Overview of microalgal extracellular polymeric substances (EPS) and their applications

Rapid formation of partial denitrification biofilm using gas-liquid separation membrane as carrier: Performance and mechanism

Partial denitrification (PD) can ensure stable supply of electron acceptors for anaerobic ammonia oxidation, and biofilm is an effective method to prevent biomass loss, which are crucial for stable operation of PD. In this study, hydrophobic hollow-fiber gas-liquid separation membranes were placed in a denitrification sequencing batch reactor, and dense biofilms were formed within just 3 days. Confocal laser microscopy showed the preferential attachment of the protein (PN) content in extracellular polymeric substances (EPS) to the membrane surface, followed by exopolysaccharides. Further analyses showed the decrease in the types of signal molecules from six to two (i.e., C4-HSL, C6-HSL) due to negative pressure operation. Importantly, the concentration of C4-HSL increased dramatically with the increase in PN concentration, suggesting that negative pressure promoted the synthesis of C4-HSL signal molecules, which further mediated the secretion of PN for biofilm formation. In addition, biofilm formation was accompanied by nitrite accumulation, leading to successful achievement of PD. Furthermore, 60 % of nitrate-to-nitrite transformation ratio was obtained even when COD/N was increased from 4.5 to 5.0 and influent nitrate concentration was reduced to 25 mg/L. This confirmed the stability of PD, which was mainly attributed to a change in the microbial community and a decrease in nitrite reductase (Nir) activity, with microorganisms enriched through the gas-liquid separation operation exhibiting low Nir activity. This study provides a new method for rapid formation of biofilm for wastewater treatment and stable operation of PD.

Heterogeneous microstructure induces floatation in high-rate anammox granules

The floatation of anammox granules can be a serious challenge in practical wastewater treatment, as it can deteriorate reactor performance and cause bacterial loss. To deepen the understanding of floatation mechanism, in this study, both the floating (F-AnGS) and settling anammox granules (S-AnGS) from a high-rate anammox reactor were comparatively investigated. F-AnGS demonstrated 1.6 times higher specific anammox activity compared to S-AnGS, but only 65 % of produced gas could be successfully released, as quantified by anaerobic respirometry. In addition to the overall EPS accumulation, F-AnGS exhibited a heterogeneous microstructure distinct from that of S-AnGS, as revealed by 3D X-ray microscopic imaging at the single granule level. The heterogeneous distribution of EPS, which can form a dense surface layer, was the main cause for granule floatation. The heterogeneous microstructure of F-AnGS can reduce the distance between microorganisms and enhance the metabolic interaction between anammox bacteria and heterotrophs. The abundance of community members did not have a significant variation, but the functional genes related to anammox and partial denitrification pathway were significantly increased, indicating the enhanced nitrite loop in F-AnGS. This study proposed new structural insights into mechanism of anammox granule floatation, suggesting the appropriate activity control of granule-based anammox process.

Optimizing calcium and magnesium in seawater medium with high bicarbonate concentration for efficient growth and self-flocculation harvesting of Chlorella sp

Microalgae cultivation using high bicarbonate concentration in seawater medium triggers CaCO3 precipitation due to pH elevation, contaminating the photobioreactor and reduce biomass productivity. It is necessary to control Ca2+ and Mg2+ concentration in appropriate range to allow microalgae rapid growth without precipitation, followed by effective self-flocculation for harvesting. This study optimized this concentration range as 0.5-1.0 mmol L-1 for Ca2+ and 2.5-5.0 mmol L-1 for Mg2+. With this concentration, subsequent pH adjustment to 11 induced > 90 % self-flocculation efficiency. Also, outdoor cultivation in floating photobioreactors utilized treated seawater with optimized Ca2+ and Mg2+ concentration achieved productivity of 9.36 g m-2 day-1, which is 112 % higher than untreated seawater (4.42 g m-2 day-1). The optimized process reached the goal of higher biomass productivity without precipitation and efficient harvesting. On the other hand, microalgae-induced precipitation may serve as potential carbon sink, contributing to ocean-negative carbon emissions.

Microalgal biorefineries in sustainable biofuel production and other high-value products

Microalgae has been emerging as a promising solution against the backdrop of the global need for sustainable, eco-friendly alternatives. This review article analyses the use of photosynthetic microalgae as an important resource for sustainable biofuel and high value bioproduct production, emphasizing the potential of self-sustaining microalgae biorefineries. A closed-loop, integrated multi-product producing microalgal biorefinery approach could significantly reduce the indicated negative environmental and energy impact from standalone microalgal biofuel generation. The economic feasibility of these biorefineries is linked to their recovery rate, improved by integrating various unit operations as well as multiple product dimensions under optimal conditions, enhancing resource recovery, process efficiency, and profitability. This approach ensures profitability and ubiquitous implementation of microalgal biorefineries, offering a sustainable solution to market demands. In conclusion, making microalgae biorefineries a major player in sustainable bioeconomy underscores the necessity of interdisciplinary research to surmount current challenges and completely realize their advantages.

Multifaceted separations approach for elucidation of the physical and chemical properties of extracellular hydrocolloids

A multifaceted separations platform that incorporates the strengths of asymmetrical flow field-flow fractionation with multi-detectors (AF4-MD), high performance anion exchange chromatography (HPAEC), and hydrophilic interaction liquid chromatography with mass spectrometry (HILIC-MS) is developed to obtain a more complete picture of the molecular weights (MW), composition, and salt-induced aggregation behavior of extracellular polymeric substances (EPS) produced by the algae Chlorella vulgaris. The absence of a stationary phase makes AF4-MD particularly well suited for characterizing polydisperse hydrocolloid polymers as well as studies that investigate the effect of ionic environments that aligns with the natural environment of C. vulgaris. Fractionation of C. vulgaris EPS revealed three distinct MW populations ranging from 4 × 10⁴ to 3 × 10⁸ Daltons. This exceeds the previously reported MW by three orders of magnitude and reports a previously unknown size subpopulation. The optimized AF4-MD technique was then used to produce two size fractions that were probed using HPAEC and LC-MS. These orthogonal methods uncovered compositional heterogeneity across fractions, with variations in monosaccharides and amino acids. AF4-MD is also well suited for studying the behavior of EPS in the presence of different salts. For each salt studied, e.g., NaNO3, NaCl, and MgCl2, an increase in solution ionic strength results in aggregation as corroborated by a shift to higher MWs. Each salt exhibited distinct effects on EPS aggregation, with NaCl causing the least aggregation and MgCl2 the most. These findings highlight the need for multiple techniques when analyzing complex polymers such as EPS and the benefits of AF4-MD in elucidating complex polymer behaviors in different ionic environments.

A metabolic enzyme-photosynthetic machinery involved in the co-metabolism of enrofloxacin and ciprofloxacin by Chlorella pyrenoidosa

The removal of fluoroquinolone antibiotics from wastewater continues to pose significant challenges, as conventional treatment methods often prove ineffective against these persistent pollutants. However, microalgal-mediated treatment has emerged as a promising alternative, leveraging its unique potential to degrade recalcitrant contaminants. This study investigates the removal of enrofloxacin (EFX) and ciprofloxacin (CFX) by Chlorella pyrenoidosa, integrating transcriptomics, gene network analysis, and co-metabolic pathways to unravel the mechanisms driving pollutant degradation. Among the four co-metabolic substrates evaluated, glucose and glycine were identified as the most effective in enhancing the degradation of EFX and CFX, respectively. Glycine primarily upregulated genes associated with nitrogen metabolism, while glucose stimulated both photosynthesis and nitrogen metabolism pathways. This synergistic co-metabolic interaction promoted the development of an integrated metabolic enzyme-photosynthetic machinery, which enhanced electron transport, energy generation, catalytic enzyme expression, and extracellular polymeric substance (EPS) production, ultimately leading to a significant increase in the degradation rates of EFX and CFX. Mass balance analysis revealed that biotransformation processes, including defluorination, decarboxylation, hydroxylation, and other transformations, were the predominant mechanism for pollutant removal. Fluorine was detected within microalgal cells using transmission electron microscopy coupled with energy dispersive X-ray spectroscopy (TEM-EDS). A total of eight transformation products (TPs) were identified, and their non-toxic effects on three tested organisms suggest environmentally benign outcomes. These findings provide valuable insights into the mechanisms underlying microalgae-mediated degradation of fluoroquinolone antibiotics and highlight the potential of microalgae-based technologies a sustainable solution for mitigating antibiotic pollution in wastewater.

