Prevention of Cyanobacterial Blooms Using Nanosilica: A Biomineralization-Inspired Strategy

Simultaneous removal of cyanobacteria and algal organic matter by Mn(VII)/CaSO3 enhanced coagulation: Performance and mechanism

Frequent outbreaks of algal blooms greatly threatened drinking water safety, garnering widespread attention. Mn/CaSO3 is emerging in the field of organic matter removal with its efficient oxidizing capacity and wide pH application range. The performance of Mn(VII)/CaSO3 as a pre-oxidation process enhancing coagulation for algae removal (Microcystis aeruginosa, 2 (±0.5) × 106 cells/mL) was investigated. The results suggested that the Mn(VII)/CaSO3 process efficiently achieved over 90 % removal of algae cells, notably with a reduced chemical dosage (5.0 μM Mn(VII) and 40.0 μM CaSO3). Simultaneously, algal organic matters (AOM) and microcystins were effectively controlled due to the oxidative degradation of Mn(VII)/CaSO3 and the formation of denser flocs owing to the in-situ MnO2 generation. In addition, it demonstrated that the addition of CaSO3 broadened the pH range for Mn(VII) application and reduced the Mn residue. Subsequent experiments conducted in this study, such as electron spin resonance, methyl phenyl sulfoxide probe and free radical quenching experiments, demonstrated that Mn(III) may be the key active substance of the Mn(VII)/CaSO3 system enhancing coagulation for algal removal. Active radicals (SO4•- and •OH) in this system also played a relatively minor role. In conclusion, this study highlights the potential of the Mn(VII)/CaSO3 process as an environmentally friendly adjunct technology for algal removal and AOM control.

Cyanobacteria-probiotics symbionts for modulation of intestinal inflammation and microbiome dysregulation in colitis

Inflammatory bowel disease (IBD) is often associated with excessive inflammatory response and highly dysregulated gut microbiota. Traditional treatments utilize drugs to manage inflammation, potentially with probiotic therapy as an adjuvant. However, current standard practices often suffer from detrimental side effects, low bioavailability, and unsatisfactory therapeutic outcomes. Microbial complexes characterized by mutually beneficial symbiosis hold great promise for IBD therapy. Here, we aggregated Synechocystis sp. PCC6803 (Sp) with Bacillus subtilis (BS) by biomimetic mineralization to form cyanobacteria-probiotics symbionts (ASp@BS), which reshaped a healthy immune system and gut microbiota in a murine model of acute colitis. The symbionts exhibited excellent tolerance to the harsh environment of the gastrointestinal tract. Importantly, probiotics within the symbionts created a local anaerobic environment to activate the [NiFe]-hydrogenase enzyme of cyanobacteria, facilitating the production of hydrogen gas (H2) to persistently scavenge elevated reactive oxygen species and alleviate inflammatory factors. The resulting reduced inflammation improves the viability of the probiotics to efficiently regulate the gut microbiota and reshape the intestinal barrier functions. Our research elucidates that ASp@BS leverages the synergistic interaction between Sp and BS to create a therapeutic platform that addresses multiple aspects of IBD, offering a promising and comprehensive solution for IBD treatment.

Impact of facemask debris on marine diatoms: Physiology, surface properties, sinking rate, and copepod ingestion

Discarded surgical masks have become a new source of plastic waste in seawater capable of releasing numerous micro and nano plastic fragments. However, little information is available about how this waste impacts the ecological state of marine phytoplankton. Here, we exposed two model marine diatoms (Phaeodactylum tricornutum and Thalassiosira weissflogii) to mask-released debris (MD) that is characterized by various differently-charged functional groups. Although MD could only bind loosely to diatoms, it still inhibited their growth and significantly altered cell surface physicochemical properties. At the nanoscale, MD-exposed cell walls showed enhanced roughness and modulus, besides declined electrical potential, adhesion, and proportion of oxygen-containing compounds. As a result, diatom ingestion by copepods was reduced, and the sinking rate of the carbon pool consisting of MD plus diatoms decreased as well. Our study indicated that MD effects on diatoms have the potential to slow down carbon export from surface seawater to the deep sea. Since oxidation and generation of functional groups are common during the aging process of microplastics (MPs) in nature, the interactions between the diatom cell surface and MD have important environmental significance.

