Antioxidant enzymes are induced by phenol in the marine microalga Lingulodinium polyedrum

Assessing indicators of arsenic toxicity using variable fluorescence in a commercially valuable microalgae: Physiological and toxicological aspects

Indicators signaling Arsenic (As) stress through physiology of microalgae using non-destructive methods like variable fluorescence are rare but requisite. This study reports stress markers indicating arsenic (As) toxicity (in two concentrations 11.25 µg/L and 22.5 µg/L compared to a control) exposed to a microalga (Diacronema lutheri), using fast repetition rate fluorometry (FRRf). Growth and physiological parameters such as cell density, chl a and the maximum quantum yield F_v/F_m showed coherence and impeded after the exponential phase (day 9 - day 12) in As treatments compared to the control (p < 0.05). On contrary photo-physiological constants were elevated showing higher optical (a_LHII) and functional [Sigma (σ_PSII)] absorption cross-section for the As treatments (p < 0.05) further implying the lack of biomass production yet an increase in light absorption. In addition, As exposure increased the energy dissipation by heat (NPQ-NSV) showing a strong relationship with the de-epoxidation ratio (DR) involving photoprotective pigments. Total As bioaccumulation by D. lutheri showed a strong affinity with Fe adsorption throughout the algal growth curve. This study suggests some prompt photo-physiological proxies signaling As contamination and endorsing its usefulness in risk assessments, given the high toxicity and ubiquitous presence of As in the ecosystem.

A Sensitive Response Index Selection for Rapid Assessment of Heavy Metals Toxicity to the Photosynthesis of Chlorella pyrenoidosa Based on Rapid Chlorophyll Fluorescence Induction Kinetics

Heavy metals as toxic pollutants have important impacts on the photosynthesis of microalgae, thus seriously threatening the normal material circulation and energy flow of the aquatic ecosystem. In order to rapidly and sensitively detect the toxicity of heavy metals to microalgal photosynthesis, in this study, the effects of four typical toxic heavy metals, chromium (Cr(VI)), cadmium (Cd), mercury (Hg), and copper (Cu), on nine photosynthetic fluorescence parameters (φ_Po, Ψ_Eo, φ_Eo, δ_Ro, Ψ_Ro, φ_Ro, F_V/F_O, PI_ABS, and S_m) derived from the chlorophyll fluorescence rise kinetics (OJIP) curve of microalga Chlorella pyrenoidosa, were investigated based on the chlorophyll fluorescence induction kinetics technique. By analyzing the change trends of each parameter with the concentrations of the four heavy metals, we found that compared with other parameters, φ_Po (maximum photochemical quantum yield of photosystem II), F_V/F_O (photochemical parameter of photosystem II), PI_ABS (photosynthetic performance index), and S_m (normalized area of the OJIP curve) demonstrated the same monotonic change characteristics with an increase in concentration of each heavy metal, indicating that these four parameters could be used as response indexes to quantitatively detect the toxicity of heavy metals. By further comparing the response performances of φ_Po, F_V/F_O, PI_ABS, and S_m to Cr(VI), Cd, Hg, and Cu, the results indicated that whether it was analyzed from the lowest observed effect concentration (LOEC), the influence degree by equal concentration of heavy metal, the 10% effective concentration (EC₁₀), or the median effective concentration (EC₅₀), the response sensitivities of PI_ABS to each heavy metal were all significantly superior to those of φ_Ro, F_V/F_O, and S_m. Thus, PI_ABS was the most suitable response index for sensitive detection of heavy metals toxicity. Using PI_ABS as a response index to compare the toxicity of Cr(VI), Cd, Hg, and Cu to C. pyrenoidosa photosynthesis within 4 h by EC₅₀ values, the results indicated that Hg was the most toxic, while Cr(VI) toxicity was the lowest. This study provides a sensitive response index for rapidly detecting the toxicity of heavy metals to microalgae based on the chlorophyll fluorescence induction kinetics technique.

