Streptomycin affects the growth and photochemical activity of the alga Chlorella vulgaris

Hormetic effect of a short-chain PFBS on Microcystis aeruginosa and its molecular mechanism

Short-chain Perfluorinated compounds (PFCs), used as substitutes for highly toxic long-chain PFCs, are increasingly entering the aquatic environment. However, the toxicity of short-chain PFCs in the environment is still controversial. This study investigated the effects of short-chain perfluorobutanesulfonic acid (PFBS) at different concentrations (2.5, 6, 14.4, 36, and 90 mg/L) on M. aeruginosa growth under 12-day exposure and explored the molecular mechanism of toxicity using transcriptomics. The results showed that M. aeruginosa exhibited hormetic effects after exposure to PFBS. Low PFBS concentrations stimulated algal growth, whereas high PFBS concentrations inhibited it, and this inhibitory effect became progressively more pronounced with increasing PFBS exposure concentrations. Transcriptomics showed that PFBS promoted the pathways of photosynthesis, glycolysis, energy metabolism and peptidoglycan synthesis, providing the energy required for cell growth and maintaining cellular morphology. PFBS, on the other hand, caused growth inhibition in algae mainly through oxidative stress, streptomycin synthesis, and genetic damage. Our findings provide new insights into the toxicity and underlying mechanism of short-chain PFCs on algae and inform the understanding of the hormetic effect of short-chain PFCs, which are crucial for assessing their ecological risks in aquatic environments.

Seasonal variation in structural and functional distribution of periphyton in a macrolide antibiotics-contaminated river

Periphyton, a microbial assemblage of autotrophic and heterotrophic organisms, is vital to aquatic ecosystems. While exposure to macrolide antibiotics has been confirmed to reduce the biodiversity and damage the critical ecological functions in indoor microcosm bioassays, the distribution of periphyton along a macrolide antibiotic pollution gradient in a river has yet to be determined. Herein, we established the spatiotemporal distribution of five major macrolides, i.e., azithromycin (AZI), roxithromycin (ROX), erythromycin (ERY), clarithromycin (CLA), and anhydro erythromycin (ERY-H2O) in water and periphyton of Zao River (Xi'an, China), after which we evaluated the effects on the structures, photosynthetic activity, and carbon utilization capacity of periphyton in March, June, and September 2023. In contrast with the reference sites, the macrolides were identified in all sewage treatment plants (STPs) impacted sites with concentrations ranging from 0.05 to 2.18 μg/L in water and from not detected - 9.67 μg/g in periphyton. Regarding community structure, the occurrence of macrolides was negatively linked to FirmicutesExiguobacterium undae and Exiguobacterium sibiricum, CyanobacteriaOscillatoriales and Vischeria sp., and ChlorophytaMonostroma grevillei, Selenastrum sp. LU21 and Desmodesmus subspicatus. At the functional level, only the metabolism of phenolic acids was significantly decreased in river reach with high antibiotic levels in June, compared to the other five carbon sources that were not altered. The overall photosynthetic activity of periphytic photosystem II remained unchanged in both reference and STPs impacted groups throughout three seasons. Overall, the macrolides released from STPs were correlated with the altered periphytic structures in the river, whereas a similar trend was not detected for the community functions owing to the functional redundancy. A mesocosm experiments warrants further consideration to validate the field results.

Effect of suspended particulate matter on physiological, biochemical and photosynthetic characteristics of Chlorella pyrenoidosa in the Jinjiang Estuary (Fujian, China)

Suspended particulate matter (SPM), an important component of the natural water environment, can act as a carrier of many pollutants that affect aquatic organisms. In the present study, the effect of SPM obtained from Jinjiang Estuary on the physiological, biochemical, and photosynthetic properties of typical freshwater algae (Chlorella pyrenoidosa) was investigated. The results showed that under different concentrations of SPM treatment, the superoxide dismutase (SOD), catalase (CAT) activities, and malondialdehyde (MDA) content of C. pyrenoidosa increased, but the soluble protein content decreased. SPM with different particle sizes had less effect on SOD of C. pyrenoidosa, but showed a promoting effect on CAT and MDA as well as soluble protein content. In terms of photosynthetic activity, high concentrations (70, 90 mg/L) and small particle sizes (0-75, 75-120 μm) of SPM had a greater effect on the chlorophyll a content of C. pyrenoidosa. In addition, different concentrations of SPM had no significant effect on the potential photosynthetic activity of PS II (Fv/F0) and the maximum quantum yield of PS II (Fv/Fm), but the inhibition of the initial slope (alpha), the maximum photosynthetic rate (ETRmax) and the semi-light saturation point (Ik) increased with the increase of SPM concentration. Fv/F0, ETRmax, and Ik of C. pyrenoidosa showed some degree of recovery after inhibition in the presence of SPM of different particle sizes.

