Chlorella Sorokiniana Research Articles

Multiparameter Sensing of Oxygen and pH at Biological Interfaces via Hyperspectral Imaging of Luminescent Sensor Nanoparticles.

Chemical dynamics in biological samples are seldom stand-alone processes but represent the outcome of complicated cascades of interlinked reaction chains. In order to understand these processes and how they correlate, it is important to monitor several parameters simultaneously at high spatial and temporal resolution. Hyperspectral imaging is a promising tool for this, as it provides broad-range spectral information in each pixel, enabling the use of multiple luminescent indicator dyes, while simultaneously providing information on sample structures and optical properties. In this study, we first characterized pH- and O2-sensitive indicator dyes incorporated in different polymer matrices as optical sensor nanoparticles to provide a library for (hyperspectral) chemical imaging. We then demonstrate the successful combination of a pH-sensitive indicator dye (HPTS(DHA)3), an O2-sensitive indicator dye (PtTPTBPF), and two reference dyes (perylene and TFPP), incorporated in polymer nanoparticles for multiparameter chemical imaging of complex natural samples such as green algal biofilms (Chlorella sorokiniana) and seagrass leaves (Zostera marina) with high background fluorescence. We discuss the system-specific challenges and limitations of our approach and further optimization possibilities. Our study illustrates how multiparameter chemical imaging with hyperspectral read-out can now be applied on natural samples, enabling the alignment of several chemical parameters to sample structures.

Near telomere-to-telomere genome assemblies of two Chlorella species unveil the composition and evolution of centromeres in green algae

BackgroundCentromeres play a crucial and conserved role in cell division, although their composition and evolutionary history in green algae, the evolutionary ancestors of land plants, remains largely unknown.ResultsWe constructed near telomere-to-telomere (T2T) assemblies for two Trebouxiophyceae species, Chlorella sorokiniana NS4-2 and Chlorella pyrenoidosa DBH, with chromosome numbers of 12 and 13, and genome sizes of 58.11 Mb and 53.41 Mb, respectively. We identified and validated their centromere sequences using CENH3 ChIP-seq and found that, similar to humans and higher plants, the centromeric CENH3 signals of green algae display a pattern of hypomethylation. Interestingly, the centromeres of both species largely comprised transposable elements, although they differed significantly in their composition. Species within the Chlorella genus display a more diverse centromere composition, with major constituents including members of the LTR/Copia, LINE/L1, and LINE/RTEX families. This is in contrast to green algae including Chlamydomonas reinhardtii, Coccomyxa subellipsoidea, and Chromochloris zofingiensis, in which centromere composition instead has a pronounced single-element composition. Moreover, we observed significant differences in the composition and structure of centromeres among chromosomes with strong collinearity within the Chlorella genus, suggesting that centromeric sequence evolves more rapidly than sequence in non-centromeric regions.ConclusionsThis study not only provides high-quality genome data for comparative genomics of green algae but gives insight into the composition and evolutionary history of centromeres in early plants, laying an important foundation for further research on their evolution.

Self-flocculation behaviour of cellulose-based bioflocculant synthesized from sewage water grown Chlorella sorokiniana and Scenedesmus abundans.

The global energy crisis has spurred a shift from conventional to clean and sustainable energy sources. Biomass derived from microalgae is emerging as an alternative energy source with diverse applications. Despite the numerous advantages of microalgae, large-scale biomass harvesting is not economical and convenient. Self-flocculation is considered an effective phenomenon facilitated by extracting the flocculating substances from microalgae that assist aggregation of algal cells into flocs. A novel cellulose-based bioflocculant has been synthesized from sewage water grown Chlorella sorokiniana and Scenedesmus abundans for harvesting application. The produced bioflocculant amounted to 38.5% and 19.38% of the dry weight of S. abundans and C. sorokiniana, respectively. Analysis via FTIR, XRD, and FESEM-EDX revealed the presence of cellulose hydroxyapatite (HA) in algae-derived cellulose. Harvesting efficiencies of 95.3% and 89.16% were attained for S. abundans and C. sorokiniana, respectively, at a dosage of 0.5g/L. Furthermore, the bioflocculant was recovered, enabling its reuse with recovery efficiencies of 52% and 10% for S. abundans and C. sorokiniana, respectively. This simple and efficient approach has the potential to replace other harvesting methods, thereby contributing to the economic algal biofuel production.