Hormesis effects of phenol on growth and cellular metabolites of Chlorella sp. under different nutritional conditions using response surface methodology

The present study investigated the effects of different phenol concentrations (200 - 1000 mg L^-1) towards Chlorella sp. under different culture conditions (light vs. dark) and NaNO₃ concentrations (0 - 0.1 g L^-1) using central composite design. Phenol induced hormesis effects on the algal growth and cellular metabolites. Nitrate was identified as a crucial factor for promoting the uptake of phenol by Chlorella cells, while light was a limiting factor for growth, but the phyco-toxicity of phenol was decreased in the dark. The pigment contents were generally increased in the treated cells to protect against the oxidative phenol stress. The incorporation of 200 mg L^-1 phenol and 0.05 g L^-1 NaNO₃ to the illuminated cells markedly promoted biomass and lipid contents to 0.22 g L^-1 and 26.26% w/w, which was 44 and 112% higher than the phenol-less control, respectively. Under the same conditions, the increase of phenol concentration to 600 mg L^-1, the protein contents were increased to 18.59% w/w. Conversely, the algal cells were able to accumulate more than 60% w/w of soluble carbohydrates under dark conditions at 600 mg L^-1 of phenol. Nitrate replete conditions stimulated lipid accumulation at the expense of protein biosynthesis. Furthermore, most of the treatments showed an increase of H₂O₂ and malonaldehyde contents, especially for the illuminated cells. However, catalase activity tended to increase under dark conditions, especially at low phenol and nitrate concentrations. This study is valuable in indicating the effects of phenol on microalgae by exploiting response surface methodology, which can be applied as a powerful tool in growth monitoring and toxicity assessment.

Oxidative stress responses in two marine diatoms during acute n-butyl acrylate exposure and the toxicological evaluation with the IBRv2 index

n-Butyl acrylate (nBA), a typical hazardous and noxious substance (HNS), is the largest-volume acrylate ester used to produce various types of polymers. With the increasing volume of nBA subject to maritime transportation, its accidental leakage poses a great risk to the marine organisms. Therefore, it is necessary to evaluate the ecological risk of nBA in marine environments. In this study, two species of marine microalgae, Skeletonema costatum and Phaeodactylum tricornutum, were used to explore the toxic effects of nBA based on their growth, pigment content, and oxidative stress. The growth of each species was significantly inhibited by nBA, showing a 96 h-EC₅₀ value of 2.23 mg/L for P. tricornutum and 8.19 mg/L for S. costatum, respectively. Although chlorophylls a and c exerted a hormesis effect in P. tricornutum, contents of pigments generally decreased at high concentrations. In P. tricornutum, all detected antioxidants (reduced glutathione, GSH; superoxide dismutase, SOD; catalase, CAT; and glutathione peroxidase, GPx) were stimulated at concentrations ranging from 1.50 to 3.82 mg/L. However, these elevations were not enough to reduce the oxidative damage caused by nBA, because the content of malondialdehyde (MDA) increased continuously during 96-h exposure. For S. costatum, the activities of only two antioxidants (GSH and CAT) were enhanced, which is enough to prevent the MDA content from rising, even at higher concentrations of nBA (5-10 mg/L). The Integrated Biomarker Response Version 2 (IBR_v2) index that combines responses of the above five oxidative stress biomarkers, was not only correlated positively with nBA concentration but could also indicate the occurrence of oxidative stress caused by acute concentration of nBA. These findings showed that P. tricornutum was sensitive to nBA compared to S. costatum, and the IBR_v2 index was an effective tool for evaluating ecotoxicological effects on marine microalgae due to nBA spills.

Extraction and characterization of microalgae-derived phenolics for pharmaceutical applications: A systematic review

Microalgae are regarded as a rich trove of diverse secondary metabolites that exert remarkable biological activities. In particular, microalgae-derived bioactive phenolic compounds (MBPCs) are a boon to biopharmaceutical and nutraceutical industries due to their diverse bioactivities, including antimicrobial, anticancer, antiviral, and immunomodulatory activities. The state-of-the-art green technologies for extraction and purification of MBPCs, along with the modern progress in the identification and characterization of MBPCs, have accelerated the discovery of novel active pharmaceutical compounds. However, several factors regulate the production of these bioactive phenolic compounds in microalgae. Furthermore, some microalgae species produce toxic phenolic compounds that negatively impact the aquatic ecosystem, animal, and human life. Therefore, the focus of this review paper is to bring into light the current innovations in bioprospection, extraction, purification, and characterization of MBPCs. This review is also aimed at a better understanding of the physicochemical factors regulating the production of MBPCs at an industrial scale. Finally, the present review covers the recent advances in toxicological evaluation, diverse applications, and future prospects of MBPCs in biopharmaceutical industries.

