Effect of cadmium in the microalga Chlorella sorokiniana: A proteomic study

The cadmium tolerance and bioaccumulation mechanism of Tetratostichococcus sp. P1: insight from transcriptomics analysis

Cadmium (Cd) has become a severe issue in relatively low concentration and attracts expert attention due to its toxicity, accumulation, and biomagnification in living organisms. Cd does not have a biological role and causes serious health issues. Therefore, Cd pollutants should be reduced and removed from the environment. Microalgae have great potential for Cd absorption for waste treatment since they are more environmentally friendly than existing treatment methods and have strong metal sorption selectivity. This study evaluated the tolerance and ability of the microalga Tetratostichococcus sp. P1 to remove Cd ions under acidic conditions and reveal mechanisms based on transcriptomics analysis. The results showed that Tetratostichococcus sp. P1 had a high Cd tolerance that survived under the presence of Cd up to 100 µM, and IC50, the half-maximal inhibitory concentration value, was 57.0 μM, calculated from the change in growth rate based on the chlorophyll content. Long-term Cd exposure affected the algal morphology and photosynthetic pigments of the alga. Tetratostichococcus sp. P1 removed Cd with a maximum uptake of 1.55 mg g-1 dry weight. Transcriptomic analysis revealed the upregulation of the expression of genes related to metal binding, such as metallothionein. Group A, Group B transporters and glutathione, were also found upregulated. While the downregulation of the genes were related to photosynthesis, mitochondria electron transport, ABC-2 transporter, polysaccharide metabolic process, and cell division. This research is the first study on heavy metal bioremediation using Tetratostichococcus sp. P1 and provides a new potential microalga strain for heavy metal removal in wastewater.[Figure: see text]Abbreviations:BP: Biological process; bZIP: Basic Leucine Zipper; CC: Cellular component; ccc1: Ca (II)-sensitive cross complementary 1; Cd: Cadmium; CDF: Cation diffusion facilitator; Chl: Chlorophyll; CTR: Cu TRansporter families; DAGs: Directed acyclic graphs; DEGs: Differentially expressed genes; DVR: Divinyl chlorophyllide, an 8-vinyl-reductase; FPN: FerroportinN; FTIR: Fourier transform infrared; FTR: Fe TRansporter; GO: Gene Ontology; IC50: Growth half maximal inhibitory concentration; ICP: Inductively coupled plasma; MF: molecular function; NRAMPs: Natural resistance-associated aacrophage proteins; OD: Optical density; RPKM: Reads Per Kilobase of Exon Per Million Reads Mapped; VIT1: Vacuolar iron transporter 1 families; ZIPs: Zrt-, Irt-like proteins.

Dissecting the mechanism of synergistic interactions between Aspergillus fumigatus and the microalgae Synechocystis sp. PCC6803 under Cd(II) exposure: insights from untargeted metabolomics

Co-culturing fungi and microalgae may effectively remediate wastewater containing Cd and harvest microalgae. Nevertheless, a detailed study of the mechanisms underlying the synergistic interactions between fungi and microalgae under Cd(II) exposure is lacking. In this study, Cd(II) exposure resulted in a significant enhancement of antioxidants, such as glutathione (GSH), malondialdehyde (MDA), hydrogen peroxide (H2O2) and superoxide dismutase (SOD) compared to the control group, suggesting that the cellular antioxidant defense response was activated. Extracellular proteins and extracellular polysaccharides of the symbiotic system were increased by 60.61 % and ,24.29 %, respectively, after Cd(II) exposure for 72 h. The adsorption behavior of Cd(II) was investigated using three-dimensional fluorescence excitation-emission matrix (3D-EEM), fourier transform infrared spectroscopy (FTIR), and scanning electron microscope (SEM). Metabolomics results showed that the TCA cycle provided effective material and energy supply for the symbiotic system to resist the toxicity of Cd(II); Proline, histidine, and glutamine strengthened the synergistic adsorption capacity of the fungus and microalgae. Overall, the theoretical foundation for a deep comprehension of the beneficial interactions between fungi and microalgae under Cd(II) exposure and the role of the fungal-algal symbiotic system in the management of heavy metal pollution is provided by this combined physiological and metabolomic investigation.

Unraveling the molecular response of Brassica napus hairy roots in the active Naphthol blue-black removal: Insights from proteomic analysis

In vitro plant cultures are able to remove and metabolise xenobiotics, making them promising tools for decontamination strategies. In this work, we evaluated Brassica napus hairy roots (HRs) to tolerate and remove high concentrations of the azo dye Naphthol Blue-Black (NBB). Experiments were performed using both growing and resting culture systems at different pHs. Reuse of HRs biomass was evaluated in successive decolourisation cycles. Proteomics was applied to understand the molecular responses likely to be involved in the tolerance and removal of NBB. The HRs tolerated up to 480 µg mL-1 NBB, and 100 % removal was achieved at 180 µg mL-1 NBB after 10 days using both culture systems. Interestingly, the HRs are robust enough to be reused, showing 55-60 % removal even after three reuse cycles. The highest dye removal rates were achieved during the first 2 days of incubation, as initial removal is mainly driven by passive processes. Active mechanisms are triggered later by regulating the expression of proteins with different biological functions, mainly those related to xenobiotic metabolism, such as hydrolytic and redox enzymes. These results suggest that B. napus HRs are a robust tool that could make a significant contribution to textile wastewater treatment.

New mechanistic insights of nanoplastics synergistic cadmium induced overactivation of trypsin: Joint analysis from protein multi-level conformational changes and computational modeling

Nanoplastics (NPs) are emerging global contaminants that can exacerbate the animal toxicity and cytotoxicity of cadmium (Cd). However, the mechanisms by which NPs influence the toxic effects of Cd on key functional proteins within the body remain unknown. In this study, trypsin, a protein that is prone to coexist with NPs in the digestive tract, was selected as the target protein. The effects and mechanisms of NPs on Cd2+-induced structural damage at multiple levels and alterations in the biological function of trypsin were investigated using multi-spectroscopy techniques, enzyme activity assays, and computational modeling. Results indicated that the Cd2+-induced decrease and red shift of the trypsin backbone peak were exacerbated by the presence of NPs, leading to more serve backbone loosening. Furthermore, compared to Cd2+, NPs@Cd2+ caused a more pronounced reduction in the α-helix content of trypsin. These structural changes led to the opening of the trypsin pocket and the overactivation of the enzyme (NPs@Cd2+: 227.22%; Cd2+: 53.35%). Ultimately, the formation of a "protein corona" around NPs@Cd2+ and the metal contact of Cd2+ to the trypsin surface were identified as the mechanisms by which NPs enhanced the protein toxicity of Cd2+. This study elucidates, for the first time, the effects and underlying mechanisms of NPs on the toxicity of key functional proteins of Cd2+. These findings offer novel mechanistic insights and critical evidence essential for evaluating the risks associated with NPs.