Synergistic influence of iodine and hydrogen peroxide towards the degradation of harmful algal bloom of Microcystis aeruginosa

Cyanobacterial blooming due to the influence of temperature and increased nutrients in ponds/lakes aided by the runoff from agricultural lands, is a serious environmental issue. The presence of cyanotoxins in water may poison the health of aquatic organisms, animals, and humans. In this study, we focus on chemical assisted degradation of Microcystis aeruginosa- an alga that is of special relevance owing to its consistent blooming, especially in tropical regions. The study aims to ascertain the individual iodine (I) and hydrogen peroxide (H2O2) and their combination (hereinafter referred to as IH) effects on the degradation of Microcystis aeruginosa. As expected, the collected pond water revealed the presence of metal ions viz., Ni, Zn, Pb, Cu and Mn, which enriched the blooming of M. aeruginosa. Interestingly, a complete rupture of the cells - pigment loss, biochemical degradation and oxidative damage-was observed by the IH solution after exposure for ∼9 h under ambient conditions. In comparison to control (original water without chemicals), the addition IH completely eliminated the pigments phycocyanin (99.5%) and allophycocyanin (98%), and degraded ∼81% and 91% of carbohydrates and proteins, respectively due to the synergistic action of I and H. Superior degradation of algae through a simple and eco-friendly approach presented in this study could be explored more effectively towards its large-scale applicability.

A novel biomineralization-inspired flocculation approach for harvesting high quality microalgal biomass: Dual action of cationic polyelectrolytes and nanosilica

This study posed a novel biomimetic flocculation approach, aiming to efficiently harvest high-quality biomass of Scenedesmus quadricauda cultured with anaerobic digestate. Here, that poly(diallyldimethylammonium chloride) (PDADMAC) could serve as mimetic silicified proteins to spontaneously incorporate nanosilica onto microalgal cells, imparting diatom-like characteristics to S. quadricauda. Compared to the exponential growth phase (day 3), the highest harvesting efficiency (93.49%) was obtained at a lower dosage of PDADMAC (5 mg/g) in the stationary phase (day 6), which was attributed to changes in properties and composition of microalgal LB-EPS. On day 6, the hydrophobic functional groups in LB-EPS provided more binding sites during the flocculation process and formed a network structure of microalgal cells-flocculants-nanosilica. The resulting larger and more stable biomimetic silica shell promoted microalgal flocculation and sedimentation. Compared to conventional harvesting methods (centrifugation, polyacrylamide, alkaline flocculation), this method had the minimal negative impact on harvested biomass, with 9.95% of cell membranes damaged.

Enhanced growth and auto-flocculation of Scenedesmus quadricauda in anaerobic digestate using high light intensity and nanosilica: A biomineralization-inspired strategy

Coupling municipal anaerobic digestate (MAD) treatments with microalgal cultivation can concomitantly achieve nutrient removal and microalgal bioenergy production. However, the high cost caused by dilution water and microalgal harvesting is a great challenge. In this study, Scenedesmus quadricauda was screened as the most appropriate algae strain due to its potential for growth and auto-flocculation, and the MAD diluted 5-fold with WWTP effluent was demonstrated as an ideal medium for S. quadricauda growth. Moreover, inspired by naturally generated silica shells of diatoms, a low-cost and biomimetic auto-flocculation strategy that combined high light intensity induction and microalgal silicification was proposed to accelerate the auto-flocculation process. Compared with low light intensity groups, this strategy imparted diatom-like features to S. quadricauda cells, and contributed to 3.07-fold higher auto-flocculation efficiency within 30 min. It was attributed to the fact that the high light intensity of 150 μmol·m ^- 2·s ^- 1 stimulated the extracellular polymeric substances (EPS) secretion and induced the variation in property and composition of EPS, especially the protein secondary structures, which allowed silica nanoparticles to spontaneously attach onto S. quadricauda cells in the presence of viscous EPS. Furthermore, this strategy significantly increased microalgal biomass yield to a dry weight of 1.37 g·L ^- 1, accompanied by 93.78%, 96.39% and 91.36% removals of NH₄⁺-N, TP, and COD, respectively. The productivity of valuable by-products, including lipid, carbohydrate, protein, and pigment, reached 56.30, 101.35, 30.39 and 11.28 mg·L ^- 1·d ^- 1, respectively. Overall, this study supplies a novel approach for low-cost microalgal bioenergy production from MAD and energy-efficient microalgae harvest by auto-flocculation.