Phytotoxic effect and molecular mechanism induced by nanodiamonds towards aquatic Chlorella pyrenoidosa by integrating regular and transcriptomic analyses

The growing diverse applications of nanodiamonds (NDs), especially as adsorbents and catalysts for wastewater treatment, have significantly increased their discharge and potential risk towards aquatic ecosystems. Although NDs have been certified for superior biocompatibility and lower toxicity towards numerous human cell lines, the characteristic response and underlying mechanism of aquatic microalgal response remains unclear. Here, the response of Chlorella pyrenoidosa to five concentrations of NDs was thoroughly investigated by comprehensive phenotypic and transcriptional examinations. Results indicated that higher concentration of NDs (50 mg/L) induced 75.4% growth inhibition, exacerbated oxidative stress and malformed morphology of microalgae after 48 h exposure. Meanwhile, the aggregated microalgae formed several flocs, apparently under 50 mg/L NDs. Noticeably, photosynthesis was susceptible to the NDs exposure. Although, the chlorophyll content and genes involved in photosynthesis were significantly improved by NDs, the results obtained from the photochemical parameters indicated that the excessive electrons during photosynthesis might be a pivotal reason for oxidative stress generation. Additionally, the genes included in amino acids metabolism and protein synthesis were up-regulated to alleviate the oxidative stress. Collectively, this work discloses the explicit molecular mechanisms of aquatic microalgae and provides comprehensive insights of potential aqueous environmental risk of gradually emergent NDs.

Phycoremediation of phenol-polluted petro-industrial effluents and its techno-economic values as a win-win process for a green environment, sustainable energy and bioproducts

The discharge of the toxic phenol-polluted petro-industrial effluents (PPPIE) has severe environmental negative impacts, thus it is mandatory to be treated before its discharge. The objective of this review was to discuss the sustainable application of microalgae in phenols degradation, with a special emphasis on the enzymes involved in this bioprocess and the factors affecting the success of PPPIE phycoremediation. Moreover, it confers the microalgae bioenergetic strategies to degrade different forms of phenols in PPPIE. It also points out the advantages of the latest application of bacteria, fungi and microalgae as microbial consortia in phenols biodegradation. Briefly, phycoremediation of PPPIE consumes carbon dioxide emitted from petro-industries for; valorization of the polluted water to be reused and production of algal biomass which can act as a source of energy for such integrated bioprocess. Besides, the harvested algal biomass can feasibly produce; third-generation biofuels, biorefineries, bioplastics, fish and animal feed, food supplements, natural dyes, antioxidants and many other valuable products. Consequently, this review precisely confirms that the phycoremediation of PPPIE is a win-win process for a green environment and a sustainable future. Thus, to achieve the three pillars of sustainability; social, environmental and economic; it is recommendable to integrate PPPIE treatment with algal cultivation. This integrated process would overcome the problem of greenhouse gas emissions, global warming and climate change, solve the problem of water-scarce, and protect the environment from the harmful negative impacts of PPPIE.

Acclimation of Isochrysis galbana Parke (Isochrysidaceae) for enhancing its tolerance and biodegradation to high-level phenol in seawater

Marine microalgae with high removal efficiency of phenol are needed for the remediation of polluted seawater in cases involving phenol spills. To achieve this purpose, adaptive laboratory evolution (ALE) was performed by a microalga Isochrysis galbana Parke MACC/H59, which is capable of degrading phenol at concentrations of less than 100 mg L^-1 in 4 d. Two acclimation conditions were used: (i) 90 d at 100 mg L^-1 phenol, and (ii) 90 d at 100 mg L^-1 phenol followed by another 90 d at 200 mg L^-1 phenol. By doing so, two strains (PAS-1 and PAS-2) could be obtained respectively. They grew rapidly at phenol concentrations up to 200 mg L^-1 and 300 mg L^-1, respectively, with a specific growth rate 2.52-3.40 times and 1.93-3.23 times that of the control (without phenol). Also, both strains had a higher removal capacity of phenol than the unacclimated alga. Phenol at an initial concentration of 200 mg L^-1 was completely removed in 5 d thereby. For 300 mg L^-1 phenol, a removal efficiency of 92% was achieved in 10 days by using PAS-2, with a removal rate constant of 30.01 d^-1 (about twice that of PAS-1) and a half-life of 4.90 d (about half that of PAS-1), showing that a better strain may be obtained by extending the acclimation time. The enhancement of phenol biodegradation can be explained by the elevated activity of phenol hydroxylase (PH) in both strains. These results indicated that ALE could be an efficient tool used to enhance the tolerance and biodegradation of marine microalgae to phenol in seawater.

