Influence of ofloxacin on photosystems I and II activities of Microcystis aeruginosa and the potential role of cyclic electron flow

Occurrence and dissemination of antibiotics and antibiotic resistance in aquatic environment and its ecological implications: a review

The occurrence of antibiotics and antibiotic-resistant bacteria (ARBs), genes (ARGs), and mobile genetic elements (MGEs) in aquatic systems is growing global public health concern. These emerging micropollutants, stemming from improper wastewater treatment and disposal, highlight the complex and evolving nature of environmental pollution. Current literature reveals potential biases, such as a geographical focus on specific regions, leading to an insufficient understanding of the global distribution and dynamics of antibiotic resistance in aquatic systems. There is methodological inconsistency across studies, making it challenging to compare findings. Potential biases include sample collection inconsistencies, detection sensitivity variances, and data interpretation variability. Gaps in understanding include the need for comprehensive, standardized long-term monitoring programs, elucidating the environmental fate and transformation of antibiotics and resistance genes. This review summarizes current knowledge on the occurrence and dissemination of emerging micropollutants, their ecological impacts, and the global health implications of antimicrobial resistance. It highlights the need for interdisciplinary collaborations among researchers, policymakers, and stakeholders to address the challenges posed by antibiotic resistance in aquatic resistance in aquatic systems effectively. This review highlights widespread antibiotic and antibiotic resistance in aquatic environment, driven by human and agricultural activities. It underscores the ecological consequences, including disrupted microbial communities and altered ecosystem functions. The findings call for urgent measures to mitigate antibiotics pollution and manage antibiotic resistance spread in water bodies.

Multi-biomarker response of cyanobacteria Synechocystis salina and Microcystis aeruginosa to diclofenac

The cyanobacterial response to pharmaceuticals is less frequently investigated compared to green algae. Pharmaceuticals can influence not only the growth rate of cyanobacteria culture, but can also cause changes at the cellular level. The effect of diclofenac (DCF) as one of the for cyanobacteria has been rarely tested, and DCF has never been applied with cellular biomarkers. The aim of this work was to test the response of two unicellular cyanobacteria (Synechocystis salina and Microcystis aeruginosa) toward DCF (100 mg L-1) under photoautotrophic growth conditions. Such endpoints were analyzed as cells number, DCF uptake, the change in concentrations of photosynthetic pigments, the production of toxins, and chlorophyll a in vivo fluorescence. It was noted that during a 96 h exposure, cell proliferation was not impacted. Nevertheless, a biochemical response was observed. The increased production of microcystin was noted for M. aeruginosa. Due to the negligible absorption of DCF into cells, it is possible that the biochemical changes are induced by an external signal. The application of non-standard biomarkers demonstrates the effect of DCF on microorganism metabolism without a corresponding effect on biomass. The high resistance of cyanobacteria to DCF and the stimulating effect of DCF on the secretion of toxins raise concerns for environment biodiversity.

Anticyanobacterial effect of p-coumaric acid on Limnothrix sp. determined by proteomic and metabolomic analysis

Regulating photosynthetic machinery is a powerful but challenging strategy for selectively inhibiting bloom-forming cyanobacteria, in which photosynthesis mainly occurs in thylakoids. P-coumaric acid (p-CA) has several biological properties, including free radical scavenging and antibacterial effects, and studies have shown that it can damage bacterial cell membranes, reduce chlorophyll a in cyanobacteria, and effectively inhibit algal growth at concentrations exceeding 0.127 g/L. Allelochemicals typically inhibit cyanobacteria by inhibiting photosynthesis; however, research on inhibiting harmful algae using phenolic acids has focused mainly on their inhibitory and toxic effects and metabolite levels, and the molecular mechanism by which p-CA inhibits photosynthesis remains unclear. Thus, we examined the effect of p-CA on the photosynthesis of Limnothrix sp. in detail. We found that p-CA inhibits algal growth and damages photosynthesis-related proteins in Limnothrix sp., reduces carotenoid and allophycocyanin levels, and diminishes the actual quantum yield of Photosystem II (PSII). Moreover, p-CA significantly altered algal cell membrane protein systems, and PSII loss resulting from p-CA exposure promoted reactive oxygen species production. It significantly altered algae cell membrane protein systems. Finally, p-CA was found to be environmentally nontoxic; 80 % of 48-h-old Daphnia magna larvae survived when exposed to 0.15 g/L p-CA. These findings provide insight into the mechanism of cyanobacterial inhibition by p-CA, providing a more practical approach to controlling harmful algal blooms.

