Microalgal Strains Research Articles

In vitro toxicity of microalgae species of the phyla chlorophyta and ochrophyta in CHO-k1 and HEP G2 cells for potential use in human nutrition

Microalgae are a promising component to enhance human nutrition, but to date only a few species have been authorized to be used in human nutrition. In this study, the in vitro toxicity of eight novel microalgae strains (Botryococcus braunii, Chlorococcum novae-angliae, Microchloropsis salina, Myrmecia bisecta, Stichococcus sp. Tetraselmis suecica, Tetradesmus obliquus and Spongiochloris minor) selected for their potential for human nutrition was investigated. N-hexane, acetone, ethanol and aqueous extracts of the lyophilized biomass were tested in the CHO-k1 and HEP G2 cell lines at concentrations of up to 1.81 mg ml-1 extracted biomass per well. None of the tested microalgae extracts reached values defined as a significant cytotoxic effect (IC50 < 0.02 mg ml-1). The highest cytotoxic effects were measured for Stichococcus sp. in both cell lines with IC50 values of 0.17 mg ml-1 for the acetone extract in CHO-k1 cell culture and 0.18 mg ml-1 for the acetone extract in HEP G2 cell culture. Most cytotoxic effects occurred with the acetone and ethanol extracts, while the water and n-hexane extracts showed almost no measurable cytotoxic effects. Only Tetraselmis suecica showed no cytotoxic effect under the chosen conditions in both tested cell lines, marking this microalgae as particularly interesting for further investigations into its use in human nutrition.

Mixotrophic cultivation of microalgae-bacteria consortia enhances dark fermentation effluent treatment

Dark fermentation (DF) is a waste treatment bioprocess which produces biohydrogen and volatile fatty acids (VFAs) such as acetate or butyrate. DF can be coupled with microalgae cultivation, allowing VFA conversion into valuable biomass. Nevertheless, the process is hindered by slow butyrate consumption. In this study, novel artificial microalgae-bacteria consortia were used as a strategy to accelerate butyrate removal. Three microalgal strains with various trophic metabolisms, Chlorella sorokiniana, Euglena gracilis and Ochromonas danica, were cultivated on DF effluent that was either sterile or contained endogenous bacteria. Bacteria did not impact microalgal biomass production of C. sorokiniana or E. gracilis while accelerating butyrate removal rates 2 to 10-fold. O. danica greatly impacted microbial diversity, probably due to its phagotrophic metabolism. These results show that bacteria in organic rich effluents can greatly aid in substrate removal while allowing microalgal growth, inspiring bioprocesses coupling raw fermentation effluents with microalgae biomass production and valorization.

Potential of a novel marine microalgae Dunaliella sp. MASCC-0014 as feed supplements for sustainable aquaculture

Microalgae, as live feed organisms in aquatic ecosystems, play a crucial role in enhancing water quality by providing oxygen and nutrients. The accumulation of heavy metals in microalgae, however, can pose significant threats to environmental sustainability and human health. In this study, we focused on the marine microalgae Dunaliella sp. MASCC-0014, which exhibited resilience to a wide range of salinities from 0.5 to 4.5 M NaCl, with optimal growth at 0.5 M NaCl. Phylogenetic analysis revealed that MASCC-0014 is closely related to Dunaliella salina CCAP 19/25. Biosorption assay indicated that MASCC-0014 had limited capacity to absorb cadmium, cobalt, and nickel from the liquid medium, while Dunaliella salina CCAP 19/18, Dunaliella tertiolecta FACHB-821 and Dunaliella bardawil FACHB-847 showed varied degrees of cadmium biosorption. When exposed to cadmium stress, MASCC-0014 exhibited suppressed growth and increased activities of catalase (CAT) and peroxidase (POD), suggesting cadmium still triggered cellular responses in MASCC-0014. Furthermore, MASCC-0014 displayed reduced chlorophyll content per cell but increased biomass in warmer conditions, indicating its preference of tropical water over temperate water. This unique microalga strain, which is rich in protein but with limited heavy metal biosorption capabilities, shows promise as a sustainable feed source in aquaculture. The findings in this study offer valuable insights into mitigating the risks of heavy metal enrichment in the food chain through algae-based feeds.