Global transcriptome analysis identifies critical functional modules associated with multiple abiotic stress responses in microalgae Chromochloris zofingiensis

In the current study, systems biology approach was applied to get a deep insight regarding the regulatory mechanisms of Chromochloris zofingiensis under overall stress conditions. Meta-analysis was performed using p-values combination of differentially expressed genes. To identify the informative models related to stress conditions, two distinct weighted gene co-expression networks were constructed and preservation analyses were performed using medianRankand Zsummary algorithms. Moreover, functional enrichment analysis of non-preserved modules was performed to shed light on the biological performance of underlying genes in the non-preserved modules. In the next step, the gene regulatory networks between top hub genes of non-preserved modules and transcription factors were inferred using ensemble of trees algorithm. Results showed that the power of beta = 7 was the best soft-thresholding value to ensure a scale-free network, leading to the determination of 12 co-expression modules with an average size of 128 genes. Preservation analysis showed that the connectivity pattern of the six modules including the blue, black, yellow, pink, greenyellow, and turquoise changed during stress condition which defined as non-preserved modules. Examples of enriched pathways in non-preserved modules were Oxidative phosphorylation", "Vitamin B6 metabolism", and "Arachidonic acid metabolism". Constructed regulatory network between identified TFs and top hub genes of non-preserved module such as Cz06g10250, Cz03g12130 showed that some specific TFs such as C3H and SQUAMOSA promoter binding protein (SBP) specifically regulates the specific hubs. The current findings add substantially to our understanding of the stress responsive underlying mechanism of C. zofingiensis for future studies and metabolite production programs.

Key Proteomics Tools for Fundamental and Applied Microalgal Research

Microscopic, photosynthetic prokaryotes and eukaryotes, collectively referred to as microalgae, are widely studied to improve our understanding of key metabolic pathways (e.g., photosynthesis) and for the development of biotechnological applications. Omics technologies, which are now common tools in biological research, have been shown to be critical in microalgal research. In the past decade, significant technological advancements have allowed omics technologies to become more affordable and efficient, with huge datasets being generated. In particular, where studies focused on a single or few proteins decades ago, it is now possible to study the whole proteome of a microalgae. The development of mass spectrometry-based methods has provided this leap forward with the high-throughput identification and quantification of proteins. This review specifically provides an overview of the use of proteomics in fundamental (e.g., photosynthesis) and applied (e.g., lipid production for biofuel) microalgal research, and presents future research directions in this field.

Potential use of sludge from El Ferrol Bay (Chimbote, Peru) for the production of lipids in the culture of Scenedesmus acutus (Meyen, 1829)

Despite the extensive development of microalgae biotechnology, it still requires new methodologies to lower production costs, especially in the field of biofuel production. Therefore, innovative methods that facilitate operations and enable cost-effective production are important in driving this industry. In this study, we propose a new low-cost and easy-to-use procedure, addressed to the generation of a culture medium for Scenedesmus acutus. The medium was obtained by thermal reduction of a sludge sample from El Ferrol Bay (Chimbote, Peru), whereby we obtained an aqueous medium. Our results indicated that the aqueous medium incorporates all necessary nutrients for microalgae production; allowing a maximum biomass of 0.75 ± 0.07 g/L with 60% of the medium; while high lipids production (59.42 ± 6.16%) was achieved with 20%. Besides, we quantified, in the experimental medium and at the end of the cultures, the levels of inorganic nutrients such as ammonium, nitrites, nitrates, and phosphates; in addition to COD and TOC, which were significantly reduced ( p < 0.05) after 7 days of culture, mainly in the treatment with 20%. These results suggest tremendous potential for sludge reuse, which also entails a cost reduction in microalgae biomass production, with additional positive impacts on large-scale application over highly polluted environments.

Exogenous GABA supplementation to facilitate Cr (III) tolerance and lipid biosynthesis in Chlorella sorokiniana

Microalgae possess the prospective to be efficiently involved in bioremediation and biodiesel generation. However, conditions of stress often restrict their growth and diminish different metabolic processes. The current study evaluates the potential of GABA to improve the growth of the microalga Chlorella sorokiniana under Cr (III) stress through the exogenous administration of GABA. The research also investigates the concurrent impact of GABA and Cr (III) stress on various metabolic and biochemical pathways of the microalgae. In addition to the control, cultures treated with Cr (III), GABA, and both Cr (III) and GABA treated were assessed for accurately analysing the influence of GABA. The outcomes illustrated that GABA significantly promoted growth of the microalgae, resulting in higher biomass productivity (19.14 mg/L/day), lipid productivity (3.445 mg/L/day) and lipid content (18%) when compared with the cultures under Cr (III) treatment only. GABA also enhanced Chl a content (5.992 μg/ml) and percentage of protein (23.75%). FAMEs analysis by GC-MS and total lipid profile revealed that GABA treatment can boost the production of SFA and lower the level of PUFA, a distribution ideal for improving biodiesel quality. ICP-MS analysis revealed that GABA supplementation could extend Cr (III) mitigation level up to 97.7%, suggesting a potential strategy for bioremediation. This novel study demonstrates the merits of incorporating GABA in C. sorokiniana cultures under Cr (III) stress, in terms of its potential in bioremediation and biodiesel production without disrupting the pathways of photosynthesis and protein production.

Enhanced microalgal biomass and lipid production with simultaneous effective removal of Cd using algae-bacteria-activated carbon consortium added with organic carbon source

Recently, using microalgae to remediate heavy metal polluted water has been attained a huge attention. However, heavy metals are generally toxic to microalgae and consequently decrease biomass accumulation. To address this issue, the feasibility of adding exogenous glucose, employing algae-bacteria system and algae-bacteria-activated carbon consortium to enhance microalgae growth were evaluated. The result showed that Cd2+ removal efficiency was negatively correlated with microalgal specific growth rate. The exogenous glucose alleviated the heavy metal toxicity to algal cells and thus increased the microalgae growth rate. Among the different treatments, the algae-bacteria-activated carbon combination had the highest biomass concentration (1.15 g L-1) and lipid yield (334.97 mg L-1), which were respectively 3.03 times of biomass (0.38 g L-1) and 4.92 times of lipid yield (68.08 mg L-1) in the single microalgae treatment system. Additionally, this algae-bacteria-activated carbon consortium remained a high Cd2+ removal efficiency (91.61%). In all, the present study developed an approach that had a great potential in simultaneous heavy metal wastewater treatment and microalgal lipid production.

Biochemical and proteomic response of the freshwater green alga Pseudochlorella pringsheimii to iron and salinity stressors

BACKGROUND

Pseudochlorella pringsheimii (Ppr) is a green unicellular alga rich with chlorophyll, carotenoids, and antioxidants. As a widespread organism, Ppr must face, and adapt to, many environmental stresses and these are becoming more frequent and more extreme under the conditions of climate change. We therefore focused on salinity induced by NaCl and iron (Fe) variation stresses, which are commonly encountered by algae in their natural environment.