Effects of low concentration of gallic acid on the growth and microcystin production of Microcystis aeruginosa

Gallic acid (GA) is an allelochemical that has been utilized in high concentrations for the management of harmful algal blooms (HABs). However, there is limited knowledge regarding its impact on the growth of M. aeruginosa as the GA concentration transitions from high to low during the HABs control process. This study has revealed that as the GA concentration decreases (from 10 mg/L to 0.001 μg/L), a dose-response relationship becomes apparent in the growth of M. aeruginosa and microcystin production, characterized by high-dose inhibition and low-dose stimulation. Notably, at the concentration of 0.1 μg/L GA, the most significant growth-promoting effect on both growth and MCs synthesis was observed. The growth rate and maximum cell density were increased by 1.09 and 1.16 times, respectively, compared to those of the control group. Additionally, the contents of MCs synthesis saw a remarkable increase, up by 1.85 times. Furthermore, lower GA concentrations stimulated the viability of cyanobacterial cells, resulting in substantially higher levels of reactive oxygen species (ROS) and chlorophyll-a (Chl a) compared to other concentrations. Most importantly, the expression of genes governing MCs synthesis was significantly upregulated, which appears to be the primary driver behind the significantly higher MCs levels compared to other conditions. The ecological risk quotient (RQ) value of 0.1 μg/L GA was the highest of all experimental groups, which was approximately 30 times higher than that of the control, indicating moderate risk. Therefore, it is essential to pay attention to the effect of M. aeruginosa growth, metabolism and water ecological risk under the process of reducing GA concentration after dosing during the HABs control process.

Combined effects of fluoroquinolone antibiotics and organophosphate flame retardants on Microcystis aeruginosa

As freshwater harmful algal blooms continue to rise in frequency and severity, increasing focus is made on the effects of mixed pollutants and the dominant cyanobacterial species Microcystis aeruginosa (M. aeruginosa). However, few studies have investigated whether M. aeruginosa has a synergistic relationship with two common pollutants, namely, organophosphate flame retardants (OPFRs) and fluoroquinolone antibiotics (FQs). In this paper, three FQs and three OPFRs commonly detected in freshwaters were selected to construct a ternary mixture of FQs, a ternary mixture of OPFRs, and a six-component mixture of OPFRs and FQs. The effects of single substance and mixture on the growth of M. aeruginosa were determined at 24, 48, 72, and 96 h, and the toxicities of the mixture were evaluated by concentration addition model and independent action model. The results showed that the mixture of FQs and the mixture of OPFRs do not show toxicological interaction. However, partial mixtures of OPFRs and FQs showed antagonism or synergism at different concentrations and times. This indicated that combined toxicities of OPFRs and FQs on M. aeruginosa were mixture ratio dependent, concentration dependent and time dependent. This study improves our understanding of the role of OPFRs and FQs in cyanobacterial outbreaks of Microcystis.

The effects of aqueous extract from watermelon (Citrullus lanatus) peel on the growth and physiological characteristics of Dolichospermum flos-aquae

Nowadays, the increasing Dolichospermum (Anabaena) blooms pose a major threat to the aquatic environment and public health worldwide. The use of naturally derived chemicals from plants to control cyanobacteria blooms has recently received a tremendous amount of attention. This study investigates the possibility of transforming watermelon peel (WMP) into a biological resource to allelopathically inhibit Dolichospermum flos-aquae blooms. The results demonstrated that the growth of D. flos-aquae was efficiently restricted by the aqueous extract of watermelon peel (WMPAE) in a concentration-dependent manner. Cell viability decreased quickly, intracellular structural damage occurred, chlorophyll a in algal cells degraded, and photosynthesis was clearly inhibited. At the same time, the levels of reactive oxygen species in viable cells increased significantly, as did malondialdehyde levels, indicating that WMPAE elucidated strong oxidative stress and corresponding damage to D. flos-aquae. Capsular polysaccharide (CPS) levels increased in all treatment groups, which represents an adaptive response indicative of the development of resistance to WMPAE stress and oxidative damage. Despite this, WMPAE had clear inhibitory effects on D. flos-aquae. These findings provide fundamental information on an allelopathic system that could be a novel and attractive approach for suppressing D. flos-aquae blooms in small aquatic environments, especially aquaculture ponds.

