Search Results (23)

Herbivorous protistan grazers are ubiquitous and abundant in marine and temperate freshwater environments. However, little is known about the algivorous ciliates and their feeding habits in outdoor mass algal cultures. In this study, we report on one hypotrich ciliate, identified as Sterkiella histriomuscorum, from the outdoor mass culture of Scenedesmus in Arizona, USA. A long-term field survey revealed that this species often occurs in Scenedesmus culture in spring and summer, and can graze very heavily on Scenedesmus cells. By isolating Sterkiella cells and then observing them via light microscopy and electron microscopy, detailed information about the morphology, ultrastructure, excystment process, and feeding characteristics of the ciliate was obtained. Specifically, it seems that S. histriomuscorum has a range of different strategies for excystment, and the sharp change in the ion concentration in the environment around the cyst results in osmotic shock, which likely facilitates the excystment. Feeding experiments revealed that S. histriomuscorum preferred to graze on chlorophytes as well as the diatom Phaeodactylum tricornutum and had no interaction with chrysophytes or cyanobacteria. Molecular phylogenetic analysis based on the SSU rRNA gene sequence indicated that both the genus Sterkiella and the species S. histriomuscorum are non-monophyletic. The information obtained from this study will help advance our understanding of the biodiversity and ecological function of S. histriomuscorum, and will also be very useful in the development of early warning systems and control measures for preventing or treating this contaminant in microalgal mass cultures. Full article

Microalgae have emerged as a promising renewable resource due to their biomass production and cell composition. This study aimed to evaluate a commercial nutrient source for Desmodesmus abundans L2B Bold cultivation, analyzing its metabolome, photosynthetic pigments, and biomass potential as a biostimulant for soybean crops. Samples underwent metabolomics analysis via GC/MS after derivatization. Microalgal biomass produced in a commercial fertilizer medium (CF) was applied as a biostimulant at three concentrations in soybean crops at 30, 50, and 70 days post-sowing. Pigments and dry biomass levels were similar in BG11 and CF media, but CF reduced production costs by 31.8%. Distinct metabolite profiles were observed, with major classes being organic acids (19%), amines (14%), sugars (12%), fatty acids (11%), and esters (10%). Foliar application of 20% (v/v) D. abundans L2B Bold increased stem diameter (5.88 mm), leaf fresh and dry mass, and stem mass. Additionally, there were increases in nitrogen (26%) and protein (38.1%) in seeds, alongside higher pod (10.9) and seed numbers (25.2) and seed mass (3.43 g) per plant⁻¹. These findings demonstrate the feasibility of using CF as a culture medium and the potential of D. abundans L2B Bold as a biostimulant for soybean production. Full article

Lutein, a yellow xanthophyll carotenoid, is increasingly recognized for its nutraceutical benefits, particularly in protecting the retina’s macula from age-related degeneration. Microalgae are a promising source of lutein, which can be a primary product or a coproduct in biorefineries. Certain microalgae exhibit lutein levels (up to 1.7%) surpassing those of common dietary sources like kale, spinach, and egg yolk (approximately 0.7–0.9%). Predominantly associated with photosystem II’s light-harvesting complex, lutein is crucial in photosynthesis and cellular defense. However, being quantitatively minor among cellular constituents, lutein necessitates specialized processing for efficient extraction. Although ubiquitous in microalgae, it is not as easily inducible as β-carotene and astaxanthin in Dunaliella salina and Haematococcus pluvialis, respectively. Currently, microalgal lutein production predominantly occurs at the bench scale, presenting challenges in scaling up. Factors like culture medium significantly influence biomass and lutein yields in industrial production, while downstream processing requires cost-effective, food-grade solvent extraction techniques. This review delves into contemporary methods and innovative progress in microalgal lutein production, emphasizing industrial-scale processes from biomass cultivation to final product formulation. A conceptual industrial process proposed in this review shows that two 10 m³ photobioreactors could produce 108 kg dry mass for Chlorella minutissima, which can be processed into approximately 616 g of lutein extract, or over 6000 capsules of finished nutraceutical daily. Despite lutein production via microalgae being in nascent stages at large scales, existing research provides a solid foundation for well-informed scale-up endeavors. Full article

