Growth stimulation and inhibition effects of 4-hydroxybenzoic acid and some related compounds on the freshwater green alga Pseudokirchneriella subcapitata

Methylparaben toxicity and its removal by microalgae Chlorella vulgaris and Phaeodactylum tricornutum

The widespread occurrence of methylparaben (MPB) has aroused great concern due to its weak estrogenic endocrine-disrupting property and potential toxic effects. However, the degradation potential and pathway of MPB by microalgae have rarely been reported. Here, microalgae Chlorella vulgaris and Phaeodactylum tricornutum were used to investigate their responses, degradation potential and mechanisms towards MPB. MPB showed low-dose stimulation (by 86.02 ± 0.07% at 1 mg/L) and high-dose inhibition (by 60.17 ± 0.05% at 80 mg/L) towards the growth of C. vulgaris, while showed inhibition for P. tricornutum (by 6.99 ± 0.05%-20.14 ± 0.19%). The degradation efficiencies and rates of MPB were higher in C. vulgaris (100%, 1.66 ± 0.54-5.60 ± 0.86 day^-1) than in P. tricornutum (4.3-34.2%, 0.04 ± 0.01-0.08 ± 0.00 day^-1), which could be explained by the significantly higher extracellular enzyme activity and more fluctuation of the protein ratio for C. vulgaris, indicating a higher ability of C. vulgaris to adapt to pollutant stress. Biodegradation was the main removal mechanism of MPB for both the two microalgae. Furthermore, two different degradation pathways of MPB by the two microalgae were proposed. MPB could be mineralized and completely detoxified by C. vulgaris. Overall, this study provides novel insights into MPB degradation by microalgae and strategies for simultaneous biodegradation and detoxification of MPB in the environment.

Bioaccumulation and toxicity of perfluorooctanoic acid and perfluorooctane sulfonate in marine algae Chlorella sp

The ocean is an important sink for perfluorinated alkyl acids (PFAAs), but the toxic mechanisms of PFAAs to marine organisms have not been clearly studied. In this study, the growth rate, photosynthetic activity, oxidative stress and bioaccumulation were investigated using marine algae Chlorella sp. after the exposure of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate acid (PFOS). The results showed that PFOA of <40 mg/L and PFOS of <20 mg/L stimulated algal reproduction, and high doses inhibited the algal growth. The absorbed PFOA and PFOS by algal cells damaged cell membrane and caused metabolic disorder. The photosynthesis activity was inhibited, which was revealed by the significantly reduced maximal quantum yield (Fv/Fm), relative electron transfer rate (rETR) and carbohydrate synthesis. However, the chlorophyll a content increased along with the up-regulation of its encoding genes (psbB and chlB), probably due to an overcompensation effect. The increase of ROS and antioxidant substances (SOD, CAT and GSH) indicated that PFOA and PFOS caused oxidative stress. The BCF of marine algae Chlorella sp. to PFOA and PFOS was calculated to be between 82 and 200, confirming the bioaccumulation of PFOA and PFOS in marine algae. In summary, PFOA and PFOS can accumulate in Chlorella sp. cells, disrupt photosynthesis, trigger oxidative stress and inhibit algal growth. PFOS shows higher toxicity and bioaccumulation than PFOA. The information is important to evaluate the environmental risks of PFAAs.

Allelopathic effect of benzoic acid (hydroponics root exudate) on microalgae growth