Microalgae systems - environmental agents for wastewater treatment and further potential biomass valorisation

Water is the most valuable resource on the planet. However, massive anthropogenic activities generate threatening levels of biological, organic, and inorganic pollutants that are not efficiently removed in conventional wastewater treatment systems. High levels of conventional pollutants (carbon, nitrogen, and phosphorus), emerging chemical contaminants such as antibiotics, and pathogens (namely antibiotic-resistant ones and related genes) jeopardize ecosystems and human health. Conventional wastewater treatment systems entail several environmental issues: (i) high energy consumption; (ii) high CO₂ emissions; and (iii) the use of chemicals or the generation of harmful by-products. Hence, the use of microalgal systems (entailing one or several microalgae species, and in consortium with bacteria) as environmental agents towards wastewater treatment has been seen as an environmentally friendly solution to remove conventional pollutants, antibiotics, coliforms and antibiotic resistance genes. In recent years, several authors have evaluated the use of microalgal systems for the treatment of different types of wastewater, such as agricultural, municipal, and industrial. Generally, microalgal systems can provide high removal efficiencies of: (i) conventional pollutants, up to 99%, 99%, and 90% of total nitrogen, total phosphorus, and/or organic carbon, respectively, through uptake mechanisms, and (ii) antibiotics frequently found in wastewaters, such as sulfamethoxazole, ciprofloxacin, trimethoprim and azithromycin at 86%, 65%, 42% and 93%, respectively, through the most desirable microalgal mechanism, biodegradation. Although pathogens removal by microalgal species is complex and very strain-specific, it is also possible to attain total coliform and Escherichia coli removal of 99.4% and 98.6%, respectively. However, microalgal systems' effectiveness strongly relies on biotic and abiotic conditions, thus the selection of operational conditions is critical. While the combination of selected species (microalgae and bacteria), ratios and inoculum concentration allow the efficient removal of conventional pollutants and generation of high amounts of biomass (that can be further converted into valuable products such as biofuels and biofertilisers), abiotic factors such as pH, hydraulic retention time, light intensity and CO₂/O₂ supply also have a crucial role in conventional pollutants and antibiotics removal, and wastewater disinfection. However, some rationale must be considered according to the purpose. While alkaline pH induces the hydrolysis of some antibiotics and the removal of faecal coliforms, it also decreases phosphates solubility and induces the formation of ammonium from ammonia. Also, while CO₂ supply increases the removal of E. coli and Pseudomonas aeruginosa, as well as the microalgal growth (and thus the conventional pollutants uptake), it decreases Enterococcus faecalis removal. Therefore, this review aims to provide a critical review of recent studies towards the application of microalgal systems for the efficient removal of conventional pollutants, antibiotics, and pathogens; discussing the feasibility, highlighting the advantages and challenges of the implementation of such process, and presenting current case-studies of different applications of microalgal systems.

Treatment of antibiotic-containing wastewater with self-suspended algae-bacteria symbiotic particles: Removal performance and reciprocal mechanism

Emerging contaminants such as antibiotics in wastewater have posed a challenge on conventional biological treatment processes. Algae-bacteria symbiotic mode could improve the performance of biological treatment processes. Self-suspended algae-bacteria symbiotic particles (ABSPs) were prepared with Chlorella vulgaris and Bacillus subtilis using the sol-gel method and hollow glass microspheres in this study. The removal effect of nitrogen and phosphorus as well as the feedback mechanism of ABSPs under tetracycline stress were investigated through three-cycles wastewater treatment experiments. The antioxidant enzyme activity and phycosphere extracellular polymeric substance (EPS) content were identified as well. The results indicated that the removal rates of NH₄⁺-N, TP, COD, and tetracycline in the ABSPs group finally reached 96.18%, 95.44%, 81.36%, and 74.20%, respectively, which were higher than the single algae group apparently. The phycosphere EPS content increased by 20.41% and algae cell structure maintained integrity in ABSPs group as compared with that in single algae group. This study demonstrates that the self-suspended ABSPs can improve contaminants removal performance and alleviate the antioxidant stress response of algae through algal-bacterial reciprocity mechanism.