Haematococcus species are rich sources of the antioxidant astaxanthin and have good potential for carbon dioxide reduction. A variety of culture systems for these microalgae are currently in development, but clearly profitable approaches have yet to be reported. Open outdoor culture is currently the only feasible culture system for producing large amounts of biomass. In this study, based on laboratory results, the cultivation of Haematococcus was divided into two stages: a green stage characterised by cell growth, and a red stage characterised by astaxanthin accumulation. For mass culture, we adopted a hybrid open–closed pond system for astaxanthin production. The open culture system was shown to produce approximately 50 kg (dry weight) of biomass per culture at an average rate of 0.51 g L⁻¹, with 0.52 μg mL⁻¹ of astaxanthin content in a 12 -m³ water tank. As large amounts of microalgal bioproducts are in high demand, inexpensive open outdoor culture methods should be adopted as an alternative to costly closed photobioreactors. Although the levels of biomass and astaxanthin production were found to be 30% lower in the field than in the laboratory in this study, the basic data obtained in this research may be useful for lowering astaxanthin production costs. Full article

Chlorella has been applied in the production of selenium (Se) enriched organic biomass. However, limited information exists regarding heterotrophic selenium tolerance and its incorporation into Chlorella. This study aimed to investigate the potential of using Chlorella vulgaris K-01 for selenium biotransformation. To assess the dose-response effect of Se stress on the strain, time-series growth curves were recorded, growth productivity parameters were calculated, and Gaussian process (GP) regression analysis was performed. The strain’s carbon and energy metabolism were evaluated by measuring residual glucose in the medium. Characterization of different forms of intracellular Se and residual Se in the medium was conducted using inductively coupled plasma-mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectrometer (ICP-OES). The EC50 value for the strain in response to Se stress was 38.08 mg/L. The maximum biomass productivity was 0.26 g/L/d. GP regression analysis revealed that low-level Se treatment could increase the biomass accumulation and the carrying capacity of Chlorella vulgaris K-01 in a heterotrophic culture. The maximum organic Se in biomass was 154.00 μg/g DW. These findings lay the groundwork for understanding heterotrophic microalgal production of Se-containing nutraceuticals, offering valuable insights into Se tolerance, growth dynamics, and metabolic responses in Chlorella vulgaris K-01. Full article

Microalgae are naturally adapted to the fluctuating availability of phosphorus (P) to opportunistically uptake large amounts of inorganic phosphate (P_i) and safely store it in the cell as polyphosphate. Hence, many microalgal species are remarkably resilient to high concentrations of external P_i. Here, we report on an exception from this pattern comprised by a failure of the high P_i-resilience in strain Micractinium simplicissimum IPPAS C-2056 normally coping with very high P_i concentrations. This phenomenon occurred after the abrupt re-supplementation of P_i to the M. simplicissimum culture pre-starved of P. This was the case even if P_i was re-supplemented in a concentration far below the level toxic to the P-sufficient culture. We hypothesize that this effect can be mediated by a rapid formation of the potentially toxic short-chain polyphosphate following the mass influx of P_i into the P-starved cell. A possible reason for this is that the preceding P starvation impairs the capacity of the cell to convert the newly absorbed P_i into a “safe” storage form of long-chain polyphosphate. We believe that the findings of this study can help to avoid sudden culture crashes, and they are also of potential significance for the development of algae-based technologies for the efficient bioremoval of P from P-rich waste streams. Full article

