Sulfonamides-induced oxidative stress in freshwater microalga Chlorella vulgaris: Evaluation of growth, photosynthesis, antioxidants, ultrastructure, and nucleic acids

Global omics study of Tetraselmis chuii reveals time-related metabolic adaptations upon oxidative stress

Microalgae species encounter oxidative stress in their natural environments, prompting the development of species-specific adaptation mechanisms. Understanding these mechanisms can offer valuable insights for biotechnological applications in microalgal metabolic manipulation. In this study, we investigated the response of Tetraselmis chuii, an industrially important microalga, to H2O2-induced oxidative stress. Exposure to 0.5-mM H2O2 resulted in reduced cell viability, and higher concentrations led to a drastic decline. After 1 h of exposure to H2O2, photosynthetic capacity (Qy) was negatively impacted, and this reduction intensified after 6 h of continuous stress. Global multi-omics analysis revealed that T. chuii rapidly responded to H2O2-induced oxidative stress within the first hour, causing significant changes in both transcriptomic and metabolomic profiles. Among the cellular functions negatively affected were carbon and energy flow, with photosynthesis-related PSBQ having a 2.4-fold downregulation, pyruvate kinase decreased by 1.5-fold, and urea content reduced by threefold. Prolonged exposure to H2O2 incurred a high energy cost, leading to unsuccessful attempts to enhance carbon metabolism, as depicted, for example, by the upregulation of photosystems-related PETC and PETJ by more than twofold. These findings indicate that T. chuii quickly responds to oxidative stress, but extended exposure can have detrimental effects on its cellular functions. KEY POINTS: • 0.5-mM H2O2-induced oxidative stress strongly affects T. chuii • Distinct short- and long-term adaptation mechanisms are induced • Major metabolic adaptations occur within the first hour of exposure.

Dissecting the ecological risks of sulfadiazine degradation intermediates under different advanced oxidation systems: From toxicity to the fate of antibiotic resistance genes

The incomplete degradation of antibiotics in water can produce intermediates that carry environmental risks and thus warrant concerns. In this study, the degradation of high concentrations of antibiotic sulfadiazine (SDZ) by advanced oxidation processes that leverage different reactive oxide species was systematically evaluated in terms of the influence of different degradation intermediates on the propagation of antibiotic resistance genes (ARGs). The ozone, persulfate, and photocatalytic oxidation systems for SDZ degradation are dominated by ozone, direct electron transfer, and singlet oxygen, hole, and superoxide radicals, respectively. These processes produce 15 intermediates via six degradation pathways. Notably, it was determined that three specific intermediates produced by the ozone and persulfate systems were more toxic than SDZ. In contrast, the photocatalytic system did not produce any intermediates with toxicity exceeding that of SDZ. Microcosm experiments combined with metagenomics confirmed significant changes in microbiota community structure after treatment with SDZ and its intermediates, including significant changes in the abundance of Flavobacterium, Dungenella, Archangium, and Comamonas. This treatment also led to the emergence of sulfonamide ARGs. The total abundance of sulfonamide ARGs was found to be positively correlated with residual SDZ concentration, with the lowest total abundance observed in the photocatalytic system. Additionally, the correlation analysis unveiled microbiota carrying sulfonamide ARGs.

Sudden sulfamethoxazole shock leads to nitrite accumulation in microalgae-nitrifying bacteria consortia: Physiological responses and light regulating strategy

Antibiotic shock may potentially impact the performance of promising microalgae-nitrifying bacteria consortia (MNBC) processes. This study investigated physiological behaviors of MNBC under sulfamethoxazole (SMX) shock (mg/L level) and verified a light regulating strategy for improving process performance. Results showed that SMX shock did not affect ammonium removal but caused nitrite accumulation, resulting from combined effects of excessive reactive oxidative species (ROS) production, inhibited microalgal photosynthetic activity, upregulated expressions of amoA and hao, and downregulated expression of nxrA. Moreover, high ammonium concentration aggravated nitrite accumulation and reduced ammonium removal owing to significantly reduced dissolved oxygen (DO). Increasing light intensity enhanced microalgal photo-oxygenation and promoted expressions of all nitrification-related genes, thus improving ammonium removal and alleviating nitrite accumulation. A central composite design coupled with response surface methodology (CCD-RSM) further demonstrated the negative impacts of SMX shock and high ammonium on MNBC and the effectiveness of the light regulation in maintaining stable process performance. This study provides theoretical basis for physiological responses and regulatory strategy of the MNBC process facing short-term antibiotic shock.