Microalgae for phosphorus chemical wastewater treatment and recovery of phosphorus

In this study, we have found a new method to recovery phosphorus selectively from high-fluoride-phosphoric wastewater. This new method was a microalgae-based phosphorus recovery technology.The results showed that Chlorella sp. can not only grew very well in high-fluoride-phosphoric wastewater, but also has the highest ability to reduce the phosphorus from the wastewater among Scenedesmus sp., Selenastrum bibraianum and Chlamydomonas sp. After Chlorella sp. cultured for 16 days, the concentration of phosphorus decreased from 12.76 mg/L to 5.00 mg/L. There were two ways to reduce phosphorus by Chlorella sp. One was the specific uptakes phosphorus into algal cells and the other was absorbs phosphorus through the functional groups on the EPS. These algal cells can be separated from the wastewater through harvesting or other methods, enabling the subsequent recovery of phosphorus. The results of this study could provide valuable information for phosphorus recovery from high-fluoride-phosphoric wastewater.

Ca2+ enhanced the wastewater treatment performance of microalgal-bacterial consortia: Response of extracellular polymeric substances and bacterial communities

The technology of microalgae-bacteria consortia (MBC) for wastewater treatment is currently facing a variety of challenges. One of the main issues is the construction of structurally and functionally stable symbiont. Ca2+ may be involved in this process, but the underlying mechanism is not well understood. Here the response of MBC to the regulation of Ca2+ was systematically explored from the perspectives of extracellular polymeric substances (EPS) and bacterial communities. The results showed that the exogenous addition of Ca2+ (10-50 mM) not only promoted the production of extracellular polysaccharides and proteins of MBC, but also increased the proportion of some functional groups and components of EPS, such as CO and α-helix. The change of EPS characteristics was conducive to provide more sites for bining Ca2+, which in turn favored the formation of compact MBC via overcoming electrostatic repulsive effect. Besides, the supplementation of Ca2+ favored the recruitment of more EPS-producing bacteria (such as Rhodobacter, Pedobacter, Rhizorhapis, and Sphingopyxis) and indole acetic acid producing bacteria (such as Hydrogenophaga and Agromyces). The enrichment of these functional bacteria not only promoted the adhesion between bacteria and microalgae, but also promoted the growth of symbiotic microalgae, which contributed to the formation of stable large-sized MBC. The change in structure and function of MBC was ultimately reflected in the improved performance in treating municipal wastewater. The findings of this study provided insights into the mechanism underlying the enhanced performance of MBC for wastewater treatment under the influence of Ca2+.

A 3D porous electrode for real-time monitoring of microalgal growth and exopolysaccharides yields using Electrochemical Impedance Spectroscopy

Efficient monitoring of microalgal growth is vital for biomass industrialization and management of water resources. The precise determination of growth phases of biotechnologically relevant species of microalgae is necessary as it allows controlling the onset of target metabolites production such as exopolysaccharides (EPS). However, a low-cost, real-time and ultrasensitive measurement method for direct determination of real-time microalgal growth and EPS production does not exist. Here, we show that Electrochemical Impedance Spectroscopy (EIS) in combination with porous polyurethane(PU)/poly (3,4- ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) electrodes can be used as a real-time probe to monitor microalgal growth and EPS production. We employ Lobochlamys segnis as a microalgae model system and show that growth can be continuously monitored with EIS for 14 days. A logistic growth rate from impedance data of kZ = 0.75/day is found similar to that of conventional cell counting, of kcells = 0.85/day, and is extracted from initial cell seeding densities as low as 105 cells/mL. Furthermore, the Ohmic resistance of electrolyte solution enables the detection of the time-point of maximum EPS production. The combination of ultra-large porous electrodes with EIS provides a platform for sensing and modelling of microalgae growth in real-time and opens new avenues for predictive water resource management as well as more effective large-scale microalgal production in biotechnological applications.

Mimicking natural biomineralization enabling biodegradable and highly lipophobic alginate hydrogels

Microorganisms can induce biomineralization of inorganic ions to form a lipophobic layer on the surface of cave rocks. Mimicking this, we developed and propose a protocol that produces a highly lipophobic hybrid layer of CaCO3 nanoparticles on hydrogel surfaces. This lipophobic layer endows hydrogels with an oil contact angle of 162°, causing oil droplets placed on the surface to bead up and roll off immediately. The lipophobic surface effectively resists staining from lipophilic dyes, and does not adhere to double-sided tapes. A lipophobic layer on hydrogel tubes effectively prevents the adhesion of thrombus and axunge during a three-day implantation period in rabbits. The hydrogel tubes, made of biodegradable sodium alginate, can serve as implantable scaffolds, degrading in the body, and avoiding the need for removal surgery. These properties make hydrogel tubes promising for medical devices like absorbable stents and catheters.

Accurate Quantification of Metals in Individual Synechocystis sp. PCC 6803 Cells by Single-Cell ICP-MS: Dual-Calibration and Sample Stabilization Strategies

Single-cell inductively coupled plasma mass spectrometry (SC-ICP-MS) is an emerging technique to investigate metal heterogeneity in individual cells. However, due to the absence of consistent calibration and suitable stabilization strategy for cells, accurate quantification of cellular heterogeneity and the content of metals remains a challenge. Herein, an accurate quantification method for the content and heterogeneous distribution of metals among individual microalgae cells was developed based on SC-ICP-MS using dual-calibration strategies and robust pretreatment methods. Gold nanoparticles (AuNPs) were used as calibration for measuring metal contents in single cells, but it would lead to a 13.6-63.1% underestimation of cell numbers due to inaccurate detection of cells' transport efficiency. To avoid this inaccuracy, we proposed an additional calibration strategy to measure cellular transport efficiency and cell numbers using endogenous Mg, enabling a more accurate assessment of cell heterogeneity. Then, an effective pretreatment method was optimized through fixation of cells with glutaraldehyde for 1 h to maintain the cellular stability and obtain accurate results, with satisfactory recoveries for cell number (98.4%) and Mg contents (91.7%), even after long-time storage. After optimization, the proposed method showed high sensitivity and repeatability in both cellular metal contents (Mg, Hg, Cd, and Co) and cell number, with detection limits (LODs) to be 0.14-0.53 fg/cell and 5.5 × 103 cells/mL, respectively. Finally, the proposed method was successfully used for detecting various metals and their heterogeneity in Synechocystis sp. PCC 6803 cells provided an accurate and robust tool for investigating the uptake and heterogeneous distribution of metals in microalgae.

The microalgal sector in Europe: Towards a sustainable bioeconomy

Microalgae are a diverse group of photosynthetic microorganisms that can be exploited to produce sustainable food and feed products, alleviate environmental pollution, or sequester CO2 to mitigate climate change, among other uses. To optimize resource use and integrate industrial waste streams, it is essential to consider factors such as the biology and cultivation parameters of the microalgal strains, as well as the cultivation system and processing technologies employed. This paper reviews the main commercial applications of microalgae (including cyanobacteria) and examines the biological and biotechnological aspects critical to the sustainable processing of microalgal biomass and its derived compounds. We also provide an up-to-date overview of the microalgal sector in Europe considering the strain, cultivation system and commercial application. We have identified 146 different microalgal-derived products from 66 European microalgae producers, and 49 additional companies that provide services and technologies, such as optimization and scalability of the microalgal production. The most widely cultivated microalga is 'spirulina' (Limnospira spp.), followed by Chlorella spp. and Nannochloropsis spp., mainly for human consumption and cosmetics. The preferred cultivation system in Europe is the photobioreactor. Finally, we discuss the logistic and regulatory challenges of producing microalgae at industrial scale, particularly in the European Union, and explore the potential of new genomic techniques and bioprocessing to foster a sustainable bioeconomy in the microalgal sector.

Qualitative Assessment of Microalgae-Bacteria Biofilm Development on K5 Carriers: Photoheterotrophic Growth in Wastewater

Wastewater (WW) treatment using biofilms harboring bacteria and microalgae is considered a promising polishing solution to improve current treatment technologies present in wastewater treatment plants (WWTPs), but their interaction in a sessile community remains to be understood. In this work, multi-species biofilms of Chlorella vulgaris, Chlorella sorokiniana, or Scenedesmus obliquus were selected as representative microalgae species of interest for WW bioremediation, and Rhodococcus fascians, Acinetobacter calcoaceticus, or Leucobacter sp. were selected as the bacteria for co-cultivation in a synthetic WW since they are normally found in WW treatment processes. The attached consortia were developed in specific carriers (K5 carriers) for 168 h, and their biofilm formation ability was evaluated in a profilometer and via scanning electron microscopy (SEM) imaging. From the selected microorganisms, C. sorokiniana was the microalga that adapted best to co-cultivation with R. fascians and A. calcoaceticus, developing a thicker biofilm in these two consortia (3.44 ± 0.5 and 4.51 ± 0.8 µm, respectively) in comparison to the respective axenic cultures (2.55 ± 0.7 µm). In contrast, Leucobacter sp. did not promote biofilm growth in association with C. vulgaris and C. sorokiniana, while S. obliquus was not disturbed by the presence of this bacterium. Some bacterial clusters were observed through SEM, especially in A. calcoaceticus cultures in the presence of microalgae. In some combinations (especially when C. vulgaris was co-cultivated with bacteria), the presence of bacteria was able to increase the number of microalga cells adhered to the K5 carrier. This study shows that biofilm development was distinctly dependent on the co-cultivated species, where synergy in biofilm formation was highly dependent on the microalgae and bacteria species. Moreover, profilometry appears to be a promising method for biofilm analyses.

