Microalgal Cells Research Articles

Continuous Inertial Alignment and Isolation of Spherical Microparticles and Nonspherical Flagellate Microalgae

Flagellate microalgae play an increasingly significant role in environmental management and biotechnology for valuable bioproducts, excellent photosynthetic capability, and autonomic movement. However, multiple flagellate microalgae practically live together in the ocean and lake areas, and they are susceptible to contamination as a result of improper operations. Enthused by these aspects, we develop a reliable inertial microfluidic method to overcome the influence of flagella movement and non-spherical shape on the alignment and isolation of target flagellate microalgae. Firstly, a computational model incorporating fluid-structure interaction was established to investigate influence of releasing position and shape parameters on the displacement and rotation of non-spherical microalgal cells and numerically studied the processes of shape- and size-based particle separation. Secondly, the movement of different-size particles under diverse flow rates in the channel was explored, and the capability of this method was validated by aligning and separating 10 μm and 20 μm polystyrene particles. Thirdly, this method was applied to align H. pluvialis and isolate Dunaliella salina from the mixed microalgal samples to explore the influence of flow rate on the alignment and isolation of flagellate microalgae. Fourthly, this method was engineered to select 20 μm polystyrene particles from three types of particles and isolate H. pluvialis from the mixture of multiple microalgae species. Finally, we leveraged this approach to realize separation of H. pluvialis and Synedra ulna to explore the performance of this method in shape-based cell separation, and we isolated Euglena from microalgal cell wastes, including dead cells, bacteria, and particles. This method has promising prospects to be a reliable tool to isolate target flagellate microalgae to address problematic issues in environmental monitoring, pharmaceutical synthesis, and chronic wound treatment for the advantage of good adaptability and reliability.

Developing an off-site bicarbonation absorber system to promote microalgal fixation of CO2 in exhaust gas from biogas upgrading

In order to address the risk of explosion due to CH4 from exhaust gas produced during biogas upgrading in closed carbon fixation systems employing photosynthetic microalgae, an off-site bicarbonation absorber system was developed to promote microalgal CO2 fixation under atmospheric pressure. The abundant CO2 in the biogas upgrading exhaust gas (≥90 vol.% CO2, ≤10 vol.% CH4) reacted with a Na2CO3 solution in the off-site bicarbonation absorber to produce NaHCO3, which was used as carbon source for microalgal growth in enclosed column photobioreactors. After the reaction, CH4 was discharged outside the bicarbonation absorber because it did not react with the Na2CO3 solution and was extremely difficult to dissolve in water, thereby avoiding the explosion risk due to accumulated CH4 in the enclosed column photobioreactors. The experimental results showed that the Spirulina growth rate first increased 1.7 times, peaking at 0.6g/L/d, and then decreased when the bicarbonation reaction time (optimal 50min), absorber diameter (optimal 10cm), initial Na2CO3 concentration (optimal 173mM), and exhaust gas aeration rate (optimal 100 sccm) increased. The optimal molar ratio of NaHCO3 to total inorganic carbon in the bicarbonation absorber solution reached 79%. The sufficient HCO3- supply and suitable pH of the microalgal solution improved the synthesis of photosynthetic pigments in the microalgal cells and enhanced their photochemical efficiency and carbon sequestration rates.

Innovative technology for microalgal cell preservation through immobilization in polylactic acid nanofibers

Microalgae are of great biotechnological importance. Thus, it is essential to apply maintenance methods for the utilization of microalgae at any time. Facilitating microalgae adsorption processes on nanofibers may be a promising approach for microalgae preservation. Thus, the objective of this study was to apply poly (lactic acid) nanofibers in the preservation of microalgae Chlorella fusca LEB 111 cells. The nanofibers were characterized regarding their morphology, thermal properties, structural characteristics and wettability. The microalgae cells were immobilized on the nanofibers and stored for 30 days at room temperature, refrigeration and thermostated chamber. Free microalgae cells were also maintained for the same period under the same conditions of the traditional method of microalgae preservation, continuous replication. The cell viability of the free and immobilized cells on the nanofibers was analyzed by Neutral Red (NR) and Trypan Blue (TB). At the end of the experiment, the immobilized cells showed greater viability (94 and 100 %) compared to the free cells (84 %). The cultivation of immobilized cells showed significant cell growth on the 25th day of cultivation for the evaluated storage conditions (3.6, 3.6 and 2.8 g L−1 for refrigeration, room temperature and thermostatted chamber, respectively). Therefore, poly (lactic acid) nanofibers (PLA) are characterized as an innovative technology for microalgae maintenance.