Loss of algal production from the crashes of algal mass cultivation systems represents a significant barrier to the economic production of microalgal-based biofuels. Current strategies for crash prevention can be too costly to apply broadly as prophylaxis. Bacteria are ubiquitous in microalgal mass production cultures, however few studies investigate their role and possible significance in this particular environment. Previously, we demonstrated the success of selected protective bacterial communities to save Microchloropsis salina cultures from grazing by the rotifer Brachionus plicatilis. In the current study, these protective bacterial communities were further characterized by fractionation into rotifer-associated, algal-associated, and free-floating bacterial fractions. Small subunit ribosomal RNA amplicon sequencing was used to identify the bacterial genera present in each of the fractions. Here, we show that Marinobacter, Ruegeria, and Boseongicola in algae and rotifer fractions from rotifer-infected cultures likely play key roles in protecting algae from rotifers. Several other identified taxa likely play lesser roles in protective capability. The identification of bacterial community members demonstrating protective qualities will allow for the rational design of microbial communities grown in stable co-cultures with algal production strains in mass cultivation systems. Such a system would reduce the frequency of culture crashes and represent an essentially zero-cost form of algal crop protection. Full article

The development of kinetic models aims at predicting the behavior of a system or analyzing the underlying mechanisms. This process is essential for understanding microalgal growth and optimizing culture conditions. In the case of microalgal cultivation in wastewater, the analysis becomes even more difficult as growth is often inhibited by several factors, such as nutrient limitation and light inadequacy. In this context, a mathematical model was developed to describe the microbial growth of the species Parachlorella kessleri in different reactor setups using either sterile or non-sterile anaerobic digestion effluent as a substrate. Three different mass balances were taken into consideration to describe biomass growth, phosphorus, and nitrogen consumption. Concerning biomass growth, the logistic model was applied to evaluate the inhibition in biomass formation due to lack of illumination. The maximum optical density under which these species could grow was quantified with an OD_max parameter, which was estimated at 4.07 AU/cm for the Erlenmeyer flask and 2.79 AU/cm for cylindrical photobioreactors. Regarding the nitrogen mass balance, two different terms concerning microalgal assimilation and ammonia stripping were implemented into the equation. The proposed model predicted biomass growth with high accuracy in model training (R² = 0.90) and validation (R² = 0.89). Full article

An alternative way to remove CO₂ from biogas is the use of photosynthetic microorganisms, such as microalgae. This can be achieved by the operation of an open photobioreactor, connected with a mass transfer column, such as a counterflow column. This technology provides up-graded biogas with high quality. The microalgal uptake of CO₂ from the biogas in counterflow columns generates pH changes in microalgae culture. To clarify the potential effect of these dynamic pH conditions in the culture, the effect of pH change on the photosynthetic activity and PSII quantum yield was studied for microalgae Chlorella sorokiniana. Thus, assays were carried out, where the pH drop reported in the counterflow columns was replicated in batch microalgae culture through HCl addition and CO₂ injection, moving the culture pH from 7.0 to 5.0 and from 7.0 to 5.8, respectively. Moreover, the effect of light/darkness on photosynthetic activity was tested when the pH decreased. The results obtained in this research showed that the photosynthetic activity decreased for the light conditions when the pH was shifted by HCl addition and CO₂ injection. Despite this, the value of the PSII quantum yield remained at 0.6–0.7, which means that the microalgae culture did not suffer a negative effect on the photosynthetic system of cells because a high value of PSII efficiency remained. In the same way, the results indicated that when the pH change was corrected, the photosynthetic activity recovered. Moreover, the apparent affinity constant for dissolved inorganic carbon (KDIC) was 0.9 µM at pH 5 and 112.0 µM at pH 7, which suggests that the preferred carbon source for C.sorokniana is CO₂. Finally, all the results obtained indicated that the pH drop in the counter-flow column for biogas upgrading did not cause permanent damage to the photosynthetic system, and the decrease in the photosynthetic activity as a result of the pH drop can be recovered when the pH is corrected. Full article