Silicon enhanced the resistance of Chinese cabbage (Brassica rapa L. ssp. pekinensis) to ofloxacin on the growth, photosynthetic characteristics and antioxidant system

The negative impact of the misuse of antibiotics on agriculture and human health has become a popular research topic with the increasing usage of antibiotics; however, little information is available about the mechanisms of OFL (ofloxacin) and Si (silicon). In this experiment, we applied 7 OFL concentrations to two Chinese cabbage cultivars (Qinghua and Biyu) to screen proper OFL concentrations. OFL concentrations of 0, 1, 2.5 and 5 mg L-1 were selected for the subsequent test and 1.2 mmol L-1 Si was used as mitigation. The results showed that Biyu suffered more damage than Qinghua and the injury degree increased in a concentration-dependent manner. With increasing OFL concentrations, the photosynthetic fluorescence was weakened significantly; under 1, 2.5 and 5 mg L-1 OFL, the Pn reduced by 5.35%, 35.92% and 43.62% in Qinghua and 33.98%, 41.94% and 64.66% in Biyu, respectively. The production rate of O2-, H2O2 and the MDA content were increased and Biyu appeared higher increase rates. In addition, the antioxidant enzymes contents first increased and then decreased and that of Qinghua increased more than Biyu. Si ensured the growth under OFL and protected its photosynthetic ability. Under the OFL1+Si, OFL2.5 + Si and OFL5+Si treatments, Pn increased by 3.91%, 15.95 and 15.69% in Qinghua and 28.82%, 20.40% and 39.01% in Biyu. Si also maintained the structural integrity of leaf organelles and improved the scavenging ability of ROS by increasing the activity and relative gene expression of antioxidant enzymes. Moreover, varietal differences may play a more important role than Si.

Sources of antibiotics pollutants in the aquatic environment under SARS-CoV-2 pandemic situation

During the last decades, the growth of concern towards different pollutants has been increasing due to population activities in large cities and the great need for food production by the agri-food industry. The effects observed in specific locations have shown the impact over the environment in air, soil and water. Specifically, the current pandemic of COVID-19 has brought into the picture the intensive use of different medical substances to treat the disease and population intensive misuse. In particular, the use of antibiotics has increased during the last 20 years with few regulations regarding their excessive use and the disposal of their residues from different sources. Within this review, an overview of sources of antibiotics to aquatic environments was done along with its impact to the environment and trophic chain, and negative effects of human health due prolonged exposure which endanger the environment, population health, water, and food sustainability. The revision indicates the differences between sources and its potential danger due toxicity, and accumulation that prevents water sustainability in the long run.

Ecotoxicological effects, environmental fate and risks of pharmaceutical and personal care products in the water environment: A review

Due to the extensive use and incomplete removal, pharmaceutical and personal care products (PPCPs) are introduced into the water continuously. It has been proved that the unique properties of PPCPs are influential to organisms and the environment, and gradually affect human health. In this paper, the toxicological effects of typical PPCPs, and the environmental behavior of PPCPs in aquatic are reviewed. The risk assessments of PPCPs in the water are summarized. The research directions of environmental toxicology research of PPCPs in the future are proposed. Many PPCPs were found to be toxic or even highly toxic toward aquatic organisms, and have the potential for bioaccumulation. It is essential to study the acute and long-term toxicity of PPCPs and their metabolites, evaluate the environmental behaviors and make a reasonable assessment of ecotoxicology and human health risks of PPCPs.