Optimization of microalgal-bacterial consortium flocculation through chitosan-diatomite composite materials: A sustainable approach to biomass harvesting

Chitosan-based flocculants are emerging as a promising technology for microalgae harvesting. However, the implementation of cost-effective and sustainable chitosan-inorganic composites within algal-bacterial symbiosis (ABS) systems for harvesting microalgal-bacterial consortiums (MBC) is still underdeveloped. This study addresses this gap by synthesizing and evaluating chitosan-diatomite composite materials (CTS/DTE), with a focus on their concentration impact on MBC flocculation. Optimal biomass production and flocculation performance were achieved at a CTS/DTE concentration of 60 mg/L during MBC co-culture. Comprehensive characterizations revealed that the largest particle size significantly contributed to superior flocculation efficiency. This efficacy was primarily attributed to the synergistic effects of net trapping and adsorption cross-linking, facilitated by the unique interaction between CTS and DTE. These interactions not only enhanced the bond between the flocculant and microalgal cells but also promoted the structural stabilization of the MBC flocs. Additionally, tryptophan-like proteins in the extracellular polymeric substances (EPS), as identified through three-dimensional fluorescence (EEM) analysis, were found to be the primary contributor to the hydrophobic properties of MBC flocs, significantly enhancing their adhesion and aggregation thermodynamics. Collectively, this research elucidates innovative strategies and provides both theoretical and practical insights for the efficient and cost-effective harvesting of MBC, underscoring the potential of CTS/DTE composites in enhancing the sustainability of ABS systems.

Integrated proteome and pangenome analysis revealed the variation of microalga Isochrysis galbana and associated bacterial community to 2,6-Di-tert-butyl-p-cresol (BHT) stress.

The phenolic antioxidant 2,6-Di-tert-butyl-p-cresol (BHT) has been detected in various environments and is considered a potential threat to aquatic organisms. Algal-bacterial interactions are crucial for maintaining ecosystem balance and elemental cycling, but their response to BHT remains to be investigated. This study analyzed the physiological and biochemical responses of the microalga Isochrysis galbana and the changes of associated bacterial communities under different concentrations of BHT stress. Results showed that the biomass of I. galbana exhibited a decreasing trend with increasing BHT concentrations up to 40mg/L. The reduction in chlorophyll, carotenoid, and soluble protein content of microalgal cells was also observed under BHT stress. The production of malondialdehyde and the activities of superoxide dismutase, peroxidase, and catalase were further determined. Scanning electron microscopy analysis revealed that BHT caused surface rupture of the algal cells and loss of intracellular nutrients. Proteomic analysis demonstrated the upregulation of photosynthesis and citric acid cycle pathways as a response to BHT stress. Additionally, BHT significantly increased the relative abundance of specific bacteria in the phycosphere, including Marivita, Halomonas, Marinobacter, and Alteromonas. Further experiments confirmed that these bacteria had the ability to utilize BHT as the sole carbon resource for growth, and genes related to the degradation of phenolic compounds were detected through pangenome analysis.

Visible-light-activated Fe2O3–TiO2 nanoparticles enhance biofouling resistance of polyethersulfone ultrafiltration membranes against marine algae Chlorella vulgaris