Potential use of engineered nanoparticles in ocean fertilization for large-scale atmospheric carbon dioxide removal

Artificial ocean fertilization (AOF) aims to safely stimulate phytoplankton growth in the ocean and enhance carbon sequestration. AOF carbon sequestration efficiency appears lower than natural ocean fertilization processes due mainly to the low bioavailability of added nutrients, along with low export rates of AOF-produced biomass to the deep ocean. Here we explore the potential application of engineered nanoparticles (ENPs) to overcome these issues. Data from 123 studies show that some ENPs may enhance phytoplankton growth at concentrations below those likely to be toxic in marine ecosystems. ENPs may also increase bloom lifetime, boost phytoplankton aggregation and carbon export, and address secondary limiting factors in AOF. Life-cycle assessment and cost analyses suggest that net CO₂ capture is possible for iron, SiO₂ and Al₂O₃ ENPs with costs of 2-5 times that of conventional AOF, whereas boosting AOF efficiency by ENPs should substantially enhance net CO₂ capture and reduce these costs. Therefore, ENP-based AOF can be an important component of the mitigation strategy to limit global warming.

Sediment Bacteria and Phosphorus Fraction Response, Notably to Titanium Dioxide Nanoparticle Exposure

Titanium dioxide nanoparticle (TiO₂ NP) toxicity to the growth of organisms has been gradually clarified; however, its effects on microorganism-mediated phosphorus turnover are poorly understood. To evaluate the influences of TiO₂ NPs on phosphorus fractionation and the bacterial community, aquatic microorganisms were exposed to different concentrations of TiO₂ NPs with different exposure times (i.e., 0, 10, and 30 days). We observed the adhesion of TiO₂ NPs to the cell surfaces of planktonic microbes by using SEM, EDS, and XRD techniques. The addition of TiO₂ NPs resulted in a decrease in the total phosphorus of water and an increase in the total phosphorus of sediments. Additionally, elevated TiO₂ NPs enhanced the sediment activities of reductases (i.e., dehydrogenase [0.19–2.25 μg/d/g] and catalase [1.06–2.92 μmol/d/g]), and significantly decreased the absolute abundances of phosphorus-cycling-related genes (i.e., gcd [1.78 × 10⁴–9.55 × 10⁵ copies/g], phoD [5.50 × 10³–5.49 × 10⁷ copies/g], pstS [4.17 × 10²–1.58 × 10⁶ copies/g]), and sediment bacterial diversity. TiO₂ NPs could noticeably affect the bacterial community, showing dramatic divergences in relative abundances (e.g., Actinobacteria, Acidobacteria, and Firmicutes), coexistence patterns, and functional redundancies (e.g., translation and transcription). Our results emphasized that the TiO₂ NP amount—rather than the exposure time—showed significant effects on phosphorus fractions, enzyme activity, phosphorus-cycling-related gene abundance, and bacterial diversity, whereas the exposure time exhibited a greater influence on the composition and function of the sediment bacterial community than the TiO₂ NP amount. Our findings clarify the responses of phosphorus fractions and the bacterial community to TiO₂ NP exposure in the water–sediment ecosystem and highlight potential environmental risks of the migration of untreated TiO₂ NPs to aquatic ecosystems.