Hydroponic effluent (HE) contains a reasonable amount of residual nutrients. Therefore, HE could be used as a low-cost growth media for microalgae mediated resource recovery and water recycling. However, the presence of root exudates (particularly, benzoic acid) may lead to toxicity in microalgae.In the present study, the allelopathic effects of benzoic acid on microalgal growth was tested. During 96 h batch growth, Chlorella pyrenoidosa showed the highest biomass concentration (0.064-0.037 g.L^-1) compared to Chlorella sorokiniana (0.09-0.26 g.L^-1) at the tested benzoic acid doses. Moreover, both the species showed growth stimulation and growth inhibition up to certain benzoic acid doses. Hence, both the microalgal species showed allelopathic behaviour at different doses of benzoic acid. Further, the observed half effective concentration (96 h EC₅₀) were 65.10 mg.L^-1 and 105.27 mg.L^-1, respectively, for Chlorella pyrenoidosa and C. sorokiniana with 95% confidence limits. Further, Haldane's model best fitted with experimental data of both the microalgae (r ∼ 0.99). Overall, the study reveals that the HE with low benzoic acid dose may serve as a suitable growth media for microalgae. However, further in-depth research interventions using real HE are desirable to determine its real-world applicability.

Metabolomics Unravels Grazing Interactions under Nutrient Enrichment from Aquaculture

Our goal was to understand the mechanisms behind the impact of nutrient enrichment at intermediate distances from aquaculture on the interactions of a subtidal macroalgae community with its main grazer, the sea urchin Paracentrotus lividus. We assessed the diversity and cover of the macroalgal community, the abundance and biometrics of the sea urchins, the carbon and nitrogen elemental and isotopic compositions, and their metabolome in two stations, at an intermediate distance (station A) and away (station B) from a fish cage facility in the Aegean Sea (Greece), during the warm and cold seasons. The nutrient input at station A favored a shift to a macroalgal assemblage dominated by turf-forming species, depleted of native-erected species and with a higher abundance of invasive algae. A stable isotope analysis showed fish-farm-associated nitrogen enrichment of the macroalgae and trophic transfer to P. lividus. A decrease in metabolites related to grazing, reproduction, and energy reserves was found in P. lividus at station A. Furthermore, the metabolomic analysis was able to pinpoint stress in P. lividus at an intermediate distance from aquaculture. The chosen combination of traditional ecology with omics technology could be used to uncover not only the sublethal effects of nutrient loading but also the pathways for species interactions.

Ecotoxicological Consequences of the Abatement of Contaminants of Emerging Concern by Ozonation—Does Mixture Complexity Matter?

Ozonation has been used to degrade persistent water contaminants, namely, pharmaceuticals and personal care products (PPCPs). However, ozonation can lead to by-products that can be more toxic than the parent compounds. This work aims to assess whether the ecotoxicological effects of ozonation are modified as the initial matrix being treated increases in complexity, considering mixtures of 2, 3, 4 and 5 PPCPs. The following PPCPs were used: two parabens (metylparaben (MP) and propylparaben (PP)), paracetamol (PCT), sulfamethoxazole (SMX) and carbamazepine (CBZ). The following model species were used to assess toxicity: the crustacean Daphnia magna, the microalgae Raphidocelis subcapitata, the macrophyte Lemna minor and the watercress Lepidium sativum. There was a trend of increased toxicity with increasing mixture complexity of the untreated samples, except for D. magna. The same was observed after ozonation with the exception of the mixture MP+PP, which showed high toxicity to all the tested species, namely 100% immobilization of D. magna. The toxicity of SMX to the primary producers decreased pronouncedly after ozonation, except for L. minor. This study highlights the importance of considering the complexity of the matrix being treated and of using an ecotoxicological test battery with a wide diversity of species for assessing ozonation efficiency.

Improvement of caffeic acid biotransformation into para-hydroxybenzoic acid by Candida albicans CI-24 via gamma irradiation and model-based optimization

Para-hydroxybenzoic acid (PHBA) has great potential in biological applications due to its putative antiviral activity against SARS-CoV-2 and its antimicrobial activity in the face of the radically increasing number of multidrug-resistant pathogens. This is in addition to its antimutagenic, anti-inflammatory, antioxidant, hypoglycemic, antiestrogenic, and antiplatelet aggregating activities. In this study, an approximate sixfold increase in the production of PHBA was achieved via biotransformation of caffeic acid by Candida albicans. The improvement was performed in two steps: first, through mutation by gamma irradiation (5 KGy dose), resulting in the recovery of a mutant (CI-24), which produced approximately triple the amount of PHBA produced by the wild-type isolate. Then, biotransformation by this mutant was further optimized via response surface methodology model-based optimization. The maximum PHBA production (7.47 mg/mL) was obtained in a fermentation medium composed of 1% w/v yeast extract as a nitrogen source, with an initial pH of 6.6, incubated at 28 °C at an agitation rate of 250 rpm. To further enhance the performance and economics of the process, cells of the CI-24 mutant were immobilized in calcium alginate beads and could retain an equivalent biotransformation capacity after three successive biotransformation cycles.

