Search Results (288)

Routine microalgal cell counting requires sampling and microscopy. We developed a low-cost portable machine-vision system (LPMVS) for non-destructive density estimation of visibly green Dunaliella sp. cultures. The compact benchtop LPMVS combines motorized flask loading, a light-isolated dark box with diffuse light-emitting diode (LED) illumination, fixed camera–flask geometry, red–green–blue (RGB) imaging through the flask, mask-derived liquid-region extraction, Raspberry Pi inference, and a local liquid-crystal display (LCD). A ready-state load-to-unload cycle required approximately 37 s, including 6 s of processing. The two 40-day flask trajectories yielded 240 image–hemocytometer pairs; 200 records were used to compare three regressors with 20 features selected from 339 descriptors. K-nearest neighbors (KNN) performed best in the flask-mixed record-level comparison ($R^2$ = 0.98; mean absolute percentage error (MAPE) = 6.41%; $n=40$). Reciprocal leave-one-flask-out transfer analysis on complete trajectories with independently retrained pipelines gave KNN $R^2$ values of 0.914 and 0.803. In the reverse direction, $R^2$ was 0.936 within the overlapping range ($n=79$), but 41 above-range densities were systematically underestimated. Bootstrap resampling identified recurrent color-based features in both trajectories. An edge-device check using 10 additional measurements yielded preliminary reference-density tracking ($R^2$ = 0.94). These findings support the feasibility of the LPMVS workflow for non-destructive monitoring under controlled laboratory conditions, but extrapolation and generalization to independent batches and optical configurations remain unestablished. Full article

To date, the taxonomic revision of the class Chlorodendrophyceae remains incomplete; the diversity of its halophilic representatives is poorly studied, and the precise phylogenetic position of Tetraselmis indica, its only known halophilic species, remains unresolved. Two novel halophilic green microalgal strains related to Tetraselmis indica, isolated from geographically distant hypersaline habitats (Crimean lakes and rivers of the Lake Elton basin), were examined using an integrative approach combining morpho-physiological characterization with multilocus molecular phylogenetic analysis (18S rRNA gene, ITS1-5.8S-ITS2 region, 28S rRNA gene, and rbcL gene); ITS2 metabarcoding was additionally used to clarify their distribution in the temperate zone of Eurasia. As a result, Halotetraselmis gen. nov. and H. indica comb. nov. were described. The early-diverging (basal) position of Halotetraselmis within Chlorodendrophyceae, the substantial genetic distances separating it from Tetraselmis, and its obligate halophily, together with the previously described morphological and chemotaxonomic differences, consistently support recognition of this lineage at the genus level. Genetic markers determined for H. indica for the first time (the 28S rRNA gene, the rbcL gene, and the ITS1-5.8S-ITS2 region) showed a differing diagnostic value for genus/subgenus-level versus species-level differentiation. Analysis of the ITS1-5.8S-ITS2 region and of ITS2 secondary structure, used for delimitation within Halotetraselmis, revealed potentially novel species among unidentified cultured strains. The combination of culture-based methods and metabarcoding yielded new data on the geographic distribution and ecology of the genus. These findings broaden current understanding of the diversity, phylogeny, and ecology of the class Chlorodendrophyceae and represent an important step toward a comprehensive taxonomic revision of the class. Full article

Water purification is the most crucial process for recirculating aquaculture systems (RASs), while microalgae exhibit significant potential for nutrient removal from aquaculture wastewater. Four microalgal species with removal capacities for ammonia nitrogen (NH₄⁺-N), nitrite nitrogen (NO₂-N) and total phosphorus (TP) were isolated and identified from the land-based RASs, namely, Kirchneriella cornuta HY-1, Desmodesmus abundans HY-1, Coccomyxa sp. HY-1 and Oocystis sp. HY-1. The growth kinetics were characterized through measurements of cell density, chlorophyll content, and dry biomass in the in situ wastewater. Based on zeta potential, the flocculation efficiencies of seven agents were evaluated. Preservation parameters were optimized under nutrient-supplemented conditions with protective agents. Under large-scale culture conditions, over a 7-day period, the highest NH₄⁺-N removal efficiency of 87.20 ± 0.56% was achieved by C. sp. HY-1, the highest NO₂-N removal efficiency (85.63 ± 2.56%) was obtained by O. sp. HY-1, and the maximum TP removal efficiency (71.19 ± 3.35%) was exhibited by K. cornuta HY-1. Moreover, the harvest period could be reached after about 14 days of cultivation. FeCl₃ was identified as the optimal harvesting flocculant for all four species. Optimal preservation conditions were determined as 25 °C and 31.25 μmol·m⁻²·s⁻¹ for D. abundans HY-1, C. sp. HY-1, and O. sp. HY-1, and 25 °C and 18.75 μmol·m⁻²·s⁻¹ for K. cornuta HY-1. This work provides theoretical guidance for large-scale microalgal production and confirms the technical feasibility of microalgae-driven in situ wastewater remediation. Full article