Effect of ofloxacin levels on growth, photosynthesis and chlorophyll fluorescence kinetics in tomato

Antibiotic pollution has become a global environmental pollution problem. Chlorophyll fluorescence is one of the most important indicators reflecting the degree to which plants are influenced by the environment. Ofloxacin (OFL) is a highly toxic antibiotic pollutant, and there are few reports on the effects of changes in OFL levels on tomato chlorophyll fluorescence parameters. In this study, we investigated the responses of tomato growth, photosynthetic activity and chlorophyll fluorescence kinetics to exogenous OFL exposure (as the concentrations of 0, 2.5, 5, 10 and 20 mg L^-1). The results showed that lower concentrations of OFL (2.5 mg L^-1) had little impact on tomato growth, while plant growth was inhibited with the OFL concentration increasing. At higher OFL concentrations (5, 10 and 20 mg L^-1), chloroplasts ruptured, and chlorophyll became degraded, resulting in leaf etiolation. Furthermore, the photosynthetic and photochemical efficiency and electron transfer rate were significantly inhibited by OFL. Moreover, damage to the oxygen-evolving complex on the donor side of PSⅡ prevented electron transfer from QA to QB and led to photoinhibition. In conclusion, higher OFL concentration reduced photosynthesis by destroying the photosynthetic mechanism in tomato, resulting in tomato leaf etiolation and plant growth inhibition.

Physiological responses and antibiotic-degradation capacity of duckweed (Lemna aequinoctialis) exposed to streptomycin

Aquatic plants are constantly exposed to various water environmental pollutants. Few data on how antibiotics affect duckweed health and its removal ability. The aim of this study was to investigate the impact of streptomycin on the physiological change and uptake capability in duckweed (Lemna aequinoctialis) after exposure at different time points (0, 5, 10, 15 and 20 days). Duckweeds were exposed to streptomycin at a range of concentrations (0.1-10 mM). Results indicated that the high streptomycin concentrations (≥1 mM) resulted in a lower duckweed biomass (21.5-41.5%), RGR (0.258-0.336 g d^-1), decrease in total Chl and increase in carotenoids. Antioxidative enzymes, including CAT (18-42.88 U mg protein^-1), APX (0.41-0.76 U mg protein^-1), and SOD (0.52-0.71 U mg protein^-1) were found to accumulate in the streptomycin groups in comparison to the control group. The significant reduction (72-82%) in streptomycin content at 20 d compared to the control (40-55%) suggested that duckweed has a high ability in removing streptomycin. Transcriptome analysis showed that the secondary metabolic pathways including phenylpropanoid biosynthesis and flavonoid biosynthesis were significantly upregulated in the streptomycin setup compared to the control. Therefore, our findings suggested that duckweed can contribute to the streptomycin degradation, which should be highly recommended to the treatment of aquaculture wastewater and domestic sewage.

Selection of a suitable photosynthetically active microalgae strain for the co-cultivation with mammalian cells

Preventing hypoxic zones in 3D bioprinted mammalian cell-laden constructs using an internal oxygen supply could enable a more successful cultivation both in vitro and in vivo. In this study, the suitability of green microalgae as photosynthetic oxygen generators within bioprinted constructs was evaluated by defining and investigating important parameters for a successful co-culture. First, we assessed the impact of light–necessary for photosynthesis–on two non-light adapted mammalian cell types and defined red-light illumination and a temperature of 37°C as essential factors in a co-culture. The four thermotolerant microalgae strains Chlorella sorokiniana, Coelastrella oocystiformis, Coelastrella striolata, and Scenedesmus sp. were cultured both in suspension culture and 3D bioprinted constructs to assess viability and photosynthetic activity under these defined co-culture conditions. Scenedesmus sp. proved to be performing best under red light and 37°C as well as immobilized in a bioprinted hydrogel based on alginate. Moreover, the presence of the antibiotic ampicillin and the organic carbon-source glucose, both required for mammalian cell cultures, had no impact on bioprinted Scenedesmus sp. cultures regarding growth, viability, and photosynthetic activity. This study is the first to investigate the influence of mammalian cell requirements on the metabolism and photosynthetic ability of different microalgal strains. In a co-culture, the strain Scenedesmus sp. could provide a stable oxygenation that ensures the functionality of the mammalian cells.