Cultivation of the macrophyte Lemna minor and the microalgae Chlorella sorokiniana in thermal mineral waters: Biomass characteristics, radioisotopes and heavy metals content

Microalgae and macrophytes are commonly used as human and animal food supplements. We examined the cultivation of the microalgae Chlorella sorokiniana and the duckweed Lemna minor in thermal waters under batch and sequencing batch conditions and we characterized the produced biomass for the presence of essential nutrients as well as for heavy metals and radioisotope content. The highest specific growth rate for the microalgae was observed when 5 or 15 mg/L N were supplemented while the optimal conditions for Lemna minor were observed in the co-presence of 5 mg/L N and 1.7 mg/L P. Lemna minor presented higher concentrations of proteins and lipids comparing to the studied microalgae. Both organisms contained high amounts of lutein (up to 1378 mg/kg for Lemna minor) and chlorophyll (up to 1518 mg/kg for Lemna minor) while β-carotene and tocopherols were found at lower concentrations, not exceeding a few tens of mg/kg. The heavy metal content varied between the two species. Lemna minor accumulated more Cd, Cu, K, Mn, Na, Ni, and Zn whereas Al, Ca and Mg were higher in Chlorella sorokiniana. Both organisms could be a significant source of essential metals but the occasional exceedance of the statutory levels of toxic metals in food products raises concern for potential risk to either humans or animals. Application of gamma-spectroscopy to quantify the effective dose to humans from 228Ra, 226Ra and 40K showed that Chlorella sorokiniana was well under the radiological limits while the collected mass of Lemna minor was too small for radiological measurements with confidence.

Assessment of Phycoremediation Potential of Chlorella sorokiniana Wastewater Treatment: Analysis of Biochemical Component Changes

Using algae for wastewater treatment offers significant advantages, including providing oxygen for bacteria through photosynthesis, reducing energy demand by eliminating the need for aeration, minimizing the formation of hazardous toxic slush producing useful algal biomass, and recycling nutrients present in the wastewater. In the study, Chlorella sorokiniana was isolated from domestic wastewater samples collected from municipal wastewater of the Katsina metropolis (River Ginzo). The isolated Chlorella sorokiniana was cultured in BG-11 media for ten weeks, and cell density was monitored using a haemacytometer. Twelve flasks containing 100mL wastewater samples each were inoculated with 10mL of cultured Chlorella sorokiniana and incubated at 25°C under 12/12h light/dark photoperiods for four weeks. Physicochemical parameters were analysed weekly. Results showed an increase in Chlorella sorokiniana cell density from (6.33±2.31) x104 at week one to (53.33±26.60) x104 at week ten. Remediation efforts resulted in reduction percentages for various parameters: total dissolved solids (57.7%), nitrate (99.96%), phosphorus (100%), ammonium (99.98%), potassium (91.65%), zinc (87.03%), manganese (90.63%), iron (79.44%), copper (50.62%), and nickel (30.10%). pH remained neutral, and dissolved oxygen increased over the weeks. Significant differences in biochemical components were observed before and after treatment. The remediation of diverse wastewater samples using Chlorella sorokiniana was effective, leading to the accumulation of biomass rich in biochemical components such as lipids, carbohydrates, and proteins. The accumulated biomass can be utilized for further research purposes. This study highlights the potential of Chlorella sorokiniana for phycoremediation and underscores its ability to improve water quality while generating valuable biomass for additional applications.