Antibiotics are widely used to decontaminate microalgal cultures, but their effects on algal physiology and associated bacterial communities remain unclear. We examined the concentration- and compound-dependent responses of Chlorella pyrenoidosa to ampicillin sodium, sulfanilamide, chloramphenicol, and streptomycin sulfate. Growth, culturable bacterial abundance, pigment content, photosynthetic performance, and fatty-acid composition were assessed across a mixed-antibiotic concentration gradient and under individual treatments. Higher antibiotic concentrations suppressed bacteria but inhibited algal growth, reduced chlorophyll accumulation, and altered fatty-acid composition. Physiological disruption increased in the order ampicillin sodium < sulfanilamide < chloramphenicol < streptomycin sulfate. Streptomycin sulfate produced the strongest response, reducing maximum quantum yield of PSII photochemistry (Fv/Fm) and light-use efficiency by 51.4% and 44.4%, respectively, while increasing total polyunsaturated fatty acids from 59.68% to 79.57%. 16S rRNA gene sequencing and untargeted metabolomics showed that streptomycin sulfate reduced bacterial diversity and increased the relative abundance of Proteobacteria from 44.54% to 90.66%. Lipid-related pathways were altered, particularly α-linolenic acid and glycerophospholipid metabolism. Bacterial-community and metabolomic changes covaried under STRS exposure, and responsive taxa correlated with phospholipid- and oxylipin-related metabolites. These findings identify antibiotic acts as a selective stressor that alters algal physiology, lipid metabolism, and associated bacterial communities, highlighting the need for species-specific decontamination strategies. Full article

Microalgae-based wastewater treatment represents a sustainable approach for simultaneous nutrient removal and biodiesel feedstock production. This study evaluated the growth, total organic carbon (TOC) removal, FAME productivity, fatty acid composition, and predicted biodiesel properties of Chlorella vulgaris and Scenedesmus obliquus cultivated in urban wastewater and synthetic medium under photoautotrophic and mixotrophic conditions, with and without nitrogen limitation using a two-stage cultivation strategy. S. obliquus showed greater adaptability to urban wastewater, with better growth and the highest TOC removal efficiency (92%) under mixotrophic cultivation with nitrogen limitation. Nitrogen limitation significantly enhanced FAME productivity in both species, with increases of 43.06–79.35% for C. vulgaris and 48.11–69.98% for S. obliquus relative to the corresponding photoautotrophic cultures. Fatty acid analysis revealed higher saturated fatty acid contents in C. vulgaris and higher polyunsaturated fatty acid levels in S. obliquus. Based on the fatty acid composition, C. vulgaris showed lower predicted iodine values and greater predicted oxidative stability than S. obliquus. The predicted cetane numbers were below the minimum values cited in international biodiesel specifications, while predicted kinematic viscosity was within the ranges reported by ASTM D6751 and EN 14214. However, the predicted cold filter plugging point (CFPP) values of 14.9–15.0 °C indicated limited suitability for low-temperature applications, and oxidative stability met the cited EN 14214 threshold only for some C. vulgaris treatments. These results indicate the potential of urban wastewater as a culture medium for sustainable microalgal FAME production and as a feedstock source for biodiesel applications, particularly when combined with fatty acid profile optimization or blending strategies. Full article

Microalgae biomanufacturing is a promising technology that converts carbon dioxide into valuable products. However, it faces limitations in scaling, online monitoring, and controlling biological variables. In photobioreactors, light intensity influences growth and operational efficiency. This study presents Alg-flex, a low-cost, open-source monitoring and control platform based on a Raspberry Pi 4. Alg-flex integrates sensors for light intensity regulation and real-time monitoring of pH, temperature, and dissolved oxygen, enabling data visualization and logging, while providing full portability without hardware modifications. These features offer broader applicability than conventional single-variable loggers. The hardware was obtained for under $1834 USD, approximately 4% of the average cost of similar commercial units. Its performance was evaluated during the cultivation of Haematococcus lacustris in a bubble column photobioreactor. The pH and temperature sensors were validated against certified benchtop probes over the operating range used in this study, yielding median errors below 1.5%. Under the tested conditions, bioreactor cultures showed approximately two-fold higher final optical density that was significantly different than flask cultures (p = 0.0333). These results confirm that growth dynamics in small-volume microalgal cultures may differ substantially from controlled photobioreactor systems. The affordability, reliability, and multi-reactor compatibility of Alg-flex support broader biomanufacturing applications beyond microalgae cultivation. Full article

