Long-term acclimation to organic carbon enhances the production of loliolide from Scenedesmus deserticola.

Production of functional biocompounds from microalgae has garnered interest from different industrial sectors; however, their overall productivity must be substantially improved for commercialization. Herein, long-term acclimation of Scenedesmus deserticola was conducted using glucose as an organic carbon source to enhance its heterotrophic capabilities and the production potential of loliolide. A year-long acclimation on agar plates led to the selection of S. deserticola HS4, which exhibited at least 2-fold increase in loliolide production potential; S. deserticola HS4 was subjected to further screening of its cultivation conditions and fed-batch cultivation was subsequently performed in liter-scale reactors. While S. deserticola HS4 exhibited shifts in cellular morphology and biochemical composition, the results suggested a substantial increase in its loliolide productivity regardless of trophic modes. Collectively, these results highlight the potential of long-term acclimation as an effective strategy for improving microalgal crops to align with industrial production practices.

Analysis of oil accumulation mechanisms in plasma induced mutant Scenedesmus strains compared to original Scenedesmus strains.

Scenedesmus sp. is a species of the Scenedesmus genus within the phylum Chlorophyta, commonly found as a planktonic algal species in freshwater and known for its rapid growth rate. This study employs room-temperature, atmospheric-pressure plasma mutagenesis for the breeding of Scenedesmus sp., utilizing transcriptomic analysis to investigate the biosynthesis mechanism of triglycerides. Further analysis of differentially expressed genes in transcriptome by measuring the macroscopic biological indicators of mutant and original algal strains. The findings of the study suggest that the mutant strain's photosynthesis has been enhanced, leading to improved light energy utilization and CO2 fixation, thereby providing more carbon storage and energy for biomass and lipid production. The intensification of glycolysis and the TCA (tricarboxylic acid) cycle results in a greater shift in carbon flux towards lipid accumulation. An elevated expression level of related enzymes in starch and protein degradation pathways may enhance acetyl CoA accumulation, facilitating a larger substrate supply for fatty acid production and thereby increasing lipid yield.

Scenedesmus sp. as a phycoremediation agent for heavy metal removal from landfill leachate in a comparative study: batch, continuous, and membrane bioreactor (MBR).

Improper disposal of municipal solid waste led to the release of heavy metals into the environment through leachate accumulation, causing a range of health and environmental problems. Phycoremediation, using microalgae to remove heavy metals from contaminated water, was investigated as a promising alternative to traditional remediation methods. This study explored the potential of Scenedesmus sp. as a phycoremediation agent for heavy metal removal from landfill leachate. The study was conducted in batch, continuous, and membrane bioreactor (MBR). In the batch system, Scenedesmus sp. was added to the leachate and incubated for 15 days before the biomass was separated from the suspension. In the continuous system, Scenedesmus sp. was cultured in a flow-through system, and the leachate was continuously fed into the system with flow rates measured at 120, 150, and 180 mL/h for 27 days. The MBR system was similar to the continuous system, but it incorporated a membrane filtration step to remove suspended solids from the treated water. The peristaltic pump was calibrated to operate at five different flow rates: 0.24 L/h, 0.30 L/h, 0.36 L/h, 0.42 L/h, and 0.48 L/h for the MBR system and ran for 24 h. The results showed that Scenedesmus sp. was effective in removing heavy metals such as lead (Pb), cobalt (Co), chromium (Cr), nickel (Ni), and zinc (Zn) from landfill leachate in all three systems. The highest removal efficiency was observed for Ni, with a removal of 0.083 mg/L in the MBR and 0.068 mg/L in batch mode. The lowest removal efficiency was observed for Zn, with a removal of 0.032 mg/L in the MBR, 0.027 mg/L in continuous mode, and 0.022 mg/L in batch mode. The findings depicted that the adsorption capacity varied among the studied metal ions, with the highest capacity observed for Ni (II) and the lowest for Zn (II), reflecting differences in metal speciation, surface charge interactions, and affinity for the adsorbent material. These factors influenced the adsorption process and resulted in varying adsorption capacities for different metal ions. The study also evaluated the biomass growth of Scenedesmus sp. and found that it was significantly influenced by the initial metal concentration in the leachate. The results of this study suggest that Scenedesmus sp. can be used as an effective phycoremediation agent for removing heavy metals from landfill leachate.

