.

Callitriche cophocarpa (water starwort) proteome under chromate stress: evidence for induction of a quinone reductase

Chromate-induced physiological stress in a water-submerged macrophyte Callitriche cophocarpa Sendtn. (water starwort) was tested at the proteomic level. The oxidative stress status of the plant treated with 1 mM Cr(VI) for 3 days revealed stimulation of peroxidases whereas catalase and superoxide dismutase activities were similar to the control levels. Employing two-dimensional electrophoresis, comparative proteomics enabled to detect five differentiating proteins subjected to identification with mass spectrometry followed by an NCBI database search. Cr(VI) incubation led to induction of light harvesting chlorophyll a/b binding protein with a concomitant decrease of accumulation of ribulose bisphosphate carboxylase (RuBisCO). The main finding was, however, the identification of an NAD(P)H-dependent dehydrogenase FQR1, detectable only in Cr(VI)-treated plants. The FQR1 flavoenzyme is known to be responsive to oxidative stress and to act as a detoxification protein by protecting the cells against oxidative damage. It exhibits the in vitro quinone reductase activity and is capable of catalyzing two-electron transfer from NAD(P)H to several substrates, presumably including Cr(VI). The enhanced accumulation of FQR1 was chromate-specific since other stressful conditions, such as salt, temperature, and oxidative stresses, all failed to induce the protein. Zymographic analysis of chromate-treated Callitriche shoots showed a novel enzymatic protein band whose activity was attributed to the newly identified enzyme. We suggest that Cr(VI) phytoremediation with C. cophocarpa can be promoted by chromate reductase activity produced by the induced quinone oxidoreductase which might take part in Cr(VI) → Cr(III) bioreduction process and thus enable the plant to cope with the chromate-generated oxidative stress.

Modifications of the soluble proteome of a mediterranean strain of the invasive neurotoxic dinoflagellate Alexandrium catenella under metal stress conditions

The soluble proteome of the mediterranean strain ACT03 of the invasive neurotoxic dinoflagellate Alexandrium catenella exposed to lead or zinc at 6, 12 or 18μM (total concentrations), or under control conditions, was characterized by two-dimensional gel electrophoresis (2-DE). Zinc reduced (P<0.05) the total number of protein spots (-41%, -52% and -60%, at 6, 12 or 18μM, respectively). Besides, most of the proteins constituting the soluble proteome were down-regulated in response to lead or zinc stresses. These proteins were involved mainly in photosynthesis (20-37% for lead; 36-50% for zinc) (ribulose-1,5-bisphosphate carboxylase/oxygenase: RUBISCO; ferredoxin-NADP⁺ reductase: FNR; peridinin-chlorophyll a-protein: PCP), and in the oxidative stress response (29-34% for lead; 17-36% for zinc) (superoxide dismutase: SOD; proteasome α/β subunits). These negative effects could be partly compensated by the up-regulation of specific proteins such as ATP-synthase β subunit (+16.3 fold after exposure to lead at 12μM). Indeed, an increase in the abundance of ATP-synthase could enrich the ATP pool and provide more energy available for the cells to survive under metal stress, and make the ATP-synthase transport of metal cations out of the cells more efficient. Finally, this study shows that exposure to lead or zinc have a harmful effect on the soluble proteome of A. catenella ACT03, but also suggests the existence of an adaptative proteomic response to metal stresses, which could contribute to maintaining the development of this dinoflagellate in trace metal-contaminated ecosystems.

Responses of the alga Pseudokirchneriella subcapitata to long-term exposure to metal stress

The green alga Pseudokirchneriella subcapitata has been widely used in ecological risk assessment, usually based on the impact of the toxicants in the alga growth. However, the physiological causes that lead algal growth inhibition are not completely understood. This work aimed to evaluate the biochemical and structural modifications in P. subcapitata after exposure, for 72 h, to three nominal concentrations of Cd(II), Cr(VI), Cu(II) and Zn(II), corresponding approximately to 72 h-EC10 and 72 h-EC50 values and a high concentration (above 72 h-EC90 values). The incubation of algal cells with the highest concentration of Cd(II), Cr(VI) or Cu(II) resulted in a loss of membrane integrity of ~16, 38 and 55%, respectively. For all metals tested, an inhibition of esterase activity, in a dose-dependent manner, was observed. Reduction of chlorophyll a content, decrease of maximum quantum yield of photosystem II and modification of mitochondrial membrane potential was also verified. In conclusion, the exposure of P. subcapitata to metals resulted in a perturbation of the cell physiological status. Principal component analysis revealed that the impairment of esterase activity combined with the reduction of chlorophyll a content were related with the inhibition of growth caused by a prolonged exposure to the heavy metals.

