Xenobiotic biotransformation in unicellular green algae. Involvement of cytochrome P450 in the activation and selectivity of the pyridazinone pro-herbicide metflurazon

Vital role of CYP450 in the biodegradation of antidiabetic drugs in the aerobic activated sludge system and the mechanisms

The extensive use of antidiabetic drugs (ADDs) and their detection in high concentrations in the environment have been extensively documented. However, the mechanism of ADDs dissipation in aquatic environments is still not well understood. This study thoroughly investigates the dissipation behavior of ADDs and the underlying mechanisms in the aerobic activated sludge system. The results indicate that the removal efficiencies of ADDs range from 3.98% to 100% within 48 h, largely due to the biodegradation process. Additionally, the gene expression of cytochrome P450 (CYP450) is shown to be significantly upregulated in most ADDs-polluted samples (P < 0.05), indicating the vital role of CYP450 enzymes in the biodegradation of ADDs. Enzyme inhibition experiments validated this hypothesis. Moreover, molecular docking and simulation results indicate that a strong correlation between the biodegradation of ADDs and the interactions between ADDs and CYP450 (Ebinding). The differences in dissipation behavior among the tested ADDs are possibly due to their electrophilic characteristics. Overall, this study makes the initial contribution to a more profound comprehension of the crucial function of CYP450 enzymes in the dissipation behavior of ADDs in a typical aquatic environment.

Efficiency, mechanism, influencing factors, and integrated technology of biodegradation for aromatic compounds by microalgae: A review

Aromatic compounds have received widespread attention because of their threat to ecosystem and human health. However, traditional physical and chemical methods are criticized due to secondary pollution and high cost. As a result of ecological security and the ability of carbon sequestration, biodegradation approach based on microalgae has emerged as a promising alternative treatment for aromatic pollutants. In light of the current researches, the degradation efficiency of BTEX (benzene, toluene, ethylbenzene, and xylene), polycyclic aromatic hydrocarbons (PAHs), and phenolic compounds by microalgae was reviewed in this study. We summarized the degradation pathways and metabolites of p-xylene, benzo [a]pyrene, fluorene, phenol, bisphenol A, and nonylphenol by microalgae. The influence factors on the degradation of aromatic compounds by microalgae were also discussed. The integrated technologies based on microalgae for degradation of aromatic compounds were reviewed. Finally, this study discussed the limitations and future research needs of the degradation of these compounds by microalgae.

Green alga Chlamydomonas reinhardtii can effectively remove diclofenac from the water environment - A new perspective on biotransformation

The use of unicellular algae to remove xenobiotics (including drugs) from wastewaters is one of the rapidly developing areas of environmental protection. Numerous data indicate that for efficient phycoremediation three processes are important, i.e. biosorption, bioaccumulation, and biotransformation. Although biosorption and bioaccumulation do not raise any serious doubts, biotransformation is more problematic since its products can be potentially more toxic than the parent compounds posing a threat to organisms living in a given environment, including organisms that made this transformation. Thus, two questions need to be answered before the proper algae strain is chosen for phycoremediation, namely what metabolites are produced during biotransformation, and how resistant is the analyzed strain to a mixture of parent compound and metabolites that appear over the course of culture? In this work, we evaluated the remediation potential of the model green alga Chlamydomonas reinhardtii in relation to non-steroidal anti-inflammatory drugs (NSAIDs), as exemplified by diclofenac. To achieve this, we analysed the susceptibility of C. reinhardtii to diclofenac as well as its capability to biosorption, bioaccumulation, and biotransformation of the drug. We have found that even at a relatively high concentration of diclofenac the algae maintained their vitality and were able to remove (37.7%) DCF from the environment. A wide range of phase I and II metabolites of diclofenac (38 transformation products) was discovered, with many of them characteristic rather for animal and bacterial biochemical pathways than for plant metabolism. Due to such a large number of detected products, 18 of which were not previously reported, the proposed scheme of diclofenac transformation by C. reinhardtii not only significantly contributes to broadening the knowledge in this field, but also allows to suggest possible pathways of degradation of xenobiotics with a similar structure. It is worth pointing out that a decrease in the level of diclofenac in the media observed in this study cannot be fully explained by biotransformation (8.4%). The mass balance analysis indicates that other processes (total 22%), such as biosorption, a non-extractable residue formation, or complete decomposition in metabolic cycles can be involved in the diclofenac disappearance, and those findings open the prospects of further research.

Algal mediated intervention for the retrieval of emerging pollutants from aqueous media

Water is a crucial elemental contributor for all sectors; however, the agricultural sector alone accounts for 70% of the world's total water withdrawal. The anthropogenic activity from various industries including agriculture, textiles, plastics, leather, and defence has resulted in the release of contaminants into water systems, resulting harm to the ecosystem and biotic community. Algae-based organic pollutant removal uses several methods, such as biosorption, bioaccumulation, biotransformation, and biodegradation. The adsorption of methylene blue by algal species Chlamydomonas sp. showed a maximum adsorption capacity of 2744.5 mg/g with 96.13% removal efficiency; on the other hand, Isochrysis galbana demonstrated a maximum of 707 µg/g nonylphenol accumulation in the cell with 77% removal efficiency indicating the potential of algal systems as efficient retrieval system for organic contaminants. This paper is a compilation of detailed information about biosorption, bioaccumulation, biotransformation, biodegradation, and their mechanism, along with the genetic alteration of algal biomass. Where the genetic engineering and mutations on algae can be advantageously utilized for the enhancement of removal efficiency without any secondary toxicity.

Microalgal-induced remediation of wastewaters loaded with organic and inorganic pollutants: An overview

The recent surge in industrialization has intensified the accumulation of various types of organic and inorganic pollutants due to the illegal dumping of partially and/or untreated wastewater effluents in the environment. The pollutants emitted by several industries pose serious risk to the environment, animals and human beings. Management and diminution of these hazardous organic pollutants have become an incipient research interest. Traditional physiochemical methods are energy intensive and produce secondary pollutants. So, bioremediation via microalgae has appeared to be an eco-friendly and sustainable technique to curb the adverse effects of organic and inorganic contaminants because microalgae can degrade complex organic compounds and convert them into simpler and non-toxic substances without the release of secondary pollutants. Even some of the organic pollutants can be exploited by microalgae as a source of carbon in mixotrophic cultivation. Literature survey has revealed that use of the latest modification techniques for microalgae such as immobilization (on alginate, carrageena and agar), pigment-extraction, and pretreatment (with acids) have enhaced their bioremedial potential. Moreover, microalgal components i.e., biopolymers and extracellular polymeric substances (EPS) can potentially be exploited in the biosorption of pollutants. Though bioremediation of wastewaters by microalgae is quite well-studied realm but some aspects like structural and functional responses of microalgae toward pollutant derivatives/by-products (formed during biodegradation), use of genetic engineering to improve the tolerance of microalgae against higher concentrations of polluatans, and harvesting cost reduction, and monitoring of parameters at large-scale still need more focus. This review discusses the accumulation of different types of pollutants into the environment through various sources and the mechanisms used by microalgae to degrade commonly occurring organic and inorganic pollutants.