RESULTS

The relatively low stress levels improved the biomass, growth rate, and biochemical components of Ppr. In addition, the radical-scavenging activity, reducing power, and chelating activity were stimulated by lower iron concentrations and all NaCl concentrations. We believe that the alga has adapted to the stressors by increasing certain biomolecules such as carotenoids, phenolics, proteins, and carbohydrates. These act as antioxidants and osmoregulators to protect cell membranes and other cellular components from the harmful effects of ions. We have used SDS-PAGE and 2D-PAGE in combination with tandem mass spectrometry to identify responsive proteins in the proteomes of stressed vs. non-stressed Ppr. The results of 2D-PAGE analysis showed a total of 67 differentially expressed proteins, and SDS-PAGE identified 559 peptides corresponding to 77 proteins. Of these, 15, 8, and 17 peptides were uniquely identified only under the control, iron, and salinity treatments, respectively. The peptides were classified into 12 functional categories: energy metabolism (the most notable proteins), carbohydrate metabolism, regulation, photosynthesis, protein synthesis, stress proteins, oxido-reductase proteins, transfer proteins, ribonucleic-associated proteins, hypothetical proteins, and unknown proteins. The number of identified peptides was higher under salinity stress compared to iron stress.

CONCLUSIONS

A proposed mechanism for the adaptation of Ppr to stress is discussed based on the collected data. This data could serve as reference material for algal proteomics and the mechanisms involved in mediating stress tolerance.

Utilizing proteomics to identify and optimize microalgae strains for high-quality dietary protein: a review

Algae-derived protein has immense potential to provide high-quality protein foods for the expanding human population. To meet its potential, a broad range of scientific tools are required to identify optimal algal strains from the hundreds of thousands available and identify ideal growing conditions for strains that produce high-quality protein with functional benefits. A research pipeline that includes proteomics can provide a deeper interpretation of microalgal composition and biochemistry in the pursuit of these goals. To date, proteomic investigations have largely focused on pathways that involve lipid production in selected microalgae species. Herein, we report the current state of microalgal proteome measurement and discuss promising approaches for the development of protein-containing food products derived from algae.

Realization process of microalgal biorefinery: The optional approach toward carbon net-zero emission

Increasing carbon dioxide (CO2) emission has already become a dire threat to the human race and Earth's ecology. Microalgae are recommended to be engineered as CO2 fixers in biorefinery, which play crucial roles in responding climate change and accelerating the transition to a sustainable future. This review sorted through each segment of microalgal biorefinery to explore the potential for its practical implementation and commercialization, offering valuable insights into research trends and identifies challenges that needed to be addressed in the development process. Firstly, the known mechanisms of microalgal photosynthetic CO2 fixation and the approaches for strain improvement were summarized. The significance of process regulation for strengthening fixation efficiency and augmenting competitiveness was emphasized, with a specific focus on CO2 and light optimization strategies. Thereafter, the massive potential of microalgal refineries for various bioresource production was discussed in detail, and the integration with contaminant reclamation was mentioned for economic and ecological benefits. Subsequently, economic and environmental impacts of microalgal biorefinery were evaluated via life cycle assessment (LCA) and techno-economic analysis (TEA) to lit up commercial feasibility. Finally, the current obstacles and future perspectives were discussed objectively to offer an impartial reference for future researchers and investors.

Quantitative proteomic analysis of the mechanism of Cd toxicity in Enterobacter sp. FM-1: Comparison of different growth stages

Enterobacter sp. are widely used in bioremediation, but the mechanism of Cadmium (Cd) toxicity in Enterobacter sp. has been poorly studied. In the present study, we determined the tolerance of Enterobacter sp. FM-1 to Cd by analyzing the physiological and biochemical responses of FM-1 induced under Cd stress. Differentially expressed proteins (DEPs) under exposure to different Cd environments were analyzed by 4D-label-free proteomics to provide a comprehensive understanding of Cd toxicity in FM-1. The greatest total number of DEPs, 1148, was found in the High concentration vs. Control comparison group at 10 h. When protein expression was compared after different incubation times, FM-1 showed the highest Cd tolerance at 48 h. Additionally, with an increasing incubation time, different comparison groups gradually began to show similar growth patterns, which was reflected in the GO enrichment analysis. Notably, only 815 proteins were identified in the High concentration vs. Control group, and KEGG enrichment analysis revealed that these proteins were significantly enriched in the pyruvate metabolism, oxidative phosphorylation, peroxisome, glyoxylate and dicarboxylate metabolism, and citrate cycle pathways. These results suggested that an increased incubation time allows FM-1 adapt and survive in an environment with Cd toxicity, and protein expression significantly increased in response to oxidative stress in a Cd-contaminated environment during the pre-growth period. This study provides new perspectives on bacterial participation in bioremediation and expands our understanding of the mechanism of bacterial resistance under Cd exposure.

Mitigation of oxidative stress damage caused by abiotic stress to improve biomass yield of microalgae: A review

Microalgae have been recognized as emerging cell factories due to the high value-added bio-products. However, the balance between algal growth and the accumulation of metabolites is always the main contradiction in algal biomass production. Hence, the security and effectiveness of regulating microalgal growth and metabolism simultaneously have drawn substantial attention. Since the correspondence between microalgal growth and reactive oxygen species (ROS) level has been confirmed, improving its growth under oxidative stress and promoting biomass accumulation under non-oxidative stress by exogenous mitigators is feasible. This paper first introduced ROS generation in microalgae and described the effects of different abiotic stresses on the physiological and biochemical status of microalgae from these aspects associated with growth, cell morphology and structure, and antioxidant system. Secondly, the role of exogenous mitigators with different mechanisms in alleviating abiotic stress was concluded. Finally, the possibility of exogenous antioxidants regulating microalgal growth and improving the accumulation of specific products under non-stress conditions was discussed.

Metabolic Responses to Manganese Toxicity in Soybean Roots and Leaves

Soybean is one of the most crucial beans in the world. Although Mn (manganese) is a kind of important nutritive element helpful to plant growth and health, excess Mn is harmful to crops. Nevertheless, the effect of Mn toxicity on soybean roots and leaves metabolism is still not clear. To explore this, water culture experiments were conducted on the development, activity of enzyme, and metabolic process of soybeans under varying levels of Mn treatment (5 and 100 μM). Compared with the control, the soybeans under Mn stress showed inhibited growth and development. Moreover, the activity of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), and the soluble protein content in leaves and roots of soybean were all increased. However, soluble sugar and proline contents in soybean roots and leaves showed the opposite trend. In addition, the Mg (magnesium) and Fe (iron) ion contents in soybean leaves significantly decreased, and the Mn ion content greatly increased. In roots, the Mn and Fe ion content increased, whereas the Mg ion content decreased. Furthermore, the metabolomic analysis based on nontargeted liquid chromatography-mass spectrometry identified 136 and 164 differential metabolites (DMs) that responded to Mn toxicity in roots and leaves of soybean, respectively. These DMs might participate in five different primary metabolic pathways in soybean leaves and roots, suggesting that soybean leaves and roots demonstrate different kinds of reactions in response to Mn toxicity. These findings indicate that Mn toxicity will result in enzymes activity being changed and the metabolic pathway being seriously affected, hence inhibiting the development of soybean.