Effects of antibiotics stress on growth variables, ultrastructure, and metabolite pattern of Brassica rapa ssp. chinensis

Antibiotics frequently contaminate agricultural fields and through plant uptake enter into the food chain. This study aimed to explore the effects of antibiotics; tetracycline (TC), oxytetracycline (OTC) and norfloxacin (NF) on the growth, cell ultrastructure, and metabolite pattern of Brassica rapa ssp. chinensis. Oxytetracycline accumulated more than other antibiotics followed by TC and NF. Plant growth, chlorophyll fluorescence, and antioxidant activities were negatively affected under all antibiotic treatments. Ultrastructural investigation of mesophyll of leaves performed by transmission electron microscopy indicated that antibiotic stress caused the changes in thylakoid orientation, number of plastoglobuli, and starch grains. Identification of functional groups through Fourier transform infrared analysis indicated that carboxyl group, carbonate and ammonium ions are involved in the adsorption of antibiotics. The metabolic profiling of B. rapa leaves demonstrated that all of the antibiotics treatments distorted phenylalanine, tyrosine and tryptophan biosynthesis, d-glutamine and d-glutamate metabolism, alanine, aspartate and glutamate metabolism, phenylalanine metabolism and TCA cycle. Metabolic alterations as a result of antibiotics stress provide insights of metabolites that affect the physiological changes attributed to antibiotic stress. These results will improve the understanding of antibiotic contamination effects on plants.

Light modulates the effect of antibiotic norfloxacin on photosynthetic processes of Microcystis aeruginosa

Norfloxacin is one of the widely used antibiotics, often detected in aquatic ecosystems, and difficultly degraded in the environment. However, how norfloxacin affects the photosynthetic process of freshwater phytoplankton is still largely unknown, especially under varied light conditions. In this study, we investigated photosynthetic mechanisms of Microcystis aeruginosa in responses to antibiotic norfloxacin (0-50 μg/L) for 72 h under low (LL; 50 μmol photons m^-2 s^-1) and high (HL; 250 μmol photons m^-2 s^-1) growth light regimes. We found that environmentally related concentrations of norfloxacin inhibited the growth rate and operational quantum yield of photosynthesis system II (PSII) of M. aeruginosa more under HL than under LL, suggesting HL increased the toxicity of norfloxacin to M. aeruginosa. Further analyses showed that norfloxacin deactivated PSII reaction centers under both growth light regimes with increased minimal fluorescence yields only under HL, suggesting that norfloxacin not only damaged reaction centers of PSII, but also inhibited energy transfer among phycobilisomes in M. aeruginosa under HL. However, non-photosynthetic quenching decreased in the studied species by norfloxacin exposure under both growth light regimes, suggesting that excess energy might not be efficiently dissipated as heat. Also, we found that reactive oxygen species (ROS) content increased under norfloxacin treatments with a higher ROS content under HL compared to LL. In addition, HL increased the absorption of norfloxacin by M. aeruginosa, which could partly explain the high sensitivity to norfloxacin of M. aeruginosa under HL. This study firstly reports that light can strongly affect the toxicity of norfloxacin to M. aeruginosa, and has vitally important implications for assessing the toxicity of norfloxacin to aquatic microorganisms.

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 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.

Ofloxacin induces etiolation in Welsh onion leaves

Antibiotic pollution has become an important global issue, and ofloxacin (OFL) is widely used worldwide. However, little is known about the potential adverse effects of OFL on plants. We assessed the toxic effects of OFL on Welsh onion and explored its toxicity mechanism. The leaf pigment content increased in 0.1 mg/L of OFL but decreased in a dose-dependent manner (0.5-2 mg/L OFL) until leaf etiolation. The ultrastructure of leaves showed that the treatment of 2 mg/L OFL produced significant toxicity. Furthermore, photosynthetic and fluorescence parameters were negatively affected by OFL treatment. The photosynthetic electron transport chain was significantly inhibited by OFL treatment, especially between Q_A and Q_B. The hydrogen peroxide and malondialdehyde content also increased with OFL concentration, indicating that antioxidant enzymes' role in antibiotic response is limited. In conclusion, OFL can damage chloroplasts by promoting ROS accumulation, which results in the etiolation of Welsh onion leaves.

Removal of ofloxacin with biofuel production by oleaginous microalgae Scenedesmus obliquus

Microalgae-based technology is an environmental-friendly and cost-effective method for biofuel production and pollutants removal. In this study, Scenedesmus obliquus (S. obliquus) was cultured with varying concentrations of ofloxacin (OFL) in BG11 medium. In the algae-antibiotics culture system, S. obliquus could effectively remove OFL with a concentration of 10 mg/L; however, the removal efficiency was restricted under higher doses (20-320 mg/L). Meanwhile, the lipid content significantly increased by 21.10-49.63%, which was caused by carbon being converted from carbohydrate to lipid. The greatest lipid productivity (7.53 mg/L/d) occurred at an OFL concentration of 10 mg/L, which was approximately 1.5-fold greater than the control. Moreover, S. obliquus cultured with OFL was able to improve the biodiesel quality due to an increase of saturated fatty acids and a decrease of unsaturated fatty acids. This study demonstrates that an algae-antibiotics system is a promising solution to simultaneously achieve antibiotics removal and biofuel production.