Improvement of organisms by biomimetic mineralization: A material incorporation strategy for biological modification

Biomineralization, a bio-organism controlled mineral formation process, plays an important role in linking biological organisms and mineral materials in nature. Inspired by biomineralization, biomimetic mineralization is used as a bridge tool to integrate biological organisms and functional materials together, which can be beneficial for the development of diversified functional organism-material hybrids. In this review, recent progresses on the techniques of biomimetic mineralization for organism-material combinations are summarized and discussed. Based upon these techniques, the preparations and applications of virus-, prokaryotes-, and eukaryotes-material hybrids have been presented and they demonstrate the great potentials in the fields of vaccine improvement, cell protection, energy production, environmental and biomedical treatments, etc. We suggest that more researches about functional organism and material combination with more biocompatible techniques should be developed to improve the design and applications of specific organism-material hybrids. These rationally designed organism-material hybrids will shed light on the production of "live materials" with more advanced functions in future. STATEMENT OF SIGNIFICANCE: This review summaries the recent attempts on improving biological organisms by their integrations with functional materials, which can be achieved by biomimetic mineralization as the combination tool. The integrated materials, as the artificial shells or organelles, confer diversified functions on the enclosed organisms. The successful constructions of various virus-, prokaryotes-, and eukaryotes-material hybrids have demonstrated the great potentials of the material incorporation strategy in vaccine development, cancer treatment, biological photosynthesis and environment protection etc. The suggested challenges and perspectives indicate more inspirations for the future development of organism-material hybrids.

A possible environmental-friendly removal of Microcystis aeruginosa by using pyroligneous acid

Cyanobacteria blooms are crucial environmental issues by threatening both aquatic ecosystem and human health. A biomass by-product with antimicrobial activity, pyroligneous acid (PA) was tested for its suitability for removal of the cyanobacteria Microcystis aeruginosa (M. aeruginosa) in this work. Results show that the removal efficiency could reach up to 90% in the presence of 0.45% of PA and the inhibition to M. aeruginosa growth could extend to at least 40 days. The removal mechanism was studied. Both organic acids and phenols are functional content in M. aeruginosa removal and acetic acid is the most important one. Zeta potential analysis and morphology study show that the damage of cells dominates the flocculation and sedimentation of M. aeruginosa under low PA concentration (<0.7%), and increasing PA (≥0.7%) resulted in a trend of zeta potential to zero, thus removing any "shield" and triggering flocculation. Finally, study on the phenols residual after M. aeruginosa treatment shows that it could be close to 0 in 70 h. Therefore, this work proposes a possible method for world-wide treatment of cyanobacteria bloom and a new way for further utilization of PA.

The behaviors of Microcystis aeruginosa and microcystins during the Fe2+/persulfate (PS) preoxidation-coagulation and flocs storage period

The frequent occurrence of toxin-producing cyanobacteria blooms driven by anthropogenic eutrophication has become a major threat to aquaculture ecosystems worldwide. In this study, the behavior of M. aeruginosa cells during flocs storage period of 6 days was first investigated after pre-oxidation and coagulation of Fe²⁺/PS. Fe²⁺/PS achieved a superior removal efficiency of 90.7% for OD₆₈₀ and 90.4% for chl-a. The contents of extracellular MCs in the pre-oxidation and coagulation system were significantly (P < 0.05) lower than those in the control. A significant (P < 0.05) difference in intracellular protein between the control and the coagulated systems was observed. Three-dimensional fluorescence excitation emission matrix (EEM) was employed to investigate the variations in extracellular organic matter (EOM) during flocs storage. The results indicated the presence of four peaks, representing protein-like substances, intermediate dissolved microbial metabolites, fulvic and humic-like compounds in the Fe²⁺/PS process. And the intensities of four peaks were all decreased in the Fe²⁺/PS system compared to those in the control. A low level of accumulated residual Fe of 0.28 mg/L was observed without posing potential environmental risk. The results showed that the M. aeruginosa cells were under stressful conditions after 3-d storage due to the decomposition of extracellular polymeric substances (EPSs) and the insufficient supply of nutrients. However, SEM results indicated that no significant alteration in cell morphology was observed. Therefore, with high removal of M. aeruginosa, low MCs concentrations, and trivial cell damage, the Fe²⁺/PS preoxidation-coagulation was proved to be an environmental-friendly method for cyanobacteria removal without yielding serious secondary pollution. This work will contribute to better understanding and managing the cyanobacteria-laden aquaculture water after pre-oxidation and coagulation.