Interactive effects of ammonium sulfate and lead on alfalfa in rare earth tailings: Physiological responses and toxicity thresholds

Ion-adsorption rare earth ore contains significant levels of leaching agents and heavy metals, leading to substantial co-contamination. This presents significant challenges for ecological rehabilitation, yet there is limited understanding of the toxicity thresholds associated with the co-contamination of ammonium sulfate (AS) and lead (Pb) on pioneer plants. Here, we investigated the toxicity thresholds of various aspects of alfalfa, including growth, ultrastructural changes, metabolism, antioxidant system response, and Pb accumulation. The results indicated that the co-contamination of AS-Pb decreased the dry weight of shoot and root by 26 %-77 % and 18 %-92 %, respectively, leading to irregular root cell morphology and nucleus disintegration. The high concentration and combined exposures to AS and Pb induced oxidative stress on alfalfa, which stimulated the defense of the antioxidative system and resulted in an increase in proline levels and a decrease in soluble sugars. Structural equation modeling analysis and integrated biomarker response elucidated that the soluble sugars, proline, and POD were the key physiological indicators of alfalfa under stresses and indicated that co-exposure induced more severe oxidative stress in alfalfa. The toxicity thresholds under single exposure were 496 (EC5), 566 (EC10), 719 (EC25), 940 (EC50) mg kg-1 for AS and 505 (EC5), 539 (EC10), 605 (EC25), 678 (EC50) mg kg-1 for Pb. This study showed that AS-Pb pollution notably influenced plant growth performance and had negative impacts on the growth processes, metabolite levels, and the antioxidant system in plants. Our findings contribute to a theoretical foundation and research necessity for evaluating ecological risks in mining areas and assessing the suitability of ecological restoration strategies.

Effects of sulfamonomethoxine and trimethoprim co-exposures at different environmentally relevant concentrations on microalgal growth and nutrient assimilation

In aquaculture around the world, sulfamonomethoxine (SMM), a long-acting antibiotic that harms microalgae, is widely employed in combination with trimethoprim (TMP), a synergist. However, their combined toxicity to microalgae under long-term exposures at environmentally relevant concentrations remains poorly understood. Therefore, we studied the effects of SMM single-exposures and co-exposures (SMM:TMP=5:1) at concentrations of 5 μg/L and 500 μg/L on Chlorella pyrenoidosa within one aquacultural drainage cycle (15 days). Photosynthetic activity and N assimilating enzyme activities were employed to evaluate microalgal nutrient assimilation. Oxidative stress and flow cytometry analysis for microalgal proliferation and death jointly revealed mechanisms of inhibition and subsequent self-adaptation. Results showed that exposures at 5 μg/L significantly inhibited microalgal nutrient assimilation and induced oxidative stress on day 7, with a recovery to levels comparable to the control by day 15. This self-adaptation and over 95 % removal of antibiotics jointly contributed to promoting microalgal growth and proliferation while reducing membrane-damaged cells. Under 500 μg/L SMM single-exposure, microalgae self-adapted to interferences on nutrient assimilation, maintaining unaffected growth and proliferation. However, over 60 % of SMM remained, leading to sustained oxidative stress and apoptosis. Remarkably, under 500 μg/L SMM-TMP co-exposure, the synergistic toxicity of SMM and TMP significantly impaired microalgal nutrient assimilation, reducing the degradation efficiency of SMM to about 20 %. Consequently, microalgal growth and proliferation were markedly inhibited, with rates of 9.15 % and 17.7 %, respectively, and a 1.36-fold increase in the proportion of cells with damaged membranes was observed. Sustained and severe oxidative stress was identified as the primary cause of these adverse effects. These findings shed light on the potential impacts of antibiotic mixtures at environmental concentrations on microalgae, facilitating responsible evaluation of the ecological risks of antibiotics in aquaculture ponds.