Sulfamethoxazole and tetracycline induced alterations in biomass, photosynthesis, lipid productivity, and proteomic expression of Synechocystis sp. PCC 6803

Since antibiotics show hormesis effects in cyanobacteria at the nanogram per liter concentration level, the possibility for two commonly used antibiotics (sulfamethoxazole and tetracycline) to increase lipid productivity in Synechocystis sp. PCC 6803 was assessed in the present study. The two target antibiotics significantly promoted (p < 0.05) the biofuel productivity of Synechocystis sp. PCC 6803 through the increase of both biomass and lipid content. Sulfamethoxazole and tetracycline significantly stimulated (p < 0.05) cyanobacterial growth by upregulating proteins related to cell differentiation, cell division, and gene expression; significantly enhanced (p < 0.05) the photosynthetic activity by upregulating photosynthesis-related proteins; and significantly increased (p < 0.05) the lipid content in cyanobacterial cells by downregulating carbohydrate catabolic proteins and carbohydrate transport proteins. Due to the altered expression pattern of biosynthesis-related proteins, the two antibiotics increased the proportion of monounsaturated fatty acids, while tetracycline reduced the proportions of saturated and polyunsaturated fatty acids. The changes in fatty acid composition may improve the combustion performance of biofuel. This study provided insights into the application of antibiotics in cyanobacteria-based biofuel production. Graphical abstract.

Physiological and morphological response of Aphanizomenon flos-aquae to watermelon (Citrullus lanatus) peel aqueous extract

Natural algaecides are more likely to be specific and biodegradable, and may offer an environmentally friendly method for control of cyanobacterial blooms. We explored, for the first time, the potential for watermelon peel aqueous extract (WMPAE) to control the growth of the harmful blue-green alga Aphanizomenon flos-aquae. The growth inhibition and several physiological parameters of A. flos-aquae, in response to WMPAE, were analyzed. Results showed that WMPAE significantly inhibited the growth of A. flos-aquae in a concentration-dependent way. The highest inhibition reached 94 % after 3 days' treatment with 6 g L^-1 of WMPAE and a significant effect was obtained with lower doses and shorter times as well. The cell viability decreased quickly, cell shape changed, and intracellular structural damage occurred. At the same time, the antioxidant enzymes (superoxide dismutase SOD, catalase CAT and peroxidase POD) and malondialdehyde (MDA) levels all increased significantly, indicating that WMPAE between 2-6 g L^-1 induced severe oxidative stress and damage to A. flos-aquae. Moreover, production of the four pigments chlorophyll a (Chl a), carotenoids, phycocyanin (PC), and allophycocyanin (APC) were all stimulated, though photosynthesis of A. flos-aquae was clearly inhibited. The maximum quantum yield of photosystem II (F_v/F_m) and the effective quantum yield of photosystem II ( F_v^'/F_m^') declined sharply, suggesting the decreased photosystem capacity of A. flos-aquae to convert light energy into chemical energy. In addition, non-photochemical quenching (NPQ) of A. flos-aquae increased after a very short time exposure to WMPAE, and decreased significantly with prolonged exposure time, which indicated the failure of photo protection mechanisms. These results suggest that the loss of cell viability, and increases in oxidative stress, and damage to intracellular structure and photosynthetic systems might be the mechanisms for the inhibitory effects. Our results suggested that WMPAE could be a novel and effective approach for controlling the growth of A. flos-aquae in aquatic environments.