Impact of seawater salinity on the sonochemical removal of emerging organic pollutants

The results presented in this study illustrate the multiple roles of seawater salinity toward the sonochemical degradation, at variable frequencies (300-1700 kHz), of several hazardous substances, i.e. propylparaben (PPR) endocrine disruptor and several synthetic dyes: naphthol blue black (NBB), malachite green (MG), basic red 29 (BR29), acid orange 7 (AO7), Rhodamine B (RhB) and basic fuchsin (BF). Sonochemical treatment degraded all pollutants in seawater at faster rates than in deionized water. The seawater-salts through increasing the ionic strength of the solution act as a potential pusher of hydrophilic pollutants toward the reactive interfacial area of cavitation bubbles. Additionally, the salts reduce the bubble coalescence, which yields higher number of active bubbles in the irradiating media. Analysing the degradation rate of PPR and NBB with two heterogeneous models based on Langmuir kinetics mechanism indicated that the bubble interfacial area was the preferred reaction zone for the ultrasonic degradation of PPR and NBB in seawater.

Salicylic acid and aspirin stimulate growth of Chlamydomonas and inhibit lipoxygenase and chloroplast desaturase pathways

Chemical stimulants, used to enhance biomass yield, are highly desirable for the commercialisation of algal products for a wide range of applications in the food, pharma and biofuels sectors. In the present study, phenolic compounds, varying in substituents and positional isomers on the arene ring have been evaluated to determine structure-activity relationship and growth. The phenols, catechol, 4-methylcatechol and 2, 4-dimethyl phenol were generally inhibitory to growth as were the compounds containing an aldehyde function. By contrast, the phenolic acids, salicylic acid, aspirin and 4-hydroxybenzoate markedly stimulated cell proliferation enhancing cell numbers by 20-45% at mid-log phase. The order of growth stimulation was ortho > para > meta with respect to the position of the OH group. Both SA and aspirin reduced 16:3 in chloroplast galactolipids. In addition, both compounds inhibited lipoxygenase activity and lowered the levels of lipid hydroperoxides and malondialdehydes in the cells. The present study has demonstrated the possibility of using SA or aspirin to promote algal growth through the manipulation of lipid metabolising enzymes.

Carbamazepine toxicity and its co-metabolic removal by the cyanobacteria Spirulina platensis

Bioremediation of pharmaceutical-contaminated wastewater using microalgae has attracted increasing attention. Cyanobacteria, which are important prokaryotic microalgae, are widely distributed in different water environments, and have the advantages of simple culture and a fast growth rate. However, studies on either the toxicity of pharmaceutical contaminants (PhCs) to cyanobacteria or the removal of PhCs by cyanobacteria are scarce. In this study, carbamazepine (CBZ) and Spirulina platensis were selected as model PhCs and cyanobacteria, respectively. CBZ (>1 mg/L) had toxicity effects on S. platensis, showing maximal growth inhibition (34.0%) at 100 mg/L after 10 days of cultivation. At CBZ < 25 mg/L, S. platensis showed a trend similar to that of eukaryotic microalgae in increasing superoxide dismutase and catalase activities and content of chlorophylls, carotenoids, carbohydrates, and lipids. These results indicated that S. platensis had a similar protective mechanism to CBZ toxicity as that of the eukaryotic microalgae. Increasing CBZ concentration (50-100 mg/L) significantly decreased these biochemical characteristics and photosynthetic activity owing to the serious damage of the structure and function of S. platensis. However, with increasing cultivation time, the growth and photosynthetic activity of S. platensis recovered from the toxicity of CBZ. S. platensis showed a maximum of 30.97 ± 1.30% removal of CBZ (1 mg/L), mainly through biodegradation. Addition of 0.3 mg/L glucose enhanced this removal efficiency to 50.13 ± 2.51% via co-metabolism. These findings indicated that S. platensis can be used for the removal of CBZ or other PhCs from wastewater.