Antioxidant Bioprospecting in Microalgae: Characterisation of the Potential of Two Marine Heterokonts from Irish Waters

Microalgae constitute a heterogeneous and diverse range of organisms capable of accumulating bioactive metabolites, making them promising feedstock for applications in the nutraceutical, functional food, animal feed, biofertilisation or biofuel sectors. There has been renewed interest in recent times in natural sources of antioxidants, particularly as health products and preserving agents. Microalgae strains isolated from aquatic habitats in Ireland were successfully brought into culture. The 91 strains were grown phototrophically in nutrient-enriched media to generate biomass, which was harvested and assessed for antioxidant potential. Extracts were screened for antioxidant activity using a modified volumetric Trolox-ABTS assay and the Folin-Ciocalteu method. Two heterokont marine strains of interest were further studied to ascertain variations in antioxidant capacity across different stages of batch culture growth. The antioxidant activity of extracts of bacillariophyte cf. Stauroneis sp. LACW24 and ocrophyte cf. Phaeothamnion sp. LACW34 increased during growth with a maximum being observed during the late stationary or early death phase (2.5- to 8-fold increases between days 20 and 27). Strains LACW24 and LACW34 contained 5.9 and 3.0 mg g^-1 (DW) of the xanthophyll fucoxanthin, respectively. Extracts of strains also showed no cytotoxicity towards mouse cell lines. These results highlight the potential of these strains for biomass valorisation and cultivation upscaling and to be further considered as part of ongoing bioprospecting efforts towards identifying novel species to join the relatively narrow range of commercially exploited marine microalgae species.

Biodegradation of phenol by Chlamydomonas reinhardtii

The data presented in this particular study demonstrate that the biodegradation of phenol by Chlamydomonas reinhardtii is a dynamic bioenergetic process mainly affected by the production of catechol and the presence of a growth-promoting substrate in the culture medium. The study focused on the regulation of the bioenergetic equilibrium resulting from production of catechol after phenol oxidation. Catechol was identified by HPLC-UV and HPLC-ESI-MS/MS. Growth measurements revealed that phenol is a growth-limiting substrate for microalgal cultures. The Chlamydomonas cells proceed to phenol biodegradation because they require carbon reserves for maintenance of homeostasis. In the presence of acetic acid (a growth-promoting carbon source), the amount of catechol detected in the culture medium was negligible; apparently, acetic acid provides microalgae with sufficient energy reserves to further biodegrade catechol. It has been shown that when microalgae do not have sufficient energy reserves, a significant amount of catechol is released into the culture medium. Chlamydomonas reinhardtii acts as a versatile bioenergetic machine by regulating its metabolism under each particular set of growth conditions, in order to achieve an optimal balance between growth, homeostasis maintenance and biodegradation of phenol. The novel findings of this study reveal a paradigm showing how microalgal metabolic versatility can be used in the bioremediation of the environment and in potential large-scale applications.

Degradation pathways and kinetics of anthraquinone compounds along with nitrate removal by a newly isolated Rhodococcus pyridinivorans GF3 under aerobic conditions

A novel Rhodococcus pyridinivorans GF3 capable of degrading anthraquinone compounds (ACs) was isolated from 1-amino-4-bromoanthraquinone-2-sulfonic acid contaminated soil under aerobic conditions. Strain GF3 could degrade nine ACs at 150 rpm and 30 °C. LC-MS analysis showed that ACs were degraded via catechol and salicylic acid-produced pathways, which were different from previously reported phthalic acid-produced pathway. Strain GF3 could also completely remove ACs along with nitrate removal via aerobic denitrification. Further analysis found that the catechol as a metabolite of ACs could contribute to aerobic denitrification. The degradation of the mixture of five ACs used in 1-amino-4-bromoanthraquinone-2-sulfonic acid-producing process followed the modified Gompertz model under aerobic denitrification. During this process, except for anthraquinone (29.5% removal), the degradation efficiencies of hydrophilic and hydrophobic ACs reached over 90% and 60% in 48 h, respectively. These results show that strain GF3 is of potential application for the treatment of anthraquinone dye intermediates-containing wastewaters.