Accumulation characteristics and biological response of ginger to sulfamethoxazole and ofloxacin

The potential risk to human health of antibiotics that pass through the food chain has become an important global issue, but there are few reports on the response of ginger (Zingiber officinale) to antibiotic pollution. In this study, we investigated the enrichment characteristics and biological response of ginger to sulfamethoxazole (SMZ) and ofloxacin (OFL) residues, which are common in the environment. Lower levels of SMZ, OFL and their combined duplex treatment (SMZ+OFL) promoted the growth of ginger, but the critical doses necessary to stimulate growth differed among treatments: 10 mg L-1 SMZ, 1 mg L-1 OFL and 1 mg L-1 (SMZ+OFL) had the strongest stimulating effects. At higher dosages, the root growth and light energy utilization efficiency of ginger were impaired, and (SMZ+OFL) had the strongest inhibitory effect. Treatments with lower levels of antibiotics had no significant effect on reactive oxygen species and antioxidant enzyme activities. However, when SMZ, OFL and SMZ+OFL concentrations exceeded 10 mg L-1, the contents of H2O2, O2- and MDA continued to increase, while the activities of SOD, POD, CAT first increased and then decreased, especially in SMZ+OFL. Ginger accumulated more SMZ and OFL in rhizomes and less in leaves, and accumulation increased significantly as antibiotic concentration increased. When SMZ concentration was 1 mg L-1, the SMZ concentrations in rhizomes, roots, and leaves were 0.23, 0.15, and 0.05 mg kg-1, respectively, and the residual SMZ in the rhizome was 2.3 times higher than the maximum residue limit. The abundance of the resistance genes sul1, sul2, qnrS, and intI1 increased with increasing antibiotic concentrations, and intI1 abundance was the highest. OFL induced higher levels of intI1 expression than did SMZ.

Antibiotics promoted the recovery of Microcystis aeruginosa after UV-B radiation at cellular and proteomic levels

Elevated UV-B radiation due to ozone layer depletion may prevent the growth of bloom-forming cyanobacteria in aquatic environments, while antibiotic contaminants may cause effects opposite to that of UV-B due to hormesis. This study investigated the influence of a quaternary antibiotic mixture on Microcystis aeruginosa after UV-B radiation through a 15-day exposure test. UV-B radiation extended the lag phase of M. aeruginosa at doses of 600 and 900 mJ/cm², and significantly (p < 0.05) reduced the growth rate and the F_v/F_m value at doses of 300-900 mJ/cm². Although UV-B radiation significantly (p < 0.05) stimulated the microcystin production ability in each cyanobacterial cell, the total microcystin concentration still significantly (p < 0.05) decreased due to the reduction of cell density. Mixed antibiotics and UV-B regulated the proteomic expression profile of M. aeruginosa in different manners. UV-B radiation upregulated 19 proteins and downregulated 49 proteins in M. aeruginosa, while mixed antibiotics upregulated 45 proteins and downregulated 25 proteins in UV-B treated cells. Mixed antibiotics significantly (p < 0.05) stimulated growth and photosynthesis, increased cell density and microcystin concentration, and reduced oxidative stress in UV-B treated cells through the upregulation of proteins involved in photosynthesis, biosynthesis, cell division, oxidation-reduction, gene expression and microcystin synthesis. This study verified the hypothesis that antibiotics accelerated the recovery of M. aeruginosa from UV-B induced damage. A safe threshold of 20 ng/L was suggested for mixed antibiotics (5 ng/L for each antibiotic), in order to eliminate the stimulatory effects of antibiotics on bloom-forming cyanobacteria.

Anthropogenic contaminants of high concern: Existence in water resources and their adverse effects

Existence of anthropogenic contaminants (ACs) in different environmental matrices is a serious and unresolved concern. For instance, ACs from different sectors, such as industrial, agricultural, and pharmaceutical, are found in water bodies with considerable endocrine disruptors potency and can damage the biotic components of the environment. The continuous ACs exposure can cause cellular toxicity, apoptosis, genotoxicity, and alterations in sex ratios in human beings. Whereas, aquatic organisms show bioaccumulation, trophic chains, and biomagnification of ACs through different entry route. These problems have been found in many countries around the globe, making them a worldwide concern. ACs have been found in different environmental matrices, such as water reservoirs for human consumption, wastewater treatment plants (WWTPs), drinking water treatment plants (DWTPs), groundwaters, surface waters, rivers, and seas, which demonstrate their free movement within the environment in an uncontrolled manner. This work provides a detailed overview of ACs occurrence in water bodies along with their toxicological effect on living organisms. The literature data reported between 2017 and 2018 is compiled following inclusion-exclusion criteria, and the obtained information was mapped as per type and source of ACs. The most important ACs are pharmaceuticals (diclofenac, ibuprofen, naproxen, ofloxacin, acetaminophen, progesterone ranitidine, and testosterone), agricultural products or pesticides (atrazine, carbendazim, fipronil), narcotics and illegal drugs (amphetamines, cocaine, and benzoylecgonine), food industry derivatives (bisphenol A, and caffeine), and personal care products (triclosan, and other related surfactants). Considering this threatening issue, robust detection and removal strategies must be considered in the design of WWTPs and DWTPs.

