Sensitivity of Chlamydomonas reinhardtii to cadmium stress is associated with phototaxis

Discovery of N-benzyl-6-methylpicolinamide as a potential scaffold for bleaching herbicides

BACKGROUND

In pesticide research, bleaching herbicides have always been a hot topic. Our previous research showed that N-(4-fluorobenzyl)-2-methoxybenzamide is an innovative lead compound for bleaching herbicides.

RESULTS

A total of 40 derivatives of picolinamides were prepared and evaluated for their herbicidal activity by Petri dish tests and postemergence trials. The structure-activity relationship (SAR) revealed that introducing electron-withdrawing groups at the 3- or 4-positions of the benzyl significantly enhances herbicidal activity. Furthermore, ZI-04 induced similar symptoms such as bleaching effect in treated weeds and accumulation of biosynthetic precursors for carotenoids as observed with diflufenican. ZI-04 also exhibited significant cross-resistance to diflufenican and had a lower resistance risk than diflufenican.

CONCLUSION

N-benzyl-6-methylpicolinamides were discovered as a novel scaffold for bleaching herbicides. The accumulation of phytoene, phytofluene and ζ-Carotene in radish cotyledons, and cross-resistance observed with diflufenican, showed that title compounds can interfere with carotenoid biosynthesis. © 2024 Society of Chemical Industry.

Exploring cell aggregation as a defense strategy against perchlorate stress in Chlamydomonas reinhardtii through multi-omics analysis

Perchlorate (ClO4-) is a type of novel, widely distributed, and persistent inorganic pollutant. However, the impacts of perchlorate on freshwater algae remain unclear. In this study, the response and defense mechanisms of microalgae (Chlamydomonas reinhardtii) under perchlorate stress were investigated by integrating physiological and biochemical monitoring, transcriptomics, and metabolomics. Weighted gene co-expression network analysis (WGCNA) of transcriptome data was used to analyze the relationship between genes and phenotype and screen the key pathways. C. reinhardtii exhibited aggregate behavior when exposed to 100- and 200-mM perchlorate but was restored to its unicellular lifestyle when transferred to fresh medium. WGCNA results found that the "carbohydrate metabolism" and "lipid metabolism" pathways were closely related to cell aggregation phenotype. The differential expression genes (DEGs) and differentially accumulated metabolites (DAMs) of these pathways were upregulated, indicating that the lipid and carbohydrate metabolisms were enhanced in aggregated cells. Additionally, most genes and metabolites related to phytohormone abscisic acid (ABA) biosynthesis and the mitogen-activated protein kinase (MAPK) signaling pathway were significantly upregulated, indicating their crucial roles in the signal transmission of aggregated cells. Meanwhile, in aggregated cells, extracellular polymeric substances (EPS) and lipid contents increased, photosynthesis activity decreased, and the antioxidant system was activated. These characteristics contributed to C. reinhardtii's improved resistance to perchlorate stress. Above results demonstrated that cell aggregation behavior was the principal defense strategy of C. reinhardtii against perchlorate. Overall, this study sheds new light on the impact mechanisms of perchlorate to aquatic microalgae and provides multi-omics insights into the research of multicellular-like aggregation as an adaptation strategy to abiotic stress. These results are beneficial for assessing the risk of perchlorate in aquatic environments.

Toxicity mechanisms of graphene oxide and cadmium in Microcystis aeruginosa: evaluation of photosynthetic and oxidative responses

The potential ecotoxicological hazard of gaphene oxide (GO) is not fully clarified for photoautotrophic organisms, especially when the interactions of GO with other environmental toxicants are considered. The objective of the current study was to better understand the mechanisms of toxicity of GO in the cyanobacteria Microcystis aeruginosa, and to identify its interactions with cadmium (Cd). The individual and combined contribution of both pollutants in cyanobacteria were evaluated after 96 hours of exposure to GO and/or Cd, using photosynthetic pigments, photosynthetic parameters, cellular indicators of peroxidative damage, viability, and intracellular ROS formation as indicators of toxicity. Interactions between GO and Cd were evaluated using Toxic Units based on the EC50 of each parameter evaluated. The results of this study indicate that single concentrations ≥ 5 µg mL-1 of GO and ≥ 0.1 µg mL-1 of Cd induced a decrease in cell biomass and a change in the photosynthetic parameters associated with primary productivity in M. aeruginosa. In the combined experiments, higher GO ratios (≥ 9.1 µg mL-1) in terms of Toxic Units decreased photochemical processes and cellular metabolism, increased oxidative stress, and ultimately affected the size of M. aeruginosa. Finally, the relationship between GO concentration, Cd concentration, and the adsorption capacity of GO with respect to the co-pollutant must be taken into account when assessing the environmental risk of GO in aquatic environments.