Characterization of cellular toxicity induced by sub-lethal inorganic mercury in the marine microalgae Chlorococcum dorsiventrale isolated from a metal-polluted coastal site

Mercury (Hg) is a global pollutant that affects numerous marine aquatic ecosystems. We isolated Chlorococcum dorsiventrale Ch-UB5 microalga from coastal areas of Tunisia suffering from metal pollution and analyzed its tolerance to Hg. This strain accumulated substantial amounts of Hg and was able to remove up to 95% of added metal after 24 and 72 h in axenic cultures. Mercury led to lesser biomass growth, higher cell aggregation, significant inhibition of photochemical activity, and appearance of oxidative stress and altered redox enzymatic activities, with proliferation of starch granules and neutral lipids vesicles. Such changes matched the biomolecular profile observed using Fourier Transformed Infrared spectroscopy, with remarkable spectral changes corresponding to lipids, proteins and carbohydrates. C. dorsiventrale accumulated the chloroplastic heat shock protein HSP70B and the autophagy-related ATG8 protein, probably to counteract the toxic effects of Hg. However, long-term treatments (72 h) usually resulted in poorer physiological and metabolic responses, associated with acute stress. C. dorsiventrale has potential use for Hg phycoremediation in marine ecosystems, with the ability to accumulating energetic reserves that could be used for biofuel production, supporting the notion of using of C. dorsiventrale for sustainable green chemistry in parallel to metal removal.

Evaluating the Combined Effects of Erythromycin and Levofloxacin on the Growth of Navicula sp. and Understanding the Underlying Mechanisms

Navicula sp., a type of benthic diatom, plays a crucial role in the carbon cycle as a widely distributed algae in water bodies, making it an essential primary producer in the context of global carbon neutrality. However, using erythromycin (ERY) and levofloxacin (LEV) in medicine, livestock, and aquaculture has introduced a new class of pollutants known as antibiotic pollutants, which pose potential threats to human and animal health. This study aimed to investigate the toxic effects of ERY and LEV, individually or in combination, on the growth, antioxidant system, chlorophyll synthesis, and various cell osmotic pressure indexes (such as soluble protein, proline, and betaine) of Navicula sp. The results indicated that ERY (1 mg/L), LEV (320 mg/L), and their combined effects could inhibit the growth of Navicula sp. Interestingly, the combination of these two drugs exhibited a time-dependent effect on the chlorophyll synthesis of Navicula sp., with ERY inhibiting the process while LEV promoted it. Furthermore, after 96 h of exposure to the drugs, the activities of GSH-Px, POD, CAT, and the contents of MDA, proline, and betaine increased. Conversely, the actions of GST and the contents of GSH and soluble protein decreased in the ERY group. In the LEV group, the activities of POD and CAT and the contents of GSH, MDA, proline, and betaine increased, while the contents of soluble protein decreased. Conversely, the mixed group exhibited increased POD activity and contents of GSH, MDA, proline, betaine, and soluble protein. These findings suggest that antibiotics found in pharmaceutical and personal care products (PPCPs) can harm primary marine benthic eukaryotes. The findings from the research on the possible hazards linked to antibiotic medications in aquatic ecosystems offer valuable knowledge for ensuring the safe application of these drugs in environmental contexts.

Effect of cadmium in the gonads of mussel (Mytilus coruscus): an ionomics and proteomics study

The mussel Mytilus coruscus is an important and very popular seafood in China and widespread along the eastern coast of China. In this study, we investigated the molecular response of mussel gonads to cadmium accumulation at two concentrations (80 and 200 µg/L) for 30 days using ionomics and proteomics techniques. The shrinkage of the cells and moderate hemocytic infiltration were observed in the Cd-treated groups. The strontium, selenium (Se), and zinc contents were significantly altered, and the relationships between iron, copper, Se, manganese, calcium, sodium, and magnesium were also significantly altered. Label-free quantitative proteomics analysis revealed a total of 227 differentially expressed proteins. These proteins were associated with multiple biological processes, including the tricarboxylic acid cycle, structural reorganization of cells, biosynthesis of amino acids, inflammatory response of cells, and tumorigenesis. Nonetheless, our ionomics and proteomics analysis revealed that mussels could partly alleviate the adverse effects of Cd by altering the metal contents and correlations between minerals, thereby enhancing the biosynthesis of some amino acids and activity of antioxidant enzymes. Overall, this study provides an insight into the mechanism underlying Cd toxicity in mussel gonads from a metal and protein perspective.

Cadmium tolerance and hyperaccumulation in plants - A proteomic perspective of phytoremediation

Cadmium (Cd) is a major environmental pollutant and poses a risk of transfer into the food chain through contaminated plants. Mechanisms underlying Cd tolerance and hyperaccumulation in plants are not fully understood. Proteomics-based approaches facilitate an in-depth understanding of plant responses to Cd stress at the systemic level by identifying Cd-inducible differentially abundant proteins (DAPs). In this review, we summarize studies related to proteomic changes associated with Cd-tolerance mechanisms in Cd-tolerant crops and Cd-hyperaccumulating plants, especially the similarities and differences across plant species. The enhanced DAPs identified through proteomic studies can be potential targets for developing Cd-hyperaccumulators to remediate Cd-contaminated environments and Cd-tolerant crops with low Cd content in the edible organs. This is of great significance for ensuring the food security of an exponentially growing global population. Finally, we discuss the methodological drawbacks in current proteomic studies and propose that better protocols and advanced techniques should be utilized to further strengthen the reliability and applicability of future Cd-stress-related studies in plants. This review provides insights into the improvement of phytoremediation efficiency and an in-depth study of the molecular mechanisms of Cd enrichment in plants.