Comparative physiological tolerance of unicellular and colonial Microcystis aeruginosa to extract from Acorus calamus rhizome

Microcystis blooms and their associated microcystins pose a significant health risk to humans. Microcystis normally occurs as colonies in eutrophic water bodies, and its physiological tolerance to algaecides is dissimilar to that of unicellular forms. However, the differences of physiological response to algaecides between unicellular and colonial Microcystis have been poorly explored. The current study investigated the effects of hexane extract of Acorus calamus rhizome (HEACR) on the physiological and photosynthetic mechanisms of unicellular and colonial M. aeruginosa in the laboratory. We analyzed the cell density, reactive oxygen species (ROS) level, malonaldehyde (MDA) content, photosynthetic pigments, capsular polysaccharide (CPS), and photosystem (PS II) parameters of the two morphological forms of Microcystis. Our results show that HEACR suppresses the growth of both unicellular and colonial M. aeruginosa, increases the intracellular ROS level and cause lipid peroxidation, as well as exerting a detrimental effect on chlorophyll a (chl a) content and photosynthetic efficiency. Almost 100% inhibition was observed for unicellular and colonial M. aeruginosa after 3 d exposure to 50 and 100 mg L^-1 HEACR, respectively. The ROS level increase, MDA accumulation, the chl a decrease and carotenoid increase in unicellular M. aeruginosa were all more obvious than that in colonial cells. The fall in photosynthetic efficiency of unicellular M. aeruginosa were also more significant than that of colonial cells. After 3d exposure, the maximum quantum yield of PS II photochemistry (Fv/Fm), effective quantum yield of PS II photochemistry (Fv'/Fm') and effective quantum yield of photochemical energy conversion in PS II (YII) of unicellular M. aeruginosa was almost totally inhibited by 20 mg L^-1 HEACR, while the F_v/F_m, F_v'/F_m' and YII of colonial M. aeruginosa decreased by 43%, 26% and 66% for 100 mg L^-1 of HEACR, respectively. Comparing the two morphological forms of Microcystis, colonies show a greater increase in CPS level to more effectively resist the stress of HEACR and to mitigate ROS generation thereby better defending against oxidative damage. Furthermore, colonial M. aeruginosa shows better photoprotection ability than the unicellular form when exposed to HEACR. The colonies also sustain their maximum electron transport rate, increase their tolerance to strong light, and maintain a higher ability to disperse excess energy. These results demonstrated that HEACR can significantly interfere with the growth and physiological processes of both unicellular and colonial M. aeruginosa, but that colonial M. aeruginosa has a greater ability to adjust physiological tolerance to resist the stresses of HEACR.

Comparing effects of berberine on the growth and photosynthetic activities of Microcystis aeruginosa and Chlorella pyrenoidosa

Berberine is a potent algicidal allelochemical of Microcystis aeruginosa. To optimize its application in the control of Microcystis blooms, the effects of berberine on the growth and photosynthetic activities of M. aeruginosa and a non-target green alga, Chlorella pyrenoidosa, were compared. The results showed that the algicidal activity of berberine on M. aeruginosa was light dependent. Berberine had no algicidal effects on C. pyrenoidosa with or without light exposure. Under light-dark conditions, berberine significantly decreased the chlorophyll fluorescence parameters in M. aeruginosa while no significant berberine-induced changes were observed under constant darkness. Significant reductions of photosystem II (PSII) and whole chain electron transport activities in M. aeruginosa exposed to berberine suggested that PSII was the important target site attacked by berberine. Contrary to M. aeruginosa, no berberine-induced inhibition in photosynthesis activities were observed in C. pyrenoidosa. The differences in photosynthetic apparatuses of these two algae might be responsible for their different sensitivities to berberine.