Coral reefs are increasingly threatened by elevated seawater temperatures associated with heatwaves and El Niño events. These phenomena challenge conventional management practices, highlighting an urgent need for innovative interventions to enhance reef resilience. Investigating the role of oxidative stress—one of the main explanations for coral bleaching—is central to these efforts, as excessive production of reactive oxygen species can impair coral physiology, disrupt the coral–algal symbiosis, and ultimately lead to mortality. Here, we investigated an antioxidant-rich food web approach by feeding the reef-building coral Stylophora pistillata with Artemia that had been pre-fed with (i) low-cost and in-house-produced pellets containing curcumin, fucoxanthin, astaxanthin, vitamins C or E, or (ii) the phytoplankton species Pavlova lutheri, Symbiodinium sp., Nannochloropsis sp., Dunaliella salina or Synechococcus sp. Curcumin and the microalga P. lutheri offered the best protection to corals against oxidative stress, and represent the best candidates for potential scalable coral conservation interventions involving targeted feeding of antioxidants. Curcumin pellets offer a streamlined alternative to P. lutheri by eliminating the need for multi-stage microalgal culturing. Direct enrichment of Artemia with antioxidant-rich pellets simplifies production and may provide a cost-effective, scalable strategy to enhance coral resilience to oxidative stress, bleaching and potential mortality. Full article

This study aimed to evaluate the effects of establishing a population of the green microalgae Chlorella sp. on different key aspects of a biofloc culture of Penaeus vannamei in comparison with those obtained with a commercial probiotic. The aspects evaluated were shrimp zootechnical performance, nutritional composition of biofloc and microbial populations of shrimp intestinal microbiota and biofloc. Four treatments were tested: two of them included Chlorella sp. alone (M) or in combination to a bacterial probiotic (MP), while the other two included only the probiotic (P) or none of them (C). The presence of Chlorella sp. enhanced protein and phosphorus bioavailability in the biofloc and contributed to nutrient bioremediation within the system. However, shrimp growth performance and survival were significantly reduced, likely due to greater and more prolonged nitrate exposure following microalgae inoculation. Although overall nitrate and phosphate concentrations were higher in microalgae treatment, their accumulation over the experimental period was lower in the presence of Chlorella sp. In addition, microalgal supplementation reduced the abundance of bacterial groups associated with oligotrophic lifestyles, complex organic matter degradation, and nitrogen cycling in the intestinal microbiota. In contrast, probiotic supplementation increased protein content in shrimp and phosphorus bioavailability in the biofloc, while zootechnical performance remained comparable to the control and was higher than in microalgae treatments. Furthermore, probiotic addition reduced the abundance of Flavobacteriaceae, a bacterial family proposed as a bioindicator of White Feces Syndrome (WFS) in P. vannamei. Full article

Microalgal bioprocesses increasingly rely on predictive modelling to support automated control and reduce the cost of laboratory experimentation. Yet, the scarcity of high-quality datasets and the nonlinear nature of microalgal growth severely limit the accuracy and robustness of conventional machine-learning approaches. This study introduces an ensemble-learning framework for forecasting biomass accumulation in Limnospira platensis cultures supplemented with Effective Microorganism (EM) consortia. The method combines temporally consistent, strictly causal feature engineering with tree-based ensemble learning under a prospective validation protocol designed to mirror real deployment. Growth measurements are transformed into temporal descriptors that encode phase transitions, short-term growth dynamics, and treatment effects, enabling tree-based ensemble algorithms to capture nonlinear patterns inaccessible to traditional models. When features are restricted to information available strictly before each prediction, and models are evaluated only on real held-out measurements, one-step nowcasting does not surpass a trivial persistence baseline. For genuine multi-horizon forecasting of a monitored culture, the regime with practical value, a horizon-aware gradient-boosting model trained jointly on two cultivation media (Jordan and Zarrouk), attains R² ≈ 0.72 on the held-out Jordan observations (0.72 ± 0.02, mean ± SD over 30 seeds; RMSE ≈ 0.20 g L⁻¹, Pearson r ≈ 0.85) and remains stable across forecast horizons of 1–28 days, outperforming persistence roughly fourfold in pooled R² (0.72 vs. 0.16) at medium-to-long horizons where the naive baseline collapses. Permutation-based feature-importance analysis identifies current biomass and the EM dilution level as the leading predictors, whereas EM treatment identity contributes only modestly. Including an independent second-medium experiment (Zarrouk) in joint training did not materially change held-out Jordan performance, indicating that, under these data-limited conditions, neither additional model complexity nor a second training medium substantially improved forecasting once the causal, horizon-aware framework was in place. Among treatments, EM3 most strongly suppressed biomass accumulation. Overall, the study provides an honest, fully reproducible, two-medium benchmark for microalgal biomass forecasting under data-limited conditions, and identifies the forecast horizon as the regime in which ensemble learning adds genuine value over trivial baselines. Full article