Antibiotic study of non-polar microalgae extract <i>Chlorella sorokiniana</i> against gram-positive bacteria

A study of the antibacterial properties of a non-polar extract of microalgae Chlorella sorokiniana on gram-positive bacteria is presented along with a determination of the minimum inhibitory concentrations of the mixture and the individual metabolites that make up the extract. A regular effect of illumination on the intensity of the antibiotic effect of non-polar microalgae extract on gram-positive bacteria is demonstrated. A mixture of substances extracted from disintegrated cells of the microalgae biomass Chlorella sorokiniana has an inhibitory effect on bacterial growth at a photosynthetically active radiation level of 100±6 μmol photons/(m2×s). The minimum effective amount of the extract is 330±11.09 µg. When analysing the chemical structure of the components of the non-polar fraction extracted from the cells of microalgae Chlorella sorokiniana, the composition of the non-polar extract was shown to include triacylglycerides, fatty acids, o-dialkyl monoglycerides and ethers of sterols or waxes, or trialkyl esters of glycerol. When studying the antibiotic properties of individual fractions of substances, triacylglycerides and fatty acids were found to have an antibiotic effect on gram-positive bacteria. In this case, the minimum effective amount of triacylglycerides is 400±13.37 μg, while that of fatty acids is 600±20.05 μg. The combined effect of a mixture of non-polar extract substances gives the most pronounced antibiotic effect on gram-positive bacteria at a photosynthetically active radiation level of 100±6 μmol of photons/(m2×s). Thus, an increase in antibacterial action was demonstrated when using a mixture of substances of the non-polar extract of microalgae Chlorella sorokiniana at a photosynthetically active radiation level of 100±6 μmol of photons/(m2×s).

Enhanced starch accumulation in Chlorella sorokiniana as sugar platform and the expression profiling of key regulatory proteins

Microalgae can accumulate considerable starch as a renewable sugar platform for biofuel production. In this study, Chlorella sorokiniana exhibited a significant increase in starch content from 3.0% to 49.5% DM under sulfur limitation (SL) conditions, and the lower the concentration of sulfur was, the more effective it was. Direct enzymatic hydrolysis of wet biomass resulted in a glucose yield of 97.1%, indicating its potential for fermentable sugar production. However, C. sorokiniana grew slowly, and cell division and biomass accumulation decreased under SL conditions, which could be explained by the decreased photosynthetic efficiency and protein content. The sulfur replenishment (SR) confirmed the rapid response of C. sorokiniana in starch accumulation to sulfur availability. Thus, we further investigated the expression profiling of key regulatory proteins under Control-SL-SR stages. The expression of AGPase A was strongly induced in the SL stage and subsequently downregulated during SR stage, suggesting its role as a key regulatory protein for enhanced starch accumulation. Additionally, downregulation of SBE and GBE expression likely contributed to structural modifications of the starch molecules. These proteins could serve as potential targets for metabolic engineering in further improving the starch production capacity in C. sorokiniana.

Harmony in detoxification: Microalgae unleashing the potential of lignocellulosic pretreatment wastewater for resource utilization

Lignocellulosic biomass is a pivotal renewable resource in biorefinery process, requiring pretreatment, primarily chemical pretreatment, for effective depolymerization and subsequent transformation. This process yields solid residue for saccharification and lignocellulosic pretreatment wastewater (LPW), which comprises sugars and inhibitors such as phenols and furans. This study explored the microalgal capacity to treat LPW, focusing on two key hydrolysate inhibitors: furfural and vanillin, which impact the growth of six green microalgae. Chlorella sorokiniana exhibited higher tolerance to furfural and vanillin. However, both inhibitors hindered the growth of C. sorokiniana and disrupted algal photosynthetic system, with vanillin displaying superior inhibition. A synergistic inhibitory effect (Q < 0.85) was observed with furfural and vanillin on algal growth. Furfural transformation to low-toxic furfuryl alcohol was rapid, yet the addition of vanillin hindered this process. Vanillin stimulated carbohydrate accumulation, with 50.48 % observed in the 0.1 g/L furfural + 0.1 g/L vanillin group. Additionally, vanillin enhanced the accumulation of C16: 0 and C18: 2, reaching 21.71 % and 40.36 %, respectively, with 0.1 g/L vanillin. This study proposed a microalgae-based detoxification and resource utilization approach for LPW, enhancing the comprehensive utilization of lignocellulosic components. The observed biomass modifications also suggested potential applications for biofuel production, contributing to the evolving landscape of sustainable biorefinery processes.