Effect of PHRs and PCPs on Microalgal Growth, Metabolism and Microalgae-Based Bioremediation Processes: A Review

In this review, the effect of pharmaceuticals (PHRs) and personal care products (PCPs) on microalgal growth and metabolism is reported. Concentrations of various PHRs and PCPs that cause inhibition and toxicity to growths of different microalgal strains are summarized and compared. The effect of PHRs and PCPs on microalgal metabolism (oxidative stress, enzyme activity, pigments, proteins, lipids, carbohydrates, toxins), as well as on the cellular morphology, is discussed. Literature data concerning the removal of PHRs and PCPs from wastewaters by living microalgal cultures, with the emphasis on microalgal growth, are gathered and discussed. The potential of simultaneously bioremediating PHRs/PCPs-containing wastewaters and cultivating microalgae for biomass production in a single process is considered. In the light of reviewed data, the feasibility of post-bioremediation microalgal biomass is discussed in terms of its contamination, biosafety and further usage for production of value-added biomolecules (pigments, lipids, proteins) and biomass as a whole.

Biocatalytic Degradation of Parabens Mediated by Cell Surface Displayed Cutinase

Parabens are emerging environmental contaminants with known endocrine-disrupting effects. This study created a novel biocatalyst (named as SDFsC) by expressing the enzyme Fusarium solani pisi cutinase (FsC) on the cell surface of Baker's yeast Sacchromycese cerevisiae and demonstrated successful enzyme-mediated removal of parabens for the first time. Parabens with different side chain structures had different degradation rates by the SDFsC. The SDFsC preferentially degraded the parabens with relatively long alkyl or aromatic side chains. The structure-dependent degradability was in a good agreement with the binding energy between the active site of FsC and different parabens. In real wastewater effluent solution, the SDFsC effectively degraded 800 μg/L of propylparaben, butylparaben, and benzylparaben, either as a single compound or as a mixture, within 48 h. The estrogenic activity of parabens was considerably reduced as the parent parabens were degraded into 4-hydroxybenzoic acid via hydrolysis pathway by the SDFsC. The SDFsC showed superior reusability and maintained 93% of its initial catalytic activity after six rounds of paraben degradation reaction. Results from this study provide scientific basis for developing biocatalysis as a green chemistry alternative for advanced treatment of parabens in sustainable water reclamation.

Toxicity, degradation and metabolic fate of ibuprofen on freshwater diatom Navicula sp

Ibuprofen (IBU) is one of the most widely used and frequently detected human pharmaceuticals in aquatic environment. However, the toxicity of IBU on diatom and its fate remain still unkown. In the present study, the toxicity of IBU on the diatom was evaluated by the algal growth rate, the chlorophyll-a and carotenoids contents. The degradation of IBU including in particular the potential for the formation of incomplete degradation products was also explored. Biochemical characteristics of Navicula sp. were significantly inhibited at IBU concentrations up to 50mgL^-1 after 10days of exposure. The degradation of IBU was retarded by Navicula sp. at low concentration (1mgL^-1), with t_1/2 being extended from 9.6±1.8 d to 12.0±1.5 d, indicating that Navicula sp. could prolong the exposure time of IBU. A total of 8 metabolites were identified by LC-MS/MS and the degradation pathway of IBU in Navicula sp. was proposed. Hydroxylation, acylation, demethylation, and glucuronidation contributed to IBU transformative reactions in diatom cells. These findings indicate that the presence of diatom Navicula sp. could hinder degradation of IBU, and IBU and/or its metabolites may pose high risks on aquatic ecosystem in natural waters.