Thallium-mediated NO signaling induced lipid accumulation in microalgae and its role in heavy metal bioremediation

Thallium (Tl⁺) is a trace metal with extreme toxicity and is highly soluble in water, posing a great risk to ecological and human safety. This work aimed to investigate the role played by Tl⁺ in regulating lipid accumulation in microalgae and the removal efficiency of Tl⁺. The effect of Tl⁺ on the cell growth, lipid production and Tl⁺ removal efficiency of Parachlorella kessleri R-3 was studied. Low concentrations of Tl⁺ had no significant effect on the biomass of microalgae. When the Tl⁺ concentration exceeded 5 μg L^-1, the biomass of microalgae showed significant decrease. The highest lipid content of 63.65% and lipid productivity of 334.55 mg L^-1 d^-1 were obtained in microalgae treated with 10 and 5 μg L^-1 Tl⁺, respectively. Microalgae can efficiently remove Tl⁺ and the Tl⁺ removal efficiency can reach 100% at Tl⁺ concentrations of 0-25 μg L^-1. The maximum nitric oxide (NO) level of 470.48 fluorescence intensity (1 × 10⁶ cells)^-1 and glutathione (GSH) content of 343.51 nmol g^-1 (fresh alga) were obtained under 5 μg L^-1 Tl⁺ stress conditions. Furthermore, the exogenous donor sodium nitroprusside (SNP) supplemented with NO was induced in microalgae to obtain a high lipid content (59.99%), lipid productivity (397.99 mg L^-1 d^-1) and GSH content (430.22 nmol g^-1 (fresh alga)). The corresponding analysis results indicated that NO could participate in the signal transduction pathway through modulation of reactive oxygen species (ROS) signaling to activate the antioxidant system by increasing the GSH content to eliminate oxidative damage induced by Tl⁺ stress. In addition, NO regulation of ROS signaling may enhance transcription factors associated with lipid synthesis, which stimulates the expression of genes related to lipid synthesis, leading to increased lipid biosynthesis in microalgae. Moreover, it was found that the change in Tl⁺ had little effect on the fatty acid components and biodiesel properties. This study showed that Tl⁺ stress can promote lipid accumulation in microalgae for biodiesel production and simultaneously effectively remove Tl⁺, which provided evidence that NO was involved in signal transduction and antioxidant defense, and improved the understanding of the interrelation between NO and ROS to regulate lipid accumulation in microalgae.

Effect of mercury in the influx and efflux of nutrients in the microalga Desmodesmus armatus

Anthropogenic activities such as mining and the metallurgical industry are the main sources of mercury contamination. Mercury is one of the most serious environmental problems in the world. This study aimed to investigate, using experimental kinetic data, the effect of different inorganic mercury (Hg²⁺) concentrations on the response of microalga Desmodesmus armatus stress. Cell growth, nutrients uptake and mercury ions from the extracellular medium, and oxygen production were determined. A Compartment Structured Model allowed elucidating the phenomena of transmembrane transport, including influx and efflux of nutrients, metal ions and bioadsorption of metal ions on the cell wall, which are difficult to determine experimentally. This model was able to explain two tolerance mechanisms against mercury, the first one was the adsorption of Hg²⁺ions onto the cell wall and the second was the efflux of mercury ions. The model predicted a competition between internalization and adsorption with a maximum tolerable concentration of 5.29 mg/L of HgCl₂. The kinetic data and the model showed that mercury causes physiological changes in the cell, which allow the microalga to adapt to these new conditions to counteract the toxic effects. For this reason, D. armatus can be considered as a Hg-tolerant microalga. This tolerance capacity is associated with the activation of the efflux as a detoxification mechanism that facilitates the maintenance of the osmotic balance for all the modeled chemical species. Furthermore, the accumulation of mercury in the cell membrane suggests the presence of thiol groups associated with its internalization, leading to the conclusion that metabolically active tolerance mechanisms are dominant over passive ones.

Investigation of cytotoxic cadmium in aquatic green algae by synchrotron radiation-based Fourier transform infrared spectroscopy: Role of dissolved organic matter

The heavy metal Cd can cause severe toxicity on aquatic algae, but there are few studies on the cytotoxicity of heavy metal on algae based on synchrotron radiation technology. In this study, synchrotron radiation-based Fourier transform infrared spectromicroscopy (SR-FTIR) was used to characterize in vivo the toxic effects of Cd on Cosmarium sp. cells, emphasizing the influence of dissolved organic matter (DOM) on Cd toxicity. Results showed that, in the absence of DOM, obvious growth inhibition, cell volume reduction, and photosynthesis disruption could be observed with increasing Cd concentrations (0-500 μg/L). Based on the SR-FTIR imaging and functional group quantification, it was shown that the biosynthesis of biomolecules such as proteins, lipids, and carbohydrates was inhibited in algal cells. However, the addition of DOM caused significant heterogeneities in biomacromolecule biosynthesis that an increased biosynthesis of carbohydrates and structural lipids but an inhibited biosynthesis of proteins and storage lipids were observed. Furthermore, the correlation analysis and principal component analysis showed a good correlation between v(C-OH)/Amide II and biochemical parameters, indicating that changes of carbohydrates could be used as the biomarker to indicate the cytotoxicity of heavy metals to algal cells. These findings provide insight into the mechanisms of heavy metal cytotoxicity to aquatic algae and systematic cytotoxicity assessment under various aquatic conditions.

Salinization and heavy metal cadmium impair growth but have contrasting effects on defensive colony formation of Scenedesmus obliquus

Driven by anthropogenic activities, freshwater salinization has become an emerging global environmental issue. Recent studies indicate that salinization increases the mobility of heavy metals in soil and causes higher flux into surface waterbodies. The present study assessed the combined effects of salinization (0, 3, 6 PSU) and the heavy metal Cd²⁺ (0, 0.2, 0.4 mg L^-1) on the anti-grazing colony formation and population growth of Scenedesmus obliquus, a common freshwater alga. The results showed that the increase in salinity promoted colony formation of S. obliquus with or without the presence of grazing cues and, in contrast, Cd²⁺ contamination depressed the defensive colony formation of S. obliquus to Daphnia filtrate. The increase in both salinity and Cd²⁺ concentration depressed the population growth of S. obliquus, including impaired photosynthesis and a decreased population growth rate. Salinization moderated the negative effects of Cd²⁺ on defensive colony formation of S. obliquus, suggesting increased absorption of Cd²⁺ ions by a thicker outer layer of the algal cell wall under saltier conditions. As a result, larger defensive colonies of S. obliquus under freshwater salinization may cause higher bioaccumulation of heavy metals by algal cells and heavier influence on zooplankton. This study provides evidence that freshwater salinization could interfere with plankton interactions by affecting algal defense and growth, which may lead to bottom-up cascading effects on freshwater food webs.

Bivalent copper ions presence triggers removal and homeostatic mechanisms in the metal-resistant microorganism Apiotrichum loubieri M12

Microorganisms, especially those habiting mining environments, are of great importance for the retention of toxic metals in the environment. This work aimed to isolate a copper removing-microorganism from sediments of an Acid Mine Drainage-affected environment and to study the cellular responses trigger by metal presence. Apiotrichum loubieri M12 was able to tolerate and remove Cu(II) from liquid culture media, reaching a 30-35% removal capacity when it was exposed to 40 μg mL^-1 Cu(II) after 48 h. Analysis of the biomass exposed to the metal through SEM-EDS showed copper presence on the cell surface and variations in the proportion of other biomass constituent elements. Proteomics revealed that the presence of Cu(II) induces differential expression of intracellular proteins involved in a wide variety of metabolic processes. Interestingly, a specific response to the metal was detected in cell-free supernatants, in which copper binding proteins were identified. A large number of proteins with metal ion binding sites were detected both at intra and extracellular levels. The microorganism responds not only by adjusting intracellular protein expression, but also by adjusting expression of proteins in the extracellular space.