Plant-Derived Products Selectively Suppress Growth of the Harmful Alga Prymnesium parvum

Prymnesium parvum is a harmful alga found in brackish waters worldwide whose toxins can be lethal to aquatic organisms. Established field methods to control blooms of this species, however, are unavailable. Earlier studies showed that various extracts of giant reed (Arundo donax) can suppress P. parvum growth and that ellipticine, an allelochemical present in giant reed, is a potent algicide against this species. The unintended effects of giant reed products on nontarget organisms, however, are not fully understood. This study determined the effects of giant reed leachate (aqueous extract of dried chips) and ellipticine on growth of P. parvum and the green microalga Chlorella sorokiniana; survival and reproduction of the planktonic crustacean Daphnia pulex; and hatching success, larval survival, and larval swimming behavior of the teleost fish Danio rerio. Leachate made with 3 g chips L−1 was lethally toxic to P. parvum and D. pulex, stimulated C. sorokiniana growth, and impaired D. rerio behavior. Leachate at 1 g L−1 fully suppressed P. parvum growth, had moderate effects on D. pulex reproductive output, and had no effects on D. rerio. Ellipticine at 0.01 mg L−1 irreversibly inhibited P. parvum growth, acutely but reversibly inhibited C. sorokiniana growth, slightly delayed D. pulex reproduction, and had no effects on D. rerio. These observations suggest that when applied at appropriate concentrations, natural products derived from giant reed can be used as tools to specifically control P. parvum growth with minimal effects on nontarget species.

Mitigating salinity stress through interactions between microalgae and different forms (free-living & alginate gel-encapsulated) of bacteria isolated from estuarine environments

Salinity stress in estuarine environments poses a significant challenge for microalgal survival and proliferation. The interaction between microalgae and bacteria shows promise in alleviating the detrimental impacts of salinity stress on microalgae. Our study investigates this interaction by co-cultivating Chlorella sorokiniana, a freshwater microalga, with a marine growth-promoting bacterium Pseudomonas gessardii, both of which were isolated from estuary. In this study, bacteria were encapsulated using sodium alginate microspheres to establish an isolated co-culture system, preventing direct exposure between microalgae and bacteria. We evaluated microalgal responses to different salinities (5 PSU, 15 PSU) and interaction modes (free-living, gel-encapsulated), focusing on growth, photosynthesis, cellular metabolism, and extracellular polymeric substances (EPS) properties. High salinity inhibited microalgal proliferation, while gel-fixed interaction boosted Chlorella growth rate by 50.7 %. Both attached and free-living bacteria restored Chlorella's NPQ to normal levels under salt stress. Microalgae in the free-living interaction group exhibited a significantly lower respiratory rate compared to the pure algae group (−17.2 %). Increased salinity led to enhanced EPS polysaccharide secretion by microalgae, particularly in interaction groups (19.7 %). Both salt stress and interaction increased the proportion of aromatic proteins in microalgae's EPS, enhancing its stability by modulating EPS glycosidic bond C-O-C and protein vibrations. This alteration caused microalgal cells to aggregate, free-living bacteria co-culture group, and fixed co-culture group increasing by 427.5 %, 567.1 %, and 704.1 %, respectively. In gel-fixed bacteria groups, reduced neutral lipids don't accumulate starch instead, carbon redirects to cellular growth, aiding salt stress mitigation. These synergistic activities between salinity and bacterial interactions are vital in mitigating salinity stress, improving the resilience and growth of microalgae in saline conditions. Our research sheds light on the mechanisms of microalgal-bacterial interactions in coping with salt stress, offering insights into the response of estuarine microorganisms to global environmental changes and their ecological stability.