Mechanistic insights into the potential application of Scenedesmus strains towards the elimination of antibiotics from wastewater.

Scenedesmus strains have been reported to have the potential to tolerate and bioremediate antibiotic pollutants through bioadsorption, bioaccumulation, and biodegradation mechanism from the wastewater medium. Hormesis effects have been observed in the Scenedesmus strains when exposed to different concentrations of antibiotic pollutants. Lower concentrations of antibiotic pollutants are known to trigger growth-stimulating effects by triggering adaptive responses such as increased metabolic activity and activating detoxifying mechanisms leading to the biotransformation pathway. The present review examines the existing body of information pertaining to biotransformation pathways tolerance, hormesis effects, and efficiency of Scenedesmus strains in removing various antibiotic pollutants. This review provides critical information on using Scenedesmus species to treat antibiotic-polluted wastewater by boosting growth and resilience tolerant doses and avoiding toxicity at higher doses.

Exploring phosphate impact on arsenate uptake and distribution in freshwater phytoplankton: Insights from single-cell ICP-MS.

In this study, we investigated the interaction between arsenate (AsV) and phosphate (PO43-) in freshwater phytoplankton using single-cell inductively coupled plasma mass spectrometry (SC-ICP-MS). This study aimed to elucidate the influence of varying PO43- concentrations on arsenic (As) uptake and distribution at the single-cell level, providing insights into intraspecies diversity. Two species of freshwater phytoplanktons, Scenedesmus acutus and Pediastrum duplex, were cultured under different concentrations of PO43- and AsV in a controlled laboratory environment. Scenedesmus acutus, a species with strong salt tolerance, and Pediastrum duplex, known for its weak salt tolerance, were selected based on their contrasting behaviors in previous studies. SC-ICP-MS revealed non-uniform uptake of As by individual phytoplankton cells, with distinct variations in response to PO43- availability. Arsenic uptake by both species declined with a high PO43- level after 7 days of exposure. However, after 14 days, As uptake increased in S. acutus with higher PO43- concentrations, but decreased in P. duplex. Moreover, our findings revealed differences in cell morphology and membrane integrity between the two species in response to AsV and various PO43- concentrations. S. acutus maintained cell integrity under all experimental culture conditions, whereas P. duplex experienced cell lysis at elevated AsV and PO43- concentrations. This study highlights the varying responses of freshwater phytoplankton to changes in AsV and PO43- levels and underscores the advantages of SC-ICP-MS over conventional ICP-MS in providing detailed, cellular level insights. These findings are crucial for understanding and managing As pollution in aquatic ecosystems.

Bicarbonate concentration influences carbon utilization rates and biochemical profiles of freshwater and marine microalgae.

Selecting the optimal microalgal strain for carbon capture and biomass production is crucial for ensuring the commercial viability of microalgae-based biorefinery processes. This study aimed to evaluate the impact of varying bicarbonate concentrations on the growth rates, inorganic carbon (IC) utilization, and biochemical composition of three freshwater and two marine microalgal species. Parachlorella kessleri, Vischeria cf. stellata, and Porphyridium purpureum achieved the highest carbon removal efficiency (>85%) and biomass production at 6 g L-1 sodium bicarbonate (NaHCO3), while Phaeodactylum tricornutum showed optimal performance at 1 g L-1 NaHCO3. The growth and carbon removal rate of Scenedesmus quadricauda increased with increasing NaHCO3 concentrations, although its highest carbon removal efficiency (∼70%) was lower than the other species. Varying NaHCO3 levels significantly impacted the biochemical composition of P. kessleri, S. quadricauda, and P. purpureum but did not affect the composition of the remaining species. The fatty acid profiles of the microalgae were dominated by C16 and C18 fatty acids, with P. purpureum and P. tricornutum yielding relatively high polyunsaturated fatty acid content ranging between 14% and 30%. Furthermore, bicarbonate concentration had a species-specific effect on the fatty acid and chlorophyll-a content. This study demonstrates the potential of bicarbonate as an effective IC source for microalgal cultivation, highlighting its ability to select microalgal species for various applications based on their carbon capture efficiency and biochemical composition.