Maximizing resource efficiency with dairy and municipal wastewater as nutrient media for Chlorella vulgaris with simultaneous CO2 sequestration

Addressing critical environmental challenges such as greenhouse gas emissions, global warming, and eutrophication demands urgent and innovative solutions. In recent years, microalgae have emerged as a promising avenue for addressing these pressing issues. In this study, the combination of dairy and municipal wastewater is proposed as a culture medium for cultivating microalgae strains capable of sequestering atmospheric CO2. Specifically, the growth of Chlorella vulgaris was investigated using Bold's basal medium, along with varying concentrations of municipal and dairy wastewater, both with and without CO2 supplementation, to assess their CO2 capture potential. Concurrently, the efficiency of chemical oxygen demand (COD), total nitrogen, potassium, and phosphate removal from the wastewater was evaluated. Additionally, the combination of wastewater media with CO2 supplementation yielded the highest CO2 uptake rates, indicating the feasibility of simultaneous CO2 capture during microalgae cultivation. Media composition with 25% municipal wastewater: 75% dairy wastewater supplemented with CO2 demonstrated superior COD elimination with a higher percentage of nutrient removal from wastewater compared to other wastewater proportions. The nutrient removal capacity of aforementioned media also comes in line with high CO2 sequestration rate (13.57 mg L−1 h−1). These findings underscore the potential of utilizing wastewater from diverse sources as a viable culture medium for microalgae cultivation, facilitating concurrent CO2 capture and wastewater treatment.

Maximizing diclofenac bioremoval efficiency using Chlorella vulgaris strain H1 and Chlorella sorokiniana strain H2: Unveiling the impact of acetic acid on microalgae

BackgroundDiclofenac (DFC) is a commonly detected pharmaceutical pollutant in wastewater, posing environmental risks. Microalgae have emerged as potential candidates for bioremediation due to their ability to degrade pollutants. This study focuses on investigating the biodegradation potential of two newly isolated microalgae strains, Chlorella vulgaris strain H1 and Chlorella sorokiniana strain H2, towards DFC removal. The optimization of pH is crucial for enhancing the efficiency of bioremediation processes. Therefore, in addition to assessing the biodegradation potential of microalgae, this study also investigates the impact of adjusting the pH of the culture medium using acetic acid as an additional carbon source on the biodegradation process. MethodsThrough genetic analysis using 18S rDNA sequencing, the microalgae strains were identified. Various parameters including growth dynamics, chlorophyll content, cell proliferation, photosynthetic activity, and DFC biodegradation efficiency were comprehensively assessed. Additionally, the impact of incorporating acetic acid as an additional carbon source in the culture medium on the biodegradation process was examined. Significant FindingsC. sorokiniana strain H2 demonstrated superior biodegradation rates compared to C. vulgaris strain H1 across varying DFC concentrations. Specifically, C. sorokiniana strain H2 exhibited remarkable biodegradation rates of 84 %, 83.72 %, and 29.57 % for DFC concentrations of 12.5 mg L−1, 25 mg L−1, and 100 mg L−1, respectively. In contrast, C. vulgaris strain H1 showed lower biodegradation rates of 66.64 %, 29.24 %, and 1.83 % for the corresponding DFC concentrations. The study highlights the potential of C. sorokiniana strain H2 as a promising candidate for the removal of pharmaceutical pollutants like DFC from wastewater. Furthermore, the use of acetic acid as a supplementary carbon source enhanced the biodegradation efficiency, suggesting a potential strategy for optimizing bioremediation processes.