In Situ Formed Microalgae-Integrated Living Hydrogel for Enhanced Tumor Starvation Therapy and Immunotherapy through Photosynthetic Oxygenation.

The effectiveness of various cancer therapies for solid tumors is substantially limited by the highly hypoxic tumor microenvironment (TME). Here, a microalgae-integrated living hydrogel (ACG gel) is developed to concurrently enhance hypoxia-constrained tumor starvation therapy and immunotherapy. The ACG gel is formed in situ following intratumoral injection of a biohybrid fluid composed of alginate, Chlorella sorokiniana, and glucose oxidase, facilitated by the crossing-linking between divalent ions within tumors and alginate. The microalgae Chlorella sorokiniana embedded in ACG gel generate abundant oxygen through photosynthesis, enhancing glucose oxidase-catalyzed glucose consumption and shifting the TME from immunosuppressive to immunopermissive status, thus reducing the tumor cell energy supply and boosting antitumor immunity. In murine 4T1 tumor models, the ACG gel significantly suppresses tumor growth and effectively prevents postoperative tumor recurrence. This study, leveraging microalgae as natural oxygenerators, provides a versatile and universal strategy for the development of oxygen-dependent tumor therapies.

Simultaneous production of algal biomass and lipid by heterotrophic cultivation of linoleic acid-rich oleaginous microalga Chlorella sorokiniana using high acetate dosage

The low-cost carbon source, acetate, was utilized to feed a linoleic acid-rich Chlorella sorokiniana for microalgal biomass and lipid accumulation. Remarkably high tolerance capability to high acetate dosage up to 30 g/L was observed, with heterotrophy being the preferred trophic mode for algal growth and lipogenesis when supplemented 20 g/L acetate. Transcriptome analysis revealed a marked activation of pathways involved in acetate bioconversion and lipogenesis upon exposure to high-level of acetate. However, the enhancement of photorespiration inhibited photosynthesis, which ultimately led to a decrease in biomass and lipid under mixotrophy. Heterotrophic acetate-feeding generated more superior amino acid profiling of algal biomass and a predominant linoleic acid content (50 %). Heterotrophic repeat fed-batch strategy in 5 L fermenter significantly increased the growth performance and lipid titer, with the highest levels achieved being 23.4 g/L and 7.0 g/L, respectively. This work provides a viable approach for bio-products production through acetate-based heterotrophic algal cultivation.

Optimization of a Chlorella–Saccharomyces co–culture system for enhanced metabolite productivity

Microalgae and yeast co–culture systems are gaining interest as a promising method for higher production of biomass and metabolites. However, because these organisms have particular cultivation requirements, optimization of culture conditions is needed for suitable growth and productivity of the co–culture. This work examines the effects of cultivation media macronutrient composition on the growth and metabolite production of co–cultures of either Chlorella vulgaris or Chlorella sorokiniana with a strain of Saccharomyces cerevisiae. Specifically, the consequence of glucose, yeast extract and peptone supplementation on the physiological responses of the co–culture system was investigated. The co–culture responses were equivalent for both Chlorella species, although C. sorokiniana could maintain a more stable population ratio with yeast. The addition of glucose with peptone significantly enhanced biomass production of the co–culture by approximately 2–fold in comparison to microalgae or yeast monocultures, while the addition of glucose alone or in combination with yeast extract did not exhibit the same effect. An approximately 3–fold increase in lipid content was observed in the co–culture samples under glucose–only supplementation, where yeast growth was restricted. The addition of glucose and yeast extract enhanced the growth of yeast monocultures, but this did not benefit the co–culture. Fourier transform infrared spectroscopy analysis revealed different metabolic fingerprints of the monoculture and the co–culture samples grown in glucose and peptone containing medium, which indicated higher abundance of metabolites including lipids, proteins, carbohydrates in the co–culture samples. Specifically, total protein yields in the co–cultures were increased by 1.6– to 1.7–fold in comparison to microalgae monoculture while total lipid yields were increased by 3.6– to 5.1–fold in the co–cultures. This work highlights the importance of organic carbon and nitrogen availability for microalgae–yeast co–culture growth and their potential for a wide range of valuable applications including nutritional and bioenergy uses.