The locally isolated harpacticoid copepods Tigriopus sp. and Tisbe holothuriae were subjected to salinity tolerance experimentation at salinities under and above of 40 ppt, and presented high halotolerances in Tigriopus LC50 (24 h) of 1 ± 4.43 ppt and 132 ± 5.35 ppt, respectively, and in Tisbe of 15 ± 2.41 ppt and 93 ± 3.23 ppt, respectively. Tetraselmis suecica, among other microalgal feeds (Asteromonas gracilis, Rhodomonas salina, Dunaliella salina and Isochrysis galbana), resulted in the higher production of nauplii in Tigriopus and R. salina and D. salina in Tisbe (also close to T. suecica in Tigriopus). The demographics (number of nauplii, egg sacs, completion of hatching) of both copepods, using combinations of salinities in the range of 22–60 ppt and D. salina and R. salina as feeds, exhibited almost the same preference for microalgae but were negatively affected by the salinity of 60 ppt. The present experiments showed that these local copepods that have extreme salinity tolerance and a wide preference for easily cultured microalgae can be used in ecological studies and for mass production as live feed in marine fish hatcheries. Full article

Biogas production by anaerobic digestion from different wastes represents a growing interest in the panel of renewable energy. Digestate has already been a subject of numerous studies as part of microalgal culturing because it is still rich in nutrients. This study wants to use it as a reference to investigate the possibility to exploit Slurry for the same applications. The first part of this research aims to evaluate microalgae-bacterial flocs growth for nutrient recycling from liquid digestate and slurry, working at three different dilutions (10%, 30%, and 50%) of these two substrates, in order to determine the best value for nutrients and pollutants removal (ammonia and chemical oxygen demand removal rate) and microalgae-bacterial biomass production (autotrophic index). The best dilutions were 30% for digestate and 10% for slurry, allowing the highest ammonia and chemical oxygen demand removal rates. The second part evaluated methane production during anaerobic digestion at different ratios of substrate/inoculum (0.2, 0.5, and 0.8), using microalgae-bacterial flocs as a substrate and digestate or slurry as the inoculum. After 30 days, the anaerobic digestion without flocs showed the best performance compared to digestion with flocs (726.7 mL CH₄·g⁻¹ slurry, 245.6 mL CH₄·g⁻¹ digestate), whereas, for flocs digestion, the best ratio for both inocula was 0.2 substrate/inoculum with 317.2 mL CH₄·g⁻¹ slurry and 165.7 mL CH₄·g⁻¹ digestate. All solid masses are expressed in terms of volatile solids (VS). Full article

Given that vanadium is a valuable material, the implementation of vanadium recycling processes is thus necessary to enhance the element’s value chain as well as minimize its undesirable environmental consequences. Among various remediation methods available, a biological method based on microalgal adsorption is known to be eco-friendly and calls for further investigations. Herein, we evaluated V₂O₅ adsorption efficiencies of four different microalgal strains: Nannochloropsis oculata, Heterocapsa circularisquama, Chattonella marina, and Chattonella antiqua. Inductively coupled plasma mass spectrometry (ICP-MS) data indicated that vanadium concentration in the culture medium of Nannochloropsis oculata was reduced from 4.61 ± 0.11 mg L⁻¹ to 1.85 ± 0.21 mg L⁻¹ after being exposed to V₂O₅ solution for 24 h, whereas the supernatants of the other three strains displayed no change in vanadium ion concentration. Therefore, our results indicated a strong potential of Nannochloropsis oculata for recycling vanadium with approximately 59.9% of vanadium ion removal efficiency. Furthermore, morphological observation of Nannochloropsis oculata using scanning electron microscopy (SEM) indicated that the cells were able to maintain their intact morphology even under the presence of high concentrations of heavy metals. Due to the high adsorption efficiency and robustness of Nannochloropsis oculata, the results collectively support it as a potential strain for V₂O₅ recovery. Full article

It has long been explored to use EPA-rich unicellular microalgae as a fish oil alternative for production of the high-value omega-3 fatty acid eicosapentaenoic acid (EPA, 20:5, n-3). However, none of the efforts have ever reached commercial success. This study reported a filamentous yellow-green microalga Tribonema aequale that possesses the ability to grow rapidly and synthesize significant amounts of EPA. A series of studies were conducted in a glass column photobioreactor under laboratory culture conditions and in pilot-scale open raceway ponds outdoors. The emphasis was placed on the specific nutrient requirements and the key operational parameters in raceway ponds such as culture depth and mixing regimes. When optimized, T. aequale cells contained 2.9% of EPA (w/w) and reached a very high biomass concentration of 9.8 g L⁻¹ in the glass column photobioreactor. The cellular EPA content was increased further to 3.5% and the areal biomass and EPA productivities of 16.2 g m⁻² d⁻¹ and 542.5 mg m⁻² d⁻¹, respectively, were obtained from the outdoor pilot-scale open raceway ponds, which were the record high figures reported thus far from microalgae-based EPA production. It was also observed that T. aequale was highly resistant to microbial contamination and easy for harvesting and dewatering, which provide two additional competitive advantages of this filamentous microalga over the unicellular counterparts for potential commercial production of EPA and other derived co-products. Full article