Upcycling food waste as a low-cost cultivation medium for Chlorella sp. microalgae.

Global food loss and waste have raised environmental concerns regarding the generation of greenhouse gases (e.g., carbon dioxide and methane gas), which directly contribute to climate change. To address these concerns, the present research aims to upcycle food waste into an alternative culture medium for the cultivation of microalgae. Various parameters including pretreatment of food waste (i.e., autoclave and non-autoclave), concentration of food waste culture medium (i.e., 10%, 30%, 50%, 70%, 90% and 100%), harvesting efficiency and biochemical compounds of Chlorella sp. microalgae were carried out. Based on the preliminary findings, the highest biomass concentration obtained from 10% food waste culture medium in the autoclave for Chlorella sp., including strains FSP-E, ESP-31 and CY-1, were 2.869 ± 0.022, 2.385 ± 0.018 and 0.985 ± 0.0026 g L-1, respectively. Since Chlorella vulgaris FSP-E exhibited the highest biomass concentration, this microalgal strain was selected to examine the subsequent parameters. Cultivation of C. vulgaris FSP-E in 100FW achieves a biomass concentration of 4.465 ± 0.008 g L-1 with biochemical compounds of 6.94 ± 1.396, 248.24 ± 0.976 and 406.23 ± 0.593 mg g-1 for lipids, carbohydrates and proteins, respectively. This study shows that using food waste as an alternative culture medium for C. vulgaris FSP-E can achieve substantial biomass productivity and biochemical content. This research work would contribute to the concept of net zero emission and transitioning toward a circular bioeconomy by upcycling food waste as an alternative culture medium for the cultivation of microalgae. © 2024 Society of Chemical Industry.

Microalgae Flocculation: Assessment of Extraction Yields and Biological Activity

Downstream costs represent one of the main obstacles to enabling microalgae to become widespread. The development of an economical, easily scaled-up strategy could reduce the overall process costs. Here, different flocculants were tested on different microalgae strains and a cyanobacterium. The results indicate that flocculation could be an alternative to centrifugation, as CaCl2 induced a complete flocculation of green and red marine strains (96 ± 4% and 87.0 ± 0.5%, respectively), whereas Chitosan was the only agent able to induce flocculation on the cyanobacterium (46 ± 1%). As for the thermoacidophilic red microalga, 100% flocculation was achieved only by increasing the pH. Carotenoids were extracted from the flocculated biomass, and the strategy improved with the use of the wet biomass. The results indicate that flocculation does not affect carotenoid yield, which is at least the same than that obtained upon centrifugation and extraction from the wet biomass. Then, for the first time, the biological activity of the extracts obtained from the flocculated biomasses was evaluated. The results indicate that only the green microalga extract shows increased antioxidant activity. In conclusion, this work highlights that a general downstream procedure cannot be developed for microalgae strains but should be rationally tailored.

An indigenous microalgal pool containing Klebsormidium sp. K39 as a stable and efficacious biotechnological strategy for Escherichia coli removal in urban wastewater treatment

AbstractBACKGROUNDIn recent decades the demand for freshwater has drastically increased as a consequence of population growth, economic development, climate change and pollution. Therefore, any strategy for wastewater treatment can play a role in alleviating the pressure on freshwater sources.RESULTSIn the present study an autochthonous microalgal pool (MP), isolated from a constructed wetland, was proposed as an alternative to the secondary treatment of an urban wastewater treatment system. The MP removal efficacy was compared to those obtained using Chlorella vulgaris and Scenedesmus quadricauda, against E. coli. Results exhibited a comparable removal efficacy and after 2 days, in samples inoculated with E. coli at lower density, S. quadricauda and C. vulgaris induced a decrease of 2.0 units Log and the autochthonous MP of 1.8 units Log, whereas in samples with E. coli at higher density the bacteria were reduced 2.8, 3.4 and 2.0 units Log by S. quadricauda, C. vulgaris and the autochthonous MP, respectively. Moreover, the identification of microalgal strains isolated from the MP revealed the presence of Klebsormidium sp. K39, C. vulgaris, Tetradesmus obliquus and S. quadricauda. Although the MP composition remained quite constant, at the end of the treatment, a different distribution among the microalgal species was observed with Klebsormidium sp. K39 found as dominant.CONCLUSIONThe microalgal‐based wastewater treatment appears as a valuable alternative, although further investigations, based on ‘omics’ approaches, could be applied to better explore any fluctuation within the MP species composition in an in situ trial. © 2024 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The production and characteristics of glycogen synthesized by various strains of the thermoacidophilic red microalgae Galdieria grown heterotrophically