Effects of chitosan, gallic acid, and algicide on the physiological and biochemical properties of Microcystis flos-aquae

The effects of chitosan, gallic acid, and algicide chitosan-gallate on the activities of antioxidant enzymes, malonaldehyde (MDA) content, and photosynthetic activity of Microcystis flos-aquae were investigated to explore the physiological and biochemical mechanisms of algicides. Results demonstrated that chitosan did not significantly affect catalase (CAT) and superoxide dismutase (SOD) activities, MDA content, and photosynthetic activity in this alga. At 30 mg L(-1), gallic acid, CAT, and SOD activities and MDA of M. flos-aquae cells showed maximums of 2.872 × 10(-10) mg·cell(-1) min(-1), 0.787 × 10(-8) U·cell(-1), and 0.626 × 10(-8) nmol·cell(-1), respectively. Photosynthetic organs in algal cells were severely damaged under the stress of high gallic acid concentrations, inducing blockage of photosynthetic electron transport and resulting in the inability to restore normal photosynthetic activity. CAT and SOD activities and MDA content with lower algicide concentration were significantly higher than the control group (p < 0.05) and, in higher algicide groups, significantly lower than the control (p < 0.05). Algicide releasing gallic acid in groups treated with 60, 90, and 130 mg/L algicide was strong enough to cause severe damage to photosynthetic organs in these algal cells. The algicide suppression time was longer than that of directly added gallic acid.

Multiparameter-based bioassay of 2-(4-chlorophenyl)-4-(4-methoxyphenyl) quinazoline, a newly-synthesized quinazoline derivative, toward Microcystis aeruginosa HAB5100 (cyanobacteria)

Quinazoline derivatives have wide biological activities and therapeutic properties, implying their potential for development and application on a large scale. In the present study, 2-(4-chlorophenyl)-4-(4-methoxyphenyl) quinazoline (CMQ), was selected to examine its effect on unicellular cyanobacteria, Microcystis aeruginosa by evaluating growth, physiological and molecular responses. Growth was inhibited by CMQ, with a 96 h EC50 of 1.93 ± 0.19 mg L(-1). The up-regulated expression of prx was shown, reflecting that oxidative stress might be a toxic factor of CMQ. At higher concentrations of CMQ, the quantum yields of Y(II) and Y(NPQ) in photosystem II decreased seriously and Y(NO) increased sharply, and psbA gene encoding for D1 protein was over-expressed. These results demonstrated that high concentrations of CMQ had different inhibitory targets associated with photosystem electron transport and with sites beyond the electron transport chain, leading to severe toxicity.

Emerging contaminants in Belgian marine waters: single toxicant and mixture risks of pharmaceuticals

Knowledge on the effects of pharmaceuticals on aquatic marine ecosystems is limited. The aim of this study was therefore to establish the effect thresholds of pharmaceutical compounds occurring in the Belgian marine environment for the marine diatom Phaeodactylum tricornutum, and subsequently perform an environmental risk assessment for these substances. Additionally, a screening-level risk assessment was performed for the pharmaceutical mixtures. No immediate risk for acute toxic effects of these compounds on P. tricornutum were apparent at the concentrations observed in the Belgian marine environment. In two Belgian coastal harbours however, a potential chronic risk was observed for the β-blocker propranolol. No additional risks arising from the exposure to mixtures of pharmaceuticals present in the sampling area could be detected. However, as risk characterization ratios for mixtures of up to 0.5 were observed, mixture effects could emerge should more compounds be taken into account.

Impact of two different humic substances on selected coccal green algae and cyanobacteria--changes in growth and photosynthetic performance

BACKGROUND, AIM AND SCOPE

There is growing evidence to show that dissolved humic substances, HSs, can directly interact with freshwater organisms, such as phototrophic organisms, cladocerans, amphipods and fish. The responses are-at least in part-transcriptionally controlled. These interactions can lead to stress symptoms in the exposed organisms. In phototrophs, stress symptoms include a reduction in photosynthetic oxygen release and antioxidative stress. Besides the direct effects, HSs also cause indirect effects that provoke different physiological adaptations in the phototrophs.

