Metabolomic response of microalgae towards diclofenac sodium during its removal from water and concomitant recovery of pigments and lipids

Re-vitalizing wastewater: Nutrient recovery and carbon capture through microbe-algae synergy using omics-biology

Increasing amounts of wastewater is the most pervasive and challenging environmental problem globally. Conventional treatment methods are costly and entail huge energy, carbon consumption and greenhouse gas emissions. Owing to their unique ability of carbon capturing and resource recovery, microalgae-microbiome based treatment is a potential approach and is widely used for carbon-neutral wastewater treatment. Microalgae-bacteria synergy (i.e., the functionally beneficial microbial synthetic communities) performs better and enhances carbon-sequestration and nutrient recovery from wastewater treatment plants. This review presents a comprehensive information regarding the potential of microalgae-microbiome as a sustainable agent for wastewater and discusses synergistic approaches for effective nutrient removal. Moreover, this review discusses, the role of omics-biology and Insilco approaches in unravelling and understanding the algae-microbe synergism and their response toward wastewater treatment. Finally, it discusses various microbiome engineering approaches for developing the effective microalgae-bacteria partners for carbon sequestration and nutrient recovery from wastewater, and summarizes future research perspectives on microalgae-microbiome based bioremediation.

Sulfamethoxazole removal and ammonium conversion in microalgae consortium: Physiological responses and microbial community changes

Microalgae (Mychonastes sp.) consortium was investigated for nutrient and antibiotics removal and its responses to varying sulfamethoxazole (SMX) concentrations (0-1000 μg/L) in ammonia-rich wastewater. The results showed that the introduction of SMX (100-1000 μg/L) slightly improved ammonium nitrogen removal efficiency instead of inhibition. Swift SMX degradation was observed across all SMX-treated systems, with the highest SMX removal efficiency (96 %) at an SMX concentration of 100 μg/L. Biodegradation remained the dominant SMX removal mechanism, contributing 78 % of SMX removal at an SMX concentration of 800 μg/L, while adsorption and photolysis played minor roles. Addition of SMX augmented biomass and lipid productivity, but decreased chlorophyll contents in the microalgae consortium. Furthermore, extracellular polymeric substance (EPS) production correlated positively with SMX input concentration, with the microalgae consortium exposed to 800 μg/L SMX displaying the most pronounced stimulation of protein production (51.5 ± 2.0 mg/g DCW) and polysaccharides production (74.8 ± 3.9 mg/g DCW). In response to an increase in SMX concentrations, enzyme activities associated with antioxidant defense, such as superoxide dismutase (SOD), peroxidase (POD) and malondialdehyde (MDA) increased, the catalase (CAT) decreased, indicating an initial defense mechanism. Concurrently, the relative abundance of Mychonastes sp. within the consortium rose from 87 % at 300 μg/L SMX to 99.9 % at 800 μg/L SMX. while Shannon indices of the bacterial community increased from 1.415 to 2.867. This shift inhibited the initially dominant Saprospiraceae bacteria, facilitating the profound increase of adapted Aquimonas. These findings demonstrate the feasibility of the simultaneous removal of antibiotics and nutrients from wastewater with a microalgae consortium system.

Insights into the removal of antibiotics from livestock and aquaculture wastewater by algae-bacteria symbiosis systems

With the burgeoning growth of the livestock and aquaculture industries, antibiotic residues in treated wastewater have become a serious ecological threat. Traditional biological wastewater treatment technologies-while effective for removing conventional pollutants, such as organic carbon, ammonia and phosphate-struggle to eliminate emerging contaminants, notably antibiotics. Recently, the use of microalgae has emerged as a sustainable and promising approach for the removal of antibiotics due to their non-target status, rapid growth and carbon recovery capabilities. This review aims to analyse the current state of antibiotic removal from wastewater using algae-bacteria symbiosis systems and provide valuable recommendations for the development of livestock/aquaculture wastewater treatment technologies. It (1) summarises the biological removal mechanisms of typical antibiotics, including bioadsorption, bioaccumulation, biodegradation and co-metabolism; (2) discusses the roles of intracellular regulation, involving extracellular polymeric substances, pigments, antioxidant enzyme systems, signalling molecules and metabolic pathways; (3) analyses the role of treatment facilities in facilitating algae-bacteria symbiosis, such as sequencing batch reactors, stabilisation ponds, membrane bioreactors and bioelectrochemical systems; and (4) provides insights into bottlenecks and potential solutions. This review offers valuable information on the mechanisms and strategies involved in the removal of antibiotics from livestock/aquaculture wastewater through the symbiosis of microalgae and bacteria.