Unravelling the mechanism of residual sludge promoting rapid formation of microalgal-bacterial granular sludge: Enhancement of extracellular polymers substances and electron transfer efficiency

Microalgal-bacterial granular sludge (MBGS) is a sustainable biotechnology that has attracted increasing attention, but there remains limited knowledge about the utilization of residual sludge generated from MBGS. This present work proposed a promising approach to rapidly construct the MBGS system from activated sludge by inoculating residual microalgal-bacterial sludge. Compared with inoculated activated sludge, the newly formed MBGS maintained a stable structure, higher biomass content (4.51 g/L), better settleability (42 mL/g), and higher pollutant removal. The results indicated that inoculation of residual sludge resulted in higher extracellular polymeric substances (EPS) content and promoted the microbial aggregation. Besides, this increase effectively improved the electron transfer efficiency within the particle, which facilitated the granulation of MBGS. Microbial community analysis revealed that the dominant bacteria (Pseudofulvimonas and Thauera) were mainly responsible for the secretion of EPS. Furthermore, the nitrogen and phosphorus metabolic pathways were also promoted to some certain extent. In conclusion, the inoculation of residual sludge can achieve an effective reduction in granulation period. This study provides a novel insight and fills the gap in the utilization of residual sludge generated by MBGS.

Extracellular polymers substances towards the toxicity effect of Microcystis flos-aquae under subjected to nanoplastic stress

The widespread presence of nanoplastics in aquatic ecosystems and their harmful effects on algae have garnered significant attention. However, little is known about the mechanisms of extracellular polymeric substances (EPS) derived from algae in response to nanoplastic stress. This study investigated the impact of EPS on the toxicity of polyvinyl chloride (PVC, 537 nm) and polymethyl methacrylate (PMMA, 485 nm) nanoplastics on Microcystis flos-aquae (MFa)under nanoplastic stress. The results revealed that EPS removal reduced algal biomass. PVC nanoplastics (250 mg L-1) caused biomass inhibition of -16.87% before and -9.82% after EPS removal. PMMA nanoparticles exhibited a more significant inhibition of growth and chlorophyll synthesis compared to PVC. After EPS removal, algal cells gradually recovered their maximum quantum yield of photosystem II and exhibited increased superoxide dismutase (SOD) enzyme activity, suggesting a self-regulation mechanism. Nanoplastic stress elevated EPS protein and polysaccharide levels, with maxima of 12.38 mg L-1 at 50 mg L-1 PVC and 17.24 mg L-1 at 100 mg L-1 PMMA. At the same time, the polysaccharide content in nanoplastics was significantly higher than that of proteins, with the maximum value being 2.82 times that of proteins. Fourier-transform infrared spectroscopy (FTIR) and excitation-emission matrix (EEM) analyses showed that aldehyde functional groups on the surface of algal cells were oxidized into carboxylic acids by both types of nanoparticles. Exposure to different nanoplastics increased humic-like substances in tightly bound EPS (TB-EPS), indicating that EPS dynamically adjusts to reduce nanoplastic toxicity by enhancing viscosity and algal aggregation. These results demonstrate that EPS mitigates the direct contact between algal cells and nanoplastics by increasing viscosity and promoting algal self-aggregation, thereby reducing the toxicity of nanoplastics to algae. This phenomenon is consistent across various stress conditions, providing valuable insights into the self-protection mechanisms of microalgae against nanoplastic stress.

Spotlight on the long-term effects of micro/nanoplastics exposure on Spirulina platensis: Algal cells, extracellular polymeric substances, and phycocyanin

Spirulina platensis (SP) provides humans with proteins and natural pigments. The effects of micro/nanoplastics (MNPs) on SP are of great interest. We focused on the effects of high concentrations (100-300 mg/L) of polystyrene MNPs on SP for 50 days. MNPs caused growth retardation, a decrease in peak concentration of algal cells, the emergence of surface cracks and pores, and stimulated the secretion of extracellular polymeric substances that promoted heterogeneous aggregation of SP. During the first 35 days, there were significant differences between the exposure groups in the phycocyanin concentration, yield and purity and the ratio of phycocyanin to phycobiliprotein, with the higher MNPs concentration resulting in lower values, whereas on day 50 there were no statistically significant differences in any of these metrics between the control or exposure groups. This study enriches the knowledge about the long-term effects of MNPs on SP for microalgae culture and food industry.

Differences in Carbon and Nitrogen Cycling Strategies and Regional Variability in Biological Soil Crust Types

Biological soil crusts (BSCs) play a pivotal role in maintaining ecosystem stability and soil fertility in arid and semi-arid regions. However, the biogeographical differences in soil functional composition between cyanobacterial BSCs (C-BSCs) and moss BSCs (M-BSCs), particularly how environmental changes affect nutrient cycling strategies and microbial community functions, remain poorly understood. In this study, we investigated BSCs across aridity gradients (semi-humid, semi-arid, and arid regions) in China, focusing on carbon and nitrogen cycling pathways, enzyme activities, and nutrient acquisition strategies. It was found that aridity and BSC type had significant effects on the functional characteristics of microorganisms. This was demonstrated by significant differences in various soil microbial activities including enzyme activities and carbon and nitrogen nutrient cycling. With increasing aridity, C-BSCs exhibited reduced carbon cycling activity but enhanced nitrogen cycling processes, whereas M-BSCs displayed diminished activity in both carbon and nitrogen cycling. These divergent strategies were linked to soil properties such as pH and organic carbon content, with C-BSCs adapting through nitrogen-related processes (e.g., nifH, amoA) and M-BSCs relying on C fixation and degradation. These findings provide novel insights into the functional gene diversity of BSCs across different regions, offering valuable references for ecological restoration in arid areas. Specifically, our study highlights the potential of BSC inoculation for carbon and nitrogen enrichment in arid regions, with implications for climate-resilient restoration practices.

Microalgae-Derived Microparticles Improve Immunomodulation via Combined Glycolysis and MAPK Activation

Natural polysaccharides possess potent immunostimulatory properties, but their poor solubility impedes efficiency of cellular delivery. This study focuses on extraction of microparticles (MPs) fromEuglena gracilis, a microalgae species characterized by abundant intracellular β-1,3-glucan and flexible cell membrane. We introduce anE. gracilis-derived MP (MPEG) system as a natural carrier for solubilized β-glucan. The MPEG system enhances β-glucan's solubility and loading efficiency through sequential sonication and cell extrusion. In vitro studies reveal that MPEG utilizes multiple endocytosis pathways, including phagocytosis, clathrin-mediated, and lipid raft-mediated routes, for effective β-glucan delivery into cells. Upon cellular internalization, MPEG components trigger dual activation of the MAPK signaling pathway and glycolysis in macrophages, leading to enhanced production of pro-inflammatory cytokines and lactic acid, ultimately strengthening innate immune responses. This MPEG system offers a promising approach to harnessing the immunostimulatory properties of natural polysaccharides while overcoming their solubility limitations, opening new avenues for targeted cellular delivery in immunomodulation therapies.

Impact of Heterosigma akashiwo on the environmental behavior of microplastics: Aggregation, sinking, and resuspension dynamics

Aggregation processes of microalgae have significant effects on the vertical distribution of microplastics (MPs) in the marine environment. This study explored how the harmful microalga Heterosigma akashiwo affects the aggregation and sinking characteristics of four types of MPs: low and high-density polyethylene (PE) spheres, and small and large polypropylene (PP) fragments. The aggregation of MPs was primarily driven by extracellular polymeric substances (EPS) rather than direct attachment to the cells, contributing to their sinking. The sinking of low-density PE spheres followed a logistic function, saturating at 28 % with a half-saturation time of 9 days. In contrast, small PP fragments sank minimally (under 2 %) and large PP fragments showed almost no sinking, indicating the varying impacts of MP density and size. The sinking velocity of the MP aggregates was significantly lower for low-density PE spheres (0.63 mm∙s-1) than for high-density PE spheres (0.81 mm∙s-1), despite no significant differences in aggregate size or MP particle number. This result may suggest that low-density MPs could potentially affect marine carbon cycle. Furthermore, no clear evidence was found for the resuspension of the settled aggregates due to bacterial decomposition under dark and cold conditions. As the first experimental study to explore the aggregation, sinking, and resuspension of different MPs in the presence of H. akashiwo, these findings, when integrated with field observations and modeling studies, provide valuable insights for predicting MP distribution in marine environments.