This study investigated the modification of polyethersulfone (PES) ultrafiltration membranes with TiO2 and Fe2O3–TiO2 nanoparticles to enhance their hydrophilicity and biofouling resistance against the marine microalgae Chlorella vulgaris. It is a common freshwater and marine microalga that readily forms biofilms on membrane surfaces, leading to significant flux decline and increased operational costs in ultrafiltration processes. The microalgae cells and their extracellular polymeric substances (EPS) adhere to the membrane surface, creating a dense fouling layer that impedes water permeation. The modified membranes were characterized using contact angle measurements, scanning electron microscopy, and pure water flux/resistance tests. Short-term ultrafiltration experiments evaluated the membranes’ antifouling performance by measuring flux decline, flux recovery ratio, and relative flux reduction during C. vulgaris filtration. The TiO2 membrane showed improved hydrophilicity and antifouling over the pristine PES membrane, while the Fe2O3–TiO2 nanocomposite membrane exhibited the best performance. It reduced the water contact angle and showed only a 5% relative flux reduction compared to 60% for the pristine membrane. SEM images confirmed reduced microalgal deposition on the nanocomposite surface. Long-term tests with microalgal cells under dark and visible light conditions in saline water further assessed the membranes’ biofouling resistance. The Fe2O3–TiO2 membrane maintained 59 L/m2 h water flux under visible light after immersion in the microalgal solution, outperforming the pristine (38 L/m2 h) and TiO2 (52 L/m2 h) membranes. This superior antifouling was attributed to photocatalytic generation of reactive oxygen species inhibiting microalgal adhesion. This study demonstrates a promising strategy for mitigating biofouling in membrane-based water treatment and desalination processes.

Viscoelastic Fluid Focusing Chip-ICP-MS Single-Cell Analysis Enables Elucidating the Effect of Extracellular Polymeric Substances on Bioaccumulation of Hg2+/HgS in Microcystis aeruginosa Cell.

Understanding the interactions between mercury and microalgae, especially the interactions between inorganic mercury (IHg) and extracellular polymeric substances (EPS, a protective barrier between cells and their external environment), is essential for elucidating mercury's toxicological mechanisms. Given the inherent cell heterogeneity, a novel analysis system of an online viscoelastic fluid focusing chip-time-resolved analysis inductively coupled plasma mass spectrometry has been developed to investigate the bioaccumulation of HgS nanoparticles and Hg2+ in single Microcystis aeruginosa (M. aeruginosa) cells, exploring the interaction mechanisms between HgS/Hg2+ accumulation in algal cells and EPS. The single-cell analysis results reveal minimal bioavailability of HgS within algal cells, with mercury's toxicity to M. aeruginosa being species-dependent. Notably, algal cells exhibited more heterogeneity in HgS uptake than in Hg2+ uptake. Under Hg2+/HgS stress, M. aeruginosa cells with EPS removed (EPS-R algal cells) showed an increased level of bioaccumulation of mercury compared to those with EPS (EPS-C algal cells), highlighting the critical role of EPS in mercury bioaccumulation. Overall, the designed viscoelastic fluid microfluidic focusing chip integrates focusing and cleaning functions, featuring easy fabrication, simple operation, low sample loss, and relatively high throughput. Under the optimal conditions, the sample throughput is 1195 min-1 and the cell recovery is 90%. Besides, this research offers novel insights into the interaction mechanisms between Hg2+/HgS and EPS in microalgal cells and unveils the specific toxic effects of Hg2+/HgS on M. aeruginosa at the single-cell level, contributing to a deeper understanding of mercury's ecological and toxicological impact in aquatic environments.

Unraveling the risks of nAl2O3 on harmful algal blooms: Insights from paralytic shellfish toxins production of Alexandrium tamarense

As one of the commonly used and cost-effective nanomaterials, nanosized aluminum oxide (nAl2O3) posses unique properties and chemical stability. However, its extensive use and resultant dissemination into aquatic ecosystems prompt concerns over the proliferation and repercussions of harmful algal blooms, particularly those caused by dinoflagellates producing toxins. This study investigated the sub-chronic effects of nAl2O3 on growth, physiological activities, and paralytic shellfish toxins (PSTs) production in Alexandrium tamarense. Results showed dose-dependent inhibition in growth (EC50 = 20.6 mg L−1), esterase activity, and photosynthetic efficiency (Fv/Fm) during the sub-chronic exposure (13-day). The internalization of nAl2O3 in microalgal cells and the significant decrease in the total cellular PSTs content were observed under high nAl2O3 concentrations (>40 mg L−1). The study also demonstrated a clear decrease in the content of some derivatives of PSTs (GTX5, C1/2, and GTX2/3) with the increase in nAl2O3 concentrations, accompanied by the induction of an unknown derivative. Excessive ROS production, dissolved Al, and physical inhibition were suggested as potential mechanisms for nAl2O3 toxicity and changes in PSTs toxin profile. Overall, this research enhances our understanding of the potentiated risks and threats on the possible concurrent events of toxic dinoflagellate, such as Alexandrium species and nanoparticles in aquatic environments.