Utilization of piperonyl butoxide and 1-aminobenzotriazole for metabolic studies of toxic chemicals in Daphnia magna and Chironomus yoshimatsui

Daphnids and chironomids have been used to assess the ecological effects of chemicals released into water bodies; however, the toxicity mechanisms in organisms are generally difficult to identify. Here, we developed a system capable of estimating the contribution of cytochrome P450 (CYP) to the metabolism of test substances in Daphnia magna and Chironomus yoshimatsui based on toxicity differences in the absence and presence of the CYP inhibitors piperonyl butoxide (PBO) and 1-aminobenzotriazole (ABT). The optimum concentrations of PBO and ABT that could effectively reduce the toxicity of diazinon, which is toxic after oxidative metabolism in vivo, were determined as 0.5 and 0.6 mg/L for D. magna, and 2.0 and 40.0 mg/L for C. yoshimatsui, respectively. Acute immobilization tests of 15 insecticides were conducted for D. magna and C. yoshimatsui, with and without the optimum concentrations of PBO or ABT. In the presence of either inhibitor, chlorpyrifos and chlorfenapyr toxicity was reduced in both organisms, whereas those of thiocyclam, nereistoxin, and silafluofen were enhanced in C. yoshimatsui. Liquid chromatography-mass spectrometry analysis of D. magna and C. yoshimatsui samples exposed to chlorfenapyr confirmed that the level of the active metabolite produced by CYP was decreased by PBO or ABT in both organisms. The system to which the test substance was co-exposed to PBO or ABT will be valuable for estimating the contribution of CYPs to metabolism and elucidating the toxicity mechanism in daphnids and chironomids.

Carbamazepine degradation and genome sequencing of a novel exoelectrogen isolated from microbial fuel cells

Extracellular electron transfer and pharmaceutical products degradation mechanisms of electrochemical active microbial are helpful in optimizing electricity generation and biotoxic contaminants removal for microbial fuel cells (MFCs). An exoelectrogenic bacterial strain (designated as LYK-6) capable of degrading carbamazepine was first isolated from MFCs operated with carbamazepine as unique fuel. The strain LYK-6 was identified as the member of Pseudomonas genus according to morphological characteristics and 16S rRNA gene sequence analysis. Carbamazepine degradation rate of the strain LYK-6 was determined as 56.28% in inorganic salt medium using carbamazepine as sole carbon source. There were two oxidation peaks located at -0.044 V and 0.288 V revealed with differential pulse voltammetry analysis of the strain LQK-6. The maximum voltage of MFCs inoculated the strain LYK-6 reached to 187 mV when the MFCs fed with carbamazepine. The complete genome of the strain LYK-6 was of 4,454,672 bp in length and encoding 4209 protein genes. Genome annotation and functional gene analysis showed that the strain LYK-6 had significant genes encoding proteins responsible for the degradation of carbamazepine. The results demonstrated that the strain LYK-6 was promising application for the treatment of carbamazepine contaminant water by MFCs. This finding increases the known diversity of exoelectrogens.

Biotransformation of sulfamethoxazole by microalgae: Removal efficiency, pathways, and mechanisms

Recently, the biotransformation of sulfamethoxazole (SMX) by microalgae has attracted increasing interest. In particular, cytochrome P450 (CYP450) has been suggested to be the main enzymatic contributor to this biodegradation. However, the molecular evidence of CYP450 enzymes being involved in SMX biodegradation remains relatively unclear, hindering its applicability. Herein, the biodegradation of SMX by Chlorella sorokiniana (C. sorokiniana) was investigated, and comprehensively elucidated the reaction mechanism underlying CYP450-mediated SMX metabolism. C. sorokiniana was able to efficiently remove over 80% of SMX mainly through biodegradation, in which CYP450 enzymes responded substantially to metabolize SMX in cells. Additionally, screening of transformation products (TPs) revealed that N⁴-hydroxylation-SMX (TP270) was the main TP in the SMX biodegradation pathway of microalgae. Molecular dynamics (MD) simulation suggested that the aniline of SMX was the most prone to undergo metabolism, while density functional theory (DFT) indicated that SMX was metabolized by CYP450 enzymes through H-abstraction-OH-rebound reaction. Collectively, this work reveals key details of the hydroxylamine group of SMX, elucidates the SMX biodegradation pathway involving CYP450 in microalgae in detail, and accelerates the development of using microalgae-mediated CYP450 to eliminate antibiotics.

Enantioselective toxicity, degradation and transformation of the chiral insecticide fipronil in two algae culture

The occurrence of pesticides and their metabolites in the environment can alter the ecological relationships between aquatic food chains. Fipronil is a broad-spectrum insecticide which release in the environment may harm the non-target organisms. However, the toxicity and biotransformation of its two enantiomers are far from fully understood. The present study aimed to investigate the aquatic toxicity and environmental behavior of fipronil at enantiomeric level using two freshwater algae, Scenedesmus quaclricauda (S. quaclricauda), and Chlorella vulgaris (C. vulgaris) through an integrative approach the transformation process of the individual enantiomer isolated and in racemic form. The 72 h-EC₅₀ values of rac-, R-, S-fipronil varied from 3.27 to 7.24 mg L^-1 with R-fipronil posing a more significant effect on algal growth inhibition. Chlorophyll a was more susceptible to fipronil exposure than chlorophyll b and carotenoids. Enantioselective alterations on physiological and biochemical parameters (chlorophyll a, chlorophyll b, carotenoids, and the activities of antioxidant enzyme catalase (CAT) and superoxide dismutase (SOD)) were also observed. The half-lives (T_1/2) of R-fipronil and S-fipronil in algae culture were 3.4-3.5 d and 4.0-4.9 d, respectively. By the end of the 17-d exposure, the enantiomer fractions (EFs) increased to 0.59, indicating a preferential depuration of R-fipronil. The metabolites monitoring showed the fipronil sulfide was the main metabolite followed by fipronil sulfone. The results revealed that the enantiomers of fipronil pose enantiospecific behaviors induced by these two algae, with the R-enantiomer more toxic to algal growth and favorable in degradation. These analyses are beneficial for understanding the ecological effect of chiral pesticide in aquatic environment, and the enantiomeric differences of the toxicity, degradation and the formation of toxic metabolites could be helpful for the eco-environmental risk evaluation.

A Review of Microalgae- and Cyanobacteria-Based Biodegradation of Organic Pollutants

This review proposes a new bioremediation method based on the diverse functionalities of algae. A greenway for cleansing wastewater is more ecologically friendly and environmentally sustainable than prior methods with other bacteria. New bioremediation technology employing algae and cyanobacteria for the removal of a wide range of organic contaminants is reasonable and has great potential. The prevalence of organic contaminants in aquatic habitats may endanger the health and well-being of several marine creatures. Agriculture, industry, and household trash are just a few of the human-caused sources of organic pollutants that contaminate waterways around the world. Before wastewater can be released into waterways, it must be cleaned. Algae-based wastewater treatment systems are becoming increasingly popular because of their environmental sustainability and lack of secondary pollutants. According to the kind of pollutant, the physicochemical properties of wastewater, and the algal species, algae and cyanobacteria can absorb and accumulate a wide spectrum of organic pollutants at different rates. In addition, phytoremediation is a cost-effective alternative to conventional treatments for degrading organic contaminants. Phycoremediationally produced algal biomass may also be an important part of the bioenergy value chain. This article focuses on microalgae and cyanobacteria species, which may remove many organic contaminants from water systems.

Cytochrome P450s in algae: Bioactive natural product biosynthesis and light-driven bioproduction

Algae are a large group of photosynthetic organisms responsible for approximately half of the earth's total photosynthesis. In addition to their fundamental ecological roles as oxygen producers and as the food base for almost all aquatic life, algae are also a rich source of bioactive natural products, including several clinical drugs. Cytochrome P450 enzymes (P450s) are a superfamily of biocatalysts that are extensively involved in natural product biosynthesis by mediating various types of reactions. In the post-genome era, a growing number of P450 genes have been discovered from algae, indicating their important roles in algal life-cycle. However, the functional studies of algal P450s remain limited. Benefitting from the recent technical advances in algae cultivation and genetic manipulation, the researches on P450s in algal natural product biosynthesis have been approaching to a new stage. Moreover, some photoautotrophic algae have been developed into “photo-bioreactors” for heterologous P450s to produce high-value added pharmaceuticals and chemicals in a carbon-neutral or carbon-negative manner. Here, we comprehensively review these advances of P450 studies in algae from 2000 to 2021.