Mixotrophic Ochromonas Addition Improves the Harmful Microcystis-Dominated Phytoplankton Community in In Situ Microcosms

Driven by global warming and eutrophication, outbreaks of cyanobacterial blooms have severely impacted ecosystem stability and water safety. Of the organisms used to control cyanobacteria, protozoa can highly resist cyanotoxins, efficiently control cyanobacterial populations, and show considerably different feeding strategies from those of metazoans. Thus, protozoa have great potential to control harmful cyanobacteria and improve phytoplankton composition in eutrophic waters. To evaluate the actual effects of protozoa in controlling cyanobacteria and improving the phytoplankton community structure in the field, an in situ microcosm study was performed using a flagellate Ochromonas gloeopara that ingests Microcystis. Results showed that adding Ochromonas reduced the cyanobacterial populations and increased the chlorophyte and diatom proportions. Furthermore, the species richness and diversity of the phytoplankton community were enhanced in microcosms with Ochromonas. Additionally, there was a gradual increase in the chlorophyte population in the unicellular Microcystis control, while Ochromonas addition significantly accelerated the replacement of dominant species. This study was the first to show the practical effects of protozoa on controlling cyanobacteria in the field, highlighting that a reduction in in situ cyanobacteria via protozoa can improve the phytoplankton community structure, dredge the toxic cyanobacteria-dominated microbial food web, and mitigate harmful cyanobacteria risks in fresh waters.

Metal Oxide Mediated Extracellular NADPH Regeneration Improves Ethanol Production by Engineered Synechocystis sp. PCC 6803

The ethanol synthesis pathway engineered Synechocystis sp. PCC 6803 (hereafter Synechocystis) was used to investigate the influence of metal oxide mediated extracellular NADPH regeneration on ethanol synthesis. The in-vitro studies proved that the metal oxides have the potential to generate the NADPH in the presence of electron donor, the usual components of photoautotrophic growth conditions. When the NADPH regeneration was applied in Synechocystsis, the strain showed improved growth and ethanol production. This improved ethanol synthesis is attributed to the increased availability of NADPH to the ethanol synthesis pathway and redirection of closely related carbon metabolism into the ethanol synthesis. Under optimized light intensity and NADP addition, the maximum ethanol production of 5,100 mg/L was observed in MgO mediated extracellular NADPH regeneration after 25 days of cultivation, which is 2-fold higher than the control. This study indicates the feasibility of metal oxide mediated extracellular NADPH regeneration of Synechocystis to increase the production of ethanol.

Changes in Microcystis aeruginosa cell integrity and variation in microcystin-LR and proteins during Tanfloc flocculation and floc storage

The objective of this study was to determine the influence of Tanfloc on Microcystis aeruginosa cell integrity, microcystin-LR (MC-LR), and proteins during flocculation and floc storage. The effects of Tanfloc addition, stirring, and floc storage time were considered to minimize cell damage and the release of MC-LR and proteins. Optimal flocculation conditions (Tanfloc dosage 10.42 mg L^-1, rapid agitation for 0.36 min at 568.88 rpm and slow agitation for 14.14 min at 12.1 rpm) were obtained using the response surface methodology. Up to 98.9% of the M. aeruginosa cells were removed intact at low Tanfloc dosage. During floc storage, Tanfloc initially protected the cells. After 8 d, large-scale cell lysis occurred because Tanfloc had substantially decomposed. Nevertheless, Tanfloc also extended the extracellular MC-LR and protein release time to 8 d. This delay ensured adequate time to decontaminate sludge containing the algae, thereby reducing the risk of secondary pollution. In addition, the low cost of Tanfloc facilitates its widespread application in the management of harmful algal blooms.