AbstractRed microalgae from the Cyanidiophyceae, particularly Galdieria sulphuraria and Cyanidioschyzon merolae, are primitive photosynthetic thermoacidophiles that thrive in acidic hot springs and geysers. Unlike most Cyanidiophyceae, Galdieria strains are metabolically flexible as they can switch from photoautotrophic growth in the light to heterotrophic growth in complete darkness. Galdieria sulphuraria is especially noteworthy for its accumulation of various commercially valuable, functional compounds such as glycogen and phycocyanin. Glycogen, a branched fractal-like polysaccharide composed of several thousands of anhydroglucopyranose units, can be added to cosmetic products and sports drinks as a moisturizer or slow-digestible carbohydrate. While the production and structural characteristics of the glycogen of G. sulphuraria 108.79, isolated from Yellowstone National Park, have been previously described, our investigation aimed to explore glycogen production and properties across various Galdieria strains from different locations. Our findings reveal that all examined strains produce substantial amounts of highly branched glycogen when grown heterotrophically on glycerol in the dark. Notably, the structural characteristics of Galdieria glycogen distinguish it from both eukaryotic and prokaryotic glycogen, exhibiting a significantly higher degree of branching, substantially shorter side chains, and a considerable extent of indigestibility. These findings support the hypothesis that this highly branched, small glycogen is a long-term energy store, enabling survival during extended periods of complete darkness.

Exploring microalgae and endophyte as biostimulants: Antioxidant and anti-inflammatory properties of Cannabis sativa L. sprouts under standard and enrichment conditions

Sprouts from germinated seeds of edible herbaceous plants are richer in bioactive compounds and micronutrients than mature plants. In recent years, the consumption of sprouted seeds in diets and the interest in exploring vegetable sprout's potential beneficial effects on human health has increased. In this work, the five-day-old sprouts of Cannabis sativa L. cultivar “Futura 75” were investigated and characterized. Hemp sprouts were obtained by germination tests under standard and enrichment conditions using the microalgal strain Chlorella sp. C2 and the bacterium Sphingomonas sp. Can_S11. The biochemical properties of hemp sprouts were analyzed for total polyphenol and flavonoid content and antioxidant activities (DPPH, ABTS, FRAP, ORAC, and Fe2+-chelating activity) by in vitro assays. A significant increase in phenolic compounds and greater antioxidant and anti-radical activities were observed for hemp sprouts obtained under enrichment conditions (dry microalgal biomass C2 and the bacterium Can_S11). Additionally, these sprouts and C. sativa seeds demonstrated enhanced protective effects on inflamed A549 cells, effectively mitigating the TNF-α induced changes and reducing the expression of IL-8 and COX-2. Overall, PGP (Plant Growth Promoting) microorganisms and microalgae represent a good strategy to promote the development of hemp sprouts and increase their phytochemical content, and antioxidant and anti-inflammatory activity.

Microalgae-based sunscreens as green and sustainable cosmetic products.