The Piezocatalytic Degradation of Sulfadiazine by Lanthanum-Doped Barium Titanate

Piezocatalysis, a heterogeneous catalytic technique, leverages the periodic electric field changes generated by piezoelectric materials under external forces to drive carriers for the advanced oxidation of organic pollutants. Antibiotics, as emerging trace organic pollutants in water sources, pose a potential threat to animals and drinking water safety. Thus, piezoelectric catalysis can be used to degrade trace organic pollutants in water. In this work, BaTiO3 and La-doped BaTiO3 were synthesized using an improved sol-gel-hydrothermal method and used as piezocatalytic materials to degrade sulfadiazine (SDZ) with ultrasound activation. High-crystallinity products with nano cubic and spherical morphologies were successfully synthesized. An initial concentration of SDZ ranging from 1 to 10 mg/L, a catalysis dosage range from 1 to 2.5 mg/mL, pH, and the background ions in the water were considered as influencing factors and tested. The reaction rate constant was 0.0378 min-1 under the optimum working conditions, and the degradation efficiency achieved was 89.06% in 60 min. La-doped BaTiO3 had a better degradation efficiency, at 14.98% on average, compared to undoped BaTiO3. Further investigations into scavengers revealed a partially piezocatalytic process for the degradation of SDZ. In summary, our work provides an idea for green environmental protection in dealing with new types of environmental pollution.

Micro- and nanoplastics interact with conventional pollutants on microalgae: Synthesis through meta-analysis

Micro- and nanoplastics (MNPs) have been found to occur intensively in aquatic environments, along with other conventional pollutants (Po) such as heavy metals, pesticides, pharmaceuticals, etc. However, our understanding of how MNPs and Po interact on aquatic primary producers is fragmented. We performed a quantitative meta-analysis based on 933 published experimental assessments from 44 studies to examine the coupled effects of MNPs and Po on microalgae. Although the results based on interaction type frequency (the proportion of each interaction type in all results) revealed dominantly additive interactions (56%) for overall physiological performance, an overall antagonistic effect was observed based on the mean interaction effect sizes. A higher proportion of antagonistic interaction type frequency was found in marine species compared to fresh species. The antagonistic effects were particularly significant for growth, oxidative responses, and photosynthesis, which could be attributed to the adsorption effect of MNPs on Po and thus the decreasing concentrations of pollutants in the medium. Larger-sized, negatively charged or uncharged and aged MNPs had higher proportions of antagonistic effects compared to smaller-sized, positively charged and virgin MNPs, due to their stronger adsorption capacity to Po. This study provides a comprehensive insight into the interactive effects of MNPs and Po on microalgae.

Oxidative stress responses in two marine diatoms during sulfamethoxazole exposure and the toxicological evaluation using the IBRv2 index

Sulfamethoxazole (SMX) is widely present in water systems, and its stable properties and poor biodegradability can result in high residues of SMX in the water environment. This, in turn, can have detrimental effects on the entire aquatic habitat and human life and health. This study aimed to investigate the toxic effects of SMX on the growth, photosynthetic pigment content, and oxidative stress of two marine microalgae species: Skeletonema costatum and Phaeodactylum tricornutum. SMX demonstrated a significant inhibitory effect on microalgae proliferation, with 96-h median effective concentration (EC50) values of 0.93 mg/L and 4.65 mg/L for S. costatum and P. tricornutum, respectively. At low concentrations, SMX significantly increased the production of Chl a in both microalgae species. However, in the higher concentration SMX treatment group, Chl a content in P. tricornutum experienced a significant decrease, whereas Chl c showed no sensitivity to SMX. The activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx), along with the glutathione (GSH) content, exhibited a significant increasing trend in response to higher SMX concentrations. However, these changes effectively inhibited the accumulation of malondialdehyde (MDA) content. In the treatment group with the highest SMX concentration, MDA content in both microalgae species was significantly higher compared to the control group. The Integrated Biomarker Response Version 2 (IBRv2) index showed a significant positive correlation with SMX concentration, suggesting its potential for assessing the ecotoxicological effects of lower SMX concentrations on marine microalgae.