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.

Translatomics and physiological analyses of the detoxification mechanism of green alga Chlamydomonas reinhardtii to cadmium toxicity

Cadmium (Cd) is one of the most toxic pollutants found in aquatic ecosystems. Although gene expression in algae exposed to Cd has been studied at the transcriptional level, little is known about Cd impacts at the translational level. Ribosome profiling is a novel translatomics method that can directly monitor RNA translation in vivo. Here, we analyzed the translatome of the green alga Chlamydomonas reinhardtii following treatment with Cd to identify the cellular and physiological responses to Cd stress. Interestingly, we found that the cell morphology and cell wall structure were altered, and starch and high-electron-density particles accumulated in the cytoplasm. Several ATP-binding cassette transporters that responded to Cd exposure were identified. Redox homeostasis was adjusted to adapt to Cd toxicity, and GDP-L-galactose phosphorylase (VTC2), glutathione peroxidase (GPX5), and ascorbate were found to play important roles in maintaining reactive oxygen species homeostasis. Moreover, we found that the key enzyme of flavonoid metabolism, i.e., hydroxyisoflavone reductase (IFR1), is also involved in the detoxification of Cd. Thus, in this study, translatome and physiological analyses provided a complete picture of the molecular mechanisms of green algae cell responses to Cd.

A cyclic lipopeptide produced by an antagonistic bacterium relies on its tail and transient receptor potential-type Ca2+ channels to immobilize a green alga

The antagonistic bacterium Pseudomonas protegens secretes the cyclic lipopeptide (CLiP) orfamide A, which triggers a Ca²⁺ signal causing rapid deflagellation of the microalga Chlamydomonas reinhardtii. We performed chemical synthesis of orfamide A derivatives and used an aequorin reporter line to measure their Ca²⁺ responses. Immobilization of algae was studied using a modulator and mutants of transient receptor potential (TRP)-type channels. By investigating targeted synthetic orfamide A derivatives, we found that N-terminal amino acids of the linear part and the terminal fatty acid region are important for the specificity of the Ca²⁺ -signal causing deflagellation. Molecular editing indicates that at least two distinct Ca²⁺ -signaling pathways are triggered. One is involved in deflagellation (Thr³ change, fatty acid tail shortened by 4C), whereas the other still causes an increase in cytosolic Ca²⁺ in the algal cells, but does not cause substantial deflagellation (Leu¹ change, fatty acid hydroxylation, fatty acid changes by 2C). Using mutants, we define four TRP-type channels that are involved in orfamide A signaling; only one (ADF1) responds additionally to low pH. These results suggest that the linear part of the CLiP plays one major role in Ca²⁺ signaling, and that orfamide A uses a network of algal TRP-type channels for deflagellation.

Investigation of toxic effect of mercury on Microcystis aeruginosa: Correlation between intracellular mercury content at single cells level and algae physiological responses

Single-cell studies can help to understand individual differences and obtain atypical cellular characteristics in view of cellular heterogeneity. Herein, the accumulation of mercury (Hg) in single algae cells was studied by droplet chip-time resolved inductively coupled plasma mass spectrometry analytical system, and the relation of Hg accumulation to the physiological responses of algae cell was explored. When low concentrations of Hg²⁺ (5-20 μg/L) were used in the exposure experiment, the content of Hg in single cells increased in first 2 h, then decreased with further increase of exposure time to 96 h, probably due to the growth dilution effect of the algae. When exposed to 30 μg/L Hg²⁺, the uptake of Hg by individual cells increased over time, which was associated with increased cell membrane permeability. The exposure to Hg²⁺ (5-30 μg/L) inhibited the growth of algae in a concentration-dependent manner and serious growth inhibition occurred under the exposure concentration of 30 μg/L. While the exposure concentration was lower than 20 μg/L, algal cells exhibited a recover tendency due to the self-protection mechanism of algal cells. Bivariate results showed that intracellular Hg accumulation was significantly negatively correlated with cells growth in terms of OD₆₈₀, photosynthetic pigments, F_v/F_m and PI_abs. On the contrast, reactive oxygen species content, superoxide dismutase activity, and cell membrane permeability were significantly positively correlated with the accumulation of intracellular Hg. These results are helpful to further understand the toxic effect of Hg on algae.