Degradation of dyes using reactive species of atmospheric pressure dielectric barrier discharge formed by a pencil plasma jet

The dye degradation efficacy of the cold plasma pencil jet is presented in the present investigation. Dye degradation studies were performed using air plasma, six different types of selected dyes (erythrosine, metanil yellow, sudan I, crystal violet, rhodamine B, and Indigo). The degradation of dyes is analyzed using UV visible spectroscopy, total organic carbon, and chemical oxygen demand. The results showed complete degradation of all types of dyes in UV visible analysis with minimum time for indigo (3 min) and maximum time for erythrosine (45 min). Moreover, erythrosine (k = 1.08 mg l−1 min−1), sudan I (k = 3.46 mg l−1 min−1), rhodamine B (k = 3.955 mg l−1 min−1), and Indigo (k = 18.915 mg l−1 min−1) follows approximate zeroth-order degradation kinetic, and metanil yellow (k = 0.094 min−1) and crystal violet (k = 0.25 min−1), closer to first-order degradation kinetics. Additionally, a substantial enhancement in mineralization and reduction in chemical oxygen demand of all the dyes occurs after plasma treatment. In this study, air plasma is produced in the cylindrical coaxial dielectric barrier discharge configuration. Electrical characterization of plasma is performed and the plasma species are identified using optical emission spectroscopy. The toxicity of plasma degraded dyes solutions toward freshwater algae species (Chlorella Sorokiniana and Chlorella Pyrenoidosa) are significantly low compared to virgin dyes solutions. The study reveals that pencil plasma jet substantially degrades dyes as well as converts the dyes solutions non-toxic.

Axenic green microalgae for the treatment of textile effluent and the production of biofuel: a promising sustainable approach

An integrated approach to nutrient recycling utilizing microalgae could provide feasible solutions for both environmental control and energy production. In this study, an axenic microalgae strain, Chlorella sorokiniana ASK25 was evaluated for its potential as a biofuel feedstock and textile wastewater (TWW) treatment. The microalgae isolate was grown on TWW supplemented with different proportions of standard BG-11 medium varying from 0 to 100% (v/v). The results showed that TWW supplemented with 20% (v/v) BG11 medium demonstrated promising results in terms of Chlorella sorokiniana ASK25 biomass (3.80 g L−1), lipid production (1.24 g L−1), nutrients (N/P, > 99%) and pollutant removal (chemical oxygen demand (COD), 99.05%). The COD level dropped by 90% after 4 days of cultivation, from 2,593.33 mg L−1 to 215 mg L−1; however, after day 6, the nitrogen (-NO3−1) and total phosphorus (TP) levels were reduced by more than 95%. The biomass-, total lipid- and carbohydrate- production, after 6 days of cultivation were 3.80 g L−1, 1.24 g L−1, and 1.09 g L−1, respectively, which were 2.15-, 2.95- and 3.30-fold higher than Chlorella sorokiniana ASK25 grown in standard BG-11 medium (control). In addition, as per the theoretical mass balances, 1 tonne biomass of Chlorella sorokiniana ASK25 might yield 294.5 kg of biodiesel and 135.7 kg of bioethanol. Palmitic acid, stearic acid, and oleic acid were the dominant fatty acids found in the Chlorella sorokiniana ASK25 lipid. This study illustrates the potential use of TWW as a microalgae feedstock with reduced nutrient supplementation (20% of TWW). Thus, it can be considered a promising feedstock for economical biofuel production.Graphical abstract

Interaction of Fe2O3 nanoparticles with marine microalga Chlorella sorokiniana: Analysis of growth, morphological changes and biochemical composition