Plants, animals, and fisheries waste-mediated bioremediation of contaminants of environmental and emerging concern (CEECs)-a circular bioresource utilization approach

The release of contaminants of environmental concern including heavy metals and metalloids, and contaminants of emerging concern including organic micropollutants from processing industries, pharmaceuticals, personal care, and anthropogenic sources, is a growing threat worldwide. Mitigating inorganic and organic contaminants, which can be coined as contaminants of environmental and emerging concern (CEECs), is a big challenge as traditional physicochemical processes are not economically viable for managing mixed contaminants of low concentrations. As a result, low-cost materials must be designed to provide high CEEC removal efficiency. One of the environmentally viable and energy-efficient approaches is biosorption, which involves using biomass or biopolymers isolated from plants or animals to decontaminate heavy metals in contaminated environments using inherent biological mechanisms. Among chemical constituents in plant biomass, cellulose, lignin, hemicellulose, proteins, polysaccharides, phenolic compounds, and animal biomass include polysaccharides and other compounds to bind heavy metals covalently and non-covalently. These functional groups include carboxyl, hydroxyl, carbonyl, amide, amine, and sulfhydryl. Cation-exchange capacities of these bioadsorbents can be improved by applying chemical modifications. The relevance of chemical constituents and bioactives in biosorbents derived from agricultural production such as food and fodder crops, bioenergy and cash crops, fruit and vegetable crops, medicinal and aromatic plants, plantation trees, aquatic and terrestrial weeds, and animal production such as dairy, goatery, poultry, duckery, and fisheries is highlighted in this comprehensive review for sequestering and bioremediation of CEECs, including as many as ten different heavy metals and metalloids co-contaminated with other organic micropollutants in circular bioresource utilization and one-health concepts.

Antibiotic sorption onto microplastics in water: A critical review of the factors, mechanisms and implications

Microplastics as vectors for contaminants in the environment is becoming a topic of public interest. Microplastics have been found to actively adsorb heavy metals, per-fluorinated alkyl substances (PFAS), polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons (PAHs), pharmaceuticals and personal care products (PPCPs) and polybrominated diethers (PBDs) onto their surface. Particular interest in microplastics capacity to adsorb antibiotics needs further attention due to the potential role this interaction plays on antibiotic resistance. Antibiotic sorption experiments have been documented in the literature, but the data has not yet been critically reviewed. This review aims to comprehensively assess the factors that affect antibiotic sorption onto microplastics. It is recognised that the physico- chemical properties of the polymers, the antibiotic chemical properties, and the properties of the solution all play a crucial role in the antibiotic sorption capacity of microplastics. Weathering of microplastics was found to increase the antibiotic sorption capacity by up to 171%. An increase in solution salinity was found to decrease the sorption of antibiotics onto microplastics, in some instances by 100%. pH also has a substantial effect on sorption capacity, illustrating the significance of electrostatic interactions on the sorption of antibiotics onto microplastics. The need for a uniform experimental design when testing antibiotic sorption is highlighted to remove inconsistencies in the data currently presented. Current literature examines the link between antibiotic sorption and antibiotic resistance, however, further studies are still required to fully understand this emerging global crisis.

How do freshwater microalgae and cyanobacteria respond to antibiotics?