Toxicity, biodegradation of moxifloxacin and gatifloxacin on Chlamydomonas reinhardtii and their metabolic fate

The novel fourth-generation fluoroquinolones (FQs) were developed to improve the antimicrobial activity and their utilization has rapidly increased in recent years. However, knowledge of the ecotoxicity and microalgae-mediated biodegradation of these novel FQs is limited. In this research, the toxic effects of moxifloxacin (MOX) and gatifloxacin (GAT) on Chlamydomonas reinhardtii as well as their biodegradation and metabolic fate were investigated. The results showed that the toxicity of MOX to C. reinhardtii was higher than that of GAT, and increased with culture time. Chlorophyll fluorescence and pigment content analyses suggested that the decrease in photosynthetic efficiency was primarily caused by the inhibition of electron transport after Q_A in PSII complex. These FQs induced oxidative damage in cells, and the antioxidation mechanisms of C. reinhardtii were analyzed. The maximum MOX removal of 77.67% by C. reinhardtii was achieved at 1 mg/L MOX, whereas the maximum GAT removal of 34.04% was attained at 20 mg/L GAT. The different hydrophilicity and lipophilicity of these FQs resulted in distinct findings in biodegradation experiments. Identification of the transformation products suggested that the likely biodegradation pathways of FQs by C. reinhardtii were hydroxylation, demethylation, and ring cleavage.

Transcriptome analysis of the toxicity response of green macroalga Caulerpa lentillifera J. Agardh to high dissolved arsenite

Arsenic (As) is a hazardous pollutant that negatively impacts the physiological functions of alga. So far, a detailed understanding of algal response to As stress is still lacking. In this study, a transcriptome analysis was performed to illustrate the toxicity response of Caulerpa lentillifera J. Agardh, an edible algae with rich nutrition, to arsenite [As(III)], a toxic form of As. Totally, 1913 differentially expressed genes (DEGs) were screened, of which 642 were up- and 1271 were downregulated in C. lentillifera under As(III) stress (30 mg·L^-1) compared with control. As(III) stress promoted the growth of C. lentillifera at low concentration (0.1 mg·L^-1) and inhibited the growth at high concentration (≥ 0.5 mg·L^-1). Multiple DEGs involved in oxidoreductase activities were significantly affected by As(III), and several DEGs related to antioxidant enzyme activity were downregulated, resulting in suffering from oxidative stress in C. lentillifera. Results also showed that As(III) stress inhibited chlorophyll and carotenoid synthesis, destroyed the integrity of chloroplasts, and interfered with the absorption of light energy, thereby inhibiting photosynthesis in C. lentillifera. The highly enriched ABC transporter-related genes involved in the detoxification process were upregulated under As(III) stress, indicating their critical role in the resistance to As stress in C. lentillifera. The gene expressions for 10 selected DEGs were confirmed by qRT-PCR, showing the reliability of the data revealed by RNA sequencing. Our novel work illustrated the toxicity of C. lentillifera under As(III) stress at the molecular level, serving as a basis for future investigations on the prevention and treatment of such pollutants.

Breaking the Rebellion: Photodynamic Inactivation against Erwinia amylovora Resistant to Streptomycin

Global crop production depends on strategies to counteract the ever-increasing spread of plant pathogens. Antibiotics are often used for large-scale treatments. As a result, Erwinia amylovora, causal agent of the contagious fire blight disease, has already evolved resistance to streptomycin (Sm). Photodynamic Inactivation (PDI) of microorganisms has been introduced as innovative method for plant protection. The aim of this study is to demonstrate that E. amylovora resistant to Sm (E. amylovora^SmR) can be killed by PDI. Two photosensitizers, the synthetic B17-0024, and the natural derived anionic sodium magnesium chlorophyllin (Chl) with cell-wall-permeabilizing agents are compared in terms of their photo-killing efficiency in liquid culture with or without 100 µg/mL Sm. In vitro experiments were performed at photosensitizer concentrations of 1, 10 or 100 µM and 5 or 30 min incubation in the dark, followed by illumination at 395 nm (radiant exposure 26.6 J/cm²). The highest inactivation of seven log steps was achieved at 100 µM B17-0024 after 30 min incubation. Shorter incubation (5 min), likely to represent field conditions, reduced the photo-killing to 5 log steps. Chlorophyllin at 100 µM in combination with 1.2% polyaspartic acid (PASA) reduced the number of bacteria by 6 log steps. While PASA itself caused some light independent toxicity, an antibacterial effect (3 log reduction) was achieved only in combination with Chl, even at concentrations as low as 10 µM. Addition of 100 µg/mL Sm to media did not significantly increase the efficacy of the photodynamic treatment. This study proves principle that PDI can be used to treat plant diseases even if causative bacteria are resistant to conventional treatment. Therefore, PDI based on natural photosensitizers might represent an eco-friendly treatment strategy especially in organic farming.

