An experimental study on the synergistic effects between Azolla and Anabaena in removal of uranium from solutions by Azolla–anabaena symbiotic system

Anabaena azollae - The cyanobacterial partner of Azolla filiculoides reciprocates variably to dose- and duration-dependent Bisphenol-A exposure

Bisphenol A (BPA) is one of the most studied endocrine-disrupting chemicals (EDC), for its large-scale production and disposal, and ubiquitous presence in the environment. It is also known to impart significant phytotoxic effects on almost all aquatic flora including cyanobacteria. Yet, there are limited studies on the responses of symbiotic cyanobacteria i.e. Anabaena azollae - residing inside Azolla filiculoides. In this context, this study aimed to investigate the response of A. azollae upon exposure to different doses and durations of BPA, which marks this as one of the first such studies. Morphological study reaffirmed the infiltration of BPA through the host's physical barrier and induced various anomalies like filament fragmentation, and cellular disruption especially heterocysts in the case of the higher doses of BPA (20, and 30 mg L-1). Additionally, exposure to higher doses further stimulated the antioxidative enzymes, secondary metabolites and stress/defence markers. However, the exaggerated ROS production (nearly 190%-230% O2.- and 557%-783% H2O2) at 30 mg L-1 severely disrupted the membrane integrity, osmotic balance, and reduced essential biomolecules like sugars, proteins and lipid accumulation. Moreover, higher doses of BPA treatment compromised photosynthetic activity by reducing the photosynthetic pigments and phycobiliproteins (PBPs). Conversely, up to the dose of 10 mg L-1, better cellular integrity, improved accumulation of biomolecules, pigments, and ROS detoxification denoted the neutral/positive effect on the symbionts. The lower doses (≥10 mg L-1) also showed positive indications like higher accumulation of biomolecules proteins (16%-30%), lipids (9%-49%), sugar (18%-52%), and pigments like phycobiliproteins (6%-97%), phycocyanins (6%-134%), which seemed to support the biomass of cyanobionts. Moreover, the said doses stimulated the accumulation of phenolics (98%-117%), flavonoids (159%-224%), and released polysaccharides (60%-183%) alongside stress markers like ascorbate and proline indicating the evocation of defense strategy against BPA stress.

Pollutant removal from dairy wastewater using live Azolla filiculoides in batch and continuous bioreactors

Fast and proper treatment of dairy wastewater is necessary before discharging it to the environment. In this study, healthy Azolla filiculoides was used to remove pollutants, including phosphorus (P), sodium (Na), chemical oxygen demand (COD), biological oxygen demand (BOD), and total dissolved solids (TDS) of dairy effluent in batch, continuous system, as well as continuous with the slow stirring system. These systems were handmade. The maximum removal efficiency was related to the P, which obtained 66.25% after 12 h in the batch bioreactor system. The highest removal of 13.69% after 21 h was obtained for Na using continuous with a slow stirring method. The highest removal related to the COD and BOD was 33.53% and 29.93% after 18 h, respectively, in continuous with the slow stirring system. TDS removal was achieved 31.44% after 24 h using the batch system. The results of these three systems were compared with each other using a one-way analysis of variance (ANOVA). There was no significant difference between them. Azolla filiculoides is an abundant plant in northern nature that a biosystem was used for optimum usage. It can be used as an efficient, inexpensive, and affordable bioadsorbent for dairy wastewater treatment. PRACTITIONER POINTS: Live Azolla filiculoides was used to remove pollutants. P, Na, BOD, COD, and TDS were removed from dairy wastewater. Batch, continuous, and continuous with the slow stirring systems were used. Live Azolla was an efficient, inexpensive, and affordable bio-adsorbent for dairy wastewater treatment.

Uranium (U) source, speciation, uptake, toxicity and bioremediation strategies in soil-plant system: A review

Uranium(U), a highly toxic radionuclide, is becoming a great threat to soil health development, as returning nuclear waste containing U into the soil systems is increased. Numerous studies have focused on: i) tracing the source in U contaminated soils; ii) exploring U geochemistry; and iii) assessing U phyto-uptake and its toxicity to plants. Yet, there are few literature reviews that systematically summarized the U in soil-plant system in past decade. Thus, we present its source, geochemical behavior, uptake, toxicity, detoxification, and bioremediation strategies based on available data, especially published from 2018 to 2021. In this review, we examine processes that can lead to the soil U contamination, indicating that mining activities are currently the main sources. We discuss the relationship between U bioavailability in the soil-plant system and soil conditions including redox potential, soil pH, organic matter, and microorganisms. We then review the soil-plant transfer of U, finding that U mainly accumulates in roots with a quite limited translocation. However, plants such as willow, water lily, and sesban are reported to translocate high U levels from roots to aerial parts. Indeed, U does not possess any identified biological role, but provokes numerous deleterious effects such as reducing seed germination, inhibiting plant growth, depressing photosynthesis, interfering with nutrient uptake, as well as oxidative damage and genotoxicity. Yet, plants tolerate U toxicity via various defense strategies including antioxidant enzymes, compartmentalization, and phytochelatin. Moreover, we review two biological remediation strategies for U-contaminated soil: (i) phytoremediation and (ii) microbial remediation. They are quite low-cost and eco-friendly compared with traditional physical or chemical remediation technologies. Finally, we conclude some promising research challenges regarding U biogeochemical behavior in soil-plant systems. This review, thus, further indicates that the combined application of U low accumulators and microbial inoculants may be an effective strategy for the bioremediation of U-contaminated soils.

Accumulation and effects of uranium on aquatic macrophyte Nymphaea tetragona Georgi: Potential application to phytoremediation and environmental monitoring

This study analyzed the ability of Nymphaea tetragona Georgi (N. tetragona) to accumulate water-borne uranium and any effects this could exert on this plant species. In accumulation experiments, N. tetragona was exposed (21 d) to different concentrations of uranium (0-55 mg L^-1) and the content of uranium was determined in water and plant tissues (leaves, submerged position and plant) to determine the translocation factor (TF) and bioconcentration factor (BCF). The content of uranium in the plant and plant tissues showed concentration-dependent uptake, leaves were the predominant tissue for uranium accumulation, and TF and BCF values were both affected by the concentration of uranium in the water. In this research, the uranium content and BCF value in the leaves of N. tetragona were upto 3446 ± 155 mg kg^-1 and 73 ± 3, respectively. In physiological experiments, uranium treatment boosted the activity of peroxidase (POD), superoxide dismutase (SOD), catalase (CAT) and malondialdehyde (MDA) in the leaves, and increasing uranium concentrations aggravated damage to the cell membrane system. Uranium contamination significantly inhibited the content of soluble protein, as well as chlorophyll-a, chlorophyll-b and carotene in the leaves, indicating the structure and function of chloroplast were destroyed, reducing the photosynthetic performance of plants. These results indicate that the macrophyte N. tetragona can accumulate uranium while showing a stress response via metabolic mechanisms under uranium exposure, and it may be a suitable bioremediation candidate for aquatic marine contamination.