Less toxic combined microplastics exposure towards attached Chlorella sorokiniana in the presence of sulfamethoxazole while massive microalgal nitrous oxide emission under multiple stresses

Microalgae-based wastewater treatment could realize simultaneous nutrients recovery and CO2 sequestration. However, impacts of environmental microplastics (MPs) and antibiotic co-exposure on microalgal growth, nutrients removal, intracellular nitric oxide (NO) accumulation and subsequent nitrous oxide (N2O) emission are unclarified, which could greatly offset the CO2 sequestration benefit. To reveal the potential impacts of environmental concentrations of MPs and antibiotic co-exposure on microalgal greenhouse gas mitigation, this study investigated the effects of representative MPs (PE, PVC, PA), antibiotic sulfamethoxazole (SMX), and nitrite (NO2--N) in various combinations on attached Chlorella sorokiniana growth, nutrients removal, anti-oxidative responses, and N2O emission originated from intracellular NO build-up. Microalgal biofilm growth was more inhibited under 10 μg/L MPs than 100 μg/L SMX, and MPs+SMX co-exposure displayed toxicity antagonism while MPs+MPs co-exposure caused toxicity synergism (up to 66 % growth inhibition). Extracellular polysaccharides content correlated well with microalgal biofilm density under various stresses, while SMX involved stresses displayed chlorophyll a content reduction. Microalgal assimilation and MPs adsorption contributed to nutrients removal, and phosphorus removal displayed less variance among different stresses (residual phosphorus <0.5 mg/L) than nitrogen. Intracellular NO conversion to N2O almost doubled during the co-exposure processes, and N2O emission under NO2--N + PE+PVC co-exposure could offset the contribution of microalgal CO2 sequestration by as high as 176.2 %. Results of this study appealed for urgent concern regarding environmental MPs and antibiotic co-exposure on primary producers' growth characteristics and their greenhouse gas mitigation properties.

Deciphering the promotion and inhibition of bicarbonate fertilization on microalgal activity and nutrient uptake from wastewater

Microalgal bioremediation is a promising alternative for biological wastewater treatment but constrained by low microalgal activities. Here, bicarbonate fertilization was introduced to enhance microalgal wastewater treatment, with systematic investigations of its biphasic dose-dependent effects on microalgal activity and nutrient uptake. The results showed that moderate inorganic carbon (MIC, 0.05 M) group significantly improved the biomass production, NH4+-N removal, and PO43--P removal by 76.0%, 21.3%, and 11.9%, respectively; whereas high inorganic carbon (HIC, 0.1 M) group inhibited them by 11.0%, 4.48%, and 52.7%, respectively, compared with low inorganic carbon (LIC, 0.005 M) group. Mechanistic analyses suggested that LIC group encountered high alkalinity, exacerbated carbon/trace element limitation, and attenuated extracellular polymeric substances (EPS) barriers and antioxidant systems; while HIC group increased salinity stresses, triggered morphological defense, and diminished light harvesting and phycospheric mass transfer, restricting microalgal activity and nutrient uptake. In contrast, MIC group relieved carbon limitation, accelerated photosynthetic electron transfer, and sustained intracellular redox homeostasis, underpinning the highest biomass production and nutrient removal. These findings could facilitate the practical application of bicarbonate fertilization in microalgal wastewater treatment.

Recent advances in polysaccharide-dominated extracellular polymeric substances from microalgae: A review

Microalgae are an environmentally friendly and sustainable alternative resource for future food and pharmaceutical production. Microalgal extracellular polymeric substances (EPMS) are polymers consisting of polysaccharides, proteins, lipids and nucleic acids secreted by microalgal cells. This review systematically summarizes the research progress of microalgal EPMS, including its composition, structure, formation, biological activity and application. The diversity of structural units and binding modes confers microalgal EPMS with unique structural and biological activity, which is species-specific. In addition to the polysaccharides with antioxidant, antiviral, and antitumor effects, extracellular vesicles isolated from microalgal EPMS are emerging as new drug carriers. However, challenges such as relatively low yields, complex separation techniques, intricate processing-secretion pathways, and unclear mechanisms of action still hinder the industrial application of microalgal EPMS. By scientifically summarizing the research progress and leveraging strategies such as metabolic regulation, genetic modification, and advanced separation and characterization technologies, microalgal EPMS is expected to see widespread applications in the food, cosmetics, and therapeutic industries.

Responses of different species of marine microalgae and their community to gear-derived microplastics

The impact of gear-derived microplastics (MPs) on microalgal community stability is unknown. In this work, three types of gear-derived MPs were obtained from floats, pallets, and tires. After exposure to individual microalgal species (Phaeodactylum tricornutum, Chaetoceros curvisetus, Chlorella vulgaris, Isochrysis galbana), small-sized MPs (22 μm) exhibited stronger toxicity than large-sized MPs (135 μm), and the toxicity was MPs concentration independent. The three MPs (1 mg/L) significantly inhibited the growth of P. trichodinium, C. curvisetus and I. galbana. P. tricornutum was the most sensitive species, and the MPs decreased its chl a content, increased ROS level and reduced membrane integrity. Strong heteroaggregation with MPs is a cause of the observed toxicity. Furthermore, algal community was constructed using these four algal species, and P. tricornutum became the dominant species after community stability. After 96-h exposure to small-sized MPs at all the tested concentrations, the proportion of P. tricornutum highly decreased, thus increasing community stability and diversity maintenance. Photo-aging (20 days) further decreased algal number in the community from 16.54 % (original MPs) to 25.12 % (photo-aged MPs), while the Shannon diversity index increased from 0.93 to 0.99. The introduction of harmful algae (Alexandrium tamarense) decreased total algal number in algal community by 45.10 %, and led to the replacement of dominant species to C. vulgaris. Interestingly, algal number after the exposure of MPs and aged MPs recovered by 7.59 % and 14.71 %, respectively. This work provides useful information on the risk of gear-derived MPs to microalgal community in marine environments (especially mariculture areas).

Lead biosorption and chemical composition of extracellular polymeric substances isolated from mixotrophic microalgal cultures

Extracellular polymers (EPS) produced by microalgae are considered an important factor in the process of biosorption of environmental contaminants. The study investigated the impact of mixotrophic cultivation of unicellular algae Chlorella vulgaris, Parachlorella kessleri, and Vischeria magna on the specific productivity and yield of total and soluble EPS as well as the biochemical composition and sorption properties of extracellular polymers in order to explore their potential to be used for biosorption. The results showed that the mixotrophic conditions enhanced the productivity and contributed to changes in the biochemical and monomer composition of EPS. Higher levels of total sugars, reducing sugars, protein, and phenolic compounds and reduced content of uronic acids were observed in the EPS isolated in the mixotrophic conditions. Rhamnose, xylose, mannose, glucose, and galactose were detected in the mixotrophic EPS samples. FTIR and ICP-OES were applied to characterise the structure of EPS and their role in Pb(II) removal. The results showed that the carboxyl groups and hydroxyl groups observed in the mixotrophic EPS played an important role in the Pb(II) sorption process. The EPS from the mixotrophic C. vulgaris cultures showed the highest potential for the removal of Pb(II) and the highest sorption capacity.

Mixotrophic Cultivation of Dunaliella tertiolecta in Cheese Whey Effluents to Enhance Biomass and Exopolysaccharides (EPS) Production: Biochemical and Functional Insights

The rapid growth of the dairy industry has resulted in a significant increase in the generation of effluents, which are characterized by a high organic content that poses environmental challenges. In alignment with sustainable practices and the principles of the circular economy, this study investigates the valorization of cheese whey (CW) effluents through the cultivation of the microalga Dunaliella tertiolecta under mixotrophic conditions. The research aims to utilize cheese whey effluents as a supplemental growth medium to enhance the production of algal biomass and extracellular polymeric substances (EPSs). The results reveal that CW facilitated a 37% improvement in D. tertiolecta growth and led to an approximately eight times greater biomass productivity compared to under photoautotrophic conditions, while the EPS production increased by 30%. Chemical and techno-functional analyses of the microalgal biomass and EPSs suggest promising applications as natural product additives for the food industry. Biomass derived from photoautotrophic culture demonstrated greater antioxidant activity and total polyphenols content. Additionally, the lipid profile revealed 16 distinct fatty acids. On the other hand, biomass from the mixotrophic culture exhibited higher protein levels and eight fatty acids, indicating the influence of the cultivation mode on the biochemical composition. Regarding the EPSs, mixotrophic cultivation resulted in elevated antioxidant activity and total polyphenols content, as well as higher protein and sugar levels. Furthermore, the EPSs produced under mixotrophic conditions exhibited superior techno-functional properties compared to those of the photoautotrophic culture, making them ideal candidates for use as alternative natural food additives.