Toxic effect of fluorene-9-bisphenol to green algae Chlorella vulgaris and its metabolic fate

Fluorene-9-bisphenol (BHPF), a bisphenol A (BPA) alternative, has recently attracted attention due to its wide use and potential toxicity. However, the toxic effects and fate of BHPF in freshwater algae remains to be elucidated. In this study, the impact of BHPF on Chlorella vulgaris was explored and the removal and bioaccumulation of BHPF by Chlorella vulgaris were investigated. Results showed that C. vulgaris was sensitive to BHPF at the concentration of >1 mg L-1, and lipid peroxidation was significantly increased under the exposure of >0.1 mg BHPF L-1. An oxidative stress was caused by BHPF, as the activities of superoxide dismutase (SOD) were significantly decreased in algal cells by >0.5 mg BHPF L-1. The removal rate of BHPF was significantly enhanced by the addition of algae. In addition, the increasing accumulation of BHPF in algae at concentrations ranging from 0.5 to 5 mg L-1 was observed and may contribute for the increased toxicity of BHPF to C. vulgaris. Ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) results demonstrated that three metabolites of BHPF were identified in algal cells, which may pose an unexpected effect in aquatic environment.

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.

Sustainable microalgae-based technology for biotransformation of benzalkonium chloride in oil and gas produced water: A laboratory-scale study

Many countries have implemented stringent regulatory standards for discharging produced water (PW) from the oil and gas extraction process. Among the different chemical pollutants occurring in PW, surfactants are widely applied in the oil and gas industry to provide a barrier from metal corrosion. However, the release of these substances from the shale formation can pose serious hazardous impacts on the aquatic environment. In this study, a low-cost and eco-friendly microalgae laboratory-scale technology has been tested for biotransformation of benzalkonium chloride (BAC_C12 and BAC_C14) in seawater and PW during 14-days of treatment (spiked at 5 mg/L). From the eight microalgae strains selected, Tetraselmis suecica showed the highest removal rates of about 100% and 54% in seawater and PW, respectively. Suspect screening analysis using liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS) allowed the identification of 12 isomeric intermediates generated coming from biotransformation mechanisms. Among them, the intermediate [OH-BAC_C12] was found as the most intense compound generated from BAC_C12, while the intermediate [2OH-BAC_C14] was found as the most intense compound generated from BAC_C14. The suggested chemical structures demonstrated a high reduction on their amphiphilic properties, and thus, their tendency to be adsorbed into sediments after water discharge. In this study, Tetraselmis suecica was classified as the most successful specie to reduce the surfactant activity of benzalkonium chloride in treated effluents.

Study of uptake, translocation, and metabolic behavior of pesticides in water milfoil

Water milfoil is a sediment-rooted macrophyte contributing to the aquatic ecosystem, and the risk evaluation of pesticides on this new assessment species has attracted much attention. Knowledge of the shoot/root uptake, inner-plant translocation, and the metabolism of pesticides in water milfoil is essential for a detailed risk assessment and understanding toxicological mechanisms thereof; however, the behaviors have not been studied in detail. Using model studies, the author clarified shoot and root uptake dynamics of 3-phenoxybenzoic acid via water and sediment exposure, respectively, followed by transportation and metabolism at each plant portion; uptake and metabolism kinetics of simple phenols amended with regression analysis on physico-chemical parameters of the compounds; detailed metabolic fate of flumioxazin in various aquatic plants/phytoplankton, and an interspecies comparison. Similar approaches are fully applicable to clarifying the fate of pesticides in water milfoil and are expected to be useful for implementing advanced risk characterizations.

Enhanced excretion of extracellular polymeric substances associated with nonylphenol tolerance in Dictyosphaerium sp

Dictyosphaerium sp. is tolerant to nonylphenol (NP); however, knowledge regarding the mechanisms involved in NP tolerance is limited. In this study, a batch of algal culture experiments were carried out to elucidate the underlying mechanisms by investigating the production and composition of extracellular polymeric substances (EPS) in algae exposed to NP. The excretion of EPS was significantly enhanced (P < 0.001) in algae exposed to 4 and 8 mg/L of NP. The polysaccharides in soluble EPS and the proteins in bound EPS were specifically overproduced. The three-dimensional excitation and emission matrix fluorescence spectra analyses indicated that tyrosine- and tryptophan-like substances were the main functional compositions in the proteins of EPS. In addition, enhanced EPS secretion significantly alleviated the toxicity of NP to the algae by the reduction of cell internalization, as indicated by the higher IC₅₀, biomass, and cell growth rate in the algae with EPS. These discoveries along with the characterizations by algal cell surface hydrophobicity analysis, scanning electron microscopy, and Fourier transform infrared spectra spectroscopy demonstrated the vital role of EPS in the algal resistance to NP.

Degradation and metabolic pathways of sulfamethazine and enrofloxacin in Chlorella vulgaris and Scenedesmus obliquus treatment systems

The degradation and metabolic pathways of sulfamethazine (SMZ) and enrofloxacin (ENR) via microalgal treatment systems were investigated in this study. SMZ and ENR applied at 1-25 mg L^-1 did not significantly inhibit the growth of Chlorella vulgaris or Scenedesmus obliquus. SMZ and ENR exposure did not significantly alter the maximum quantum efficiencies of C. vulgaris and S. obliquus. When cultured at light intensities of 45-50 μmol photon m^-2 s^-1, the C. vulgaris and S. obliquus treatment systems achieved 24% and 11% degradation, respectively. The greatest removal of ENR was 52% and 43.3%, for C. vulgaris and S. obliquus treatment systems, respectively, after 15 days. The results indicated that the degradation of SMZ and ENR occurred by a combination of biodegradation and photolysis. Kinetic investigations revealed that the removal of SMZ and ENR (5 mg L^-1) followed a first-order model, with apparent rate constants (k) ranging from 0.0141 to 0.0048 day^-1 and 0.0132 to 0.0086 day^-1, respectively. Fifteen metabolites of SMZ and five intermediates of ENR were identified by UPLC-MS, and degradation pathways for SMZ and ENR were proposed. SMZ transformation reactions included ring cleavage, hydroxylation, methylation, and oxidation, whereas ENR was degraded by dealkylation, decarboxylation, and defluorination. Graphical abstract.

Dissipation of antibiotics by microalgae: Kinetics, identification of transformation products and pathways

Dissipation potential of four algae viz. Haematococcus pluvialis, Selenastrum capricornutum, Scenedesmus quadricauda and Chlorella vulgaris was investigated against ten antibiotics (sulfamerazine, sulfamethoxazole, sulfamonomethoxine, trimethoprim, clarithromycin, azithromycin, roxithromycin, lomefloxacin, levofloxacin and flumequine) in a series of synthetic wastewater batch culture experiments, maintained at 20, 50 and 100 μg L^-1 initial concentration levels and incubated over a period of 40 days. Generally, the antibiotic removal was achieved with overall dissipation percentage (%) varying among the algal species and different antibiotics. Biodegradation was the major antibiotic removal mechanism from the dissolved fraction, with minor contributions of bioadsorption, bioaccumulation, and abiotic factors. The antibiotics dissipation followed the pseudo-first-order-kinetics with the fastest antibiotic degradation rate achieved by H. pluvialis. The Monod kinetics was successfully applied to explain the relationship between the algal growth and the removal of antibiotics and nutrients in the batch cultures. S. capricornutum and C. vulgaris showed more affinity for the macrolides and fluoroquinolones than sulfonamides, while, H. pluvialis and S. quadiricauda showed relatively higher preference for sulfonamides than the other antibiotic groups. A total of 10 transformation products were identified and the transformation pathway was proposed, accordingly. Most of the transformation products had lower toxicity compared with their parent antibiotics.