The wide utilization of iron-based nanoparticles (NPs) based on their preferential properties has led to the discharge and accumulation of these materials into the aquatic environment. In this regard, a comparative study of different concentrations of α-Fe2O3 NPs and their micro form was conducted using microalga Chlorella sorokiniana up to the stationary growth phase. This study revealed that high concentrations of NPs (100 and 200 mg L−1) imposed a stressful condition on algal cells documented by a reduction in microalga growth, including cell number and specific growth rate. The physical contact between the algal cells and NPs resulted in a shading effect as well as morphological changes validated by scanning electron microscope results. The biochemical composition of C. sorokiniana exposed to high levels of Fe2O3 NPs was also evaluated. The increase in total carbohydrate content of algal cells along with a significant reduction in unsaturated fatty acids was found. Moreover, Fe2O3 NPs exposure induced oxidative stress evidenced by an increase in lipid peroxidation. To cope with oxidative stress, superoxide dismutase activity and antioxidant potential of microalga as defensive mechanisms increased in the culture with high concentrations of NPs. Besides, due to the interactions, microalga tended to form a protective layer from further cell-NP interactions through the secretion of extracellular polymeric substances. Nonetheless, the nano form of Fe2O3 was more toxic than its micro form due to its small size. Overall, this trial may provide additional insight into the toxicological mechanism and safety assessments of Fe2O3 NPs in the aquatic environment.

Design parameters comparison of bubble column, airlift and stirred tank photobioreactors for microalgae production

Microalgae are the most propitious feedstock for biofuel production due to their lipid and fatty acid content. Microalgae cultivation shares many features with bioreactors, such as thermal and pH regulation, feeding procedures, and mixing to enhance heat and mass transfers. Aeration and stirring speeds are important parameters to reduce the costs of producing microalgae. In this study, three different photobioreactor types (stirred tank, airlift, bubble column) were characterized and compared for microalgae production. Hydrodynamics, mass transfer, and power consumption were determined for various aeration rates (0.9, 1.2, 1.5 L/min), and stirring speeds (100, 200 rpm), and Chlorella sorokiniana growth performance was compared under the conditions that provided the highest volumetric mass transfer and the lowest mixing time. Photo-bioreactor homogenization was good as indicated by low mixing times (< 10 s). Bubble column had the highest volumetric mass transfer due to its sparger design. Gas holdup and volumetric mass transfer coefficient were found to increase with the air flow rate and stirring speed. For stirred tank, bubble column, and airlift photobioreactors, maximum specific growth rates of C. sorokiniana were 0.053, 0.061, 0.057 h−1, and biomass productivities were 0.064, 0.097, 0.072 gdw/L.day, respectively. Under the conditions tested, growth was limited by the volumetric mass transfer in the airlift and stirred tank and bubble column was the best option for producing microalgae. These findings pave way for more extensive use of these systems in producing microalgae and provide a basis to compare photobioreactors of different designs.

Physiological responses and removal mechanisms of ciprofloxacin in freshwater microalgae

Antibiotics, such as ciprofloxacin (CIP), are frequently detected in various environmental compartments, posing significant risks to ecosystems and human health. In this study, the physiological responses and elimination mechanisms of CIP in Chlorella sorokiniana and Scenedesmus dimorphus were determined. The exposure CIP had a minimal impact on the growth of microalgae, with maximum inhibit efficiency (IR) of 5.14% and 22.74 for C. sorokiniana and S. dimorphus, respectively. Notably, the photorespiration in S. dimorphus were enhanced. Both microalgae exhibited efficient CIP removal, predominantly through bioaccumulation and biodegradation processes. Intermediates involved in photolysis and biodegradation were analyzed through Liquid Chromatography High Resolution Mass Spectrometer (HPLC-MS/MS), providing insights into degradation pathways of CIP. Upregulation of key enzymes, such as dioxygenase, oxygenase and cytochrome P450, indicated their involvement in the biodegradation of CIP. These findings enhance our understanding of the physiological responses, removal mechanisms, and pathways of CIP in microalgae, facilitating the advancement of microalgae-based wastewater treatment approaches, particularly in antibiotic-contaminated environments.