Antibiotic pollution is an emerging environmental challenge. Residual antibiotics from various sources, including municipal and industrial wastewater, sewage discharges, and agricultural runoff, are continuously released into freshwater environments, turning them into reservoirs that contribute to the development and spread of antibiotic resistance. Thus, it is essential to understand the impacts of antibiotic residues on aquatic organisms, especially microalgae and cyanobacteria, due to their crucial roles as primary producers in the ecosystem. This review summarizes the effects of antibiotics on major biological processes in freshwater microalgae and cyanobacteria, including photosynthesis, oxidative stress, and the metabolism of macromolecules. Their adaptive mechanisms to antibiotics exposure, such as biodegradation, bioadsorption, and bioaccumulation, are also discussed. Moreover, this review highlights the important factors affecting the antibiotic removal pathways by these organisms, which will promote the use of microalgae-based technology for the removal of antibiotics. Finally, we offer some perspectives on the opportunities for further studies and applications.

Antibiotic Toxicity Isolated and as Binary Mixture to Freshwater Algae Raphidocelis subcapitata: Growth Inhibition, Prediction Model, and Environmental Risk Assessment

Antibiotics in aqueous environments can have extremely adverse effects on non-targeted organisms. However, many research projects have only focused on the toxicological evaluation of individual antibiotics in various environments. In the present work, individual and binary mixture toxicity experiments have been conducted with the model organism Raphidocelis subcapitata (R. subcapitata), and a mixture concentration-response curve was established and contrasted with the estimated effects on the basis of both the concentration addition (CA) and the independent action (IA) models. In addition, different risk assessment methods were used and compared to evaluate the environmental risk of binary mixtures. The toxic ranking of the selected antibiotics to R. subcapitata was erythromycin (ERY) > sulfamethoxazole (SMX) > sulfamethazine (SMZ). In general, the conclusion of this study is that the adverse effects of binary mixtures are higher than the individual antibiotics. The CA model and RQSTU are more suitable for toxicity prediction and risk assessment of binary mixtures. This study reveals the potential ecological risks that antibiotics and their mixtures may pose to water ecosystems, thus providing scientific information for environmental quality regulation.

Mechanisms and application of microalgae on removing emerging contaminants from wastewater: A review

This study reviews the development of the ability of microalgae to remove emerging contaminants (ECs) from wastewater. Contaminant removal by microalgae-based systems (MBSs) includes biosorption, bioaccumulation, biodegradation, photolysis, hydrolysis, and volatilization. Usually, the existence of ECs can inhibit microalgae growth and reduce their removal ability. Therefore, three methods (acclimation, co-metabolism, and algal-bacterial consortia) are proposed in this paper to improve the removal performance of ECs by microalgae. Finally, due to the high removal performance of contaminants from wastewater by algal-bacterial consortia systems, three kinds of algal-bacterial consortia applications (algal-bacterial activatedsludge, algal-bacterial biofilm reactor, and algal-bacterial constructed wetland system) are recommended in this paper. These applications are promising for ECs removal. But most of them are still in their infancy, and limited research has been conducted on operational mechanisms and removal processes. Extra research is needed to clarify the applicability and cost-effectiveness of hybrid processes.

Commercial pesticides for urban applications induced population growth and sub-cellular alterations in Raphidocelis subcapitata (Chlorophyceae) at concerning environmental concentrations

Information regarding the safety and environmental risks of pesticides intended for urban use remains limited. This study aimed to assess the effects of four common pesticides on the microalga Raphidocelis subcapitata: DIAZINON® 25% C. E., Roundup®, URBACIN® 20C. E., and VAPODEL® 20% C. E., which are commercial formulations of diazinon, glyphosate, dichlorvos, and cypermethrin, respectively. According to 96-h inhibition of population growth bioassays, the four pesticide toxicities exemplified the following order: DIAZINON® (diazinon) > Roundup® (glyphosate) > VAPODEL® (dichlorvos) > URBACIN® (cypermethrin). Increasing pesticide concentrations elicited alterations in the specific growth rates (µmax). The macromolecule contents and photosynthetic pigments increased in groups exposed to the highest concentrations of DIAZINON® 25%, Roundup®, and URBACIN® 20 compared to the control group, despite these treatments inducing lower population growth rates. VAPODEL® 20% induced higher growth rates and lower macromolecule content compared to the control. Since active ingredients were not quantified, certain comparisons may prove limiting, but it is important to assess the effects of the whole mixtures in the form that they enter the environment, especially for urban-intended applications or generic formulations with higher additive contents. Finally, this study demonstrated that commercial pesticide formulations designed for urban applications might pose a threat to freshwater microalgae due to their underestimated toxic potential, but further studies are required.