Emerging prospects of mixotrophic microalgae: Way forward to sustainable bioprocess for environmental remediation and cost-effective biofuels

Algal bioremediation becoming most fascinating to produce biomass as biofuels feedstock while remediating wastes, also improving carbon-footprint through carbon capturing and utilization (CCU) technology. Non-algae process however offers effective treatment but metabolic CO₂ emission is major drawback towards sustainable bioprocess. Mixotrophic cultivation strategy (MCS) enables to treat organic and inorganic wastes which broadly extend microalgae application towards cleaner and sustainable bioeconomy. Latest focus of global think-tanks to encourage bioprocess holding promise of sustainability via CCU ability as important trait. Several high CO₂ emitting industries forced to improve their carbon-footprints. MCS driven microalgae treatment could be best solution for those industries. This review covers recent updates on MCS applications for waste-to-value (biofuels) and environment remediation. Moreover, recommendations to fill knowledge gaps, and commercial algal biofuel could be cost-effectiveness and sustainable technology for biocircular economy if fuelled by waste streams from other industries.

Removal and biotransformation of 4-nonylphenol by Arthrospira maxima and Chlorella vulgaris consortium

4-Nonylphenol (4-NP) is an anthropogenic contaminant found in different environmental matrices that has an effect over the biotic and abiotic factors within the environment. Bioremediation by microorganisms can be used as a potential treatment to remove this pollutant. In this work, a consortium of two microorganisms, Arthrospira maxima and Chlorella vulgaris, was employed to remove 4-NP from water. The parameters analyzed included cell growth, removal of 4-NP, and 4-NP remnant in the biomass. In addition, the metabolites produced in the process by this consortium were identified. It was found that C. vulgaris is more resistant to 4-NP than A. maxima (cell growth inhibition by 4-NP of 99%). The consortium used in this study had an IC₅₀ greater than any strain of microalgae or cyanobacteria reported for 4-NP removal (9.29 mg/L) and reduced up to 96% of 4-NP in water in the first 48 h of culture. It was also observed that there is a bio-transformation of 4-NP, comparable with the process carried out by another bacterium, in which three similar metabolites were found (4-(1-methyl-octyl)-4-hydroxy-cyclohex-2-enone, 4-nonyl-4-hydroxy-ciclohexa-2,5-dienone and 4-nonyl-4-hydroxy- ciclohex-2-enone) and one that is similar to plant metabolism (4-nonyl-(1-methyl,6,8-metoxy)-hydroxybenzene). These results indicate that microalgae and cyanobacteria consortium can be used to remove 4-NP from water.

Microalgal bioremediation of emerging contaminants - Opportunities and challenges

Emerging contaminants (ECs) are primarily synthetic organic chemicals that have a focus of increasing attention due to either increased awareness of their potential risks to humans and aquatic biota, or only recently been detected in the aquatic environment or drinking water supplies, through improved analytical techniques. . Many ECs have no regulatory standards due to the lack of information on the effects of chronic exposure. Pharmaceuticals, personal care products, pesticides and flame retardants are some of the most frequently detected ECs in aquatic environments, with over 200 individual compounds identified, to date. Current wastewater treatment is ineffective at removing ECs and there is a vital need for the development of efficient, cost-effective EC treatment systems that can be applied to a range of scales and wastewater types. Microalgae have demonstrated potential for detoxifying organic and inorganic pollutants, with a number of large-scale wastewater treatment microalgal technologies already developed. There are three main pathways that microalgae can bioremediate ECs; bioadsorption, bio-uptake and biodegradation. Microalgal bioadsorption occurs when ECs are either adsorbed to cell wall components, or onto organic substances excreted by the cells, while bio-uptake involves the active transport of the contaminant into the cell, where it binds to intracellular proteins and other compounds. Microalgal biodegradation of ECs involves the transformation of complex compounds into simpler breakdown molecules through catalytic metabolic degradation. Biodegradation provides one of the most promising technologies for the remediation of contaminants of concern as it can transform the contaminant to less toxic compounds rather than act as a biofilter. Further research is needed to exploit microalgal species for EC bioremediation properties, such as increased bioadsorption, enhanced biodegrading enzymes and optimised growth conditions. When coupled with nutrient removal, microalgal treatment of EC can be a cost-effective viable option for the reduction of contaminant pollution in waterways.

Transcriptomic Analysis Reveals the Roles of Detoxification Systems in Response to Mercury in Chromera velia

Heavy metal pollution is an increasing global concern. Among heavy metals, mercury (Hg) is especially dangerous because of its massive release into the environment and high toxicity, especially for aquatic organisms. The molecular response mechanisms of algae to Hg exposure are mostly unknown. Here, we combine physiological, biochemical, and transcriptomic analysis to provide, for the first time, a comprehensive view on the pathways activated in Chromera velia in response to toxic levels of Hg. Production of hydrogen peroxide and superoxide anion, two reactive oxygen species (ROS), showed opposite patterns in response to Hg²⁺ while reactive nitrogen species (RNS) levels did not change. A deep RNA sequencing analysis generated a total of 307,738,790 high-quality reads assembled in 122,874 transcripts, representing 89,853 unigenes successfully annotated in databases. Detailed analysis of the differently expressed genes corroborates the biochemical results observed in ROS production and suggests novel putative molecular mechanisms in the algal response to Hg²⁺. Moreover, we indicated that important transcription factor (TF) families associated with stress responses differentially expressed in C. velia cultures under Hg stress. Our study presents the first in-depth transcriptomic analysis of C. velia, focusing on the expression of genes involved in different detoxification defense systems in response to heavy metal stress.

Dual purpose microalgae-based biorefinery for treating pharmaceuticals and personal care products (PPCPs) residues and biodiesel production

Microalgal biotechnologies have emerged with high potential for removal of various organic pollutants, such as pharmaceutical and personal care products (PPCPs), from waste streams. In the present study, the removal mechanisms for three typical PPCPs and the lipid performance of Chlamydomonas sp. Tai-03 were thoroughly investigated. Bisphenol A (BPA) and Tetracycline (TCY) achieved complete removal while only ~20% Sulfamethoxazole (SMX) could be removed, even at low concentrations of 1 mg L^-1. The mechanisms of elimination showed variation as only SMX could be removed through biodegradation, while ~68.2% TCY and ~14% BPA were removed by a combination of photolysis and hydrolysis. Analysis revealed three intermediates of SMX biodegradation, two of which exhibited high toxicity. Moreover, the lipid content of Chlamydomonas sp. Tai-03 increased from 5 to 49.5% with the addition of SMX, TCY and BPA, with lipid quality varying according to the type of PPCPs. In particular, the dominant component (C18:1) abundance was increased by 15.2% at 10 mg L^-1 TCY. Overall, these findings provide a baseline for optimization of microalgal biodiesel production coupled with efficient PPCPs treatment biotechnology.