Characterization of cometabolic degradation of p-cresol with phenol as growth substrate by Chlorella vulgaris

To investigate the potential application of Chlorella vulgaris in the treatment of coal gasification wastewater, the characteristics of phenol and p-cresol cometabolism by Chlorella vulgaris were studied, including phenol degradation, ammonia nitrogen removal, antioxidant enzyme activities, and phenol hydroxylase activity. The results showed that the highest tolerable concentrations of phenol and p-cresol for Chlorella vulgaris were 800 and 400 mg/L, respectively. During cometabolism, phenol at low concentrations (100 mg/L) significantly promoted the degradation of p-cresol. Meanwhile, the removal efficiency of ammonia nitrogen was approximately 60% and was not affected by variations in phenol concentration. Furthermore, the cometabolism of phenol and p-cresol was enhanced by improvement of phenol hydroxylase activity of Chlorella vulgaris after the addition of NaHCO₃ as an exogenous nutrient. Therefore, Chlorella vulgaris has a great potential for the biochemical treatment of coal gasification wastewater.

Physiological and photosynthetic responses of Karenia mikimotoi to the modified clay mitigation method

Modified clay (MC) removed harmful algae Karenia mikimotoi effectively, and significantly inhibited residual algae growth. Hydrogen peroxides (H₂O₂) and malondialdehyde (MDA) contents of K. mikimotoi increased significantly after treatment, indicating that MC induced oxidative stress. Moreover, H₂O₂ content was significantly correlated with cell density, indicating that increased reactive oxygen species (ROS) were likely responsible for the growth inhibition. Further investigation showed that MC caused damage to photosynthesis of residual algae, indicated by decreased maximal photochemical efficiency (F_v/F_m) and performance index (PI_ABS). The density of reaction center (RC) decreased, indicating that MC induced partially inactivated RCs, then caused residual activated RCs to be over-excited. The electron transport chain was also blocked, indicated by increased W_K and V_J, and decreased S_m. These effects of photosystem II (PSII) were supposed to be the main contributors to ROS over-accumulation during photosynthesis. Overall, treatment with MC is an appropriate method for controlling K. mikimotoi blooms.

6.0 K microarray reveals differential transcriptomic responses in the dinoflagellate Prorocentrum minimum exposed to polychlorinated biphenyl (PCB)

Endocrine disrupting chemicals (EDCs) have toxic effects on algae; however, their molecular genomic responses have not been sufficiently elucidated. Here, we evaluated genome-scaled responses of the dinoflagellate alga Prorocentrum minimum exposed to an EDC, polychlorinated biphenyl (PCB), using a 6.0 K microarray. Based on two-fold change cut-off, we identified that 609 genes (∼10.2%) responded to the PCB treatment. KEGG pathway analysis showed that differentially expressed genes (DEGs) were related to ribosomes, biosynthesis of amino acids, spliceosomes, and cellular processes. Many DEGs were involved in cell cycle progression, apoptosis, signal transduction, ion binding, and cellular transportation. In contrast, only a few genes related to photosynthesis and oxidative stress were expressed in response to PCB exposure. This was supported by that fact that there were no obvious changes in the photosynthetic efficiency and reactive oxygen species (ROS) production. These results suggest that PCB might not cause chloroplast and oxidative damage, but could lead to cell cycle arrest and apoptosis. In addition, various signal transduction and transport pathways might be disrupted in the cells, which could further contribute to cell death. These results expand the genomic understanding of the effects of EDCs on this dinoflagellate protist.