Accessing the biotechnological potential of a novel isolated microalga from a semi-arid region of Brazil

The use of microalgae as a source of food and pharmaceutical ingredients has garnered growing interest in recent years. Despite the rapid growth of the nutraceutical market, knowledge about the potential of bioactive molecules from microalgae remains insufficient. The present study aimed to investigate the biotechnological potential of the green microalga Desmodesmus armatus isolated from a semi-arid region of Brazil. The algal biomass was characterized in terms of gross biochemical composition, exopolysaccharide content, enzymatic inhibition capacity, and antioxidant, antibacterial, and hemolytic activities from solvents of different polarities (water, ethanol, acetone, and hexane). D armatus biomass had 40% of crude protein content, 25.94% of lipids, and 25.03% of carbohydrates. The prebiotic potential of exopolysaccharides from D armatus was demonstrated, which stimulated the growth of Lacticaseibacillus rhamnosus and Lactiplantibacillus plantarum bacteria strains. Moreover, the enzyme inhibition capacity for the proteases chymotrypsin (34.78%-45.8%) and pepsin (16.64%-27.27%), in addition to α-amylase (24.79%) and lipase (31.05%) was confirmed. The antioxidant potential varied between the different extracts, with 2,2-diphenyl-1-picrylhydrazyl sequestration values varying between 17.51% and 63.12%, and those of the 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) method between 6.82% and 22.89%. In the antibacterial activity test, only the ethanolic extract showed inhibition against Listeria sp. (at minimum inhibitory concentration [MIC] = 256 µg mL-1). This fraction also presented the highest significant levels of hemolysis (31.88%-52.45%). In summary, the data presented in the study suggest the presence of biocompounds with biotechnological and nutraceutical potential in the D armatus biomass. Future studies may evaluate the inclusion of this biomass in foods in order to increase their biological value.

Effects of stratified microbial extracellular polymeric substances on microalgae dominant biofilm formation and nutrients turnover under batch and semi-continuous operation

Extracellular polymeric substances (EPS) are well-acknowledged to accelerate microalgal biofilm formation, yet specific role of stratified EPS is unknown. Bacterial biofilm stratified EPS could enrich phosphorus, whether microalgal biofilm stratified EPS could also realize phosphorus or nitrogen enrichment remains unclarified. This study investigated microalgae dominant biofilm growth characteristics and nutrients removal via inoculating microalgae and stratified bacterial EPS at various microalgae:bacteria ratios. Soluble-EPS favored biofilm establishment and chlorophyll synthesis, while loosely-bound (LB-EPS) and tightly-bound EPS (TB-EPS) improved phosphorus removal, and optimum microalgae:bacteria cell count ratio was 1:0.5. Under semi-continuous operation, stable and efficient nutrients removal was observed at hydraulic retention time (HRT) of 2 days. Both nitrogen and phosphorus enrichment by TB-EPS over LB-EPS (respectively up to 7.9 and 23.8 times) were innovatively discovered, with enhanced nutrients turnover efficiency at higher HRTs. This study provided direct evidences regarding the role of stratified EPS on microalgal biofilm development and nutrients turnover.

Innovative strategies for utilizing microalgae as dual-purpose biofertilizers and phycoremediators in agroecosystems

The increasing need for sustainable agricultural practices due to the overuse of chemical fertilizers has prompted interest in microalgae as biofertilizers. This review investigates the potential of microalgae as biofertilizers and phycoremediators within sustainable agroecosystems, addressing both soil fertility and wastewater management. Microalgae provide a dual benefit by absorbing excess nutrients and contaminants from wastewater, generating nutrient-rich biomass that can replace chemical fertilizers and support plant growth. Implementation strategies include cultivating microalgae in wastewater to offset production costs, using closed photobioreactor systems to enhance growth efficiency, and applying microalgal biomass directly to soil or crops. Additionally, microalgae extracts provide essential bioactive compounds, such as phytohormones and amino acids, that enhance plant growth and resilience. While microalgae offer an eco-friendly solution for nutrient recycling and crop productivity, challenges in scalability, production cost, and regulatory frameworks hinder widespread adoption. This review highlights the potential pathways and technological advancements necessary for integrating microalgae into sustainable agriculture, emphasizing the need for interdisciplinary collaboration and innovative approaches to overcome these barriers. Ultimately, microalgae biofertilizers represent a promising approach to reducing environmental impact and advancing sustainable farming practices.

Carbon dioxide removal from triethanolamine solution using living microalgae-loofah biocomposites

Nowadays, the climate change crisis is an urgent matter in which carbon dioxide (CO2) is a major greenhouse gas contributing to global warming. Amine solvents are commonly used for CO2 capture with high efficiency and absorption rates. However, solvent regeneration consumes an extensive amount of energy. One of alternative approaches is amine regeneration through microalgae. Recently, living biocomposites, intensifying traditional suspended cultivation, have been developed. With this technology, immobilizing microalgae on biocompatible materials with binder outperformed the suspended system in terms of CO2 capture rates. In this study, living microalgae-loofah biocomposites with immobilized Scenedesmus acuminatus TISTR 8457 using 5%v/v acrylic medium were tested to remove CO2 from CO2-rich triethanolamine (TEA) solutions. The test using 1 M TEA at various CO2 loading ratios (0.2, 0.4, 0.6, and 0.8 mol CO2/mol TEA) demonstrated that the biocomposites achieved CO2 removal rates 3 to 5 times higher than the suspended cell system over 28 days, with the highest removal observed at the 1 M with 0.4 mol CO2/mol TEA (4.34 ± 0.20 gCO2/gbiomass). This study triggers a new exploration of integration between biological and chemical processes that could elevate the traditional amine-based CO2 capture capabilities. Nevertheless, pilot-scale investigations are necessary to confirm the biocomposites's efficiency.

Marine Algae Polysaccharides: An Overview of Characterization Techniques for Structural and Molecular Elucidation

Polysaccharides make up a large portion of the organic material from and in marine organisms. However, their structural characterization is often overlooked due to their complexity. With many high-value applications and unique bioactivities resulting from the polysaccharides' complex and heterogeneous structures, dedicated analytical efforts become important to achieve structural elucidation. Because algae represent the largest marine resource of polysaccharides, the majority of the discussion is focused on well-known algae-based hydrocolloid polymers. The native environment of marine polysaccharides presents challenges to many conventional analytical techniques necessitating novel methodologies. We aim to deliver a review of the current state of the art in polysaccharide characterization, focused on capabilities as well as limitations in the context of marine environments. This review covers the extraction and isolation of marine polysaccharides, in addition to characterizations from monosaccharides to secondary and tertiary structures, highlighting a suite of analytical techniques.

From microalgae to gastropods: Understanding the kinetics and toxicity of silver nanoparticles in freshwater aquatic environment

Silver nanoparticles (AgNPs) are increasingly used in various consumer products and industrial applications, raising concerns about their environmental impact on aquatic ecosystems. This study investigated the physicochemical stability, trophic transfer, and toxic effects of citrate-coated AgNPs in a freshwater food chain including the diatom Cyclotella meneghiniana and the gastropod Lymnaea stagnalis. AgNPs remained stable in the exposure medium, with a minimal dissolution (<0.06%) after 24 h, indicating that particulate forms dominated during exposure. AgNPs inhibited the growth of C. meneghiniana without significantly affecting chlorophyll-a content or reactive oxygen species (ROS) production. Scanning electron microscopy revealed extracellular polymeric substance (EPS) secretion, which likely formed eco-coronas, reducing AgNPs bioavailability and oxidative damage. However, trace element analysis showed significant depletion of iron, manganese, and nickel, indicating early metabolic stress and redistribution of essential metals to support antioxidant defenses. In L. stagnalis, toxicokinetic analysis showed distinct patterns of Ag uptake and depuration across exposure routes. Waterborne and foodborne exposure resulted in similar and higher Ag accumulation compared to the combined group. Waterborne exposure showed the highest non-eliminable fraction and a bioconcentration factor (BCF) > 1, indicating efficient uptake and retention. Foodborne exposure exhibited a biomagnification factor (BMF) > 1, despite efficient elimination. Combined exposure had the highest depuration rate, with BCF >1 and BMF <1, reflecting reduced trophic transfer potential. Oxidative stress in L. stagnalis was highest during combined exposure, with increased ROS in hemolymph during uptake. Foodborne exposure caused prolonged immune stress, evidenced by elevated total antioxidant capacity (TAC) and protein levels. In the hepatopancreas, foodborne exposure during depuration led to increased lipid peroxidation and TAC, indicating oxidative and metabolic challenges specific to dietary exposure. These results highlighted the complex interactions of AgNPs with primary producers and consumers in freshwater ecosystems, emphasizing the need for multi-route assessments in nanoparticle risk evaluations.