Microalgae-based livestock wastewater treatment (MbWT) as a circular bioeconomy approach: Enhancement of biomass productivity, pollutant removal and high-value compound production

The intensive livestock activities that are carried out worldwide to feed the growing human population have led to significant environmental problems, such as soil degradation, surface and groundwater pollution. Livestock wastewater (LW) contains high loads of organic matter, nitrogen (N) and phosphorus (P). These compounds can promote cultural eutrophication of water bodies and pose environmental and human hazards. Therefore, humanity faces an enormous challenge to adequately treat LW and avoid the overexploitation of natural resources. This can be accomplished through circular bioeconomy approaches, which aim to achieve sustainable production using biological resources, such as LW, as feedstock. Circular bioeconomy uses innovative processes to produce biomaterials and bioenergy, while lowering the consumption of virgin resources. Microalgae-based wastewater treatment (MbWT) has recently received special attention due to its low energy demand, the robust capacity of microalgae to grow under different environmental conditions and the possibility to recover and transform wastewater nutrients into highly valuable bioactive compounds. Some of the high-value products that may be obtained through MbWT are biomass and pigments for human food and animal feed, nutraceuticals, biofuels, polyunsaturated fatty acids, carotenoids, phycobiliproteins and fertilizers. This article reviews recent advances in MbWT of LW (including swine, cattle and poultry wastewater). Additionally, the most significant factors affecting nutrient removal and biomass productivity in MbWT are addressed, including: (1) microbiological aspects, such as the microalgae strain used for MbWT and the interactions between microbial populations; (2) physical parameters, such as temperature, light intensity and photoperiods; and (3) chemical parameters, such as the C/N ratio, pH and the presence of inhibitory compounds. Finally, different strategies to enhance nutrient removal and biomass productivity, such as acclimation, UV mutagenesis and multiple microalgae culture stages (including monocultures and multicultures) are discussed.

Enhanced biodegradation of chlortetracycline via a microalgae-bacteria consortium

Microbial removal of Chlortetracycline (CTC) at low CTC concentrations (in the order of 10-20 mg/L) has been reported. In this study, a novel microalgae-bacteria consortium was developed for effective CTC biodegradation at higher concentrations (up to 80 mg/L). The microalgae-bacteria consortium is resistant to up to 80 mg/L CTC, while the pure microalgal culture could only tolerate 60 mg/L CTC. CTC removal in the initial 12 h was primarily via biosorption by the microalgae-bacteria consortium and the adsorption capacity increased from 61.71 to 102.53 mg/g biomass in 12 h. Further, CTC biodegradation by the microalgae-bacteria consortium was catalyzed by extracellular enzymes secreted under antibiotic stress. The symbiotic bacterial diversity was analyzed by high throughput sequencing. The aerobic bacteria Porphyrobacter and Devosia were the dominant genera in the consortium. In the presence of CTC, a microbial community shift occurred with Chloroptast, Spingopyxis, and Brevundimonas being the dominant genera.

Growth and metabolic responses to methyl viologen (1,1'-dimethyl - 4,4'-bipyridinium dichloride) on Chlorella vulgaris

Aquatic environments are especially susceptible to being contaminated by pesticides used in agricultural fields. Methyl viologen (MV) is an herbicide with high effectiveness for the control of unwanted land plants; however, it also has a high toxicity towards the algae in the aquatic environment. The objective of this work was to describe the effect of MV on photosynthetic metabolism and its relationship with respiration, growth and the content of photosynthetic pigments of Chlorella vulgaris. The cultures of C. vulgaris were exposed for 72 h at different concentrations of methyl viologen. The results show that growth, pigment content and metabolic activity decrease as the concentration of MV increases. Analysis of the photochemical activity indicates that MV produces an inhibition of electron transport between quinone A and quinone B of photosystem II. The inhibition of photosynthetic electron transport is directly related to the reduction of metabolic activity and cell growth. The results found in this research show that methyl viologen can be a toxic pollutant for primary producers in aquatic environments.