Global population growth has emphasised the need to have sustainable and alternative sources of nutrients. In this context, microalgae have emerged as a potential solution due to their rich biochemical composition, including high-quality proteins, carbohydrates, lipids, and pigments. This study investigates the variation in microalgal growth and biochemical composition over a light:dark cycle, with a focus on the night period. Batch experiments were performed with eight Chlorella vulgaris cultures over a 7-day period. On the seventh day, biomass samples were collected at four time points in four-hour intervals and stored for subsequent biochemical analyses. During the eight-hour dark period, biomass, carbohydrate, and total chlorophyll concentrations decreased by 9%, 12.5%, and 14.4%, respectively. After four hours of light exposure, these parameters increased significantly by 6%, 15.4%, and 12.7%, respectively. Total protein, carotenoids, and fatty acid contents remained relatively stable throughout the evaluated cycle, although variations were observed in the carotenoid profile. During the dark phase, zeaxanthin decreased by 38.0%, whereas violaxanthin increased by 27.2%, suggesting complementary pigment interconversion consistent with xanthophyll cycle activity. Overall, these results highlight the importance of optimising harvesting time to enhance the production of target compounds in a sustainable production of microalgal biomass. Full article

Microalgae biophotovoltaic (BPV) systems convert solar energy into electricity through photosynthetic electron transfer (PET) and have emerged as a promising solar-integrated bioenergy technology. However, high-density tubular arrays suffer from the “canyon effect” at low solar angles and from photoinhibition under peak irradiance (>450 W/m²), where non-photochemical quenching (NPQ) and reactive oxygen species (ROS) dissipate bioelectric potential as heat. To address this, a hysteresis-based dual-mode PID controller with hysteresis switching is proposed within an optical–mechanical–biological co-optimization framework, integrating array self-shading, nonlinear microalgal photoresponse, and tracking parasitic losses. In low-light mode, the system actively tracks the sun to minimize shading; in peak-light mode, it defocuses the incident angle to limit irradiance near the saturation threshold, mitigating the risk of photoinhibition. Structural control boundaries, including tube spacing and connecting rod length, are determined numerically. Under the nominal clear-sky design day, the defocusing mode reduces the daily exposure of the culture to irradiance above the saturation threshold (450 W/m²) from 5.28 h to 3.08 h. Numerical simulations indicate a daily net energy yield improvement of +14.9% over continuous dual-axis tracking and +6.3% over the latitude-based fixed-tilt baseline under idealized clear-sky design-day conditions. These values are simulation-derived estimates; experimental validation with a physical prototype is required before the framework can be interpreted as a validated system-level performance gain. Full article

The integration of microalgae cultivation into biorefinery systems represents a promising strategy to enhance carbon dioxide (CO₂) sequestration and support sustainable biomass production for diverse biotechnological applications. This study reports the CO₂ fixation performance and biomass productivity of a two-stage photobioreactor (PBR) system employed for the continuous cultivation of Haematococcus pluvialis, utilizing biogenic CO₂ generated from a heterotrophic culture. The first stage (ST1) operated as an autotrophic chemostat (ST1 PBR) with variable dilution rates (0.18–1.00 d⁻¹), while the second stage (ST2) consisted of sequential high-irradiance columns that promoted biomass and carotenoid accumulation. The two-stage PBR (ST1 + ST2 PBR) achieved a maximum CO₂ assimilation capacity of 0.747g/L/d and up to 94% CO₂ fixation efficiency. The daily CO₂ assimilation rate reached 6.53 g/d, representing a 10% improvement compared with the single-stage system (ST1 PBR). The maximum overall biomass productivity reached 0.332 g/L/d when both PBR stages were operated together, whereas the second stage alone achieved up to 1.18 g/L/d under continuous operation and a maximum biomass concentration of 3.33 g/L during batch-induced carotenogenesis. Nutrient uptake analysis revealed an increasing fraction of unconsumed major nutrients with higher dilution rates. Continuous operation under high irradiance did not induce pigment accumulation, whereas batch mode successfully triggered carotenogenesis over 13 days, resulting in visible pigment production and high biomass yield. Overall, the two-stage PBR system demonstrated high CO₂ capture efficiency, enhanced biomass productivity, and operational flexibility, offering a scalable and sustainable approach for integrating microalgal cultivation into biorefineries while contributing to carbon mitigation and circular bioeconomy goals. Full article