Simultaneous chromium removal and lipid accumulation by microalgae under acidic and low temperature conditions for promising biodiesel production

Microalgae have become the hotspot of recent researches as heavy metals (HMs) adsorbent and biodiesel production feedstock. In this study, the cell growth, lipid production and Cr⁶⁺ removal of Parachlorella kessleri R-3 at pH 3.5 and 15 °C were investigated. It was found that low concentration of Cr⁶⁺ (0.5 to 2 mg/L) promoted the algal growth, whereas Cr⁶⁺ higher than 5 mg/L inhibited the growth of P. kessleri R-3. Biomass concentration (2.40 g/L) and lipid productivity (131.79 mg/L d^-1) reached the highest at 2 mg/L Cr⁶⁺, and lipid content (61.03 %) reached the highest at 5 mg/L Cr⁶⁺. The maximum Cr⁶⁺ removal efficiency of 91 % was obtained at 0.5 mg/L Cr⁶⁺ treatment. Furthermore, fatty acid composition analysis showed that strain R-3 had a high C16-18 content of 74.88-89.21 %. This study provides new insight into the treatment of HMs and lipid production in cold regions.

Enhanced wastewater bioremediation by a sulfur-based copolymer as scaffold for microalgae immobilization (AlgaPol)

In recent years, there has been an increasing concern related to the contamination of aqueous ecosystems by heavy metals, highlighting the need to improve the current techniques for remediation. This work intends to address the problem of removing heavy metals from waterbodies by combining two complementary methodologies: adsorption to a copolymer synthesized by inverse vulcanization of sulfur and vegetable oils and phytoremediation by the microalga Chlorella sorokiniana to enhance the metal adsorption. After studying the tolerance and growth of Chlorella sorokiniana in the presence of the copolymer, the adsorption of highly concentrated Cd²⁺ (50 mg L^-1) by the copolymer and microalgae on their own and the combined immobilized system (AlgaPol) was compared. Additionally, adsorption studies have been performed on mixtures of the heavy metals Cd²⁺ and Cu²⁺ at a concentration of 8 mg L^-1 each. AlgaPol biofilm is able to remove these metals from the growth medium by more than 90%. The excellent metal adsorption capacity of this biofilm can be kinetically described by a pseudo-second-order model.

Effects of antimony stress on growth, structure, enzyme activity and metabolism of Nipponbare rice (Oryza sativa L.) roots

Some antimony (Sb) contaminated areas are used for rice cultivation in response to economic demands. However, little is known about the effects of Sb stress on the growth and metabolism of rice roots. Thus, a hydroponic experiment was carried out on the growth, root anatomy, enzyme activity, and metabolism of Nipponbare rice (Oryza sativa L. ssp. japonica cv. Nipponbare) under varying levels of Sb (III) stress (0 mg L^-1, 10 mg L^-1, and 50 mg L^-1). With the increase of Sb concentration, rice root length and root fresh weight declined by 67.8 % and 90.5 % for 10 mg L^-1 Sb stress and 94.1 % and 98.4 % for 50 mg L^-1 Sb stress, respectively. Anatomical analysis of cross-sections of Sb-treated roots showed an increase in cell wall thickness and an increase in the number of cell mitochondria. The 10 mg L^-1 and 50 mg L^-1 Sb stress increased the activity of enzyme superoxide dismutase (SOD) in root cells by 1.94 and 2.40 times, respectively. Compared to the control, 10 mg L^-1 Sb treatment increased the activity of catalase (CAT) and peroxidase (POD), as well as the concentrations of antioxidant glutathione (GSH) in the root by 1.46, 1.38, and 0.52 times, respectively. However, 50 mg L^-1 Sb treatment significantly decreased the activity or content of CAT, POD and GSH by 28.1 %, 13.5 % and 28.2 %, respectively. Nontargeted LC/MS-based metabolomics analysis identified 23 and 13 significantly differential metabolites in rice roots exposed to 10 mg L^-1 and 50 mg L^-1 Sb, respectively, compared to the control. These differential metabolites were involved in four main metabolic pathways including the tricarboxylic acid cycle (TCA cycle), butanoate metabolism, alanine, aspartate and glutamate metabolism, and alpha-linolenic acid metabolism. Taken together, these findings indicate that Sb stress destroys the structure of rice roots, changes the activity of enzymes, and affects the metabolic pathway, thereby reducing the growth of rice roots and leading to toxicity.

State-of-the-art OMICS strategies against toxic effects of heavy metals in plants: A review

Environmental pollution of heavy metals (HMs), mainly due to anthropogenic activities, has received growing attention in recent decades. HMs, especially the non-essential carcinogenic ones, including chromium (Cr), cadmium (Cd), mercury (Hg), aluminum (Al), lead (Pb), and arsenic (As), have appeared as the most significant air, water, and soil pollutants, which adversely affect the quantity, quality, and security of plant-based food all over the world. Plants exposed to HMs could experience significant decline in growth and yield. To avoid or tolerate the toxic effects of HMs, plants have developed complicated defense mechanisms, including absorption and accumulation of HMs in cell organelles, immobilization by forming complexes with organic chelates, extraction by using numerous transporters, ion channels, signalling cascades, and transcription elements, among others. OMICS strategies have developed significantly to understand the mechanisms of plant transcriptomics, genomics, proteomics, metabolomics, and ionomics to counter HM-mediated stress stimuli. These strategies have been considered to be reliable and feasible for investigating the roles of genomics (genomes), transcriptomic (coding), mRNA transcripts (non-coding), metabolomics (metabolites), and ionomics (metal ions) to enhance stress resistance or tolerance in plants. The recent developments in the mechanistic understandings of the HMs-plant interaction in terms of their absorption, translocation, and toxicity invasions at the molecular and cellular levels, as well as plants' response and adaptation strategies against these stressors, are summarized in the present review. Transcriptomics, genomics, metabolomics, proteomics, and ionomics for plants against HMs toxicities are reviewed, while challenges and future recommendations are also discussed.