Toxic effects and metabolic fate of carbamazepine in diatom Navicula sp. as influenced by humic acid and nitrogen species

Carbamazepine (CAB) is a commonly detected pharmaceutical in the surface waters. In the present study, we evaluated the effect of humic acid (HA) and nitrogen species on the toxicity of CAB in a typical diatom Navicula sp., and its metabolic fate. The Navicula sp. showed a high sensitivity to CAB (72 h EC₅₀ = 0.179 mg L^-1). The addition of HA (< 30 mg L^-1) and ammonium could promote the growth of Navicula sp. during 6 d of exposure to CAB. CAB underwent rapid dissipation in the algal culture. The degradation of CAB in Navicula sp. cultures was significantly increased by the addition of HA and higher HA contents caused more degradation of CAB. Degradation and accumulation of CAB in Navicula sp. were significantly inhibited by ammonium. Five metabolites were found and possible degradation pathways of CAB in the algal cell were proposed. Methoxylation, demethylation, glucuronidation and hydroxylation contributed to CAB transformation in the algal cell.

Soil microalgae and cyanobacteria: the biotechnological potential in the maintenance of soil fertility and health

The soil microbiota plays a major role in maintaining the nutrient balance, carbon sink, and soil health. Numerous studies reported on the function of microbiota such as plant growth-promoting bacteria and fungi in soil. Although microalgae and cyanobacteria are ubiquitous in soil, very less attention has been paid on the potential of these microorganisms. The indiscriminate use of various chemicals to enhance agricultural productivity led to serious consequences like structure instability, accumulation of toxic contaminants, etc., leading to an ecological imbalance between soil, plant, and microbiota. However, the significant role of microalgae and cyanobacteria in crop productivity and other potential options has been so far undermined. The intent of the present critical review is to highlight the significance of this unique group of microorganisms in terms of maintaining soil fertility and soil health. Beneficial soil ecological applications of these two groups in enhancing plant growth, establishing interrelationships among other microbes, and detoxifying chemical agents such as insecticides, herbicides, etc. through mutualistic cooperation by synthesizing enzymes and phytohormones are presented. Since recombinant technology involving genomic integration favors the development of useful traits in microalgae and cyanobacteria for their potential application in improvement of soil fertility and health, the merits and demerits of various such advanced methodologies associated in harnessing the biotechnological potential of these photosynthetic microorganisms for sustainable agriculture were also discussed.

The Use of Algae and Fungi for Removal of Pharmaceuticals by Bioremediation and Biosorption Processes: A Review

The occurrence and fate of pharmaceuticals in the aquatic environment is recognized as one of the emerging issues in environmental chemistry. Conventional wastewater treatment plants (WWTPs) are not designed to remove pharmaceuticals (and their metabolites) from domestic wastewaters. The treatability of pharmaceutical compounds in WWTPs varies considerably depending on the type of compound since their biodegradability can differ significantly. As a consequence, they may reach the aquatic environment, directly or by leaching of the sludge produced by these facilities. Currently, the technologies under research for the removal of pharmaceuticals, namely membrane technologies and advanced oxidation processes, have high operation costs related to energy and chemical consumption. When chemical reactions are involved, other aspects to consider include the formation of harmful reaction by-products and the management of the toxic sludge produced. Research is needed in order to develop economic and sustainable treatment processes, such as bioremediation and biosorption. The use of low-cost materials, such as biological matrices (e.g., algae and fungi), has advantages such as low capital investment, easy operation, low operation costs, and the non-formation of degradation by-products. An extensive review of existing research on this subject is presented.

Potential metabolism of pharmaceuticals in radish: Comparison of in vivo and in vitro exposure

Metabolism of pharmaceuticals in plants is important to evaluate their fate and accumulation in vegetables, and subsequently the risks to human health. However, limited knowledge is available to evaluate metabolism of pharmaceuticals in plants due to the lack of appropriate research approaches. In this study, radish was selected as a model plant to investigate metabolism of pharmaceuticals in intact plants (in vivo) growing in hydroponic solution and in plant tissue enzyme extracts (in vitro). For caffeine, six phase-I demethylation metabolites identified in the intact radish plant were also found in the plant enzyme extracts. After 7 days of in vivo exposure, the amount of the identified metabolites was about 5.4 times greater than the parent compound caffeine in radish roots. Furthermore, the metabolism potential of fifteen pharmaceuticals in radish was evaluated on the basis of mass balance. After 7 days of hydroponic exposure, oxytetracycline, trimethoprim, carbamazepine, lincomycin, monensin and tylosin manifested relatively less extent of metabolism with the mass recoveries ranging from 52.3 to 78.2%. In contrast, 17 β-estradiol, sulfamethoxazole, sulfadiazine, estrone, triclosan, acetaminophen, caffeine, carbadox and lamotrigine underwent extensive metabolism with only 3.0 to 32.1% of the parent compound recovered. In the in vitro system, 17 β-estradiol, estrone, triclosan, oxytetracycline, acetaminophen, sulfadiazine and sulfamethoxazole were readily metabolized in radish root enzyme extracts with 1.8 to 34.0% remaining after 96-h exposure. While in the leaf enzyme extracts, only triclosan was rapidly metabolized with 49.2% remaining, and others pharmaceuticals were ≥60%, indicating that the varying extents of metabolism occurred in different plant parts. This study highlights the importance of pharmaceutical metabolism in plants, and suggests that plant tissue enzyme extracts could serve as an alternative tool to assess pharmaceutical metabolism in plants.

Sorption, plant uptake and metabolism of benzodiazepines

Reuse of treated wastewater for irrigation of crops is growing in arid and semi-arid regions, whilst increasing amounts of biosolids are being applied to fields to improve agricultural outputs. Due to incomplete removal in the wastewater treatment processes, pharmaceuticals present in treated wastewater and biosolids can contaminate soil systems. Benzodiazepines are a widely used class of pharmaceuticals that are released following wastewater treatment. Benzodiazepines are represented by a class of compounds with a range of physicochemical properties and this study was therefore designed to evaluate the influence of soil properties on the sorption behaviour and subsequent uptake of seven benzodiazepines (chlordiazepoxide, clonazepam, diazepam, flurazepam, oxazepam, temazepam and triazolam) in two plant species. The sorption and desorption behaviour of benzodiazepines was strongly influenced by soil type and hydrophobicity of the chemical. The partitioning behaviour of these chemicals in soil was a key controller of the uptake and accumulation of benzodiazepines by radish (Raphanus sativus) and silverbeet (Beta vulgaris). Benzodiazepines such as oxazepam that were neutral, had low sorption coefficients (K_d) or had pH-adjusted log octanol-water partition coefficients (log D_ow, pH6.3) values close to 2 had the greatest extent of uptake. Conversely, benzodiazepines such as flurazepam that had an ionised functional groups and greater K_d values had comparatively limited accumulation in the selected plant species. Results also revealed active in-plant metabolism of benzodiazepines, potentially analogous to the known metabolic transformation pathway of benzodiazepines in humans. Along with this observed biological transformation of benzodiazepines in exposed plants, previously work has established the widespread presence of the plant signalling molecule γ-amino butyric acid (GABA), which is specifically modulated by benzodiazepines in humans. This highlights the need for further assessment of the potential for biological activity of benzodiazepines following their plant uptake.