Lipidomics analysis of microalgal lipid production and heavy metal adsorption under glycine betaine-mediated alleviation of low-temperature stress

Heavy metal pollution in the cold region is serious, affecting human health and aquatic ecology. This study investigated the ability of microalgae to remove heavy metals (HMs) and produce lipid at low temperature. The removal efficiency of different HMs (Cd2+, Cu2+, Cr3+ and Pb2+), cell growth and lipid synthesis of microalgae were analyzed at 15 °C. Moreover, addition of glycine betaine (GB) further enhanced the productivity of microalgae in treating HMs and lipid production, and simultaneously increased the antioxidant capacity of microalgae against environmental stresses. The results showed that the highest lipid productivity of 100.98 mg L-1 d-1 and the removal efficiency of 85.8 % were obtained under GB coupled with Cr3+. The highest glutathione content of 670.34 nmol g-1 fresh alga was achieved under GB coupled with Pb2+. In addition, lipidomics showed that GB was able to up-regulate the triglyceride and diglyceride content, influenced fatty acid composition to regulate the microalgal metabolism, and mediated lipid accumulation under 15 °C mainly through the regulation of glycerol ester metabolism. This study provided a new perspective on microalgal lipid production and the removal of HMs in cold regions and provided evidence for the use of phytohormones to improve the algal environmental resistance.

Exploring the biosynthetic possibilities of hydroxylated polybrominated diphenyl ethers from bromophenols in Prorocentrum donghaiense: Implications for bioremediation

Bromophenols has been proven to synthesize hydroxylated polybrominated diphenyl ethers (OH-PBDEs), which may pose additional environmental and health risks in the process of bioremediation. In this study, the removal of 2,4-dibromophenol (2,4-DBP) and 2,4,6-tribromophenol (2,4,6-TBP) and the biosynthetic of OH-PBDEs by Prorocentrum donghaiense were explored. The removal efficiencies of 2,4-DBP and 2,4,6-TBP ranged from 32.71% to 76.89% and 31.15%-78.12%, respectively. Low concentrations of 2,4-DBP stimulated algal growth, while high concentrations were inhibitory. Furthermore, exposure to 10.00 mg L-1 2,4-DBP resulted in the detection of 2'-hydroxy-2,3',4,5'-tetrabromodiphenyl ether (2'-OH-BDE-68) within P. donghaiense. In contrast, increasing concentrations of 2,4,6-TBP considerably inhibited P. donghaiense growth, with 4'-hydroxy-2,3',4,5',6-pentabromodiphenyl ether (4'-OH-BDE-121) detected within P. donghaiense under 5.00 mg L-1 2,4,6-TBP. Metabolomic analysis further revealed that the synthesized OH-PBDEs exhibited higher toxicity than their precursors and identified the oxidative coupling as a key biosynthetic mechanism. These findings confirm the capacity of P. donghaiense to remove bromophenols and biosynthesize OH-PBDEs from bromophenols, offering valuable insights into formulating algal bioremediation to mitigate bromophenol contamination.

Chronic toxic effects of erythromycin and its photodegradation products on microalgae Chlorella pyrenoidosa

The photodegradation products (PDPs) of antibiotics in the aquatic environment received increasing concern, but their chronic effects on microalgae remain unclear. This study initially focused on examining the acute effects of erythromycin (ERY), then explored the chronic impacts of ERY PDPs on Chlorella pyrenoidosa. ERY of 4.0 - 32 mg/L ERY notably inhibited the cell growth and chlorophyll synthesis. The determined 96 h median effective concentration of ERY to C. pyrenoidosa was 11.78 mg/L. Higher concentrations of ERY induced more serious oxidative damage, antioxidant enzymes alleviated the oxidative stress. 6 PDPs (PDP749, PDP747, PDP719, PDP715, PDP701 and PDP557) were identified in the photodegradation process of ERY. The predicted combined toxicity of PDPs increased in the first 3 h, then decreased. Chronic exposure showed a gradual decreasing inhibition on microalgae growth and chlorophyll content. The acute effect of ERY PDPs manifested as growth stimulation, but the chronic effect manifested as growth inhibition. The malonaldehyde contents decreased with the degradation time of ERY at 7, 14 and 21 d. However, the malonaldehyde contents of ERY PDPs treatments were elevated compared to those in the control group after 21 d. Risk assessment still need to consider the potential toxicity of degradation products under long-term exposure.