Enhancing photosynthesis of microalgae via photoluminescent g-C3N4 accelerated photoelectrons transfer in photosystem

Using photoluminescent (PL) graphitic carbon nitride (g-C3N4) to convert ultraviolet (UV) light into chloroplast absorbed blue or near infrared (NR) is an attractive methodology to facilitate sunlight energy storage and carbon sequestration by microalgae. However, most researches focus on inhibiting water bloom by g-C3N4, applying PL g-C3N4 to promote growth of microalgae is rarely reported. Accordingly, PL g-C3N4 is synthesized by a microwave heating method and co–cultured with Chlorella vulgaris (C. vulgaris) with concentration of 0, 50, and 250 mg/L, named as C. vulgaris-0, C. vulgaris-50, and C. vulgaris-250, respectively, to study effect of PL g-C3N4 on growth of C. vulgaris. Results indicate that there is no significant effect of microwave synthesized g-C3N4 on morphology of microalgae cells, while cell viability and growth rate of C. vulgaris-50 is obviously enhanced. Further analysis indicates that, on the one hand, PL fluorescence at 615 nm enlarges light absorption of microalgae; on the other hand, photogenerated electrons by g-C3N4 accelerate electron transfer in photosystem, subsequently enhancing formation of NADPH and ATP, which is favorable to growth of microalgae. Metabolism analysis illustrates that glucose, fructose, and galactose, involved in glycolysis and photosynthesis, are all up-regulated in C. vulgaris-50 group. This work reveals low concentration of PL g-C3N4 facilitates protein synthesis and energy metabolism through enhancing light absorption and electron transfers, providing a biochemical strategy to enhance carbon sequestration.

Intensified microalgae production and development of microbial communities on suspended carriers and municipal wastewater

Wastewater represents an alternative source of nutrients in which to grow microalgae, whilst improving the quality of the wastewater, and reducing the downstream treatment required. However, commercialisation of microalgal cultures for such duties faces a number of challenges, predominantly high cost and low productivity. Suspended-solid reactors (ssPBR) can reduce the operational costs, while promoting attached and suspended microalgae growth. In the present study, a novel approach was developed by integrating microalgal wastewater treatment with carrier systems to favour the growth of both attached and suspended cells of T. obliquus. This study found that T. obliquus was able to uptake nutrients from municipal wastewater, achieving removals of 99.3–99.9 % NH3-N, 54.5–88.5 % PO43− and 92.8–94.5 % DTC. The addition of a 12.5 % volumetric fill ratio of carriers in ssPBRs produced higher microalgal cell productivity (1.2·106 ± 2.5·105 cell ml−1 d−1) than the control (4.3·105 ± 2.8·105 cell ml−1 d−1). MinION nanopore sequencing was conducted to assess the impact of microalgal and carrier treatment on wastewater bacterial communities. It was found not only that bacterial communities had changed after the treatment but also the ones attached differed from the ones suspended. Untreated wastewater was characterised by the abundance of sewer bacteria genera such as Aliarcobacter and Arcobacter, whilst, after treatment, microbial communities were characterised by the presence of photosynthetic freshwater (Limnococcus, Stanieria) and bioremediation-like bacteria genera (Pseudomonas, Rheinheimera). In conclusion, the addition of 12.5 % fill carrier ratio increased microalgal productivity, while stimulating changes in the algal microbiome, and creating distinctly different populations in the free and attached environments.

Microalgal Metabolomes and Recent Biotechnological Advances for Their Industrial Application

In recent decades, microalgae have emerged as new sustainable resources for the production of various bioactive and biochemical compounds. These organisms are photosynthetic, use CO2 as their sole carbon source, and grow rapidly under different environmental conditions. This makes microalgae a promising source of feedstock for many bio-commodities. However, the economic viability for large-scale production through microalgal cells is limited to certain organisms. Recent advances in omics technologies, along with high-throughput approaches, have provided new insights for understanding microalgal metabolites. With the improvement in metabolomic technology, sensitivity for the detection of cellular metabolites has increased, and it has directly enhanced our understanding of cellular metabolism and the corresponding metabolic pathways. Moreover, these metabolic techniques, along with other omics technologies, help us to characterize the changes in the cellular functioning of the different cells under environmental conditions. Metabolomic research on microalgae explores new metabolites and the understanding of their biosynthesis at the metabolic level. In this review, we discuss how these metabolomics techniques are applied to microalgae to study their metabolic networks. Additionally, we also discuss how integrating other tools of systems biology can improve the productivity of microalgal cells, especially for industrially important commodities.