Fate of Flumioxazin in Aquatic Plants: Two Algae (Pseudokirchneriella subcapitata, Synechococcus sp.), Duckweed (Lemna sp.), and Water Milfoil (Myriophyllum elatinoides)

Flumioxazin separately ¹⁴C-labeled at 1,2-positions of the tetrahydrophthalimide moiety or uniformly labeled at the phenyl ring was exposed to two algae and duckweed via the water layer and water milfoil via the water layer or bottom sediment for 14 days to investigate uptake and metabolic profiles in these aquatic plants. While ¹⁴C-flumioxazin received immediate hydrolysis through maleimide ring opening and amide bond cleavage with its hydrolytic half-life of <1 day in both water and sediment, the ¹⁴C-plant uptake was ≤4.7% of the applied radioactivity (%AR) with water exposure for all plants and 0.9%AR with sediment exposure for water milfoil. No ¹⁴C-translocation between shoot/leaves and roots occurred in water milfoil. The components of ¹⁴C residues in plants were common among the species, which were the above hydrolysates and their transformation products, that is, dicarboxylic acid derivative metabolized via hydroxylation at the double bond of the cyclohexene ring followed by sugar conjugation with its counterpart amine derivative via acid conjugations.

Can Microalgae Remove Pharmaceutical Contaminants from Water?

The increase in worldwide water contamination with numerous pharmaceutical contaminants (PCs) has become an emerging environmental concern due to their considerable ecotoxicities and associated health issues. Microalgae-mediated bioremediation of PCs has recently gained scientific attention, as microalgal bioremediation is a solar-power driven, ecologically comprehensive, and sustainable reclamation strategy. In this review, we comprehensively describe the current research on the possible roles and applications of microalgae for removing PCs from aqueous media. We summarize several novel approaches including constructing microbial consortia, acclimation, and cometabolism for enhanced removal of PCs by microalgae, which would improve practical feasibility of these technologies. Some novel concepts for degrading PCs using integrated processes and genetic modifications to realize algal-based bioremediation technologies are also recommended.

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.

Ciprofloxacin toxicity and its co-metabolic removal by a freshwater microalga Chlamydomonas mexicana

This study evaluated the toxicity and cellular stresses of ciprofloxacin (CIP) and its co-metabolic removal in a freshwater microalga Chlamydomonas mexicana. The toxicological effects of CIP on C. mexicana were assessed by studying the growth and biochemical characteristics of the microalga including total chlorophyll, carotenoid content, malondialdehyde (MDA) and superoxide dismutase (SOD) activity. The calculated effective concentration (EC₅₀) of CIP on C. mexicana was 65±4mgL^-1 at 96h. The growth of C. mexicana was significantly inhibited at increased concentrations of CIP, showing 36±1, 75±3. and 88±3% inhibition at 40, 60 and 100mgL^-1 CIP, respectively, compared to the control after 11days of cultivation. The total chlorophyll, carotenoid, MDA and SOD activity were significantly increased as a result of relatively high concentrations of CIP stress. C. mexicana showed 13±1% removal of CIP (2mgL^-1) after 11days of cultivation; however, the addition of an electron donor (sodium acetate, 4gL^-1) highly enhanced the removal of CIP (2mgL^-1) by>3-fold after 11days. Kinetic studies showed that removal of CIP followed a first-order model (R² 0.94-0.97) with the apparent rate constants (k) ranging from 0.0121 to 0.079 d^-1.

Metabolism of xenobiotics by Chlamydomonas reinhardtii: Phenol degradation under conditions affecting photosynthesis

In the present work, the biodegradation of phenol by axenic cultures of the unicellular microalga Chlamydomonas reinhardtii was investigated. Biodegradation proved to be a dynamic bioenergetic process, affected by changes in the culture conditions. Microalgae biodegraded defined amounts of phenol, as a result of the induced stress caused at high concentrations, despite the fact that this process proved to be energy demanding and thus affected growth of the culture. High levels of biodegradation were observed both in the absence of an alternative carbon source and in the presence of acetate as a carbon source. Biodegradation of phenol by Chlamydomonas proved to be an aerobic, photoregulated process. This is the first time that Chlamydomonas reinhardtii has been used for bioremediation purposes. This study has demonstrated that the most important factor in the biodegradation of phenol is the selection of the appropriate culture conditions (presence or absence of alternative carbon source, light intensity, and oxygen availability) that provide the best bioenergetic balance among growth, induced stress, and biodegradation of phenol.

Uptake, translocation and possible biodegradation of the antidiabetic agent metformin by hydroponically grown Typha latifolia

The increasing load of pharmaceutical compounds has raised concerns about their potential residues in aquatic environments and ecotoxicity. Metformin (MET), a widely prescribed antidiabetic II medicine, has been detected in high concentration in sewage and in wastewater treatment effluents. An uptake and translocation study was carried out to assess the ultimate fate of MET in phytoremediation. MET was removed from media by Typha latifolia, and the removal processes followed first order kinetics. After 28 days, the removal efficiencies were in a range of 74.0±4.1-81.1±3.3%. In roots, MET concentration was increasing during the first two weeks of the experiment but thereafter decreasing. In contrast, MET concentration was continuously increasing in rhizomes and leaves. Bioaccumulation of MET in roots was much higher than in leaves and rhizomes. As degradation product of metformin in the plant, methylbiguanide (MBG) was detected whereas guanylurea was undetectable. Moreover, MBG concentration in roots was increasing with exposure time. An enzymatic degradation experiment showed the degradation rate followed the order of MET<MBG<<guanylurea. This may explain the low concentration of MBG in plant. The findings of this study contribute to understand and evaluate the potential for phytoremediation of such kind of contaminants.

Biodegradation of carbamazepine using freshwater microalgae Chlamydomonas mexicana and Scenedesmus obliquus and the determination of its metabolic fate

This study evaluated the toxicity and cellular stresses of carbamazepine (CBZ) on Chlamydomonas mexicana and Scenedesmus obliquus, and its biodegradation by both microalgal species. The growth of both microalgal species decreased with increase of CBZ concentration. The growth of S. obliquus was significantly inhibited (97%) at 200 mg CBZ L(-1), as compared to the control after 10days; whereas, C. mexicana showed 30% inhibition at the same experimental conditions. Biochemical characteristics including total chlorophyll, carotenoid contents and enzyme activities (SOD and CAT) for both species were affected by CBZ at relatively high concentration. C. mexicana and S. obliquus could achieve a maximum of 35% and 28% biodegradation of CBZ, respectively. Two metabolites (10,11-dihydro-10,11-expoxycarbamazepine and n-hydroxy-CBZ) were identified by UPLC-MS, as a result of CBZ biodegradation by C. mexicana. This study demonstrated that C. mexicana was more tolerant to CBZ and could be used for treatment of CBZ contaminated wastewater.

Herbicide toxicity on river biofilms assessed by pulse amplitude modulated (PAM) fluorometry

The use of Rapid light curves (RLCs) as a toxicity endpoint for river biofilms was examined in this study and compared to "classical fluorescence parameters" i.e. minimal fluorescence (F0), optimal and effective quantum yields of photosystem II (Fv/Fm and ФPSII). Measurements were performed after exposure to five concentrations of diuron (from 0.3 to 33.4μgL(-1)), its main degradation product (DCPMU) (from 1.0 to 1014μgL(-1)) and norflurazon (from 0.6 to 585μgL(-1)) with the lowest exposure concentrations corresponding to levels regularly encountered in chronically contaminated sites. Biofilm responses were evaluated after 1, 5, 7 and 14 days of exposure to the different toxicants. Overall, the responses of both "classical fluorescence parameters" and RLC endpoints were highly time dependent and related to the mode of action of the different compounds. Interestingly, parameters calculated from RLCs (α, ETRmax and Ik) were useful early markers of pesticide exposure since they revealed significant effects of all the tested toxicants from the first day of exposure. In comparison, classical fluorescence endpoints (F0 and Fv/Fm) measured at day 1 were only affected in the DCPMU treatment. Our results demonstrated the interest of RLCs as early markers of toxicant exposure particularly when working with toxicants with less specific mode of action than PSII inhibitors.