Lactic whey as a potential feedstock for exopolysaccharide production by microalgae strain Neochloris oleoabundans UTEX 1185

BACKGROUND

Lactic whey, a significant agro-industrial byproduct, poses environmental risks due to its chemical composition. Despite various valorization efforts, effective utilization remains a challenge. This study explores the potential of Neochloris oleoabundans, a microalgae known for its metabolic versatility and resilience to adverse conditions, to produce exopolysaccharides (EPS) using lactic whey as a substrate. We compared EPS production from lactose, the primary sugar in whey, with whole lactic whey. Characterization of the EPS was performed using Fourier transform infrared spectroscopy (FT-IR) and gas chromatography-mass spectrometry (GC-MS), while morphological analysis was conducted via scanning electron microscopy (SEM). This research aims to assess the feasibility of converting lactic whey into valuable EPS, providing a sustainable approach to managing this agro-industrial waste.

RESULTS

Lactic whey has produced the highest EPS and the FT-IR spectra revealed structural variations in the monomers which compose these polymers. Galactose and glucose were shown to be the primary monomers, according to GC-MS EPS analysis. SEM revealed a homogenous matrix and N. oleoabundans's bioflocculant characteristics.

CONCLUSIONS

Microalgae N. oleoabundans can produce EPS using lactic whey as feedstock and it has the potential to be employed as a wastewater treatment.

Amphora coffeiformis extracellular polymeric substances and their potential applications in lead removal

Microorganisms producing extracellular polymeric substances (EPS) are of great potential in numerous environmental applications. The present study explores the production and properties of extracellular polymeric substances (EPS) from Amphora coffeiformis diatom strain and their potential applications in environmental remediation. EPS were composed of a complex mixture of polysaccharides, proteins, humic substances and nucleic acids, with polyanionic characteristics as revealed by FTIR, Raman and zeta potential analyses. EPS showed high flocculation efficiency against kaolin clay at low dosages (5 mg/L) through a charge neutralization mechanism involving both polysaccharides and proteins. EPS also exhibited strong emulsification activity for various nonpolar substrates, mainly olive oil, corn oil, soybean oil, essence and diesel, with emulsification indexes above 80%. The emulsions were stable for 72 h under different NaCl concentrations (1-10% w/v). Moreover, EPS demonstrated remarkable adsorption capacity for lead, reaching a maximum of 1699.33 ± 89.61 mg/g under optimized conditions using Box-Behnken design. The adsorption mechanism involved multiple functional groups such as hydroxyl, carbonyl, carboxyl, phosphoric and sulfhydryl. Therefore, EPS from A. coffeiformis are a promising candidate for restoring environments contaminated by heavy metals.

Microalgae - bacteria based wastewater treatment systems: Granulation, influence factors and pollutants removal

Wastewater treatment based on microalgae and bacteria symbiosis is an environmentally friendly, sustainable technology that has attracted attention recently because of its high efficiency in treating pollutants, saving energy, and short-term biomass recovery. Among them, the granular microalgae and bacteria combination emerges with the advantages of rapid gravity settling, good resistance to adverse environmental conditions, outstanding wastewater treatment performance, and easy biomass recovery. This review aims to clarify the microalgal-bacterial granule (MBG) - based process for wastewater treatment. In particular, MBG characteristics, granulation mechanism, and influence factors on the process are also discussed. The review contributes to the knowledge system related to MBG research in recent years, thereby pointing out research gaps that need to be filled in the future.

Microalgae and microbial inoculant as partial substitutes for chemical fertilizer enhance Polygala tenuifolia yield and quality by improving soil microorganisms

Excessive utilization of chemical fertilizers degrades the quality of medicinal plants and soil. Bio-organic fertilizers (BOFs) including microbial inoculants and microalgae have garnered considerable attention as potential substitutes for chemical fertilizer to enhance yield. In this study, a field experiment was conducted to investigate the effects of BOF partially substituting chemical fertilizer on the growth and quality of medicinal plant Polygala tenuifolia. The growth parameters, bioactive component contents, soil properties and composition of rhizosphere microorganisms were measured. The results indicated that substituting 40% of chemical fertilizer with microalgae showed the most pronounced growth-promoting effect, leading to a 29.30% increase in underground biomass and a 19.72% increase in 3,6'-disinapoylsucrose (DISS) content. Substituting 20% of chemical fertilizer with microalgae improved soil quality, significantly increasing soil organic matter content by 15.68% (p<0.05). Microalgae addition significantly affected the rhizosphere bacterial community composition of P. tenuifolia, reducing the relative abundance of Cladosporium by 33.33% and 57.93%, while increasing the relative abundance of Chloroflexi by 31.06% and 38.27%, under 20% and 40% chemical fertilizer reduction, respectively. The relative abundance of Chloroflexi positively correlated with both the underground biomass and DISS content (p<0.05), indicating that microalgae may stimulate Chloroflexi species associated with carbon cycling, thereby enhancing soil fertility, nutrient absorption, and ultimately leading to increased biomass accumulation and production of bioactive components in P. tenuifolia. In addition, there was no significant difference in underground growth and bioactive component contents between reduced chemical fertilizer dosage combined with solid microbial inoculant (SMI) and polyglutamic microbial inoculant (PMI), compared with 100% chemical fertilizer. Correlation analysis revealed that PMI could increase soil phosphorus availability through Streptomyces recruitment. In conclusion, our findings demonstrated that bio-organic fertilizers can partially substitute chemical fertilizer to improve soil properties and microorganisms, enhancing the growth and quality of P. tenuifolia. This provides a theoretical basis for increasing medicinal plant productivity under chemical fertilizer reduction.

Impact of Nanoplastics on the Functional Profile of Microalgae Species Used as Food Supplements: Insights from Comparative In Vitro and Ex Vivo Digestion Studies

The widespread use of plastics in the food industry raises concerns about plastic migration and health risks. The degradation of primary polymers like polystyrene (PS) and polyethylene (PE) can generate nanoplastics (NPs), increasing food biohazard. This study assessed the impact of PS, PE, and PS + PE NPs on Chlorella vulgaris (CV) and Haematococcus pluvialis (HP) before and after in vitro and ex vivo digestion, focusing on particle size, polydispersity index, and surface charge. The modulation of total phenolic content (TPC) induced by NP contamination was also evaluated. Results demonstrated that NP behavior varied with the microalgae medium and persisted postdigestion, posing health risks. Significant size increases were noted for PS + PE in the CV and HP. TPC increased significantly with NP exposure, especially PS + PE. These findings underline the need for regulatory measures to ensure food safety in cases of plastic contamination and to address the behavior and toxicity of NPs.

Lead removal from the aqueous solution by extracellular polymeric substances produced by the marine diatom Navicula salinicola

Microbial extracellular polymeric substances (EPS) have recently emerged as significant contributors in diverse biotechnological applications. Extracellular polymeric substances (EPS), produced by a Navicula salinicola strain, have been studied for potential applications in a specific heavy metal (lead (Pb II)) removal from wastewater. The optimisation of operational parameters, mainly pH, Pb and EPS concentrations, using the Box-Behnken design (BBD) was undertaken to enhance lead uptake. The higher Pb adsorption capacity reached 2211.029 mg/g. Hydroxyl, carbonyl, carboxyl, phosphoric, and sulfhydryl groups were identified quantitatively as potential sites for Pb adsorption. EPS exhibited a notable flocculation rate of 70.20% in kaolin clay at a concentration of 15 mg/L. They demonstrated an emulsifying activity greater than 88%, showcasing their versatile potential for both sedimentation processes and stabilising liquid-liquid systems. EPS could be excellent nonconventional renewable biopolymers for treating water and wastewater.

Converging frontiers in cancer treatment: the role of nanomaterials, mesenchymal stem cells, and microbial agents-challenges and limitations

Globally, people widely recognize cancer as one of the most lethal diseases due to its high mortality rates and lack of effective treatment options. Ongoing research into cancer therapies remains a critical area of inquiry, holding significant social relevance. Currently used treatment, such as chemotherapy, radiation, or surgery, often suffers from other problems like damaging side effects, inaccuracy, and the lack of ability to clear tumors. Conventional cancer therapies are usually imprecise and ineffective and usually develop resistance to treatments and cancer recurs. Cancer patients need fresh and innovative treatment that can reduce side effects while maximizing effectiveness. In recent decades several breakthroughs in these, and other areas of medical research, have paved the way for new avenues of fighting cancer including more focused and more effective alternatives. This study reviews exciting possibilities for mesenchymal stem cells (MSCs), nanomaterials, and microbial agents in the modern realm of cancer treatment. Nanoparticles (NPs) have demonstrated surprisingly high potential. They improve drug delivery systems (DDS) significantly, enhance imaging techniques remarkably, and target cancer cells selectively while protecting healthy tissues. MSCs play a double role in tissue repair and are a vehicle for novel cancer treatments such as gene treatments or NPs loaded with therapeutic agents. Additionally, therapies utilizing microbial agents, particularly those involving bacteria, offer an inventive approach to cancer treatment. This review investigates the potential of nanomaterials, MSCs, and microbial agents in addressing the shortcomings of conventional cancer therapies. We will also discuss the challenges and limitations of using these therapeutic approaches.