Microalgal Phycoremediation: A Glimpse into a Sustainable Environment

Microalgae are continually exposed to heavy metals and metalloids (HMMs), which stifles their development and reproduction due to the resulting physiological and metabolic abnormalities, leading to lower crop productivity. They must thus change their way of adapting to survive in such a hostile environment without sacrificing their healthy growth, development, reproductive capacity, or survival. The mode of adaptation involves a complex relationship of signalling cascades that govern gene expression at the transcriptional and post-transcriptional levels, which consequently produces altered but adapted biochemical and physiochemical parameters. Algae have been reported to have altered their physicochemical and molecular perspectives as a result of exposure to a variety of HMMs. Hence, in this review, we focused on how microalgae alter their physicochemical and molecular characteristics as a tolerance mechanism in response to HMM-induced stress. Furthermore, physiological and biotechnological methods can be used to enhance extracellular absorption and clean up. The introduction of foreign DNA into microalgae cells and the genetic alteration of genes can boost the bio-accumulation and remediation capabilities of microalgae. In this regard, microalgae represent an excellent model organism and could be used for HMM removal in the near future.

Effect of heavy metals mixture on the growth and physiology of Tetraselmis sp.: Applications to lipid production and bioremediation

Phycoremediation of heavy metals from contaminated waters by oleaginous microalgae is an eco-friendly and emerging trend. Different concentrations of toxic metals such as nickel (Ni), chromium (Cr) and cobalt (Co) were added in Tetraselmis sp. culture media. Mixture Design was used to model the effect of these metals on cell growth, lipid production and heavy metals removal. Tetraselmis sp. was identified as an outstanding Ni, Cr and Co accumulator with bioconcentration factors of 675.17, 584.9 and 169.81 within binary mixtures (Ni × Cr), (Cr × Co) and (Cr × Co) at 6 mg/L, respectively. Optimization studies showed that the highest cell growth (9.22 × 10⁵ cells/mL), lipid content (31% Dry Weight) and metals removal (91%) were obtained with the optimum binary mixture Ni (54.45 %) and Cr (45.45 %). This work presents interesting results revealing the potential of Tetraselmis sp. for nickel removal up to 97 % combined to its potential for biodiesel production.

Effect of trace elements in the toxicity of copper to Chlamydomonas reinhardtii

Copper sulfate (CuSO₄) is widely used in the control of algal blooms. Cu can promote or inhibit algal growth, while also affecting trace element uptake, therefore, the response mechanisms of algae cells under Cu²⁺ interference should be studied. In this study, wild-type Chlamydomonas reinhardtii (C. reinhardtii) and wall-less mutant C. reinhardtii were selected as the research objects. Except for the cell wall, these two algae were physiologically the same. While manipulating the concentration of Cu, the accumulation of Cu, Fe, Zn, and Mn by the two algal cell types was studied. The cell wall hindered the accumulation of Cu by cells and alleviated the toxicity of Cu to C. reinhardtii. The addition of Cu increased the accumulation of Fe by both cell types. In an environment with excess Cu, the total amount of Zn and Mn accumulated by cells also increased. On the one hand, this may be due to the synergistic and antagonistic effects of trace elements in the adsorption and uptake process, and on the other hand, it may be due to the changes in metal speciation in the culture medium. In addition, the difference in the total accumulation of various trace elements between wild-type and wall-less-type C. reinhardtii may be due to the structure and function differences between cell wall and cell membrane. At the same time, by measuring the changes in the levels of glutathione (GSH) in algal cells, the relevant mechanisms underlying the algae's uptake of trace elements by algae were further explored.

Comparative morphological, physiological, biochemical and genomic studies reveal novel genes of Dunaliella bioculata and D. quartolecta in response to salt stress

BACKGROUND

Salinity is an essential abiotic stress in plants. Dunaliella is a genus of high-salt-tolerant microalgae. The present study aimed to compare the characterizations of D. bioculata and D. quartolecta at different levels and investigate novel genes response to salt stress.

METHODS AND RESULTS

High chlorophyll contents were detected in D. bioculata on the 35^th d of salt stress, while high lipid and carotenoid contents were detected in D. quartolecta via morphological and biochemical analyses. Physiological analysis showed that D. quartolecta cells had a smaller increase in osmotic potential, a smaller decrease in the Na+/K+ ratio and photochemical efficiency (Fv/Fm), and a lower relative conductivity than D. bioculata cells. The genomic lengths of D. quartolecta and D. bioculata were 396,013,629 bp (scaffold N50 = 1954 bp) and 427,667,563 bp (scaffold N50 = 3093 bp) via high-throughput sequencing and de novo assembly, respectively. Altogether, 25,751 and 26,620 genes were predicted in their genomes by annotation analysis with various biodatabases. The D. bioculata genome showed more segmental duplication events via collinearity analysis. More single nucleotide polymorphisms and insertion-deletion variants were detected in the D. bioculata genome. Both algae, which showed a close phylogenetic relationship, may undergo positive selection via bioinformatics analysis. A total of 382 and 85 novel genes were screened in D. bioculata and D. quartolecta, with 138 and 51 enriched KEGG pathways, respectively. Unlike the novel genes adh1, hprA and serA, the relative expression of livF and phbB in D. bioculata was markedly downregulated as salinity increased, as determined by qPCR analysis. The relative expression of leuB, asd, pstC and proA in D. quartolecta was markedly upregulated with the same salinity increase.