There is a notable lack of standardised and validated protocols for evaluating the potential of aquaculture effluents as culture media for microalgae. This study addresses this gap by developing and validating a comprehensive protocol for assessing the suitability of aquaculture effluents for microalgal production. The protocol was designed and standardised based on effluent characterisation, effluent pre-treatment, standardised inoculation, assessment of microalgal growth performance, and evaluation of nutrient removal. Validation was conducted through the cultivation of Phaeodactylum tricornutum in biofloc technology (BFT) shrimp (Penaeus vannamei) effluent, demonstrating the protocol’s reliability, robustness, and adaptability across media with varying nutrient profiles. The approach effectively identified nitrate and orthophosphate removal patterns of up to 97.34 ± 2.15% and 87.88 ± 1.61%, respectively, in culture media containing 100% shrimp effluent, while providing consistent and accurate growth performance data across different treatments. The treatment containing 100% shrimp effluent achieved a maximum cell density of 8488 ± 772 (×10⁴ cells mL⁻¹). As the proposed framework is based on broadly applicable performance indicators, it provides a methodological basis that can be adapted for evaluating other aquaculture effluents, microalgal species, and cultivation systems. However, additional validation under these conditions is required before broader application can be confirmed. Full article

Microalgae represent a promising alternative as biofertilizers and biostimulants, providing essential nutrients and bioactive compounds that support plant growth. In this study, a screening of seven microalgal species—including Arthrospira platensis, Nannochloris sp., Chlorella sp., Chlorella vulgaris, Acutodesmus obliquus, Parachlorella kessleri, Coelastrella vacuolata—and one isolated mixed culture was conducted to evaluate their potential as biostimulants and biofertilizers under autotrophic cultivation conditions. Whole cultures and corresponding supernatants were directly applied, without any pretreatment, reducing potential processing costs. Their biostimulant activity was evaluated through multiple bioassays, including germination index and auxin- and cytokinin-like responses, while nitrogen, phosphorus, and potassium content was analyzed to assess biofertilizer potential. The results revealed that biostimulant effects were strongly influenced by species, concentration, and sample fraction. Chlorella species consistently showed high performance across assays, combining strong germination and rooting responses with high nitrogen content (8.2–8.8% w/w), while A. platensis and Nannochloris sp. showed inhibitory effects in many cases. Overall, under the cultivation and application conditions tested, C. vulgaris, mixed culture, and A. obliquus are identified as promising candidates for combined biostimulant and biofertilizer applications. This study is a primary step in identifying the most promising species as an alternative to synthetic fertilizers, enabling further optimization towards more sustainable agricultural practices. Full article

Commercially mature products obtained by fractionation or extraction of phototrophic microalgal biomass remain concentrated in four categories: whole-cell Spirulina/Chlorella, C-phycocyanin, astaxanthin, and DHA-rich oils. Little diversification of these fractionated, mid-tier products has followed the decline in upstream costs. Whole-cell feed and live-culture markets, agricultural biostimulants, and fermentation-derived ingredients are commercially active but lie outside this phototrophic downstream-processing scope. Reported open-pond biomass production costs have fallen from ~US$10 kg⁻¹ in the 1990s to sub-US$1 kg⁻¹ nth-plant projections, yet no substantial product diversification has occurred. This review brings together three complementary lines of evidence: a bibliometric analysis of 1995–2025 publications showing that downstream fractionation, biorefinery, and integrated process design account for only 9.3% of food-core microalgal research; institutional surveys documenting the same four dominant categories across Europe, China, and global markets; and a meta-analysis of 53 whole-biomass cost rows from 16 techno-economic assessments. These sources indicate consistently that downstream processing is a necessary, though not sole, constraint on commercial diversification. A four-tier unit-operation roadmap is proposed-cell disruption at commodity energy cost, fractionation with functional ingredient preservation, decolorization and desalting at food-ingredient unit cost, and standardized transferable workflows-each linked to a quantitative threshold and to the product categories it would unlock. Closing the microalgal processing technology gap now depends less on demonstrating feasibility than on meeting these thresholds. Full article