Recently, microalgal biotechnology has attained great acceptance among various researchers and industries for the green and sustainable production of different bioactive compounds. They provide multiple metabolites and molecules, making them an ideal candidate for cosmetic formulators and cosmeceutical companies. Nevertheless, numerous microalgae strains have never been studied for their pharmaceutical, nutritional and cosmeceutical purposes. Even less, only some have been cultivated on a large scale for bioactive compound production. Here, we have studied the cosmetic and cosmeceutical potentials of different microalgal strains for sunscreen as adjuvants and boosters in a green, carbon-neutral and sustainable platform. Other bioactive compounds were exploited, and the available products in the market and the published patents were also reviewed. From our review, it will be possible to combine the fundamental and practical aspects of microalgal biotechnology toward a greener and more sustainable future for the cosmetic/cosmeceutical areas of the photoprotection scenario.

Exopolysaccharides from the Green Microalga Strain Coelastrella sp. BGV-Isolation, Characterization, and Assessment of Anticancer Potential.

Algal metabolites have been extensively studied as potential anticancer therapeutics. Among them, polysaccharides have attracted much attention because of their beneficial biological effects and safety. In the present research, the chemical characteristics, antitumor, and proapoptotic activities of extracellular polysaccharides (EPS) isolated from a new Bulgarian strain of the green microalga Coelastrella sp. BGV were investigated. A fast and convenient method of precipitation with cold ethanol was used to isolate EPS from the culture medium. The chemical characteristics of the isolated EPS were examined by colorimetric and spectrophotometric analyses, HPSEC-RID and HPLC-UV chromatography, and FT-IR spectroscopy. The results showed that the isolated EPS sample consists of three carbohydrate fractions with different molecular weights (11.5 × 104 Da, 30.7 × 104 Da, and 72.4 × 104 Da, respectively) and contains 7.14 (w/w%) protein. HPLC-UV analysis revealed the presence of galactose and fucose. The total uronic acid content in the sample was 4.5 (w/w%). The IR-FT spectrum of EPS revealed the presence of various functional groups typical of a polysaccharide (or proteoglycan) composed primarily of neutral sugars. The anticancer potential of the obtained EPS was assessed using cell lines with cancerous and non-cancerous origins as in vitro experimental models. The results of the performed MTT assay showed that EPS reduced the viability of the cervical and mammary carcinoma cell lines HeLa and MCF-7, while the control non-cancer cell lines BALB/3T3 and HaCaT were less affected. The HeLa cell line showed the highest sensitivity to the effects of EPS and was therefore used for further studies of its anticancer potential. The ability of EPS to inhibit cancer cell migration was demonstrated by wound-healing (scratch) assay. The cell cycle FACS analysis indicated that the EPS treatment induced significant increases in the sub G1 cell population and decreases of the percentages of cells in the G1, S, and G2-M phases, compared to the control. The fluorescent microscopy studies performed using three different staining methods in combination with Annexin V-FITC flow cytometric analysis clearly demonstrate the ability of EPS to induce cancer cell death via the apoptosis pathway. Moreover, an altered pattern and intensity of the immunocytochemical staining for the apoptosis- and proliferation-related proteins p53, bcl2, and Ki67 was detected in EPS-treated HeLa cancer cells as compared to the untreated controls. The obtained results characterize the new local strain of green microalgae Coelastrella sp. BGV as a producer of EPS with selective antitumor activity and provide an opportunity for further studies of its pharmacological and biotechnological potential.

Effect of cephalexin on chlorophyll and carotenoid content of Chlorella pyrenoidosa-2378 and its biodegradation in BG-11 medium