Toxicological Effects of Microplastics and Sulfadiazine on the Microalgae Chlamydomonas reinhardtii

Despite the fact that microplastics (MPs) facilitate the adsorption of environmental organic pollutants and influence their toxicity for organisms, more study is needed on the combination of MPs and antibiotics pollutant effects. In this study, polystyrene MPs (1 and 5 μm) and sulfadiazine (SDZ) were examined separately and in combination on freshwater microalga, Chlamydomonas reinhardtii. The results suggest that both the MPs and SDZ alone and in combination inhibited the growth of microalgae with an increasing concentration of MPs and SDZ (5–200 mg l^–1); however, the inhibition rate was reduced by combination. Upon exposure for 7 days, both the MPs and SDZ inhibited algal growth, reduced chlorophyll content, and enhanced superoxide dismutase (SOD) activities, whereas glutathione peroxidase (GSH-Px) activity was elevated only with the exposure of 1 μm MPs. Fluorescence microscopy and scanning electron microscopy also indicated that particle size contributed to the combined toxicity by aggregating MPs with periphery pollutants. Further, the amount of extracellular secretory protein increased in the presence of MPs and SDZ removal ratio decreased when MPs and SDZ coexisted, suggesting that MPs affected SDZ metabolism by microalgae. The particle size of microplastics affected the toxicity of MPs on microalgae and the combined effect of MPs and SDZ could be mitigated by MPs adsorption. These findings provide insight into microalgae responses to the combination of MPs and antibiotics in water ecosystems.

Bioremediation of sulfonamides by a microalgae-bacteria consortium - Analysis of pollutants removal efficiency, cellular composition, and bacterial community

Antibiotics in wastewaters (e.g., sulfonamides (SAs)) are not effectively removed by the conventional bacterial processes. In this study, a microalgae (Scenedesmus obliquus)-based process was evaluated for the removal of SAs. The maximum removal efficiency of sulfadiazine (SDZ) and sulfamethoxazole (SMX) by the consortium was 5.85% and 40.84%, respectively. The lower SDZ biodegradation efficiency could be due to the difference in the lipophilic degree related to cell binding. The presence of SAs did not significantly inhibit the biomass production of the consortium (1311-1952 mg/L biomass) but led to a 36-51% decrease in total polysaccharide content and an increase in microalgae's protein content, which caused granule formation. The presence of SMX and SDZ resulted in an increase in lipid peroxidation activity with a 6.2 and 23.5-fold increase in malondialdehyde content, respectively. Rhodobacter and Phreatobacter were abundant in the consortium with SAs' presence, while alinarimonas, Catalinimonas and Cecembia were seen in their absence.

Microalgal mediated antibiotic co-metabolism: Kinetics, transformation products and pathways

The mutual interaction of a microalga Chlorella vulgaris with four antibiotics viz. sulfamethoxazole (SMX), trimethoprim (TMP), azithromycin (AZI), and levofloxacin (LEV) individually and in mixture was studied in batch culture. SMX, TMP, and LEV stimulated algal growth, while AZI inhibited its growth. The Combination Index (CI)-isobologram indicated antagonism of the antibiotic mixture on the growth of C. vulgaris. Higher removal efficiency was observed in the mixed antibiotic than in the single antibiotic batch cultures. Biodegradation was the main antibiotic removal mechanism with a similar antibiotic biosorption pattern in single and mix antibiotic cultures. Scanning electron microscopy and Fourier transform infrared spectrophotometry showed minor biochemical alterations on algal cells surface and a stable algal population. Monod kinetics model was successfully applied to understand the growth with respect to the removal efficiency of C. vulgaris in single and mix antibiotic batch cultures. Results indicated relatively higher specific growth rate in the mix antibiotic batch culture with removal efficiency in the order of SMX > LEV > TMP > AZI. In total, 46 metabolites with 18 novel ones of the four antibiotics were identified by using high-resolution mass spectrometry based on the suspect screening approach to propose the potential transformation pathways. Most of the transformation products demonstrated lower toxicity than their respective parents. These findings implied that C. vulgaris could be an outstanding candidate for advanced treatment of antibiotic removal in wastewater.