CONCLUSION

Dunaliella quartolecta is more halophilic than D. bioculata, with more effective responses to high salt stress based on the multiphase comparative data.

Phycoremediation mechanisms of heavy metals using living green microalgae: physicochemical and molecular approaches for enhancing selectivity and removal capacity

Heavy metal (HM) contamination of water bodies is a serious global environmental problem. Because they are not biodegradable, they can accumulate in food chains, causing various signs of toxicity to exposed organisms, including humans. Due to its effectiveness, low cost, and ecological aspect, phycoremediation, or the use of microalgae's ecological functions in the treatment of HMs contaminated wastewater, is one of the most recommended processes. This study aims to examine in depth the mechanisms involved in the phycoremediation of HMs by microalgae, it also provides an overview of the prospects for improving the productivity, selectivity, and cost-effectiveness of this bioprocess through physicochemical and genetic engineering applications. Firstly, this review proposes a detailed examination of the biosorption interactions between cell wall functional groups and HMs, and their complexation with extracellular polymeric substances released by microalgae in the extracellular environment under stress conditions. Subsequently, the metal transporters involved in the intracellular bioaccumulation of HMs as well as the main intracellular mechanisms including compartmentalization in cell organelles, enzymatic biotransformation, or photoreduction of HMs were also extensively reviewed. In the last section, future perspectives of physicochemical and genetic approaches that could be used to improve the phytoremediation process in terms of removal efficiency, selectivity for a targeted metal, or reduction of treatment time and cost are discussed, which paves the way for large-scale application of phytoremediation processes.

Contrasting detoxification mechanisms of Chlamydomonas reinhardtii under Cd and Pb stress

Chlamydomonas reinhardtii has been frequently investigated for its resistance to metals; however, few studies have systematically compared the intracellular and extracellular processes involved in the detoxification of Cd and Pb by this microalga. We found that C. reinhardtii was more tolerant to Pb (concentration for 50% of the maximal effect; EC50: 29.48 ± 8.83 mg L^-1) than to Cd (EC50: 12.48 ± 1.30 mg L^-1) after 96 h of exposure. Extracellular polymeric substances (EPS), intracellular starch granules, lipid droplets, and glutathione were significantly increased under Cd and Pb treatments. Lead-containing particles were formed outside of the cells exposed to 30 mg L^-1 of Pb, whereas no minerals were present when Cd was added. Various EPS functional groups, including -COOH, C-O-C (polysaccharides), and amide I and II (proteins), were involved in the interactions with Cd and Pb. The Pb removal rate (60.46-78.27%) by C. reinhardtii was higher than that of Cd (50.61-59.38%), and the microalgal cells with intact EPS bound more metals than those without EPS. Adsorption accounted for 79.62% of the total Cd accumulation in the low-Cd treatment, whereas absorption dominated the Pb accumulation at low Pb concentrations. The distributions of Cd and Pb in and out of the microalgal cells were reversed when the concentrations of the two metals increased. The detoxification strategies of C. reinhardtii for Cd and Pb were completely different, and these findings may assist in the phycoremediation of metal pollution in aquatic environments.

Whole-genome re-sequencing and transcriptome reveal cadmium tolerance related genes and pathways in Chlamydomonas reinhardtii

Cadmium (Cd), a common environmental toxic contaminant, is easily accumulated in living organisms, leading to numerous harmful effects. Chlamydomonas reinhardtii, a unicellular eukaryotic green algae strain, is a very suitable candidate for bioremediation of Cd-contaminated water. However, for the poor resistance to Cd, application of C. reinhardtii was restricted and genes mediating Cd tolerance in C. reinhardtii remain unclear. In this paper, adaptive laboratory evolution was performed with algae constant exposure to Cd over 420-day at environmentally relevant concentrations to select C. reinhardtii strains with high tolerance to Cd. Physiological indicators, such as cell proliferation, photosynthetic pigment contents and photosynthetic activity of photosystem were detected to evaluate the Cd tolerance of selected algae strain ALE0.5. Then, whole-genome re-sequencing and transcriptome were applied to identify the genes related to Cd tolerance. Genes involved in photosynthesis (PSBP1), glutathione metabolism (CHLREDRAFT_167073, GPX5) and calcium transport (CHLREDRAFT_189266, CHLREDRAFT_191203, CHLREDRAFT_187187, CSE1) were related to Cd tolerance in C. reinhardtii. This study provides a basis for obtaining transgenic C. reinhardtii strains with high Cd tolerance used for bioremediation of Cd pollution in the future.