Metabolic and Proteomic Analysis of Chlorella sorokiniana, Chloroidium saccharofilum, and Chlorella vulgaris Cells Cultured in Autotrophic, Photoheterotrophic, and Mixotrophic Cultivation Modes

Chlorella is one of the most well-known microalgal genera, currently comprising approximately a hundred species of single-celled green algae according to the AlgaeBase. Strains of the genus Chlorella have the ability to metabolize both inorganic and organic carbon sources in various trophic modes and synthesize valuable metabolites that are widely used in many industries. The aim of this work was to investigate the impact of three trophic modes on the growth parameters, productivities of individual cell components, and biochemical composition of Chlorella sorokiniana, Chloroidium saccharofilum, and Chlorella vulgaris cells with special consideration of protein profiles detected by SDS-PAGE gel electrophoresis and two-dimensional gel electrophoresis with MALDI-TOF/TOF MS. Mixotrophic conditions with the use of an agro-industrial by-product stimulated the growth of all Chlorella species, which was confirmed by the highest specific growth rates and the shortest biomass doubling times. The mixotrophic cultivation of all Chlorella species yielded a high amount of protein-rich biomass with reduced contents of chlorophyll a, chlorophyll b, carotenoids, and carbohydrates. Additionally, this work provides the first information about the proteome of Chloroidium saccharofilum, Chlorella sorokiniana, and Chlorella vulgaris cells cultured in molasses supplementation conditions. The proteomic analysis of the three Chlorella species growing photoheterotrophically and mixotrophically showed increased accumulation of proteins involved in the cell energy metabolism and carbon uptake, photosynthesis process, and protein synthesis, as well as proteins involved in intracellular movements and chaperone proteins.

Metal stresses modify soluble proteomes and toxin profiles in two Mediterranean strains of the distributed dinoflagellate Alexandrium pacificum

HABs involving Alexandrium pacificum have been reported in metal-contaminated ecosystems, suggesting that this distributed species adapts to and/or can tolerate the effects of metals. Modifications in soluble proteomes and PST contents were characterized in two Mediterranean A. pacificum strains exposed to mono- or polymetallic stresses (zinc, lead, copper, cadmium). These strains were isolated from two anthropized locations: Santa Giusta Lagoon (Italy, SG C10-3) and the Tarragona seaport (Spain, TAR C5-4F). In both strains, metals primarily downregulated key photosynthesis proteins. Metals also upregulated other proteins involved in photosynthesis (PCP in both strains), the oxidative stress response (HSP 60, proteasome and SOD in SG C10-3; HSP 70 in TAR C5-4F), energy metabolism (AdK in TAR C5-4F), neoglucogenesis/glycolysis (GAPDH and PEP synthase in SG C10-3) and protein modification (PP in TAR C5-4F). These proteins, possibly involved in adaptive proteomic responses, may explain the development of these A. pacificum strains in metal-contaminated ecosystems. The two strains showed different proteomic responses to metals, with SG C10-3 upregulating more proteins, particularly PCP. Among the PSTs, regardless of the metal and the strain studied, C2 and GTX4 predominated, followed by GTX5. Under the polymetallic cocktail, (i) total PSTs, C2 and GTX4 reached the highest levels in SG C10-3 only, and (ii) total PSTs, C2, GTX5 and neoSTX were higher in SG C10-3 than in TAR C5-4F, whereas in SG C10-3 under copper stress, total PSTs, GTX5, GTX1 and C1 were higher than in the controls, revealing variability in PST biosynthesis between the two strains. Total PSTs, C2, GTX4 and GTX1 showed significant positive correlations with PCP, indicating that PST production may be positively related to photosynthesis. Our results showed that the A. pacificum strains adapt their proteomic and physiological responses to metals, which may contribute to their ecological success in highly anthropized areas.

Exploring the microbial community inhabiting the phosphogypsum stacks of Huelva (SW SPAIN) by a high throughput 16S/18S rDNA sequencing approach

Around 100 Mt of phosphogypsum (PG) have been deposited in large stacks on the salt marshes of the Tinto River estuary in Huelva (SW Spain), covering about 1000 ha. These stacks contain extremely acidic water (pH < 2) with high concentrations of pollutants which can cause emissions into their surroundings, generating important environmental concerns. Despite many chemical, geological or hydrological studies have been conducted to characterize the PG stacks of Huelva, the microbial community inhabiting this extreme environment remains unexplored. Using a 16S/18S-rRNA-high throughput sequencing approach, we have uncovered the main taxonomic groups able to live in the acidic metal-contaminated water, which is in direct contact with the PG, demonstrating for the first time the existence of a huge diversity of microbial species in these extreme conditions. In addition, the physicochemical characteristics of the water sampled have been analyzed. These studies have revealed that the most abundant bacteria found in two different leachate samples of the PG stacks belong to the genera Acidiphilium, Pseudomonas, Leptosprillum, Acidithrix, or Acidithiobacillus, typically found in acid mine drainage (AMD) environments, which in total represent around 50% of the total bacterial community. Biodiversity of eukaryotes in PG water is lower than that of prokaryotes, especially in the water collected from the perimeter channel that surrounds the PG stacks, where the pH reaches a value of 1.5 and the activity concentrations exceed 300 Bq L^-1 for ²³⁸U or 20 Bq L^-1 for ²¹⁰Po, values which are from four to five orders of magnitude higher than those usually found in unperturbed surface waters. Even so, an unexpected diversity of algae, fungi, and ciliates have been found in the PG stacks of Huelva, where chlorophyte microalgae and basidiomycetes fungi are the most abundant eukaryotes. Additional bioinformatics tools have been used to perform a functional analysis and predict the most common metabolic pathways in the PG microbiota. The obtained data indicate that the extreme conditions of these PG stacks hide an unexpected microbial diversity, which can play an important role in the dynamics of the contaminating compounds of the PG and provide new strains with unique biotechnological applications.

Unraveling metabolic alterations in Chlorella vulgaris cultivated on renewable sugars using time resolved multi-omics

The inherent metabolic versatility of Chlorella vulgaris that enables it to metabolize both inorganic and organic carbon under various trophic modes of cultivation makes it a promising candidate for industrial applications. To shed light on the metabolic flexibility of this microalga, time resolved proteomic and metabolomic studies were conducted in three distinct trophic modes (autotrophic, heterotrophic, mixotrophic) at two growth stages (end of linear growth at 6 days and during nutrient deprivation at 10 days). Sweet sorghum bagasse (SSB) hydrolysate was supplied to the cultivation medium as a renewable source of organic carbon mainly in the form of glucose. Integrated multi-omics data showed improved nitrogen assimilation, re-allocation, and recycling and increased levels of photosystem II (PS II) proteins indicating effective cellular quenching of excess electrons during mixotrophy. As external addition of organic carbon (glucose) to the cultivation medium decreases the cell's dependence on photosynthesis, an upregulation in the mitochondrial electron transport chain was recorded that led to increased cellular energy generation and hence higher growth rates under mixotrophy. Moreover, upregulation of the lipid-packaging proteins caleosin and 14_3_3 domain-containing protein resulted in maximum expression during mixotrophy suggesting a strong correlation between lipid synthesis, stabilization, and assembly. Overall, cells cultivated under mixotrophy showed better nutrient stress tolerance and redox balancing leading to higher biomass and lipid production. The study offers a panoramic view of the microalga's metabolic flexibility and contributes to a deeper understanding of the altered biochemical pathways that can be exploited to enhance algal productivity and commercial potential.