Susceptibility of phytoplankton to the increasing presence of active pharmaceutical ingredients (APIs) in the aquatic environment: A review

Human and veterinary pharmaceuticals either in the form of un-metabolized, incompletely metabolized, and metabolized drugs are increasingly present in aquatic ecosystems. These active pharmaceutical ingredients from pharmaceutical industries, hospitals, agricultural, and domestic discharges find their way into water systems - where they adversely affect non-target organisms like phytoplankton. Different aspects of phytoplankton life; ranging from growth, reproduction, morphology, physiology, biochemical composition, oxidative response, proteomics, and transcriptomics are altered by pharmaceuticals. This review discusses the currently available information on the susceptibility of phytoplankton to the ever-increasing presence of pharmaceutical products in the aquatic environment by focusing on the effect of APIs on the physiology, metabolome, and proteome profiles of phytoplankton. We also highlight gaps in literature concerning the salient underlining biochemical interactions between phytoplankton communities and pharmaceuticals that require an in-depth investigation. This is all in a bid to understand the imminent dangers of the contamination of water bodies with pharmaceutical products and how this process unfavorably affects aquatic food webs.

The Role of Selected Wavelengths of Light in the Activity of Photosystem II in Gloeobacter violaceus

Gloeobacter violaceus is a cyanobacteria species with a lack of thylakoids, while photosynthetic antennas, i.e., phycobilisomes (PBSs), photosystem II (PSII), and I (PSI), are located in the cytoplasmic membrane. We verified the hypothesis that blue–red (BR) light supplemented with a far-red (FR), ultraviolet A (UVA), and green (G) light can affect the photosynthetic electron transport chain in PSII and explain the differences in the growth of the G. violaceus culture. The cyanobacteria were cultured under different light conditions. The largest increase in G. violaceus biomass was observed only under BR + FR and BR + G light. Moreover, the shape of the G. violaceus cells was modified by the spectrum with the addition of G light. Furthermore, it was found that both the spectral composition of light and age of the cyanobacterial culture affect the different content of phycobiliproteins in the photosynthetic antennas (PBS). Most likely, in cells grown under light conditions with the addition of FR and G light, the average antenna size increased due to the inactivation of some reaction centers in PSII. Moreover, the role of PSI and gloeorhodopsin as supplementary sources of metabolic energy in the G. violaceus growth is discussed.

Defensive responses of microalgal-bacterial granules to tetracycline in municipal wastewater treatment

Nowadays, tetracycline has been frequently detected in municipal wastewater, posing a pressing threat for wastewater treatment. This study investigated the defensive responses of microalgal-bacterial granules to tetracycline. It was found that the physical structure of microalgal-bacterial granules tended to shift from individual granules to loosely inter-connected agglomerates. In response to tetracycline, microalgae instead of bacteria in granules were found to produce more low molecular weight polysaccharides in extracellular polymeric substances (EPS), which increased from 0.26 mg C/g VSS in the control to 17.81 and 25.15 mg C/g VSS after being exposed to 1 and 10 mg/L of tetracycline, respectively. It was further revealed that tetracycline could bind to tryptophan in EPS proteins, and this action in turn could help to alleviate the direct toxicity of tetracycline to microorganisms in granules. Moreover, it appeared that the abundance of Pseudomonas-carrying tetracycline resistant genes increased substantially, together with gradual disappearance of Cyanobacteria.

Ecotoxicological effects of sulfonamides and fluoroquinolones and their removal by a green alga (Chlorella vulgaris) and a cyanobacterium (Chrysosporum ovalisporum)

In recent years, antibiotic pollution has become worse, especially in China. In this study, the ecotoxicological effects of four frequently used antibiotics with different lipophilic degrees (log Kow) (sulfadiazine (SD), sulfamethazine (SM2), enrofloxacin (ENR), and norfloxacin (NOR)) at four concentrations of 1, 5, 20, and 50 mg L^-1 were examined using batch cultures of green alga Chlorella vulgaris and cyanobacterium Chrysosporum ovalisporum for 16 days based on changes in chlorophyll fluorescence parameters (chl a, Fv/Fm, and ΦPSII) and responses of the antioxidant system. Besides, the antibiotics removal efficiencies of the two microalgae were investigated. Sulfonamides (SD and SM2) had no significant inhibitory effect on the growth of C. ovalisporum, but had an inhibitory effect on C. vulgaris, whereas fluoroquinolones (ENR and NOR) significantly inhibited C. ovalisporum. The activities of superoxide dismutase, catalase, and glutathione reductase suggested that C. vulgaris was more tolerant to these antibiotics than C. ovalisporum. The increased malondialdehyde level in both algae indicated their tolerance against antibiotics. When compared with C. ovalisporum, C. vulgaris presented better capacity to remove antibiotics. In summary, the four antibiotics exerted time- or concentration-dependent ecotoxicological effects on the microalgae examined, whereas the microalgae could remove the antibiotics based on the log Kow of the antibiotics. The findings of this study contribute to effective understanding of the ecotoxicological effects of antibiotics and their removal by microalgae.