Cytochrome P450 Inhibitors Reduce Creeping Bentgrass (Agrostis stolonifera) Tolerance to Topramezone

Creeping bentgrass (Agrostis stolonifera L.) is moderately tolerant to the p-hydroxyphenylpyruvate dioxygenase-inhibiting herbicide topramezone. However, the contribution of plant metabolism of topramezone to this tolerance is unknown. Experiments were conducted to determine if known cytochrome P450 monooxygenase inhibitors 1-aminobenzotriazole (ABT) and malathion alone or in combination with the herbicide safener cloquintocet-mexyl influence creeping bentgrass tolerance to topramezone. Creeping bentgrass in hydroponic culture was treated with ABT (70 μM), malathion (70 μm and 1000 g ha(-1)), or cloquintocet-mexyl (70 μM and 1000 g ha(-1)) prior to topramezone (8 g ha(-1)) application. Topramezone-induced injury to creeping bentgrass increased from 22% when applied alone to 79 and 41% when applied with malathion or ABT, respectively. Cloquintocet-mexyl (70 μM and 1000 g ha(-1)) reduced topramezone injury to 1% and increased creeping bentgrass biomass and PSII quantum yield. Cloquintocet-mexyl mitigated the synergistic effects of ABT more than those of malathion. The effects of malathion on topramezone injury were supported by creeping bentgrass biomass responses. Responses to ABT and malathion suggest that creeping bentgrass tolerance to topramezone is influenced by cytochrome P450-catalyzed metabolism. Future research should elucidate primary topramezone metabolites and determine the contribution of cytochrome P450 monooxygenases and glutathione S-transferases to metabolite formation in safened and non-safened creeping bentgrass.

Enhancement by the artificial controlled culture for the algal treatment of antibiotic ceftazidime: a three-step response performance and high-removal efficiency

The improved activity of alga is critical for the biological enhanced treatment to remove contamination.

Enantioselective toxicity and degradation of the chiral insecticide fipronil in Scenedesmus obliguus suspension system

Fipronil is an effective insecticide, but it presents highly toxic effects in nontarget aquatic organisms. The present study examined the enantioselective toxicity and degradation of fipronil enantiomers in a freshwater algae Scenedesmus obliguus suspension. There was a substantial difference in the acute toxicity of the enantiomers to S. obliguus, with 72-h median effective concentrations (EC50s) of 0.29 mg L(-1) and 1.50 mg L(-1) for the R-fipronil and S-fipronil, respectively. The influences on the concentration of chlorophyll a, chlorophyll b, and carotenoids were determined, and the effects of fipronil on the concentration of chlorophyll a and chlorophyll b were also enantioselective. The degradation of fipronil in algae suspension was enantioselective, with half-lives for R-fipronil and S-fipronil of 2.9 d and 3.2 d, respectively, and the enantiomer fraction reaching 0.65 at the day 17. The enantiomeric differences should be taken into consideration for fipronil risk assessment.

Early stage hit triage for plant chemical genetic screens and target site identification

The increasing use of plant biological screens of large compound libraries to discover informative chemical probes for plant chemical genetics requires efficient methods for hit selection and advancement. Downstream target identification and validation studies with selected chemistries can also be resource-intensive and have a significant failure rate. Several steps and considerations for early stage hit triage are outlined to increase the probability of success that downstream studies with the chemical probe will be robust and productive, especially for target site discovery. Conversely, problematic compounds can be shelved or avoided entirely, saving time and resources. These steps include assessment of compound availability, purity, stability and solubility; determination of the biological dose-response; early and iterative evaluation of analogs; avoidance of promiscuous "frequent-hitters"; consideration of physicochemical parameters affecting compound bioavailability and mobility, use of "low-barrier" biological testing systems; and assessing the potential for compound metabolism or bioconversion.

Effect propagation in a toxicokinetic/toxicodynamic model explains delayed effects on the growth of unicellular green algae Scenedesmus vacuolatus

Ecotoxicological standard tests assess toxic effects by exposing an organism to high concentrations over defined periods of time. To evaluate toxicity under field conditions such as fluctuating and pulsed exposures, process-based toxicokinetic/toxicodynamic (TK/TD) models may be used for extrapolation from the existing evidence. A TK/TD model was developed that simulates the effect on growth of the green algae Scenedesmus vacuolatus continuously exposed to the model chemicals norflurazon, triclosan, and N-phenyl-2-naphthylamine. A pharmacological time-response model describing the effects of anticancer treatments on cancer cell growth was adapted and modified to model the affected growth of synchronized algae cells. The TK/TD model simulates the temporal effect course by linking the ambient concentration of a chemical to the observable adverse effect via an internal concentration and a sequence of biological events in the organism. The parameters of the toxicodynamic model are related to the growth characteristics of algae cells, a no effect concentration, the chemical efficacy as well as the ability of recovery and repair, and the delay during damage propagation. The TK/TD model fits well to the observed algae growth. The effect propagation through cumulative cell damage explained the observed delayed responses better than just the toxicokinetics. The TK/TD model could facilitate the link between several effect levels within damage propagation, which prospectively may be helpful to model adverse outcome pathways and time-dependent mixture effects.

Bioenergetic strategy for the biodegradation of p-cresol by the unicellular green alga Scenedesmus obliquus

Cultures from the unicellular green alga Scenedesmus obliquus biodegrade the toxic p-cresol (4-methylphenol) and use it as alternative carbon/energy source. The biodegradation procedure of p-cresol seems to be a two-step process. HPLC analyses indicate that the split of the methyl group (first step) that is possibly converted to methanol (increased methanol concentration in the growth medium), leading, according to our previous work, to changes in the molecular structure and function of the photosynthetic apparatus and therefore to microalgal biomass increase. The second step is the fission of the intermediately produced phenol. A higher p-cresol concentration results in a higher p-cresol biodegradation rate and a lower total p-cresol biodegradability. The first biodegradation step seems to be the most decisive for the effectiveness of the process, because methanol offers energy for the further biodegradation reactions. The absence of LHCII from the Scenedesmus mutant wt-lhc stopped the methanol effect and significantly reduced the p-cresol biodegradation (only 9%). The present contribution deals with an energy distribution between microalgal growth and p-cresol biodegradation, activated by p-cresol concentration. The simultaneous biomass increase with the detoxification of a toxic phenolic compound (p-cresol) could be a significant biotechnological aspect for further applications.

Bio-reaction of nitrobenzene with Microcystis aeruginosa: characteristics, kinetics and application

The bio-reaction of nitrobenzene (NB) with Microcystis aeruginosa was investigated at different initial algal densities and NB concentrations by performing static experiments. The results showed that the elimination of NB was enhanced by the bio-reaction, and the reaction rate varied as a function of the reaction time. Moreover, the reaction rate was significantly affected by the algal density and NB concentration. A kinetic analysis showed that the elimination of NB in a solution without algae appeared to be pseudo-first-order with respect to the NB concentration, whereas a first-order model was too oversimplified to describe the elimination of NB in a solution with algae. Assuming that different algal cells have the same effect on the bio-reaction under the same conditions, the bio-reaction can be described as dC(NB) = -k(0)C(A)(m)A(NB)(n)dt (where k(0) is the reaction rate constant, C(A) is the algae density and C(NB) is the concentration of NB). When the growth of algae was not considered, the value of k(0), m and n were 8.170 × 10(-4), 0.5887 and 1.692, respectively. Alternatively, when algae were in the exponential growth phase, the value of k(0), m and n were 1.6871 × 10(-5), 0.7248 and 2.5407, respectively, according to a nonlinear fitting analysis. The kinetic model was also used to elucidate the effect of nutritional limitation on the bio-reaction.