Metabolic changes and stress damage induced by ammonia exposure in juvenile Eriocheir sinensis

The application of nitrogen fertilizers in the rice-crab co-culture system may expose juvenile Eriocheir sinensis to high ammonia concentrations within a short period of time, potentially causing death. Currently, the molecular mechanism underlying ammonia toxicity in juvenile Eriocheir sinensis remains poorly understood. This study compared the effects of 24 h exposure to different total ammonia-N concentrations (0, 10.47, and 41.87 mg/L) on antioxidant enzyme activities and tandem mass tag (TMT)-based proteomics in the hepatopancreas of juvenile Eriocheir sinensis. During the experiment, water temperature and pH were maintained at 20.4 ± 1.4 °C and 7.69 ± 0.46, respectively. Proteomic data demonstrated that Eriocheir sinensis used different metabolic regulatory mechanisms to adapt to varying ammonia conditions. The tricarboxylic acid (TCA) cycle, glycogen degradation, and oxidative phosphorylation showed marginally upregulated trends under low ammonia exposure. High ammonia stress caused downregulation of the TCA cycle and provided energy by enhancing oxidative phosphorylation, fatty acid beta oxidation, gluconeogenesis, and glycogen degradation. The detoxification of ammonia into urea and glutamine was suppressed under high ammonia stress. Finally, ammonia exposure induced oxidative stress and caused protein damage. Antioxidant enzyme activity analysis further revealed that exposure to high concentrations of ammonia may induce more severe oxidative stress. This study provides a global perspective on the mechanisms underlying ammonia exposure-induced metabolic changes and stress damage in juvenile Eriocheir sinensis.

Impact of heavy metals in the microalga Chlorella sorokiniana and assessment of its potential use in cadmium bioremediation

The chlorophyte microalga Chlorella sorokiniana was tested for the bioremediation of heavy metals pollution. It was cultured with different concentrations of Cu²⁺, Cd²⁺, As (III) and As (V), showing a significant inhibition on its growth at concentrations of 500 µM Cu²⁺, 250 µM Cd²⁺, 750 µM AsO₃^3- and 5 mM AsO₄^3- or higher. Moreover, the consumption of ammonium was also studied, showing significant differences for concentrations higher than 1 mM of Cu²⁺ and As (III), and 5 mM of As (V). The determination of intracellular heavy metals concentration revealed that Chlorella sorokiniana is an outstanding Cd accumulator organism, able to accumulate 11,232 mg kg^-1 of Cd, and removing 65% of initial concentration of this heavy metal. Finally, antioxidant enzymes, such as catalase (CAT) and ascorbate peroxidase (APX), and enzymes involved in the production of glutamate and cysteine, such as glutamine syntethase (GS), glutamate dehydrogenase (GDH), O-acetylserine (thiol) lyase (OASTL) and NAD-isocitrate dehydrogenase (NAD-IDH) were studied both at gene expression and enzymatic activity levels. These enzymes exhibited different grades of upregulation, especially in response to Cd and As stress. However, GS expression was downregulated when Chlorella sorokiniana was cultured in the presence of these heavy metals.

Bio-indicators in cadmium toxicity: Role of HSP27 and HSP70

Heat shock proteins (HSPs) are a family of proteins that are expressed by cells in reply to stressors. The changes in concentration of HSPs could be utilized as a bio-indicator of oxidative stress caused by heavy metal. Exposure to the different heavy metals may induce or reduce the expression of different HSPs. The exposure to cadmium ion (Cd²⁺) could increase HSP70 and HSP27 over 2- to 10-fold or even more. The in vitro and in vivo models indicate that the HSP70 family is more sensitive to Cd intoxication than other HSPs. The analyses of other HSPs along with HSP70, especially HSP27, could also be useful to obtain more accurate results. In this regard, this review focuses on examining the literature to bold the futuristic uses of HSPs as bio-indicators in the initial assessment of Cd exposure risks in defined environments.

Using multiple endpoints to assess the toxicity of cadmium and cobalt for chlorophycean Raphidocelis subcapitata

Metals may cause damage to the biota of contaminated environments. Moreover, using multiple endpoints in ecotoxicological studies is useful to better elucidate the mechanisms of toxicity of these compounds. Therefore, this study aimed to evaluate the effects of cadmium (Cd) and cobalt (Co) on growth, biochemical and photosynthetic parameters of the microalgae Raphidocelis subcapitata, through quantification of lipid classes composition, chlorophyll a (Chl a) content, maximum (Φ_M) and effective (Φ'_M) quantum yields and efficiency of the oxygen-evolving complex (OEC). Both metals affected the algal population growth, with an IC_50-96h of 0.67 and 1.53 μM of Cd and Co, respectively. Moreover, the metals led to an increase in the total lipid content and reduced efficiency of OEC and Φ_M. Cell density was the most sensitive endpoint to detect Cd toxicity after 96 h of treatment. Regarding Co, the photosynthetic parameters were the most affected and the total lipid content was the most sensitive endpoint as it was altered by the exposure to this metal in all concentrations. Cd led to increased contents of the lipid class wax esters (0.89 μM) and phospholipids (PL - at 0.89 and 1.11 μM) and decreased values of triglycerides (at 0.22 μM) and acetone-mobile polar lipids (AMPL - at 0.44 and 1.11 μM). The percentage of free fatty acids (FFA) and PL of microalgae exposed to Co increased, whereas AMPL decreased in all concentrations tested. We were able to detect differences between the toxicity mechanisms of each metal, especially how Co interferes in the microalgae at a biochemical level. Furthermore, to the best of our knowledge, this is the first study reporting Co effects in lipid classes of a freshwater Chlorophyceae. The damage caused by Cd and Co may reach higher trophic levels, causing potential damage to the aquatic communities as microalgae are primary producers and the base of the food chain.

Dataset for proteomic analysis of Chlorella sorokiniana cells under cadmium stress

Cadmium is one of the most hazardous heavy metal for aquatic environments and one of the most toxic contaminants for phytoplankton. This work provides the dataset associated with the research publication “Effect of cadmium in the microalga Chlorella sorokiniana: a proteomic study” [1]. This dataset describes a proteomic approach, based on the sequential window acquisition of all theoretical fragment ion spectra mass spectrometry (SWATH-MS), derived from exposure of Chlorella sorokiniana to 250 µM Cd²⁺ for 40 h, showing the proteins that are up- or downregulated. The processing of data included the identification of the Chlamydomonas reinhardtii protein sequences equivalent to the corresponding of Chlorella sorokiniana sequences obtained, which made possible to use KEGG Database. MS and MS/MS information, and quantitative data were deposited PRIDE public repository under accession number PXD015932.