Over-accumulation of putrescine induced by cyclohexylamine interferes with chromium accumulation and partially restores pollen tube growth in Actinidia deliciosa

Both trivalent and hexavalent chromium, i.e., Cr(III) and Cr(VI), respectively, were previously demonstrated to affect in vitro germination and ultrastructure of kiwifruit (Actinidia deliciosa) pollen. In the present work, the response to chromium in germinating pollen was evaluated in terms of changes in the polyamine profile. Slight, though significant, increases in free spermidine and spermine occurred after exposure to Cr(III), while the levels remained almost unchanged after Cr(VI) treatment. The spermidine synthase inhibitor cyclohexylamine (CHA) caused a dramatic increase in free putrescine in both chromium-treated and untreated samples, while spermidine content was not affected. Interestingly, CHA positively affected the performance of chromium-treated pollen by partially, though significantly, restoring pollen tube growth. The major growth recovery was registered with 1 mM CHA in the presence of Cr(VI), concomitant with a considerable reduction in uptake of the metal. Conversely, endogenous calcium levels were more heavily affected in Cr(III)-treated pollen. The effect of CHA on production of reactive oxygen species also varied depending on the chromium species. The response of pollen to the CHA-induced putrescine excess was compared with that exerted by an exogenous supply of the same diamine. Results show that in Cr(III)-treated pollen, putrescine over-accumulation induced by CHA exerted similar effects as exogenous putrescine, while this was not true in the Cr(VI) treatment. It appears that the diamine was able to improve pollen tolerance to metal stress through different mechanisms, mostly depending upon the chromium species, namely via reduced metal uptake or by substituting for calcium.

Toxicogenomic approaches for understanding molecular mechanisms of heavy metal mutagenicity and carcinogenicity

Heavy metals that are harmful to humans include arsenic, cadmium, chromium, lead, mercury, and nickel. Some metals or their related compounds may even cause cancer. However, the mechanism underlying heavy metal-induced cancer remains unclear. Increasing data show a link between heavy metal exposure and aberrant changes in both genetic and epigenetic factors via non-targeted multiple toxicogenomic technologies of the transcriptome, proteome, metabolome, and epigenome. These modifications due to heavy metal exposure might provide a better understanding of environmental disorders. Such informative changes following heavy metal exposure might also be useful for screening of biomarker-monitored exposure to environmental pollutants and/or predicting the risk of disease. We summarize advances in high-throughput toxicogenomic-based technologies and studies related to exposure to individual heavy metal and/or mixtures and propose the underlying mechanism of action and toxicant signatures. Integrative multi-level expression analysis of the toxicity of heavy metals via system toxicology-based methodologies combined with statistical and computational tools might clarify the biological pathways involved in carcinogenic processes. Although standard in vitro and in vivo endpoint testing of mutagenicity and carcinogenicity are considered a complementary approach linked to disease, we also suggest that further evaluation of prominent biomarkers reflecting effects, responses, and disease susceptibility might be diagnostic. Furthermore, we discuss challenges in toxicogenomic applications for toxicological studies of metal mixtures and epidemiological research. Taken together, this review presents toxicogenomic data that will be useful for improvement of the knowledge of carcinogenesis and the development of better strategies for health risk assessment.

PROTEOMICS in aquaculture: applications and trends

Over the last forty years global aquaculture presented a growth rate of 6.9% per annum with an amazing production of 52.5 million tonnes in 2008, and a contribution of 43% of aquatic animal food for human consumption. In order to meet the world's health requirements of fish protein, a continuous growth in production is still expected for decades to come. Aquaculture is, though, a very competitive market, and a global awareness regarding the use of scientific knowledge and emerging technologies to obtain a better farmed organism through a sustainable production has enhanced the importance of proteomics in seafood biology research. Proteomics, as a powerful comparative tool, has therefore been increasingly used over the last decade to address different questions in aquaculture, regarding welfare, nutrition, health, quality, and safety. In this paper we will give an overview of these biological questions and the role of proteomics in their investigation, outlining the advantages, disadvantages and future challenges. A brief description of the proteomics technical approaches will be presented. Special focus will be on the latest trends related to the aquaculture production of fish with defined nutritional, health or quality properties for functional foods and the integration of proteomics techniques in addressing this challenging issue.

Proteomic changes and molecular effects associated with Cr(III) and Cr(VI) treatments on germinating kiwifruit pollen

The present study is aimed at identifying molecular changes elicited by Cr(III) and Cr(VI) on germinating kiwifruit pollen. To address this question, comparative proteomic and DNA laddering analyses were performed. While no genotoxic effect was detected, a number of proteins whose accumulation levels were altered by treatments were identified. In particular, the upregulation of some proteins involved in the scavenging response, cell redox homeostasis and lipid synthesis could be interpreted as an oxidative stress response induced by Cr treatment. The strong reduction of two proteins involved in mitochondrial oxidative phosphorylation and a decline in ATP levels were also observed. The decrease of pollen energy availability could be one of the causes of the severe inhibition of the pollen germination observed upon exposure to both Cr(III) and Cr(VI). Finally, proteomic and biochemical data indicate proteasome impairment: the consequential accumulation of misfolded/damaged proteins could be an important molecular mechanism of Cr(III) toxicity in pollen.