Cephalexin (CFX), a β-lactam antibiotic which is identified for the treatment of different disease infections, has been reported as a micropollutant in wastewater released from sewage, hospital, or pharmaceutical industries. Chlorella pyrenoidosa-2378, a green microalgal strain, is recognized for its degradation ability against wastewater pollutants and the potential of the biomass it produces. In this present study, the cultivation process of Chlorella pyrenoidosa-2378 strain with CFX concentration of 50 mg/L, 100 mg/L, 150 mg/L, and 200 mg/L added to its culture medium labeled as test I, test II, test III, and test IV, respectively, is the process being observed for evaluation of its degradation ability and as sustainable approach for antibiotic degradation. chlorophyll a in test IV, chlorophyll b in test III, and carotenoid content in test I were observed to be higher in amount than control by 0.775 mg/L, .069 mg/L, and 0.356 mg/L, respectively. Using the HPLC method, the total removal efficiency was observed to be 79.09%, 86.26%, 89.62%, and 88.03% against 50, 100, 150, and 200 mg/L concentrations of CFX, respectively. The observations that C. pyrenoidosa-2378 remained stable while being used as an alternative bioremediation method, provide an alibi for its novelty and potentiality to be used commercially for biomass production and at industrial scale for degradation.Graphical

Microalgal biofilm induces larval settlement in the model marine worm Platynereis dumerilii.

A free-swimming larval stage features in many marine invertebrate life cycles. To transition to a seafloor-dwelling juvenile stage, larvae need to settle out of the plankton, guided by specific environmental cues that lead them to an ideal habitat for their future life on the seafloor. Although the marine annelid Platynereis dumerilii has been cultured in research laboratories since the 1950s and has a free-swimming larval stage, specific environmental cues that induce settlement in this nereid worm are yet to be identified. Here, we demonstrate that microalgal biofilm is a key settlement cue for P. dumerilii larvae, inducing earlier onset of settlement and enhancing subsequent juvenile growth as a primary food source. We tested the settlement response of P. dumerilii to 40 different strains of microalgae, predominantly diatom species, finding that P. dumerilii have species-specific preferences in their choice of settlement substrate. The most effective diatom species for inducing P. dumerilii larval settlement were benthic pennate species including Grammatophora marina, Achnanthes brevipes and Nitzschia ovalis. The identification of specific environmental cues for P. dumerilii settlement enables a link between its ecology and the sensory and nervous system signalling that regulates larval behaviour and development. Incorporation of diatoms into P. dumerilii culture practices will improve the husbandry of this marine invertebrate model.

A local or a stranger? Comparison of autochthonous vs. allochthonous microalgae potential for bioremediation of coal mine drainage water

Coal mining endangers the environment by contaminating of soil, surface, and ground water with coal mine drainage water (CMW) polluted by heavy metals. Microalgal cultures, hyper-accumulators of heavy metals, represent a promising solution for CMW biotreatment. A bottleneck of this approach is the availability of microalgal strains that combine a large capacity for heavy metal biocapture with a high resilience to their toxic effects. Biotopes contaminated with heavy metals are frequently inhabited by microalgae evolved to be resilient to heavy metal toxicity. Therefore, the autochthonous (locally isolated) microalgal strains are a priori considered to be superior for biotreatment of heavy metal-polluted waste streams. Still, strains from biocollections combine a high pollutant resilience with other biotechnologically important traits such as high productivity, high CO2 sequestration rate etc. Moreover, the strains available “off-the-shelf” would enable rapid development of bioprocesses. Here, we compared the efficiency of CMW biotreatment with autochthonous (isolated from the coal mine drainage sump) and allochthonous microalgae (from a geographically distant phosphate-polluted site). Both autochthonous strains and allochthonous strains turned to be interchangeable under our experimental conditions. Still, the autochthonous strains showed a higher capacity for sequestration of iron, zinc, and manganese, the specific pollutants of the studied CMW. It can be important when the duration of unattended exploitation of the CMW treatment facility is a priority or spikes of the heavy metal concentration in CMW are expected. Therefore, the “off-the-shelf” strains can be a plausible solution for rapid development of CMW treatment technologies from scratch (although screening for acute toxicity of CMW is imperative). On the other hand, locally isolated strains can offer distinct advantages and should be always considered if sufficient time and other resources are available for the development of microalgae-based process for CMW treatment.