Microalgal multiomics-based approaches in bioremediation of hazardous contaminants

The enhanced industrial growth and higher living standards owing to the incessant population growth have caused heightened production of various chemicals in different manufacturing sectors globally, resulting in pollution of aquatic systems and soil with hazardous chemical contaminants. The bioremediation of such hazardous pollutants through microalgal processes is a viable and sustainable approach. Accomplishing microalgal-based bioremediation of polluted wastewater requires a comprehensive understanding of microalgal metabolic and physiological dynamics. Microalgae-bacterial consortia have emerged as a sustainable agent for synergistic bioremediation and metabolite production. Effective bioremediation involves proper consortium functioning and dynamics. The present review highlights the mechanistic processes employed through microalgae in reducing contaminants present in wastewater. It discusses the multi-omics approaches and their advantages in understanding the biological processes, monitoring, and dynamics among the partners in consortium through metagenomics. Transcriptomics, proteomics, and metabolomics enable an understanding of microalgal cell response toward the contaminants in the wastewater. Finally, the challenges and future research endeavors are summarised to provide an outlook on microalgae-based bioremediation.

Physiological-biochemical responses and transcriptomic analysis reveal the effects and mechanisms of sulfamethoxazole on the carbon fixation function of Chlorella pyrenoidosa

The occurrence of sulfamethoxazole (SMX) is characterized by low concentration and pseudo-persistence. However, the toxic effects and mechanisms of SMX, especially for low concentration and long-term exposure, are still not clear. This study investigated the effects and mechanisms of SMX on carbon fixation-related biological processes of Chlorella pyrenoidosa at population, physiological-biochemical, and transcriptional levels. Results showed that 1-1000 μg/L SMX significantly inhibited the dry weight and carbon fixation rate of C. pyrenoidosa during 21 d. The upregulation of superoxide dismutase (SOD) and catalase (CAT) activities, as well as the accumulation of malondialdehyde (MDA) demonstrated that SMX posed oxidative damage to C. pyrenoidosa. SMX inhibited the activity of carbonic anhydrase (CA), and consequently stimulated the activity of Rubisco. Principal component analysis (PCA) revealed that SMX concentration was positively correlated with Rubisco and CAT while exposure time was negatively correlated with CA. Transcriptional analysis showed that the synthesis of chlorophyll-a was stabilized by regulating the diversion of protoporphyrin IX and the chlorophyll cycle. Meanwhile, multiple CO2 compensation mechanisms, including photorespiratory, C4-like CO2 compensation and purine metabolism pathways were triggered in response to the CO2 requirements of Rubisco. This study provides a scientific basis for the comprehensive assessment of the ecological risk of SMX.

Polystyrene nanoplastics alter the ecotoxicological effects of diclofenac on freshwater microalgae Scenedesmus obliquus

Due to the escalating risk of plastic pollution, nanoplastics have attracted considerable attention in the recent past. They can co-exist and interact with other contaminants like pharmaceuticals in the aquatic environment. Therefore, it is pertinent to understand how these pollutants interact with one another in the ecosystem. The current study examined the individual and combined effects of fluorescent polystyrene nanoplastics (FNPs) and diclofenac (DCF) on Scenedesmus obliquus using a full factorial design. The toxicity of S. obliquus significantly increased in a dose-dependent manner upon exposure to pristine forms of DCF and FNPs. The major cause of individual toxicity of DCF and FNPs in S. obliquus was oxidative stress. In the combined toxicity tests when FNPs (0.01, 0.1, and 1 mg L-1) and DCF (1 mg L-1) were mixed, a synergistic effect was noted compared to the respective pristine FNPs. However, when the DCF concentration in the mixture was decreased to 0.25 mg L-1, the combined toxicity with FNPs (0.01, 0.1, and 1 mg L-1) reduced indicating an antagonistic effect. The independent action model also showed an antagonistic effect for low-dose combinations of DCF and a synergistic effect for high-dose combinations. The estimation of oxidative stress parameters, antioxidant enzyme activity, and photosynthetic pigment content in the algae further validated the cytotoxicity data. The mean hydrodynamic diameter and surface charge analyses further indicated that the colloidal stability of the FNPs in the medium was affected when they were combined with DCF. The key reason for differences in the cytotoxicity of combinations could be observed variations in the aggregation of FNPs and differential adsorption patterns of DCF on the FNPs. These factors efficiently altered cell-particle interactions in the mixture demonstrating a hormesis effect. Thus, this current study highlighted the hazardous nature of the nanoplastics and their co-exposure risks with pharmaceuticals on microalgae in freshwater environments.