Intensification and characterization of biosorption of microalgal cells on filamentous fungal pellets as effective tools for harvesting of microalgal biomass

Microalgae are promising resources with a variety of advantages and applications. However, their harvesting cost in large-scale cultivation may account for 20–30 % and in some instances up to 50 % of the overall production cost. This study then aimed to apply biosorption of microalgal cells by using fungal pellets as an alternative low-cost and practical harvesting technique. Among the fungal strains screened, Aspergillus tubingensis TSIP9 formed spherical, mycelium packed and consistent in size. The biosorption of microalgal cells process was optimized through response surface methodology (RSM). The maximum harvesting efficiency of 98.3 ± 1.2 % was achieved when using pellet loading of 60 % and pH 5.0. The biosorption process can be explained by Langmuir isotherm model with the maximum biosorption capacity (qmax) of 0.338 g/g and the Langmuir constant (K) of 0.999 L/g. Pseudo-first-order model is suitable for describing the biosorption kinetics of microalgal cells on fungal pellets. The application of fungal pellets in downstream process for microalgae cultivation was attempted. The fungal pellets could harvest microalgal cells as high as 3.70 × 1011 cells/g after 5 cycles of repeated harvesting process. FTIR analysis revealed the possible functional groups involved in fungi-microalgae interaction are CO, CO, CN, and CH. These results indicated that the potential of fungal pellets as effective tools for harvesting/immobilizing microalgal cells and their practical applications in harvesting on a large scale and resource recycling.

ZIF-8 confined carbon dots/bilirubin oxidase on microalgal cells to boost oxygen reduction reaction in photo-biocatalytic fuel cells for pollutants removal

ZIF-8 confined carbon dots/bilirubin oxidase on microalgal cells to boost oxygen reduction reaction in photo-biocatalytic fuel cells for pollutants removal

Flagella, palmella and cyst Haematococcus lacustris microalgae cells decorated on graphene oxide and graphene nanoplatelets-activated carbon as novel adsorbents for the removal of lead from water

Industrialization has led to generation of large quantities of waste which constitutes various toxic heavy metals such as lead (Pb). In this work, novel bio-nanostructured graphene-based microalgae nanohybrid adsorbents, using three different cell types of Haematococcus lacustris (i.e., flagella (flg-C), palmella (Pal-C) and cyst (Cyst-C)) to introduce more functional moieties and enhance the surface properties of the nanohybrids. The nanostructured graphene oxide-activated carbon modified with algae cells (GO-AC@algae) and graphene nanoplatelets-activated carbon modified with algae cells (GNPs-AC@algae) nanohybrids were characterized and used for the removal of Pb ions. The GO-AC@algae nanohybrids demonstrated a high lead removal efficiency of over 98.0%, whereas the GNPs-AC@algae nanohybrids achieved more than 85.0%. Among the GO-AC@algae nanohybrids, the nanohybrid with cyst cell (GO-AC@Cyst-C) shown remarkable efficacy as an adsorbent for the removal of Pb2+ ions from aqueous solutions due to its high specific area, abundance of oxygen-nitrogen-based functional moieties, hydrophilicity, and pore structure. Chemisorption was found to be a beneficial process for both GO-AC@algae and GNPs-AC@algae samples, where Pb2+ was adsorbed in a single layer onto the uniform material surface. Among the various adsorbents, GO-AC@Cyst-C achieved the highest monolayer adsorption capacity of 25.58 mg/g according to the Langmuir model, making it the most effective nanoadsorbents. Kinetic studies revealed that the sorption mechanism of GO-AC@algae were better described by the second-order kinetic model. Meanwhile, the first-order kinetic model was found to be suited for GNPs-AC@algae samples. The nanohybrids could be employed as greener adsorbents at industrial scale for wastewater treatment without incurring significant costs.