Tubular photobioreactor design based on mixing intensity

A novel design methodology for tubular photobioreactors (TPBRs) for the mass culture of microalgae that can account for mixing intensity is presented. To date, TPBRs have been mainly designed and operated under the assumption of perfect mixing with regard to photosynthesis performance (light integration regime). In this work we show that this simplification has been leads to significant errors in the prediction of the optimal dilution rate and biomass productivity. To this end, computational fluid dynamics and light distribution model have been employed to calculate the trajectories and light histories I(t) of a microalgal cell population represented by 50 particles of 5 μm diameter. The density of the microalgal cells was set at 1000 kg m−3 and the tube diameters (D) were 14, 24, 44, 64 and 84 mm, with the circulation velocities (v) ranging from 0.4 to 1 m s-1. This has been coupled to a dynamic photosynthesis model in order to calculate the average photosynthetic response and hence the integration factors in TPBRs. It has been demonstrated that for a generic microalgal strain, the use of the light integration simplification (Γ = 1) would result in the prediction of an optimal dilution rate of 0.0315 h−1 (for D = 14 mm and v = 0.4 m/s as an example), which would lead to an actual biomass productivity of 182.5 g biomass m−3h−1 if the predicted integration factor (Γ = 0.578) is used whereas the newly proposed method predicts an optimal dilution rate of 0.0125 h−1 and a biomass productivity of 362.3 g biomass m−3h−1. This demonstrates that simplifying the light integration regime is inadequate for TPBRs design and operation, resulting in significant inaccuracies. The estimation charts and regressions proposed in this work to estimate actual integration factors will enable the development of an optimization method for TPBRs based on mixing intensity.

Effects of Temperature and Nitrogen Limitation on Growth and Lipid Production of Oleaginous Microalgae from Hot Springs

Oleaginous microalgae have gained increasing attention as an alternative feedstock for biodiesel production due to the increasing demand of fuel, climate change, and global warming. This study aimed to isolate and screen robust microalgal strains from hot springs for cultivation in subtropical and tropical areas. The newly isolated oleaginous microalgae were cultivated at 30, 35 and 40 °C. Among mesophilic and thermophilic strains tested, Chlamydomonas sp. HP59 is considered the most robust strain as it showed high cell growth in a broad range of temperatures (30 - 40 °C), with the maximum dried cell weight at 40 °C. Un-optimal temperatures for cell growth did improve lipid content by 2 - 4 folds. To increase lipid production, the 2-stage cultivation, in which nitrogen-rich was applied to promote cell growth in the 1st stage and nitrogen-limitation was applied to stimulate lipid accumulation in the 2nd stage, was performed. The high temperature combined with nitrogen-limitation did improve lipid production by all microalgae. With this strategy, Chlamydomonas sp. HP59 showed the highest dried cell weight of 4.33 g/L and lipid production of 1.72 g/L. This study has shown the potential use of the newly isolated oleaginous microalgae from hot springs to be cultivated at high temperatures and under nitrogen-limited conditions for the production of biodiesel feedstocks. HIGHLIGHTS Mesophilic and thermophilic oleaginous microalgae were isolated from hot springs. Un-optimal temperatures for cell growth did improve lipid content by 2 - 4 folds. Combined effect of high temperature and nitrogen limitation effectively increased lipid content. Two-stage cultivation gave high dried cell weight and hence overall high lipid production. GRAPHICAL ABSTRACT

Features of the Microalgae and Cyanobacteria Growth in the Flue Gas Atmosphere with Different CO2 Concentrations

