The enhanced degradation and detoxification of chlortetracycline by Chlamydomonas reinhardtii

Light-driven photocatalysis as an effective tool for degradation of antibiotics

Antibiotic contamination has become a severe issue and a dangerous concern to the environment because of large release of antibiotic effluent into terrestrial and aquatic ecosystems. To try and solve these issues, a plethora of research on antibiotic withdrawal has been carried out. Recently photocatalysis has received tremendous attention due to its ability to remove antibiotics from aqueous solutions in a cost-effective and environmentally friendly manner with few drawbacks compared to traditional photocatalysts. Considerable attention has been focused on developing advanced visible light-driven photocatalysts in order to address these problems. This review provides an overview of recent developments in the field of photocatalytic degradation of antibiotics, including the doping of metals and non-metals into ultraviolet light-driven photocatalysts, the formation of new semiconductor photocatalysts, the advancement of heterojunction photocatalysts, and the building of surface plasmon resonance-enhanced photocatalytic systems.

The environmental risks of antiviral drug arbidol in eutrophic lake: Interactions with Microcystis aeruginosa

The environmental risks resulting from the increasing antivirals in water are largely unknown, especially in eutrophic lakes, where the complex interactions between algae and drugs would alter hazards. Herein, the environmental risks of the antiviral drug arbidol towards the growth and metabolism of Microcystis aeruginosa were comprehensively investigated, as well as its biotransformation mechanism by algae. The results indicated that arbidol was toxic to Microcystis aeruginosa within 48 h, which decreased the cell density, chlorophyll-a, and ATP content. The activation of oxidative stress increased the levels of reactive oxygen species, which caused lipid peroxidation and membrane damage. Additionally, the synthesis and release of microcystins were promoted by arbidol. Fortunately, arbidol can be effectively removed by Microcystis aeruginosa mainly through biodegradation (50.5% at 48 h for 1.0 mg/L arbidol), whereas the roles of bioadsorption and bioaccumulation were limited. The biodegradation of arbidol was dominated by algal intracellular P450 enzymes via loss of thiophenol and oxidation, and a higher arbidol concentration facilitated the degradation rate. Interestingly, the toxicity of arbidol was reduced after algal biodegradation, and most of the degradation products exhibited lower toxicity than arbidol. This study revealed the environmental risks and transformation behavior of arbidol in algal bloom waters.

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.

Efficient, fast and robust degradation of chlortetracycline in wastewater catalyzed by recombinant Arthromyces ramosus peroxidase

Chlortetracycline (CTC), a widely used antibiotic, is recalcitrant and ubiquitous in the environment. Enzymatic degradation of CTC is an economical and efficient bioremediation method. In this work, recombinant Arthromyces ramosus peroxidase (rARP) at a concentration of 3.13 × 10^-9 M was used to catalyze rapid degradation of CTC in water. The second-order rate constants of rARP showed up to 62-fold catalytic efficiency of horseradish peroxidase (HRP) toward CTC. The degradation half-life of CTC at the concentrations of 2 and 40 mg L^-1 in wastewater under the rARP catalysis was, respectively, 5.3 and 5.7 min at 25 °C, and 2.7 and 3.1 min at 40 °C, which were up to 15-fold and 111-fold faster than HRP and laccase, respectively, but use of 3 % the amount of rARP as HRP. rARP catalyzed degradation of CTC at 2-40 mg L^-1 in wastewater completed in 20-24 min, and its catalytic efficiency varied within only 2-fold at 25-40 °C. rARP showed only 2-3-fold discrepancy of catalytic efficiency among pH 5.0, 7.5 and 9.0. CTC under rARP catalysis underwent demethylation and oxidation to form nontoxic N-dedimethyl-9-hydroxy-CTC. The high catalytic efficiency of rARP agreed with a short distance between rARP's δN-His⁵⁶ and CTC's dimethylamine N as indicated by docking simulation. rARP is a useful enzyme for CTC bioremediation.