Occurrence of antibiotics in waters, removal by microalgae-based systems, and their toxicological effects: A review

Global antibiotics consumption has been on the rise, leading to increased antibiotics release into the environment, which threatens public health by selecting for antibiotic resistant bacteria and resistance genes, and may endanger the entire ecosystem by impairing primary production. Conventional bacteria-based treatment methods are only moderately effective in antibiotics removal, while abiotic approaches such as advanced oxidation and adsorption are costly and energy/chemical intensive, and may cause secondary pollution. Considered as a promising alternative, microalgae-based technology requires no extra chemical addition, and can realize tremendous CO₂ mitigation accompanying growth related pollutants removal. Previous studies on microalgae-based antibiotics removal, however, focused more on the removal performances than on the removal mechanisms, and few studies have concerned the toxicity of antibiotics to microalgae during the treatment process. Yet understanding the removal mechanisms can be of great help for targeted microalgae-based antibiotics removal performances improvement. Moreover, most of the removal and toxicity studies were carried out using environment-irrelevant high concentrations of antibiotics, leading to reduced guidance for real-world situations. Integrating the two research fields can be helpful for both improving antibiotics removal and avoiding toxicological effects to primary producers by the residual pollutants. This study, therefore, aims to build a link connecting the occurrence of antibiotics in the aquatic environment, the removal of antibiotics by microalgae-based processes, and the toxicity of antibiotics to microalgae. Distribution of various categories of antibiotics in different water environments were summarized, together with the antibiotics removal mechanisms and performances in microalgae-based systems, and the toxicological mechanisms and toxicity of antibiotics to microalgae after either short-term or long-term exposure. Current research gaps and future prospects were also analyzed. The review could provide much valuable information to the related fields, and provoke interesting thoughts on integrating microalgae-based antibiotics removal research and toxicity research on the basis of environmentally relevant concentrations.

The efficiency of microalgae biofilm in the phycoremediation of water from River Kaduna

This study is aimed at investigating the efficiency of microalgae biofilm in the phycoremediation of water from a polluted river. Freshwater microalgae biofilm inherent in a contaminated petrochemical stream was employed to remediate water from the River Kaduna, which is the largest river in Kaduna town, Kaduna State, Nigeria, and serves as the primary water source in Kaduna town. The results indicate high reduction efficiency of some physicochemical parameters and pollutants (turbidity (71%), conductivity (9.8%), sulfate (37.5%), alkalinity (62.5%), chloride (11.5%), TDS (9.9%), TSS (66.7%), nitrate (42.9%), COD (24%), and BOD (33%), Cd (70.0%), Ni (74.0%) and Pb (71.0%)), indicating the effectiveness of microalgae biofilm in the phycoremediation of water from River Kaduna. According to scanning electron microscope (SEM) observation, the microalgae biofilm has rough surface morphology after the treatment of the river water, which implies that the biofilm was capable of removing the pollutants in water via biosorption. Other characterizations such as XRF, XRD, and FTIR also buttressed that biosorption was the primary removal mechanism of pollutants by microalgae biofilm. Besides, the results also show the production of ROS during the treatment of water from the River Kaduna by the microalgae biofilm. This high concentration of ROS produced during the treatment correlates significantly with pollutant degradation. The GC-MS analysis of the microalgae biofilm shows the involvement of some phytochemicals in the process of pollutant degradation. As a result, microalgae biofilm is a simple and cost-effective method of polluted water phycoremediation with promising applications and future prospects.