MATERIALS AND METHODS

The HS-influenced photosynthetic performance and stress response of two different green algae, Pseudokirchneriella subcapitata (Koršikov) Hindák and Monoraphidium braunii (Nägeli in Kützing) Komárková-Legnerová, and two cyanobacterial species, Synechocystis sp. (PCC 6803, Institut Pasteur) and Microcystis aeruginosa (PCC 7806, Institut Pasteur), were tested. Two humic preparations were applied, the synthetic HS1500 and HuminFeed, HF, which had previously been proven effective in bioassays with invertebrates and a water mould.

RESULTS AND DISCUSSION

When the algae were grown near light saturation, most of the tested species were positively affected by HSs in growth rate or chlorophyll content. Cell sizes decreased with increasing HS concentrations for all eukaryotic phototrophs, except for the cyanobacteria. After 4 to 5 days of cultivation at the highest HS exposure, there was a decrease in total dry weight due to reduced cell sizes in contrast to an increase in cell numbers. With the exception of Synechocystis, the dry weight per cell ratio decreased with increasing HS concentration. The efficiency of utilizing absorbed light quanta increased with increasing HS concentrations; the maximum quantum yield of photosystem II (ΦPSIImax) was higher in all of the tested species, with the exception of M. aeruginosa, after exposure to HS.

CONCLUSION

The applied humic preparations did not interact directly with PSII, but changed the physiological state of the algae, especially the photosynthetic performance. Neither the green algae nor the cyanobacteria were inhibited in growth or negatively affected in their photosynthetic performance. The exposure to lower concentrations of HS stimulated better growth of the phototrophs. The tested humic preparations obviously did not have the potency to act as xenobiotic stressors; furthermore, there was no sign of herbicide potency.

Monocyclic phenolic acids; hydroxy- and polyhydroxybenzoic acids: occurrence and recent bioactivity studies

Among the wide diversity of naturally occurring phenolic acids, at least 30 hydroxy- and polyhydroxybenzoic acids have been reported in the last 10 years to have biological activities. The chemical structures, natural occurrence throughout the plant, algal, bacterial, fungal and animal kingdoms, and recently described bioactivities of these phenolic and polyphenolic acids are reviewed to illustrate their wide distribution, biological and ecological importance, and potential as new leads for the development of pharmaceutical and agricultural products to improve human health and nutrition.

Metabolic characterization of a strain (BM90) of Delftia tsuruhatensis showing highly diversified capacity to degrade low molecular weight phenols

A novel bacterium, strain BM90, previously isolated from Tyrrhenian Sea, was metabolically characterized testing its ability to use 95 different carbon sources by the Biolog system. The bacterium showed a broad capacity to use fatty-, organic- and amino-acids; on the contrary, its ability to use carbohydrates was extremely scarce. Strain BM90 was identified and affiliated to Delftia tsuruhatensis by molecular techniques based on 16S rRNA gene sequencing. D. tsuruhatensis BM90, cultivated in shaken cultures, was able to grow on various phenolic compounds and to remove them from its cultural broth. The phenols used, chosen for their presence in industrial or agro-industrial effluents, were grouped on the base of their chemical characteristics. These included benzoic acid derivatives, cinnamic acid derivatives, phenolic aldehyde derivatives, acetic acid derivatives and other phenolic compounds such as catechol and p-hydroxyphenylpropionic acid. When all the compounds (24) were gathered in the same medium (total concentration: 500 mg/l), BM90 caused the complete depletion of 18 phenols and the partial removal of two others. Only four phenolic compounds were not removed. Flow cytometry studies were carried out to understand the physiological state of BM90 cells in presence of the above phenols in various conditions. At the concentrations tested, a certain toxic effect was exerted only by the four compounds that were not metabolized by the bacterium.