Continuous degradation of a mixture of sulfonamides by Trametes versicolor and identification of metabolites from sulfapyridine and sulfathiazole

In this study, we assessed the degradation of the sulfonamides sulfapyridine (SPY) and sulfathiazole (STZ) by the white-rot fungus Trametes versicolor. Complete degradation was accomplished in fungal cultures at initial pollutant concentrations of approximately 10 mg L(-1), although a longer period of time was needed to completely remove STZ in comparison to SPY. When cytochrome P450 inhibitors were added to the fungal cultures, STZ degradation was partially suppressed, while no additional effect was observed for SPY. Experiments with purified laccase and laccase mediators caused the removal of greater than 75% of each antibiotic. Ultra-performance liquid chromatography-quadupole time of flight mass spectrometry (UPLC-QqTOF-MS) analyses allowed the identification of a total of eight degradation intermediates of SPY in both the in vivo and the laccase experiments, being its desulfonated moiety the commonly detected product. For STZ, a total of five products were identified. A fluidized bed reactor with T. versicolor pellets degraded a mixture of sulfonamides (SPY, STZ and sulfamethazine, SMZ) by greater than 94% each at a hydraulic residence time of 72 h. Because wastewater contains many diverse pollutants, these results highlight the potential of T. versicolor as a bioremediation agent not only for the removal of antibiotics but also for the elimination of a wide range of contaminants.

The role of nitrobenzene on the yield of trihalomethane formation potential in aqueous solutions with Microcystis aeruginosa

Algae are one of the most important disinfection by-product (DBP) precursors in aquatic environments. The contents of DBP precursors in algae are influenced by not only environmental factors but also some xenobiotics. Trihalomethane formation potential (THMFP) in both the separate and interactive pollution of Microcystis aeruginosa and Nitrobenzene (NB) was investigated in batch experiment to discover the effects of xenobiotics on the yield of DBP precursors in the algal solution. The results show that in the separate NB solution, NB did not react with Cl(2) to form trihalomethane (THM), whereas in the algae solution, THMFP had a significant positive linear correlation with M. aeruginosa density in both solution and extracellular organic matter (EOM). The correlation coefficients were 0.9845 (p = 3.567 × 10(-4)) and 0.9854 (p = 1.406 × 10(-4)), respectively. According to regression results, about 77.9% of the total THMFP came from the algal cells, while the rest came from EOM. When the interactive pollution of M. aeruginosa and NB occurred, the growth of algae was inhibited by NB. The density of M. aeruginosa in a high concentration NB solution (280 μg/L) was only 71.1% of that in the solution without NB after 5 days of incubation. However, THMFP in the mixture (algae and NB) and the EOM did not change significantly, and the productivity of THMFP by the algae (THMFP/10(8)cells) increased with the increase in NB concentration. There was a significant linear correlation between THMFP/10(8)cell and NB concentration (r = 0.9117, p < 0.01), which shows the contribution of the algae to THM formation was enhanced by NB. This result might be caused by the increased protein productivity and the biodegradation of NB by M. aeruginosa.

Removal and biodegradation of nonylphenol by different Chlorella species

All four Chlorella species, including one commercially available species, Chlorella vulgaris and three local isolates, Chlorella sp. (1 uoai), Chlorella sp. (2f5aia) and Chlorellaminiata (WW1), had a rapid and high ability to remove nonylphenol (NP). Among these species, C. vulgaris had the highest NP removal (nearly all NP was removed from the medium) and degradation abilities (more than 80% of NP was degraded) after 168 h, followed by WW1 and 1 uoai; 2f5aia had the lowest NP degradation ability. The NP removal by C. vulgaris was less affected by growth conditions, but its biodegradation efficiency was significantly increased by temperature and light intensity, suggesting that the biodegradation ability was positively related to photosynthetic and metabolic activities. These results indicated that C. vulgaris was the most suitable species for effective removal and biodegradation of NP, especially under 25 °C with light illumination and initial biomass between 0.5 and 1.0 mg chlorophyll l(-1).

Growth, photosynthesis and antioxidant responses of two microalgal species, Chlorella vulgaris and Selenastrum capricornutum, to nonylphenol stress

The effect of nonylphenol (NP) on growth, photochemistry and biochemistry of two green microalgae, Chlorella vulgaris and Selenanstrum capricornutum, and their ability to degrade NP were compared. The 96 h EC50 of C. vulgaris and S. capricornutum were greater than 4.0 and 1.0 mg L(-1) NP, respectively, suggesting that the former species was more tolerant to NP. Both microalgae acclimated to NP stress through down-regulating their photosynthetic activities, including antenna size (chlorophyll a content), maximal photochemistry (Fv/Fm) and the light absorbed by PSII (ABS/CS0), but the dissipation of energy from reaction centres (DI0/RC) increased with the increase of NP concentrations. In C. vulgaris, the changes of these parameters were more significant than in S. capricornutum and recovered completely after a 96 h exposure. The antioxidant responses, such as GSH content, CAT and POD activities in C. vulgaris increased with the increase of NP concentrations after a 24h exposure, but these changes disappeared with exposure time and recovered to the control levels after 96 h. In S. capricornutum, although GSH content, CAT and POD activities also increased when exposed to low- to moderate-NP concentrations, these values were significantly reduced at a high concentration (4 mg L(-1)) even after a 96 h exposure, indicating its antioxidant responses were significantly delayed. It is clear that the more NP-tolerant species, C. vulgaris, acclimated better with a faster recovery of its photosynthetic activity from the NP-induced damage, and exhibited more efficient and rapid responses to NP-induced oxidative stress. C. vulgaris also had a higher NP degradation ability than S. capricornutum.

Differential regulation by heat stress of novel cytochrome P450 genes from the dinoflagellate symbionts of reef-building corals

Exposure to heat stress has been recognized as one of the major factors leading to the breakdown of the coral-alga symbiosis and coral bleaching. Here, we describe the presence of three new cytochrome P450 (CYP) genes from the reef-building coral endosymbiont Symbiodinium (type C3) and changes in their expression during exposure to severe and moderate heat stress conditions. Sequence analysis of the CYP C-terminal region and two conserved domains, the "PERF" and "heme-binding" domains, confirmed the separate identities of the CYP genes analyzed. In order to explore the effects of different heat stress scenarios, samples of the scleractinian coral Acropora millepora were exposed to elevated temperatures incrementally over an 18-h period (rapid thermal stress) and over a 120-h period (gradual thermal stress). After 18 h of gradual heating and incubation at 26 degrees C, the Symbiodinium CYP mRNA pool was approximately 30% larger, while a further 6 degrees C increase to a temperature above the average sea temperature (29 degrees C after 72 h) resulted in a 2- to 4-fold increase in CYP expression. Both rapid heat stress and gradual heat stress at 32 degrees C resulted in 50% to 90% decreases in CYP gene transcript abundance. Consequently, the initial upregulation of expression of CYP genes at moderately elevated temperatures (26 degrees C and 29 degrees C) was followed by a decrease in expression under the greater thermal stress conditions at 32 degrees C. These findings indicate that in the coral-alga symbiosis under heat stress conditions there is production of chemical stressors and/or transcriptional factors that regulate the expression of genes, such as the genes encoding cytochrome P450 monooxygenases, that are involved in the first line of an organism's chemical defense.