The Cultivation of Halophilic Microalgae Shapes the Structure of Their Prokaryotic Assemblages.

The influence of microalgae on the formation of associated prokaryotic assemblages in halophilic microbial communities is currently underestimated. The aim of this study was to characterize shifts in prokaryotic assemblages of halophilic microalgae upon their transition to laboratory cultivation. Monoalgal cultures belonging to the classes Chlorodendrophyceae, Bacillariophyceae, Trebouxiophyceae, and Chlorophyceae were isolated from habitats with intermediate salinity, about 100 g/L, nearby Elton Lake (Russia). Significant changes were revealed in the structure of algae-associated prokaryotic assemblages, indicating that microalgae supported sufficiently diverse and even communities of prokaryotes. Despite some similarities in their prokaryotic assemblages, taxon-specific complexes of dominant genera were identified for each microalga species. These complexes were most different among Alphaproteobacteria, likely due to their close association with microalgae. Other taxon-specific bacteria included members of phylum Verrucomicrobiota (Coraliomargarita in assemblages of Navicula sp.) and class Gammaproteobacteria (Salinispirillum in microbiomes of A. gracilis). After numerous washings of algal cells, only alphaproteobacteria Marivibrio remained in all assemblages of T. indica, likely due to a firm attachment to the microalgae cells. Our results may be useful for further efforts to develop technologies applied for industrial cultivation of halophilic microalgae and for developing approaches to obtain new prokaryotes with a microalgae-associated lifestyle.

Computational fluid dynamics (CFD) simulation modeling for the cultivation of microalgal monoculture in axenic enclosed bubble column photobioreactor (BCPBR)

Researchers are more concerned with axenic-enclosed PBRs, where there is less or no chance of contamination during the production of biochemical and highly valuable metabolites, and monocultures of microalgae are being grown more frequently. It is a closed, manufactured vessel that aids in the photosynthesis of microalgal cells using artificial light or sunlight as the energy source. In this study, the bubble column PBR (BCPBR) was selected because it possessed some advantages over other PBRs for the growth of Chlorella vulgaris. The BCPBR system prevents contact between the enclosed microalgal cells and the environment, allowing the culturing of microalgae species that are difficult to grow in open pond systems. To compare BCPBR performance quantitatively, the efficient mixing expected in BCPBR, as discussed in the literature, was applied to the CFD model. The experimental results observed during the cultivation of C. vulgaris with restaurant wastewater (RWW) in BCPBR clearly showed better mixing, high growth, and improved treatment efficiency. CFD analysis was conducted on the evolution of bubbles in the BCPBR. The Pressure-Implicit with Splitting of Operators (PISO) pressure correction method is used for velocity and pressure coupling. A geo-reconstruct approach is used to construct the interface, and a second-order upwind calculation technique is used to determine the flow parameters. Therefore, CFD simulation in this study will contribute to the following aspects: (i) the volume fraction contours and velocity contours are going to validate the experimental study as the homogenous mixing favors the growth and productivity, (ii) To study how the size of the nozzle and inlet velocity affect the turbulence generated by bubbles in a BCPBR to identify the optimal nozzle size and velocity for the required turbulence.

Insights on aggregation-algae consortium based removal of sulfamethoxazole: Unraveling removal effect, enhanced method and toxicological evaluation

The escalating occurrence of the antibiotic Sulfamethoxazole (SMX) in the environment presents a significant global threat to ecological systems and human health. Despite the growing interest in using microalgae for antibiotic biodegradation, strategies to enhance SMX elimination remain underexplored. In this study, we isolated a novel aggregation-algae consortium (AAC) from a municipal wastewater treatment plant (WWTP) and examined its potential for SMX removal, optimized culture conditions, SMX metabolite fate and the physicochemical impact on microalgal cells. The findings revealed that the AAC demonstrated remarkable resistance to SMX, even at concentrations as high as 10 mg/L, and could degrade SMX via free radical reactions. Although ion repulsion limited the biodegradation of AAC, the addition of peptone and yeast extract resulted in a significant enhancement, increased by 16.71%, 39.12% and 46.77% of three SMX groups. Moreover, AAC exhibited exceptional adaptability in real wastewater, achieving removal of 87.05%, 97.39% and 20.80% for total dissolved nitrogen, total dissolved phosphorus and SMX, respectively. The decreased degradation toxicity of SMX following AAC treatment was further validated by ECOSAR software and in vitro tests using Caenorhabditis elegans. This study advanced our understanding of SMX biodegradation and provided a novel approach for treating wastewater contaminated with SMX.