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.

Influence of mixed antibiotics on Microcystis aeruginosa during the application of glyphosate and hydrogen peroxide algaecides

Antibiotics regulate various physiological functions in cyanobacteria and may interfere with the control of cyanobacterial blooms during the application of algaecides. In this study, Microcystis aeruginosa was exposed to H2 O2 and glyphosate for 7 d in the presence of coexisting mixed antibiotics (amoxicillin, spiramycin, tetracycline, ciprofloxacin, and sulfamethoxazole) at an environmentally relevant concentration of 100 ng · L-1 . The mixed antibiotics significantly (P < 0.05) alleviated the growth inhibition effect of 15-45 μM H2 O2 and 40-60 mg · L-1 glyphosate. According to the increased contents of chlorophyll a and protein, decreased content of malondialdehyde, and decreased activities of superoxide dismutase and glutathione S-transferase, antibiotics may reduce the toxicity of the two algaecides through the stimulation of photosynthesis and the reduction in oxidative stress. The presence of coexisting antibiotics stimulated the production and release of microcystins in the M. aeruginosa exposed to low concentrations of algaecides and posed an increased threat to aquatic environments. To eliminate the secondary pollution caused by microcystins, high algaecide doses that are ≥45 μM for H2 O2 and ≥60 mg · L-1 for glyphosate are recommended. This study provides insights into the ecological hazards of antibiotic contaminants and the best management practices for cyanobacterial removal under combined antibiotic pollution conditions.

Intraspecific variability of ciprofloxacin accumulation, tolerance, and metabolism in Chinese flowering cabbage (Brassica parachinensis)

To investigate the mechanism of genotype differences in ciprofloxacin (CIP) accumulation, this study was designed to compare the tolerance and metabolic responses to CIP exposure between low (Cutai) and high (Sijiu) CIP-accumulation cultivars of Brassica parachinensis. Decreases in biomass and chlorophyll content were significantly greater (p < 0.05) and toxicities were more severe within cell ultrastructures of Cutai compared to Sijiu. A sequential growth test also revealed that Sijiu was more tolerant to CIP stress compared to Cutai. Meanwhile, significantly higher (p < 0.05) root parameters and higher areas of the stele and xylem may be responsible for the increased uptake and transport of CIP in Sijiu. Ultra performance liquid chromatography-electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS) analysis revealed that CIP was metabolized to three major metabolites by the hydroxylation and breakdown of the piperazinyl substituent in the CIP molecule. The enhanced metabolic transformation of CIP in Sijiu indicated a more efficient capacity to detoxify, which in turn favored an increased accumulation of CIP in this cultivar. Thus, the present study demonstrated that the stronger tolerance and metabolism of Sijiu to CIP were responsible for its high CIP accumulation, suggesting an evolutionary mechanism for adaptation to environmental stress.

Interactions between Microcystis aeruginosa and coexisting amoxicillin contaminant at different phosphorus levels

Microcystis aeruginosa was cultured with 0.05-5 mg L(-1) of phosphorus and exposed to 200-500 ng L(-1) of amoxicillin for seven days. Amoxicillin presented no significant effect (p>0.05) on the growth of M. aeruginosa at phosphorus levels of 0.05 and 0.2 mg L(-1), but stimulated algal growth as a hormesis effect at phosphorus levels of 1 and 5 mg L(-1). Phosphorus and amoxicillin affected the contents of chlorophyll-a, adenosine triphosphate (ATP) and malondialdehyde, the expression of psbA and rbcL, as well as the activities of adenosinetriphosphatase and glutathione S-transferase in similar manners, but regulated the production and release of microcystins and the activities of superoxide dismutase and peroxidase in different ways. Increased photosynthesis activity was related with the ATP consumption for the stress response to amoxicillin, and the stress response was enhanced as the phosphorus concentration increased. The biodegradation of amoxicillin by M. aeruginosa increased from 11.5% to 28.2% as the phosphorus concentration increased. Coexisting amoxicillin aggravated M. aeruginosa pollution by increasing cell density and concentration of microcystins, while M. aeruginosa alleviated amoxicillin pollution via biodegradation. The interactions between M. aeruginosa and amoxicillin were significantly regulated by phosphorus (p<0.05) and led to a complicated situation of combined pollution.