Advancement in algal bioremediation for organic, inorganic, and emerging pollutants

Rapidly changing bioremediation prospects are key drive to develop sustainable options that can offer extra benefits rather than only environmental remediation. Algal remediating is gaining utmost attention due to its mesmerising sustainable features, removing odour and toxicity, co-remediating numerous common and emerging inorganic and organic pollutants from gaseous and aqueous environments, and yielding biomass for a range of valuable products refining. Moreover, it also improves carbon footprint via carbon-capturing offers a better option than any other non-algal process for several high CO₂-emitting industries. Bio-uptake, bioadsorption, photodegradation, and biodegradation are the main mechanisms to remediate a range of common and emerging pollutants by various algae species. Bioadsorption was a dominant remediation mechanism among others implicating surface properties of pollutants and algal cell walls. Photodegradable pollutants were photodegraded by microalgae by adsorbing photons on the surface and intracellularly via stepwise photodissociation and breakdown. Biodegradation involves the transportation of selective pollutants intracellularly, and enzymes help to convert them into simpler non-toxic forms. Robust models are from the green microalgae group and are dominated by Chlorella species. This article compiles the advancements in microalgae-assisted pollutants remediation and value-addition under sustainable biorefinery prospects. Moreover, filling the knowledge gaps, and recommendations for developing an effective platform for emerging pollutants remediation and realization of commercial-scale algal bioremediation.

Removal mechanisms of erythromycin by microalgae Chlorella pyrenoidosa and toxicity assessment during the treatment process

Microalgae-based biotechnology for antibiotic removal has received increasing attention as an economical and green method. This study investigated the removal mechanism of erythromycin by Chlorella pyrenoidosa and its correlation with the ecotoxic responses of microalgae. The degradation products (DPs) were identified, and their toxicity was predicted. The results indicated that only 4.04 %, 6.28 % and 23.53 % of erythromycin were left after 21-day microalgae treatment in 0.1, 1.0 and 10 mg/L treatments, respectively. Biodegradation contributed 48.62-67.01 %, 16.67-52.32 % and 6.42-24.82 %, while abiotic degradation contributed 8.76-29.61 %, 5.19-41.39 %, and 16.55-51.22 % to erythromycin attenuation in 0.1, 1.0, and 10 mg/L treatments, respectively. The growth and physiological-biochemical parameters of microalgae were slightly affected in low concentration treatment, which may be the main reason that biodegradation was the prominent removal mechanism. By contrast, oxidative damage in high concentration treatment inhibited the cell growth and chlorophyll content of microalgae, which hindered erythromycin biodegradation. In addition, eleven erythromycin degradation products (DPs) were identified during microalgae treatment of 21 days. Seven DPs including DP717, DP715, DP701A, DP701B, DP657, DP643, and DP557, represented higher toxicity to aquatic organisms than erythromycin.

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.

Recent advances on microalgae cultivation for simultaneous biomass production and removal of wastewater pollutants to achieve circular economy

Microalgae are known for containing high value compounds and its significant role in sequestering carbon dioxide. This review mainly focuses on the emerging microalgae cultivation technologies such as nanomaterials technology that can improve light distribution during microalgae cultivation, attached cultivation and co-cultivation approaches that can improve growth and proliferation of algal cells, biomass yield and lipid accumulation in microalgal. This review includes a comprehensive discussion on the use of microbubbles technology to enhance aerated bubble capacity in photobioreactor to improve microalgal growth. This is followed by discussion on the role of microalgae as phycoremediation agent in removal of contaminants from wastewater, leading to better water quality and high productivity of shellfish. The review also includes techno-economic assessment of microalgae biorefinery technology, which is useful for scaling up the microalgal biofuel production system or integrated microalgae-shellfish cultivation system to support circular economy.

Biodegradation of chlortetracycline by Bacillus cereus LZ01: Performance, degradative pathway and possible genes involved