Simultaneously maximizing microalgal biomass and lipid productivities by machine learning driven modeling, global sensitivity analysis and multi-objective optimization for sustainable biodiesel production

Simultaneous enhancement in the productivities of microalgal biomass and lipids that are inversely correlated to each other has been a long-standing challenge before the scientists engaged in algal biodiesel research and innovation. This study, develops an Artificial Neural Network (ANN) model and uses multi-objective optimization approach to determine the process parameters, namely, light intensity, CO2%, air flow rate, and C/N ratio to maximize biomass and lipid productivities of microalga, Chlorella sorokiniana, simultaneously. Experimental data based on central composite design (CCD) were used to train a feed-forward multilayer ANN with four critical parameters. The global sensitivity analysis was performed on the trained ANN model using Sobol's method to assess the relative significance of the four process variables. Since the objectives of maximizing biomass and lipid productivities conflict with each other, multi-objective optimization approach was used for deriving the optimal process parameters, experimental validation of which resulted in approximately 3 times increase in biomass productivity and 7 times increase in lipid productivity. On transesterification of the lipid, the biodiesel product with saturated to unsaturated fatty acids ratio of 48:52 conformed very well to the international standards, ASTM D6751 and EN14214, thereby making it an environment friendly green biofuel. Thus, the present study showcases the successful application of machine learning tool in analysing the global sensitivity analysis of process variables, and employ it for multi-objective optimization towards achieving maximum microalgal biomass and lipid productivities concomitantly for potentially sustainable production of biodiesel.

Polystyrene microplastics enhanced the effect of PFOA on Chlorella sorokiniana: Perspective from the cellular and molecular levels

Microplastics (MPs) commonly coexist with other contaminants and alter their toxicity. Perfluorooctanoic acid (PFOA), an emerging pollutant, may interact with MPs but remain largely unknown about the joint toxicity of PFOA and MPs. Hence, this research explored the single and joint effects of PFOA and polystyrene microplastics (PS-MPs) on microalgae (Chlorella sorokiniana) at the cellular and molecular levels. Results demonstrated that PS-MPs increased PFOA bioavailability by altering cell membrane permeability, thus aggravating biotoxicity (synergistic effect). Meanwhile, the defense mechanisms (antioxidant system modulation and extracellular polymeric substances secretion) of Chlorella sorokiniana were activated to alleviate toxicity. Additionally, transcriptomic analysis illustrated that co-exposure had more differential expression genes (DEGs; 4379 DEGs) than single-exposure (PFOA: 2533 DEGs; PS-MPs: 492 DEGs), which were mainly distributed in the GO terms associated with the membrane composition and antioxidant system. The molecular regulatory network further revealed that PS-MPs and PFOA primarily regulated the response mechanisms of Chlorella sorokiniana by altering the ribosome biogenesis, photosynthesis, citrate cycle, oxidative stress, and antioxidant system (antioxidant enzyme, glutathione-ascorbate cycle). These findings elucidated that PS-MPs enhanced the effect of PFOA, providing new insights into the influences of MPs and PFOA on algae and the risk assessment of multiple contaminants. Environmental implicationMPs and PFAS, emerging contaminants, are difficult to degrade and pose a non-negligible threat to organisms. Co-pollution of MPs and PFAS is ubiquitous in the aquatic environment, while risks of co-existence to organisms remain unknown. The present study revealed the toxicity and defense mechanisms of microalgae exposure to PS-MPs and PFOA from cellular and molecular levels. According to biochemical and transcriptomic analyses, PS-MPs increased PFOA bioavailability and enhanced the effect of PFOA on Chlorella sorokiniana, showing a synergistic effect. This research provides a basis for assessing the eco-environmental risks of MPs and PFAS.