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

Sulfadiazine (SD), sulfamerazine (SM1), and sulfamethazine (SM2) are widely used and disorderly discharged into surface water, causing contamination of lakes and rivers. However, microalgae are regard as a potential resource to alleviate and degrade antibiotic pollution. The physiological changes of Chlorella vulgaris in the presence of three sulfonamides (SAs) with varying numbers of –CH₃ groups and its SA-removal efficiency were investigated following a 7-day exposure experiment. Our results showed that the growth inhibitory effect of SD (7.9–22.6%), SM1 (7.2–45.9%), and SM2 (10.3–44%) resulted in increased proteins and decreased soluble sugars. Oxidative stress caused an increase in superoxide dismutase and glutathione reductase levels but decreased catalase level. The antioxidant responses were insufficient to cope-up with reactive oxygen species (hydrogen peroxide and superoxide anion) levels and prevent oxidative damage (malondialdehyde level). The ultrastructure and DNA of SA-treated algal cells were affected, as evident from the considerable changes in the cell wall, chloroplast, and mitochondrion, and DNA migration. C. vulgaris-mediated was able to remove up to 29% of SD, 16% of SM1, and 15% of SM2. Our results suggest that certain concentrations of specific antibiotics may induce algal growth, and algal-mediated biodegradation process can accelerate the removal of antibiotic contamination.

Antibiotics induced alterations in cell density, photosynthesis, microcystin synthesis and proteomic expression of Microcystis aeruginosa during CuSO4 treatment

Antibiotic contaminants have the potential to interfere with the control of cyanobacterial bloom through generating hormesis in cyanobacteria at current contamination level of ng L^-1. This study investigated the influence of a mixture of four frequently detected antibiotics, amoxicillin, ciprofloxacin, sulfamethoxazole and tetracycline, during the treatment of Microcystis aeruginosa by copper sulfate (CuSO₄) algaecide. CuSO₄ significantly (p <  0.05) inhibited cell density, growth rate, F_v/F_m value, chlorophyll a content and microcystin production ability of M. aeruginosa in a dose-dependent manner at application doses of 0.01-0.05 mg L^-1. Besides, CuSO₄ inhibited oxidation-reduction process, photosynthesis and biosynthesis in M. aeruginosa at the proteomic level. Preventative application of CuSO₄ to a low density (4 × 10⁵ cells mL^-1) of M. aeruginosa effectively prevented the formation of bloom at low CuSO₄ doses, which is a possible route for eliminating the negative effects of CuSO₄ algaecide in aquatic environments. The presence of mixed antibiotics alleviated the toxicity of CuSO₄ in M. aeruginosa, through the downregulation of cation transport proteins and the upregulation of proteins related with chlorophyll a synthesis, photosynthesis, gene expression and oxidation-reduction. Mixed antibiotics also promoted microcystin synthesis in CuSO₄ treated cells through the upregulation of microcystin synthetases. Mixed antibiotics significantly (p <  0.05) increased cell density, growth rate, F_v/F_m value, chlorophyll a content and microcystin production ability in CuSO₄ treated cells at test concentrations of 80 and 200 ng L^-1. A no-impact threshold of 20 ng L^-1 for mixed antibiotics (5 ng L^-1 for each antibiotic) was suggested for eliminating the interference of antibiotic contaminants on cyanobacterial bloom control.

Use of microalgae based technology for the removal of antibiotics from wastewater: A review

The antibiotic resistance induced by the release of antibiotics to the environment has urged research towards developing effective technologies for antibiotic removal from wastewater. Traditional technologies such as activated sludge processes are not effective for antibiotic removal. Recently, microalgae-based technology has been explored as a potential alternative for the treatment of wastewater containing antibiotics by adsorption, accumulation, biodegradation, photodegradation, and hydrolysis. In this review, the toxicities of antibiotics on microalgae, the mechanisms of antibiotic removal by microalgae, and the integration of microalgae with other technologies such as ultraviolet irradiation (photocatalysis), advanced oxidation, and complementary microorganism degradation for antibiotic removal were discussed. The limitations of current microalgae-based technology and future research needs were also discussed.