Enhancing CO2 dissolution and inorganic carbon conversion by metal-organic frameworks improves microalgal growth and carbon fixation efficiency.

Carbon supplementation strategies still have certain practical application constraints. Zn/Fe-based metal-organic frameworks (MOFs) nanoparticles that which are not toxic to Scenedesmus obliquus were successfully introduced into microalgal solutions to overcome low CO2 solubility. The maximum specific surface area of MOFs reached 342.94 m2·g-1 at a Zn/Fe molar ratio of 10/1. Under the optimal MOFs concentrations of 2.5 mg·L-1, the conversion of inorganic carbon increased by 2.6-fold. When S. obliquuswas cultured in a MOFs-modified medium with 1.50 % CO2 at 25 °C, the CO2 mass transfer coefficient and mixing time reached 9.01 × 10-3 min-1 and 55 s, respectively. The maximum chlorophyll-a content, biomass productivity, and CO2 fixation efficiency reached 32.57 mg·L-1, 0.240 g·L-1·d-1 and 21.6 %, respectively. Enriching CO2 for ribulose-1,5-bisphosphate carboxylase/oxygenase carboxylation by MOFs may be the key to improving the photosynthetic efficiency of microalgae. This strategy could serve as a reference for improving the microalgal CO2 fixation efficiency.

Microplastics with different functional groups modulate cellular and molecular mechanisms of reduced graphene oxide toxicity on the green microalga, Scenedesmus obliquus.

Even though microplastics (MPs) and graphene nanomaterials (GNMs) have demonstrated individual toxicity towards aquatic organisms, the knowledge gap lies in the lack of understanding regarding their combined toxicity. The difference between the combined toxicity of MPs and GNMs, in contrast to their individual toxicities, and furthermore, the elucidation of the mechanism of this combined toxicity are scientific questions that remain to be addressed. In this study, we examined the individual and combined toxicity of three polystyrene microplastics (MPs) with different functional groups-unmodified, carboxyl-modified (COOH-), and amino-modified (NH2-) MPs-in combination with reduced graphene oxide (RGO) on the freshwater microalga Scenedesmus obliquus. More importantly, we explored the cellular and molecular mechanisms responsible for the observed toxicity. The results indicated that the growth inhibition toxicity of RGO, either alone or in combination with the three MPs, against S. obliquus increased gradually with higher particle concentrations. The mitigating effect of MPs-NH2 on RGO-induced toxicity was most significant at a higher concentration, surpassing the effect of unmodified MPs. However, the MPs-COOH did not exhibit a substantial impact on the toxicity of RGO. Unmodified MPs and MPs-COOH aggravated the inhibition effects of RGO on the cell membrane integrity and oxidative stress-related biomarkers. Additionally, MPs-COOH exhibited a stronger inhibition effect on RGO-induced biomarkers compared to unmodified MPs. In contrast, the MPs-NH2 alleviated the inhibition effect of RGO on the biomarkers. Furthermore, the presence of differently functionalized MPs did not significantly affect RGO-induced oxidative stress and photosynthesis-related gene expression in S. obliquus, indicating a limited ability to modulate RGO genotoxicity at the molecular level. These findings can offer a more accurate understanding of the combined risks posed by these micro- and nano-materials and assist in designing more effective mitigation strategies.

Light-powered biodegradation of Imidacloprid by Scenedesmus sp. TXH202001: Assessing complete removal, metabolic pathways, and toxicity verification.

Imidacloprid (IMI) is used extensively as an insecticide and poses a significant risk to both the ecological environment and human health. Biological methods are currently gaining recognition among the different strategies tested for wastewater treatment. This study focused on evaluating a recently discovered green alga, Scenedesmus sp. TXH202001, isolated from a municipal wastewater treatment plant (WWTP), exhibited notable capacity for IMI removal. After an 18-day evaluation, medium IMI concentrations (50 and 100 mg/L) facilitated the growth of microalgae whereas low (5 and 20 mg/L) and high (150 mg/L) concentrations had no discernible impact. No statistically significant disparities were detected in Fv/Fm, Malonaldehyde or Superoxide dismutase across all concentrations, suggesting Scenedesmus sp. TXH202001 exhibited notable resilience and adaptability to IMI conditions. Most notably, Scenedesmus sp. TXH202001 successfully eliminated > 99 % of IMI within 18 days subjected to IMI concentrations as high as 150 mg/L, which was contingent on the environmental factor of illumination. Molecular docking was used to identify the chemical reaction sites between IMI and typical degrading enzyme CYP450. Furthermore, the study revealed that the primary path for IMI removal was biodegradation and verified that the toxicity of the degraded product was lower than parent IMI in Caenorhabditis elegans. The efficacy of Scenedesmus sp. TXH202001 in wastewater was exceptional, thereby validating its practical utility.