Effect of NH4Cl supplementation on growth, photosynthesis, and triacylglycerol content in Chlamydomonas reinhardtii under mixotrophic cultivation.

Ammonium chloride (NH4Cl) is one of the nitrogen sources for microalgal cultivation. An excessive amounts of NH4Cl are toxic for microalgae. However, combining mixotrophic conditions and excessive quantities of NH4Cl positively affects microalgal biomass and lipid production. In this study, we investigated the impact of NH4Cl on the growth, biomass, and triglyceride (TAG) content of the green microalga Chlamydomonas reinhardtii especially under mixotrophic conditions. Under photoautotrophic conditions (without organic carbon supplementation), adding 25 mM NH4Cl had no significant effect on microalgal growth or TAG content. However, under mixotrophic condition (with acetate supplementation), NH4Cl interfered with microalgal growth while inducing TAG content. To explore these effects further, we conducted a two-step cultivation process and found that NH4Cl reduced microalgal growth, but induced total lipid and TAG content, especially after 4-day cultivation. The photosynthesis performances showed that NH4Cl completely inhibited oxygen evolution on day 4. However, NH4Cl slightly reduced the Fv/Fm ratio indicating that the NH4Cl supplementation directly affects microalgal photosynthesis. To investigate the TAG induction effect by NH4Cl, we compared the protein expression profiles of microalgae grown mixotrophically with and without 25 mM NH4Cl using a proteomics approach. This analysis identified 1782 proteins, with putative acetate uptake transporter GFY5 and acyl-coenzyme A oxidase being overexpressed in the NH4Cl-treated group. These findings suggested that NH4Cl supplementation may stimulate acetate utilization and fatty acid synthesis pathways in microalgae cells. Our study indicated that NH4Cl supplementation can induce microalgal biomass and lipid production, particularly when combined with mixotrophic conditions.

Co-cultivation of microalgae and bacteria for optimal bioenergy feedstock production in wastewater by using response surface methodology

This work uses response surface methodology (RSM) to study the co-cultivation of symbiotic indigenous wastewater microalgae and bacteria under different conditions (inoculum ratio of bacteria to microalgae, CO2, light intensity, and harvest time) for optimal bioenergy feedstock production. The findings of this study demonstrate that the symbiotic microalgae-bacteria culture not only increases total microalgal biomass and lipid productivity, but also enlarges microalgal cell size and stimulates lipid accumulation. Meanwhile, inoculum ratio of bacteria to microalgae, light intensity, CO2, and harvest time significantly affect biomass and lipid productivity. CO2 concentration and harvest time have significant interactive effect on lipid productivity. The response of microalgal biomass and lipid productivity varies significantly from 2.1 × 105 to 1.9 × 107 cells/mL and 2.8 × 102 to 3.7 × 1012 Total Fluorescent Units/mL respectively. Conditions for optimum biomass and oil accumulation are 100% of inoculation ratio (bacteria/microalgae), 3.6% of CO2 (v/v), 205.8 µmol/m2/s of light intensity, and 10.6 days of harvest time. This work provides a systematic methodology with RSM to explore the benefits of symbiotic microalgae-bacteria culture, and to optimize various cultivation parameters within complex wastewater environments for practical applications of integrated wastewater-microalgae systems for cost-efficient bioenergy production.

Carbon-Storing Structural Material Based on Wastewater-Cultivated Chlorella Sorokiniana

Microalgae cultivation is a promising technology for carbon sequestration and wastewater remediation. It is economically and logistically critical to find viable applications for the large quantities of produced biomass. In current research, a structural material is developed by using nearly 100% Chlorella sorokiniana. The otherwise non-cohesive microalgae cells are first surface-activated and then compacted under a relatively high pressure. The resulting material is a dense solid, stronger than typical steel-reinforced concrete in flexural tests. The processing procedure is simple and fast, and the setup is scalable. This technique may be useful for next-generation green construction and provide a use-case for sustainable microalgae biomass.