Biotransformation mechanism of Vibrio diabolicus to sulfamethoxazole at transcriptional level

Sulfamethoxazole (SMX) has attracted much attention due to its high probability of detection in the environment. Marine bacteria Vibrio diabolicus strain L2-2 has been proven to be able to transform SMX. In this study, the potential resistance and biotransformation mechanism of strain L2-2 to SMX, and key genes responses to SMX at environmental concentrations were researched. KEGG pathways were enriched by down-regulated genes including degradation of L-Leucine, L-Isoleucine, and fatty acid metabolism. Resistance mechanism could be concluded as the enhancement of membrane transport, antioxidation, response regulator, repair proteins, and ribosome protection. Biotransformation genes might involve in arylamine N-acetyltransferases (nat), cytochrome c553 (cyc-553) and acyl-CoA synthetase (acs). At the environmental concentration of SMX (0.1-10 μg/L), nat was not be activated, which meant the acetylation of SMX might not occur in the environment; however, cyc-553 was up-regulated under SMX stress of 1 μg/L, which indicated the hydroxylation of SMX could occur in the environment. Besides, the membrane transport and antioxidation of strain L2-2 could be activated under SMX stress of 10 μg/L. The results provided a better understanding of resistance and biotransformation of bacteria to SMX and would support related researches about the impacts of environmental antibiotics.

The Toxic Effects of Antibiotics on Freshwater and Marine Photosynthetic Microorganisms: State of the Art

Antibiotic residues have been commonly detected worldwide in freshwater, estuarine, and marine ecosystems. The review summarizes the up-to-date information about the toxic effects of over 60 antibiotics on nontarget autotrophic microorganisms with a particular focus on marine microalgae. A comprehensive overview of the available reports led to the identification of significant knowledge gaps. The data on just one species of freshwater green algae (Raphidocelis subcapitata) constitute 60% of the total information on the toxicity of antibiotics, while data on marine species account for less than 14% of the reports. Moreover, there is a clear knowledge gap regarding the chronic effects of antibiotic exposure (only 9% of studies represent exposition time values longer than 7 days). The review summarizes the information on different physiological endpoints, including processes involved in photosynthesis, photoprotective and antioxidant mechanisms. Currently, the hazard assessment is mostly based on the results of the evaluation of individual chemicals and acute toxicity tests of freshwater organisms. Future research trends should involve chronic effect studies incorporating sensitive endpoints with the application of environmentally relevant concentrations, as well as studies on the mixture effects and combined environmental factors influencing toxicity.

The Potential of Chaetoceros muelleri in Bioremediation of Antibiotics: Performance and Optimization

Antibiotics are frequently applied to treat bacterial infections in humans and animals. However, most consumed antibiotics are excreted into wastewater as metabolites or in their original form. Therefore, removal of antibiotics from aquatic environments is of high research interest. In this study, we investigated the removal of sulfamethoxazole (SMX) and ofloxacin (OFX) with Chaetoceros muelleri, a marine diatom. The optimization process was conducted using response surface methodology (RSM) with two independent parameters, i.e., the initial concentration of antibiotics and contact time. The optimum removal of SMX and OFX were 39.8% (0.19 mg L⁻¹) and 42.5% (0.21 mg L⁻¹) at the initial concentration (0.5 mg L⁻¹) and contact time (6.3 days). Apart from that, the toxicity effect of antibiotics on the diatom was monitored in different SMX and OFX concentrations (0 to 50 mg L⁻¹). The protein (mg L⁻¹) and carotenoid (μg L⁻¹) content increased when the antibiotic concentration increased up to 20 mg L⁻¹, while cell viability was not significantly affected up to 20 mg L⁻¹ of antibiotic concentration. Protein content, carotenoid, and cell viability decreased during high antibiotic concentrations (more than 20 to 30 mg L⁻¹). This study revealed that the use of Chaetoceros muelleri is an appealing solution to remove certain antibiotics from wastewater.