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

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

Effect of elevated benzophenone-4 (BP4) concentration on Chlorella vulgaris growth and cellular metabolisms

Benzophenone-4 (BP4), as the raw material of common sunscreen products, usually shows strong eco-toxicity and endocrine-disrupting activity in aquatic animals. However, the potential adverse effect of BP4 on aquatic vegetation is still unclear. In order to evaluate the inhibitory effect of BP4 on phytoplankton, wild and acclimated Chlorella vulgaris was used as representative aquatic plant cells and experimental studies were conducted on the characteristics of its growth and cellular metabolisms upon exposure to elevated BP4 concentrations (1, 5, 10, 20, 50, and 100 mg L^-1). C. vulgaris basically appeared low sensitivity to BP4 exposure because the 96-h EC₅₀ was measured as 65.16 mg L^-1 for its wild type. The 96-h EC₅₀ of the acclimated type, which was pre-exposed to 10 mg L^-1 of BP4 and transferred twice, was 140.76 mg L^-1. By cellular response tests regarding non-enzymatic antioxidants carotenoid content, malondialdehyde (MDA), enzyme antioxidant superoxide dismutase (SOD) activity, and the photosynthetic efficiency, it was clarified that increasing exposure concentration elevated the hindrance to cellular metabolism. However, the rate of BP4 utilization as substrates for C. vulgaris growth showed a trend of decreasing with increasing BP4 concentration. The higher 96-h EC₅₀ value of the acclimated C. vulgaris to BP4 inhibition than the wild C. vulgaris showed the enhanced tolerance capability; however, the continuous stress response of acclimated type should be taken into account when using microalgae species for toxicity assessment.

Advanced nutrient removal from surface water by a consortium of attached microalgae and bacteria: A review

Innovative and cost-effective technologies for advanced nutrient removal from surface water are urgently needed for improving water quality. Conventional biotechnologies, such as ecological floating beds, or constructed wetlands, are not effective in removing nutrients present at low-concentration. However, microalgae-bacteria consortium is promising for advanced nutrient removal from wastewater. Suspended algal-bacterial systems can easily wash out unless the hydraulic retention time is long, attached microalgae-bacteria consortium is more realistic. This critical review summarizes the fundamentals and status of attached microalgae-bacteria consortium for advanced nutrient removal from surface water. Key advantages are the various nutrient removal pathways, reduction of nutrients to very low concentration, and diversified photobioreactor configurations. Challenges include poor identification of functional species, poor control of the community composition, and long start-up times. Future research should focus on the selection and engineering of robust microbial species, mathematical modelling of the composition and functionality of the consortium, and novel photobioreactor configurations.

Differential accumulation of photosynthetic proteins regulates diurnal photochemical adjustments of PSII in common fig (Ficus carica L.) leaves

Molecular processes involved in photosystem II adaptation of woody species to diurnal changes in light and temperature conditions are still not well understood. Regarding this, here we investigated differences between young and mature leaves of common fig (Ficus carica L.) in photosynthetic performance as well as accumulation of the main photosynthetic proteins: light harvesting complex II, D1 protein and Rubisco large subunit. Investigated leaf types revealed different adjustment mechanisms to keep effective photosynthesis. Rather stable diurnal accumulation of light harvesting complex II in mature leaves enabled efficient excitation energy utilization (negative L-band) what triggered faster D1 protein degradation at high light. However, after photoinhibition, greater accumulation of D1 during the night enabled them faster recovery. So, the most photosynthetic parameters, as the maximum quantum yield for primary photochemistry, electron transport and overall photosynthetic efficiency in mature leaves successfully restored to their initial values at 1a.m. Reduced connectivity of light harvesting complexes II to its reaction centers (positive L-band) in young leaves increased dissipation of excess light causing less pressure to D1 and its slower degradation. Decreased electron transport in young leaves, due to reduced transfer beyond primary acceptor Q_A^- most probably additionally induced degradation of Rubisco large subunit what consequently led to the stronger decrease of overall photosynthetic efficiency in young leaves at noon.