Investigating the role of extracellular polymeric substances produced by Parachlorella kessleri in Zn(II) bioremediation using atomic force microscopy

Microalgae, such as Parachlorella kessleri, have significant potential for environmental remediation, especially in removing heavy metals like zinc from water. This study investigates how P. kessleri, isolated from a polluted river in Argentina, can remediate zinc. Using atomic force microscopy (AFM), the research examined the interactions between Zn particles and cells grown with different nitrogen sources-nitrate or ammonium. The results showed that cells grown with nitrate produced extracellular polymeric substances (EPS), while those grown with ammonium did not. Raman spectroscopy revealed distinct metabolic responses based on the nitrogen source, with nitrate-grown cells showing altered profiles after zinc exposure. Zinc exposure also changed the surface roughness and nanomechanical properties of the cells, particularly in those producing EPS. AFM force spectroscopy experiments then confirmed strong Zn binding to EPS in nitrate-grown cells, while interactions were weaker in ammonium-grown cells that lacked EPS. Overall, our results elucidate the critical role of EPS in Zn removal by P. kessleri cells and show that Zn remediation is mediated by EPS adsorption. This study underscores the significance of regulating nitrogen sources to stimulate EPS production, offering insights that are essential for subsequent bioremediation applications.

Impact of molecular structure on the biological removal efficiency of fluoroquinolone antibiotics: An in-silico approach

Fluoroquinolone antibiotics (FQs), one of the most widely used antibacterials, have been recognized as emerging contaminants with adverse human health concerns. To overcome the adverse effects, a theoretical molecular design and screening approach was developed in this study to improve the removal efficiency of FQs by Chlorella in artificial or natural wetland systems. Among the 189 designed norfloxacin (NOR) derivatives, NOR-140 was screened with significantly improved biosorption, bioaccumulation, and biodegradation removal and functional effects, and reduced human health and ecological risks. The removal mechanism NOR-140 was also analyzed using adsorption kinetics, molecular docking, molecular dynamics simulations and machine learning models. Protein and polysaccharide structures play a major role in the adsorption process, polarizability and molecular volume of NOR-140 affect the bioaccumulation ability, and hydrogen bonding was found as the key force promoting the degradation ability of NOR-140. Modifying specific sites (5, 8, and 13) with functional groups containing highly electronegative atoms (O, F) significantly enhances the biodegradability of FQs alternatives by Chlorella. This study provided theoretical support for designing environmentally friendly FQs alternatives with improved degradation ability and advanced the understanding of how the FQs' molecular structures affect its removal by Chlorella.

Cyanobacterial and microalgae polymers: antiviral activity and applications

At the end of 2019, the world witnessed the beginning of the COVID-19 pandemic. As an aggressive viral infection, the entire world remained attentive to new discoveries about the SARS-CoV-2 virus and its effects in the human body. The search for new antivirals capable of preventing and/or controlling the infection became one of the main goals of research during this time. New biocompounds from marine sources, especially microalgae and cyanobacteria, with pharmacological benefits, such as anticoagulant, anti-inflammatory and antiviral attracted particular interest. Polysaccharides (PS) and extracellular polymeric substances (EPS), especially those containing sulfated groups in their structure, have potential antiviral activity against several types of viruses including HIV-1, herpes simplex virus type 1, and SARS-CoV-2. We review the main characteristics of PS and EPS with antiviral activity, the mechanisms of action, and the different extraction methodologies from microalgae and cyanobacteria biomass.

Adverse effects of microplastics on the growth, photosynthesis, and astaxanthin synthesis of Haematococcus pluvialis

Due to the widespread pollution, microplastics (MPs) have garnered increasing attention. Research has shown that MPs negatively affect many organisms. Microalgae are primary producers in aquatic environments and play a crucial role in the stability of aquatic ecosystems. However, research on the effects of MPs on microalgae is relatively limited. Haematococcus pluvialis is known for its ability to produce astaxanthin, a powerful antioxidant, in response to environmental stress. MP exposure is also an environmental stressor, and we are curious whether MP stress will affect astaxanthin synthesis in H. pluvialis. To investigate the effects and mechanisms of MPs on H. pluvialis growth and astaxanthin synthesis, we exposed H. pluvialis to 5 μm polystyrene MPs at different concentrations (0.1, 1, and 10 mg/L) for 18 days, followed by high light induction of astaxanthin synthesis. Growth and photosynthesis-related indicators suggested that PS-MPs had a hormesis-like effect on H. pluvialis, with short-term exposure stimulating photosynthetic activity and growth, and long-term exposure inhibiting them. Morphological observations, oxidative stress markers, soluble proteins, and extracellular polymeric substance indicators showed that prolonged PS-MP exposure primarily disrupted the morphology and normal physiological functions of H. pluvialis by inducing oxidative stress. Although H. pluvialis actively resists the oxidative stress caused by PS-MPs, it cannot fully counteract the adverse effects. Prolonged PS-MP exposure ultimately resulted in reduced levels of photosynthetic pigments and inhibited photosynthetic activity, as well as the decreased expression of genes related to astaxanthin synthesis and reduced astaxanthin production. Integrated biomarker response analysis further indicated that the overall toxic effects of MPs on H. pluvialis exhibit a dose-dependent pattern. MP exposure potentially weakens the survival capability of H. pluvialis under adverse conditions. These findings highlight the impact of MP pollution on the stability of aquatic ecosystems and underscore the urgent need for policies and actions to mitigate MP pollution and protect aquatic environments.

Optimization of hydrogen production using a coculture of Chlamydomonas reinhardtii and activated sludge bacteria

The production of biophotolytic hydrogen (H2) relies on the effective management of oxygen (O2) levels. Coculturing bacteria with microalgae helps mitigate the excess O2 produced by algal cells. After depleting O2, the bacteria activate the enzyme hydrogenase in microalgae, leading to H2 production. In this study, Chlamydomonas reinhardtii was cocultured with indigenous bacteria from activated sludge at varying algae-to-bacteria ratios (1:1, 1:1.5, 1:2, 1:2.5, and 1:3 v/v), with an illumination intensity of 2.8 mmol/m2/s (31 × 103 lux). The 1:1.5 v/v ratio yielded the highest H2 volume (1162 mL/L) and the highest O2 concentration (153.2 mL/L) over a 6-day period. Production of all gaseous components ceased for all ratios as the pH dropped below 4 due to acetate accumulation, and the concentration of acetate reached approximately 1 g/L by the end of each experiment. Gas composition analysis after the first day of coculture revealed that H2, CO2, N2, and O2 constituted 25%-46%, 20%-40%, 5%-30%, and 1%-10% of the total gas volume, respectively. Glucose (10 g/L) was introduced as an external carbon source for all cultures. After 6 days, the coculture maintained a high total organic carbon (TOC) level of 3.1 g/L, whereas the initial TOC ranged between 3.9 and 4.3 g/L. The findings illustrated a significant correlation between H2 production, acetate accumulation levels, and O2 consumption. The algae-activated sludge coculture method substantially enhanced H2 production compared with previously published methods employing only one or two types of bacterial cultures, underscoring its potential for more efficient biophotolytic H2 production.

Co-metabolism of microorganisms: A study revealing the mechanism of antibiotic removal, progress of biodegradation transformation pathways

The widespread use of antibiotics has resulted in large quantities of antibiotic residues entering aquatic environments, which can lead to the development of antibiotic-resistant bacteria and antibiotic-resistant genes, posing a potential environmental risk and jeopardizing human health. Constructing a microbial co-metabolism system has become an effective measure to improve the removal efficiency of antibiotics by microorganisms. This paper reviews the four main mechanisms involved in microbial removal of antibiotics: bioaccumulation, biosorption, biodegradation and co-metabolism. The promotion of extracellular polymeric substances for biosorption and extracellular degradation and the regulation mechanism of enzymes in biodegradation by microorganisms processes are detailed therein. Transformation pathways for microbial removal of antibiotics are discussed. Bacteria, microalgae, and microbial consortia's roles in antibiotic removal are outlined. The factors influencing the removal of antibiotics by microbial co-metabolism are also discussed. Overall, this review summarizes the current understanding of microbial co-metabolism for antibiotic removal and outlines future research directions.