Microalgae are widely used in the bioremediation of wastewaters due to their efficient removal of pollutants such as nitrogen, phosphorus, and contaminants of emerging concern (CECs). Siloxanes are CECs that reach wastewater treatment plants (WWTPs), leading to the production of biogas enriched with these compounds, associated with the breakdown of cogeneration equipment. The biological removal of siloxanes from wastewaters could be a sustainable alternative to the costly existing technologies, but no investigation has been performed using microalgal cultures for this purpose. This study evaluated the ability of Chlorella vulgaris to bioremediate primary (PE) and secondary (SE) urban effluents and remove volatile methylsiloxanes (VMSs). C. vulgaris grew successfully in both effluents, and approximately 86% of nitrogen and 80% of phosphorus were efficiently removed from the PE, while 52% of nitrogen and 87% of phosphorus were removed from the SE, and the presence of VMSs does not seem to have a negative influence on nutrient removal. Three out of the seven of the analysed VMSs were detected in the microalgal biomass at the end of the PE assay. However, dodecamethylcyclohexasiloxane (D6) was the one that accumulated to a greater extent, since 48% of the initial mass of D6 was detected in the biomass samples. D6 is one of the most lipophilic VMSs, which might contribute to the higher adsorption onto the surface of microalgae. Overall, the results indicate C. vulgaris’ potential to remove specific VMSs from effluents. Full article

Overcoming obstacles to commercialization of algal-based processes for biofuels and co-products requires not just piecemeal incremental improvements, but rather a comprehensive and fundamental re-consideration starting with the selected algae and its associated cultivation, harvesting, biomass conversion, and refinement. A novel two-stage process designed to address challenges of mass outdoor microalgal cultivation for biofuels and co-products was previously demonstrated using an oleaginous, haloalkaline-tolerant, and multi-trophic green Chlorella vulgaris. ALP2 from a soda lake. This involved cultivating the microalgae in a fermenter heterotrophically or photobioreactor mixotrophically (first-stage) to rapidly obtain high cell densities and inoculate an open-pond phototrophic culture (second-stage) featuring high levels of NaHCO₃, pH, and salinity. An improved two-stage cultivation that instead sustainably used as more cheap and sustainable inputs the organic carbon, nitrogen, and phosphorous from fractionation of waste was here demonstrated in a small-scale biorefinery process. The first cultivation stage consisted of two simultaneous batch flask cultures featuring (1) mixotrophic cell productivity of 7.25 × 10⁷ cells mL⁻¹ day⁻¹ on BG-11₀ medium supplemented with 1.587 g L⁻¹ urea and an enzymatic hydrolysate of pre-treated (torrefaction + grinding + ozonolysis + soaking ammonia) wheat-straw that corresponded to 10 g L⁻¹ glucose, and (2) mixotrophic cell productivity of 2.25 × 10⁷ cells mL⁻¹ day⁻¹ on BG-11₀ medium supplemented with 1.587 g L⁻¹ urea and a purified and de-toxified condensate of pre-treated (torrefaction + grinding) wheat straw that corresponded to 0.350 g L⁻¹ of potassium acetate. The second cultivation stage featured ¹H NMR-determined phototrophic lipid productivity of 0.045 g triacylglycerides (TAG) L⁻¹ day⁻¹ on BG-11₀ medium supplemented with 16.8 g L⁻¹ NaHCO₃ and fed batch-added 22% (v/v) anaerobically digested food waste effluent at HCl-mediated pH 9. Full article