Nowadays, it is important to create the optimal technology for the absorption of flue gases with high CO2 content. In this regard, the aim of the investigation is to study the five different microalgae strains (Chlorella vulgaris, Chlorella ellipsoidea, Elliptochoris subsphaerica, Gloeotila pulchra, and Arthrospira platensis) under the influence of flue gases. The cultivation of microalgae was carried out in the atmosphere of flue gases with a gas flow rate of approximately 1 L·min−1 at high CO2 concentrations (3, 6, or 8%—from lower to higher concentrations), under continuous (24 h·d−1) illumination intensity of 200 µmol quanta·m−2·s−1 and a constant temperature of 27 ± 1 °C. The duration of the experiments was 12 days. Chlorella vulgaris and Chlorella ellipsoidea demonstrated the highest biomass growth rate at CO2 = 6% (0.79 and 0.74 g·L−1·d−1, respectively). The lowest growth rate (0.21 g·L−1·d−1) was achieved for Arthrospira platensis at CO2 = 3 and 6%. There was no significant drop in pH in the entire series of experiments. The results of microscopy showed a lack or a minimal number of dead cells in the strains under selected conditions. The obtained results can be used for further development of CO2 capture and storage technologies.

Selection and characterization of a Parachlorella kessleri microalgal strain able to assimilate lactose, and grow on dairy waste

One of the main limitations of commercial production of algae is the cost of cultivation, largely attributed to the cost of the nutrients; hence, finding cheap alternative substrates has been a significant line of research in this field. The dairy industry produces large amounts of wastewater that might be used as a cost-effective nutrient alternative, containing lactose as a main carbon source, as well as other essential nutrients like nitrogen and phosphate. Nevertheless, just a few algal species of commercial value can grow on any organic carbon sources, and even less are able to utilize lactose. In this work we have identified a Parachlorella kessleri strain capable of utilizing lactose for growth, and have characterized its ability to accumulate metabolites of commercial interest under heterotrophic growth conditions. P. kessleri was capable to utilize lactose from dairy wastewater, and to accumulate several amino acids, dicarboxylic acids, such as tartaric acid and succinic acid, and triacylglycerols in heterotrophic conditions. These metabolites have applications in the food, feed, and pharmaceutical industries, and in the green chemical industry for the production of bio-based green polymers and biofuels. The significance of these findings for future product development is discussed.

Antibiotic Removal by Three Promising Microalgae Strains: Biotic, Abiotic Routes, and Response Mechanisms

Microalgae represent an alternative to conventional wastewater treatment, potentially improving antibiotic removal and offering a solution to combat the spread of antimicrobial resistance. Through batch assays, this study investigates the routes for antibiotic removal using three strains (Chlamydomonas acidophila, Auxhenochlorella protothecoides and Tetradesmus obliquus). Using mixtures of ciprofloxacin, clarithromycin, erythromycin, metronidazole, ofloxacin, sulfamethoxazole, and trimethoprim at concentrations simulating wastewater composition, it also assesses antibiotic effects on microalgae physiology. The three strains primarily removed antibiotics through rapid biosorption, achieving up to 91.5% removal for specific ones like ciprofloxacin. T. obliquus and C. acidophila showed efficacy, with total removals of 37.2% and 49.3%, respectively. Over time, A. protothecoides demonstrated the highest active removal efficiency, eliminating 22.1% of total antibiotics, with a notable 67.6% removal for sulfamethoxazole. Abiotic degradation through hydrolysis and photolysis contributed to ciprofloxacin, ofloxacin, clarithromycin, and erythromycin removal (34.7% to 96.7%), showing pH-dependent photolysis. However, algae induced a shading effect, reducing the photolytic and hydrolytic degradation of specific antibiotics. T. obliquus and C. acidophila were inhibited by antibiotics, whereas A. protothecoides showed a 30.6% growth rate increase. The stimulatory effect was also observed for the nutrient removal, with A. protothecoides showing a 46.6% increase in ammonium removal and a 44.8% increase in phosphate removal with antibiotics. Additionally, antioxidant activities remained stable, except for a notable increase in peroxidase activity for A. protothecoides and T. obliquus. The study confirms efficient antibiotic removal and stimulatory responses in the three algal strains, indicating their potential for wastewater treatment and combating antimicrobial resistance.