Impact of weathered and virgin polyethylene terephthalate (PET) micro- and nanoplastics on growth dynamics and the production of extracellular polymeric substances (EPS) of microalgae

The ever-increasing plastic waste accumulation in the marine environment necessitates a deeper understanding of microalgae interactions with micro- and nanoplastics (MNP), and the role of extracellular polymeric substances (EPS). EPS, known for its adhesive properties and produced as an algal stress response, may facilitate aggregation of both algae and MNPs, thereby impacting ecological and hydrodynamic processes such as the trophic transfer or vertical transport of MNPs. Moreover, gaining a deeper understanding of the impact of weathering processes on the potential toxicological effects of plastic particles, and the comparative significance of plastic-specific effects relative to those of naturally occurring particles such as kaolin clay, is imperative. Therefore, this study investigated the impact of fragmented, polydisperse virgin polyethylene terephthalate (PET, Daverage = 910 nm) and weathered PET (Daverage = 1700 nm) on the growth and the production of EPS of Rhodomonas salina. Algae were exposed to a range of low MNP concentrations (10, 100 and 1000 and 10,000 MNPs ml-1) for 11 days. A natural particle control (kaolin, Daverage = 1600 nm) was deployed to differentiate particle effects from plastic effects. It was observed that exposure to both weathered PET and virgin PET resulted in initially increased growth rates (7.80 % and 7.28 % respectively), followed by significant decreases in algae cell density (-30.1 % and -11.2 % respectively). Furthermore, exposure to weathered PET caused a simultaneous elevation in cellular EPS production (76.51 %). The effects of plastics were significantly larger than the effect of kaolin. Also, the observed effects were amplified by the weathering of the plastics. These observations underscore the interactions between particle type, age and concentration, and their distinct impacts on algae density and growth inhibition. The observations indicate a role for EPS as an algal protection mechanism, potentially affecting the environmental fate of MNP - microalgae aggregates.

Co-bioaugmentation with microalgae and probiotic bacteria: Sustainable solutions for upcycling of aquaculture wastewater and agricultural residues into microbial-rice bran complexes

Aquaculture farming generates a significant amount of wastewater, which has prompted the development of creative bioprocesses to improve wastewater treatment and bioresource recovery. One promising method of achieving these aims is to directly recycle pollutants into microbe-rice bran complexes, which is an economical and efficient technique for wastewater treatment that uses synergetic interactions between algae and bacteria. This study explores novel bioaugmentation as a promising strategy for efficiently forming microbial-rice bran complexes in unsterilized aquaculture wastewater enriched with agricultural residues (molasses and rice bran). Results found that rice bran serves a dual role, acting as both an alternative nutrient source and a biomass support for microalgae and bacteria. Co-bioaugmentation, involving the addition of probiotic bacteria (Bacillus syntrophic consortia) and microalgae consortiums (Tetradesmus dimorphus and Chlorella sp.) to an existing microbial community, led to a remarkable 5-fold increase in microbial-rice bran complex yields compared to the non-bioaugmentation approach. This method provided the most compact biofloc structure (0.50 g/L) and a large particle diameter (404 μm). Co-bioaugmentation significantly boosts the synthesis of extracellular polymeric substances, comprising proteins at 6.5 g/L and polysaccharides at 0.28 g/L. Chlorophyta, comprising 80% of the total algal phylum, and Proteobacteria, comprising 51% of the total bacterial phylum, are emerging as dominant species. These microorganisms play a crucial role in waste and wastewater treatment, as well as in the formation of microbial-rice bran complexes that could serve as an alternative aquaculture feed. This approach prompted changes in both microbial community structure and nutrient cycling processes, as well as water quality. These findings provide valuable insights into the transformative effects of bioaugmentation on the development of microbial-rice bran complexes, offering potential applications in bioprocesses for waste and wastewater management.

Assessment of extracellular polymeric substances production and antioxidant defences in periphytic communities exposed to effluent contaminants

Periphyton is frequently used in the evaluation of the ecological status of aquatic ecosystems using diatoms as a proxy. However, periphyton has a particularity, the production of extracellular polymeric substances (EPS), which might play a protective role against exposure to harmful environmental contaminants. Effluents originating in wastewater treatment plants (WWTPs) constitute some of the most complex mixtures of contaminants, to which aquatic ecosystems are frequently exposed, often containing tens to hundreds of different chemicals. In such challenging scenarios, a putative protective role of EPS may obscure the bioindicator value of diatoms. To address this problem, we sampled periphyton upstream and downstream of the effluent outfall from three different WWTPs, quantifying EPS production and simultaneously evaluating general stress responses in the community (protein and sugar content, photosynthetic pigments, antioxidant enzyme activity and oxidative damage). By combining these endpoints with a characterization of the sediments of the riverine systems receiving the effluents made in a previous study (metals, polycyclic aromatic hydrocarbons, pharmaceuticals and personal care products), we aimed to elucidate whether effluent contaminants trigger negative effects, which may be mitigated by EPS layers protecting the communities. Our results indicated that under a comparatively milder contamination burden, EPS production is enhanced in samples collected downstream of the effluent outfall; under a higher contamination burden, EPS production is hampered. Stress-coping mechanisms were activated by environmental contaminants, including the antioxidant defense, particularly through catalase and superoxide dismutase activity. The findings support the generally assumed protective effect of EPS, but also suggest that EPS production depends on the contamination burden and that protective effects should be in place under specific scenarios of, for example, relatively low contamination levels. Overall, the integrative approach used in this study contributes to a better understanding of the complex interplay of interactions between effluent-driven contamination and thriving periphytic communities inhabiting recipient waterways, including evolved protection mechanisms.

Enhancing treatment performance of Chlorella pyrenoidosa on levofloxacin wastewater through microalgae-bacteria consortia: Mechanistic insights using the transcriptome

Microalgae-bacteria consortia (MBC) system has been shown to enhance the efficiency of microalgae in wastewater treatment, yet its effectiveness in treating levofloxacin (LEV) wastewater remains unexplored. This study compared the treatment of LEV wastewater using pure Chlorella pyrenoidosa (PA) and its MBC constructed with activated sludge bacteria. The results showed that MBC improved the removal efficiency of LEV from 3.50-5.41 % to 33.62-57.20 % by enhancing the growth metabolism of microalgae. The MBC increased microalgae biomass and extracellular polymeric substance (EPS) secretion, yet reduced photosynthetic pigment content compared to the PA. At the phylum level, Proteobacteria and Actinobacteriota are the major bacteria in MBC. Furthermore, the transcriptome reveals that the growth-promoting effects of MBC are associated with the up-regulation of genes encoding the glycolysis, the citrate cycle (TCA cycle), and the pentose phosphate pathway. Enhanced carbon fixation, coupled with down-regulation of photosynthetic electron transfer processes, suggests an energy allocation mechanism within MBC. The up-regulation of porphyrin and arachidonic acid metabolism, along with the expression of genes encoding LEV-degrading enzymes, provides evidence of MBC's superior tolerance to and degradation of LEV. Overall, these findings lead to a better understanding of the underlying mechanisms through which MBC outperforms PA in treating LEV wastewater.

Cultivation modes affect the morphology, biochemical composition, and antioxidant and anti-inflammatory properties of the green microalga Neochloris oleoabundans

Microalgae are considered promising sustainable sources of natural bioactive compounds to be used in biotechnological sectors. In recent years, attention is increasingly given to the search of microalgae-derived compounds with antioxidant and anti-inflammatory properties for nutraceutical or pharmacological issues. In this context, attention is usually focused on the composition and bioactivity of algae or their extracts, while less interest is driven to their biological features, for example, those related to morphology and cultivation conditions. In addition, specific studies on the antioxidant and anti-inflammatory properties of microalgae mainly concern Chlorella or Spirulina. The present work was focused on the characterization of the Chlorophyta Neochloris oleoabundans under two combinations of cultivation modes: autotrophy and glucose-induced mixotrophy, each followed by starvation. Biomass for morphological and biochemical characterization, as well as for extract preparation, was harvested at the end of each cultivation phase. Analyses indicated a different content of the most important classes of bioactive compounds with antioxidant/anti-inflammatory properties (lipids, exo-polysaccharides, pigments, total phenolics, and proteins). In particular, the most promising condition able to prompt the production of antioxidant algal biomass with anti-inflammatory properties was the mixotrophic one. Under mixotrophy, beside an elevated algal biomass production, a strong photosynthetic metabolism with high appression of thylakoid membranes and characteristics of high photo-protection from oxidative damage was observed and linked to the overproduction of exo-polysaccharides and lipids rather than pigments. Overall, mixotrophy appears a good choice to produce natural bioactive extracts, potentially well tolerated by human metabolism and environmentally sustainable.