Microbial degradation of chlortetracycline (CTC) is an effective bioremediation method. In the present study, an enrichment technique was used to isolate a Bacillus cereus LZ01 strain capable of effectively degrading CTC from cattle manure. Response surface methodology was used to identify optimized conditions under which strain LZ01 was able to achieve maximal CTC removal (83.58%): temperature of 35.77 °C, solution pH of 7.59, CTC concentration of 57.72 mg/L and microbial inoculum of 0.98%. The antibacterial effect of CTC degradation products on Escherichia coli was investigated by the disk diffusion test, revealing that the products by LZ01 degradation of CTC exhibited lower toxicity than parent compound. Shake flask batch experiments showed that the biodegradation of CTC was a synergistic effect of intracellular and extracellular enzymes, and intracellular enzyme had a better degradation effect on CTC (77.56%). Whole genome sequencing revealed that genes associated with ring-opening hydrolysis, demethylation, deamination and dehydrogenation in strain LZ01 may be involved in the biodegradation of CTC. Subsequent seven possible biodegradation products were identified by LC-MS analyses, and the biodegradation pathways were proposed. Overall, this study provides a theoretical foundation for the characterization and mechanism of CTC degradation in the environment by Bacillus cereus LZ01.

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.

Progress in microalgal mediated bioremediation systems for the removal of antibiotics and pharmaceuticals from wastewater

Worldwide demand for antibiotics and pharmaceutical products is continuously increasing for the control of disease and improvement of human health. Poor management and partial metabolism of these compounds result in the pollution of aquatic systems, leading to hazardous effects on flora, fauna, and ecosystems. In the past decade, the importance of microalgae in micropollutant removal has been widely reported. Microalgal systems are advantageous as their cultivation does not require additional nutrients: they can recover resources from wastewater and degrade antibiotics and pharmaceutical pollutants simultaneously. Bioadsorption, degradation, and accumulation are the main mechanisms involved in pollutant removal by microalgae. Integration of microalgae-mediated pollutant removal with other technologies, such as biodiesel, biochemical, and bioelectricity production, can make this technology more economical and efficient. This article summarizes the current scenario of antibiotic and pharmaceutical removal from wastewater using microalgae-mediated technologies.

Removal of veterinary antibiotics in swine wastewater using microalgae-based process

Phycoremediation of swine wastewater is an attractive treatment to remove contaminants and simultaneously produce valuable feedstock biomass. However, there is a lack of information about the application of phycoremediation on veterinary antibiotic removal. Thus, this research investigated the degradation of tetracycline, oxytetracycline, chlortetracycline and doxycycline in swine wastewater treated with phycoremediation. The tetracyclines degradation kinetics was adjusted to the pseudo-first-order kinetics model, with kinetic constant k₁ in the following: 0.36 > 0.27>0.19 > 0.18 (d^-1) for tetracycline, doxycycline, oxytetracycline and chlortetracycline, respectively. The maximum concentration of microalgae biomass (342.4 ± 20.3 mg L^-1) was obtained after 11 days of cultivation, when tetracycline was completely removed. Chlortetracycline concentration decreased, generating iso-chlortetracycline and 4-epi-iso-chlortetracycline. Microalgae biomass harvested after antibiotics removal presented a carbohydrate-rich content of 52.7 ± 8.1, 50.1 ± 3.3, 51.4 ± 5.4 and 57.4 ± 10.4 (%) when cultured with tetracycline, oxytetracycline, chlortetracycline and doxycycline, respectively, while the control culture without antibiotics presented a carbohydrate content of 40 ± 6.5%. These results indicate that could be a valuable source for bioenergy conversion.

Microbial Degradation of Aldrin and Dieldrin: Mechanisms and Biochemical Pathways

As members of the organochlorine group of insecticides, aldrin and dieldrin are effective at protecting agriculture from insect pests. However, because of excessive use and a long half-life, they have contributed to the major pollution of the water/soil environments. Aldrin and dieldrin have been reported to be highly toxic to humans and other non-target organisms, and so their use has gradually been banned worldwide. Various methods have been tried to remove them from the environment, including xenon lamps, combustion, ion conversion, and microbial degradation. Microbial degradation is considered the most promising treatment method because of its advantages of economy, environmental protection, and convenience. To date, a few aldrin/dieldrin-degrading microorganisms have been isolated and identified, including Pseudomonas fluorescens, Trichoderma viride, Pleurotus ostreatus, Mucor racemosus, Burkholderia sp., Cupriavidus sp., Pseudonocardia sp., and a community of anaerobic microorganisms. Many aldrin/dieldrin resistance genes have been identified from insects and microorganisms, such as Rdl, bph, HCo-LGC-38, S2-RDL^A302S, CSRDL1A, CSRDL2S, HaRdl-1, and HaRdl-2. Aldrin degradation includes three pathways: the oxidation pathway, the reduction pathway, and the hydroxylation pathway, with dieldrin as a major metabolite. Degradation of dieldrin includes four pathways: oxidation, reduction, hydroxylation, and hydrolysis, with 9-hydroxydieldrin and dihydroxydieldrin as major products. Many studies have investigated the toxicity and degradation of aldrin/dieldrin. However, few reviews have focused on the microbial degradation and biochemical mechanisms of aldrin/dieldrin. In this review paper, the microbial degradation and degradation mechanisms of aldrin/dieldrin are summarized in order to provide a theoretical and practical basis for the bioremediation of aldrin/dieldrin-polluted environment.