Lipid metabolism and pro-oxidant/antioxidant balance of Halamphora oceanica from the Gulf of Mexico exposed to water accommodated fraction of Maya crude oil

Diatoms play key roles in primary production and carbon fixation at a global scale and in some cases these species live on marine ecosystems impacted by crude oil (CO) spills. Halamphora oceanica, a new diatom species from the Southwest of the Gulf of Mexico was isolated and cultured in the laboratory and was exposed to water accommodated fraction (WAF) of different Maya CO loads at 0.01, 0.1, 1 and 10g/L by 96h. A battery of biomarkers involved in oxidative stress (O₂•, H₂O₂, TBARS, ROOH, RC=O, SOD, CAT, GPx), biotransformation and conjugation (total CYP450 activity and GST) moreover fatty acid (FA) metabolism (FA levels, fatty-acid synthase and acyl-CoA oxidase) were measured. Obtained results suggest that increases of PAHs in the medium (below to EC₅₀) acts as external forces able to turn-on regulatory mechanisms on H. oceanica involved in both, on the PAHs uptake and changing its aerobic metabolism to anaerobic metabolism. However, the growth of this microalgae species evaluated as chlorophyll "a" and pheophytin levels increased as the WAF concentration indicating that PAHs and other hydrosoluble hydrocarbons were used as carbon and energy sources by unidentified enzymes not evaluated in the current study. Our hypothesis was also corroborated by IBRv2. In the current study, we suppose the change from aerobic to anaerobic metabolism as a strategy for Halamphora oceanica survival exposed to petroleum hydrocarbons.

Toxicological effects of phenol on four marine microalgae

The toxic effects of phenol on four marine microalgae (Dunaliella salina, Platymonas subcordiformis, Phaeodactylum tricornutum Bohlin, and Skeletonema costatum) were evaluated. The 96h EC₅₀ values were 72.29, 92.97, 27.32, and 27.32mgL^-1, respectively, which were lower than those values of freshwater microalgae reported in the literature. During a 96-h exposure to a sub-lethal concentration of phenol (1/2 96h EC₅₀) with green alga (D. salina) and diatom (S. costatum), reactive oxygen species (ROS) accumulation, and chlorophyll a (Chl a) content decrease were simultaneously observed in diatom cells after 48h treatment. On the contrary, other chlorophylls in both algae were unaffected. Under transmission electron microscopy (TEM), the phenol-induced ultrastructure alterations included disappearance, or shrinkage, of nucleolus and enlargement of vacuoles, which may result in programmed cell death (PCD). The increase in number of lipid droplets may be related to phenol detoxification. These results indicate that the sensitivity of marine microalgae to phenol was dependent on some biotic factors such as cell size, ROS production, and phenol degradation ability in algal cells.

Comparative transcriptomic analysis reveals phenol tolerance mechanism of evolved Chlorella strain

The growth of microalgae is inhibited by high concentration phenol due to reactive oxygen species. An evolved strain tolerated to 500mg/L phenol, Chlorella sp. L5, was obtained in previous study. In this study, comparative transcriptomic analysis was performed for Chlorella sp. L5 and its original strain (Chlorella sp. L3). The tolerance mechanism of Chlorella sp. L5 for high concentration phenol was explored on genome scale. It was identified that the up-regulations of the related genes according to antioxidant enzymes (SOD, APX, CAT and GR) and carotenoids (astaxanthin, lutein and lycopene) biosynthesis had critical roles to tolerate high concentration phenol. In addition, most of genes of PS I, PS II, photosynthetic electron transport chain and starch biosynthesis were also up-regulated. It was consistent to the experimental results of total carbohydrate contents of Chlorella sp. L3 and Chlorella sp. L5 under 0mg/L and 500mg/L phenol.

Marine-Derived Biocatalysts: Importance, Accessing, and Application in Aromatic Pollutant Bioremediation

The aim of the present review is to highlight the potential use of marine biocatalysts (whole cells or enzymes) as an alternative bioprocess for the degradation of aromatic pollutants. Firstly, information about the characteristics of the still underexplored marine environment and the available scientific tools used to access novel marine-derived biocatalysts is provided. Marine-derived enzymes, such as dioxygenases and dehalogenases, and the involved catalytic mechanisms for the degradation of aromatic and halogenated compounds, are presented, with the purpose of underpinning their potential use in bioremediation. Emphasis is given on persistent organic pollutants (POPs) that are organic compounds with significant impact on health and environment due to their resistance in degradation. POPs bioaccumulate mainly in the fatty tissue of living organisms, therefore current efforts are mostly focused on the restriction of their use and production, since their removal is still unclear. A brief description of the guidelines and criteria that render a pollutant POP is given, as well as their potential biodegradation by marine microorganisms by surveying recent developments in this rather unexplored field.