Enhanced production of microalgae-originated photosensitizer by integrating photosynthetic electrons extraction and antibiotic induction towards photocatalytic degradation of antibiotic: A novel complementary treatment process for antibiotic removal from effluent of conventional biological wastewater treatment

Antibiotic residues in effluents from bio-treated wastewaters are mainly responsible for the spread of antibiotic resistance genes in the environment. Conventional physicochemical treatments are thought to be unsustainable due to high energy consumption, large consumption of chemicals and environmental unfriendly processing step. In this study, a novel approach by integrating photosynthetic electrons extraction from microalgae with antibiotic induction was used to enhance the production of microalgae-originated photosensitizer for photolytic removal of antibiotic residues in effluents from conventional bio-treated wastewaters. Results showed that the accumulation of photoactive substances in extracellular polymeric substance (EPS) of chlorella vulgaris was positively related to the amounts of photosynthetic electrons extracted by the electrode which is a potential-dependent process and can be further enhanced by tetracycline (TC) induction. The protein and humic acid which are considered two main photoactive substances in EPS produced at 0.6 V accumulated to a high level of 320 and 24 μg/cm³ and were further increased to 380 and 48 μg/cm³ when TC was added which were 4.7 and 6.4-folds higher than that produced at potential free in the absence of TC. The EPS produced at 0.6 and 0.8 V led to 1.34 and 1.53-fold acceleration in photosensitized degradation of TC compared to that of EPS free in secondary effluent of municipal wastewater treatment plant. The complex heterocyclic ring structure of TC was broken down into simple monocyclic aromatic compounds, indicating a marked reduction in biotoxicity and recalcitrance. The hydroxyl radical played a main role for the photolysis of TC followed by singlet oxygen. This technology provides a new alternative to conventional physicochemical treatment as complementary treatment processes for biological wastewater treatment in terms of antibiotics removal.

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.

The effects of quercetin combined with nucleopolyhedrovirus on the growth and immune response in the silkworm (Bombyx mori)

Flavonoids are secondary metabolites that help plants resist insect attack. It can resist insect attack by inhibiting insect immune defense, and pathogens can also inhibit insect immune defense. It is speculated that the combination of flavonoids and pathogens may inhibit the immune defense and have stronger toxicity to silkworm. In this study, the combined treatment of quercetin with Bombyx mori nuclear polyhedrosis virus (BmNPV) had significant negative effects on the growth and survival of silkworm compared with BmNPV group. The detoxifying enzyme activity of BmNPV group was significantly increased at 96 h, while the activity of the combined treatment group was significantly decreased with the increase of quercetin exposure time (72 or 96 h). The activity of antioxidant enzymes also showed a similar trend, that was, the activity of antioxidant enzymes in the combined treatment group also decreased significantly with the increase of quercetin exposure time, which led to the increase of reactive oxygen species content. The silkworm cells would produce lipid peroxidation, malondialdehyde content was significantly increased, so that the expression of immune-related genes (the antimicrobial peptide, Toll pathway, IMD pathway, JAK-STAT pathway, and melanin genes) were decreased, leading to the damage of the immune system of silkworm. These results indicated that quercetin combined with BmNPV could inhibit the activities of protective enzymes and lead to oxidative damage to silkworm. It can also affect the immune response of the silkworm, and thus resulting in abnormal growth. This study provides the novel conclusion that quercetin accumulation will increase the susceptibility of silkworm to pathogens.