Assessment of hydrocarbon degradation capacity and kinetic modeling of Chlorella vulgaris and Scenedesmus quadricauda for crude oil phycoremediation under mixotrophic conditions.

Crude oil spills imperil aquatic ecosystems globally, prompting innovative solutions such as microalgae-based bioremediation. This study explores the potential of Chlorella vulgaris and Scenedesmus quadricauda, for crude oil spill phycoremediation under mixotrophic conditions and varying crude oil concentrations (0.5-2%). C. vulgaris demonstrated notable resilience, thriving up to 1% crude oil exposure, while S. quadricauda adapted to lower concentrations. Optimal growth for both was observed at 0.5% exposure. Chlorophyll a content in C. vulgaris increases at 0.5% exposure but declines above 1%, while a decline was noticeable in chlorophyll b in treatment groups above 1%. Carotenoid levels varied, displaying the highest levels at higher concentrations above 1.5%. Similarly, S. quadricauda showed increased chlorophyll a content at 0.5% exposure, with stable carotenoid levels and a decline in chlorophyll b content at higher concentrations. GC/MS analyses indicated C. vulgaris efficiently degraded aliphatic compounds like decane and tridecane, surpassing S. quadricauda in degrading both aliphatic and aromatic hydrocarbons. Growth kinetics was best represented by the modified Gompertz and logistic models. These findings highlight the species-specific adaptability and optimal concentration for microalgae to degrade crude oil effectively, advancing phycoremediation processes and strategies critical for environmental restoration.

This study marks the first exploration of both Chlorella vulgaris and the previously unexplored Scenedesmus quadricauda for crude oil phycoremediation potential under mixotrophic conditions. Additionally, it pioneers the modeling and study of algae growth kinetics in response to crude oil exposure. Notably, this research demonstrated the adaptability and efficiency of C. vulgaris in degrading crude oil components under mixotrophic conditions up to a level of 1%, while S. quadricauda showed similar capabilities at a concentration of 0.5%.

Comparative proteomics reveals energy and carbon metabolism changes in Scenedesmus quadricauda mutants induced by heavy-ion beam irradiation.

Microalgae's superior ability to fix carbon dioxide into biomass and high-value bioproducts remains underutilized in biotechnological applications due to a lack of comprehensive understanding of their carbon metabolism and energy conversion. In this work, the strain improvement technique heavy-ion beams (HIB) mutagenesis was employed on the environmentally adaptable microalgae Scenedesmus quadricauda. After several rounds of screening, two contrasting mutants were identified. S-#4 showed low photosynthetic activity and biomass productivity, while S-#26 exhibited adaptability to prolonged high light stress, achieving a 28.34 % increase in biomass yield compared to the wild-type strain. Integrating their photosynthetic characteristics and comparative proteomic analysis revealed that the contrasting protein regulations from central carbon metabolism mainly affects the two mutants' opposite biomass accumulation. Therefore, the divergent regulation of the tricarboxylic acid cycle following HIB mutagenesis could be potential targets for engineering microalgae with superior biomass and high-value products.

Effect of hydrothermal pretreatment on leachate fed Scenedesmus sp. biomass solubilization and biogas production.

The aim of the present study was to assess the effect of hydrothermal pretreatment on the solubilization and anaerobic digestion (AD) of Scenedesmus sp. biomass. At first, the microalgae was cultivated in 5% fresh leachate (FL) to recover nutrients such as nitrogen and phosphorus. Scenedesmus sp. grown in 5% FL obtained 100%, 77% and 97% removal efficiency of ammonium nitrogen (NH4+ - N), total Kjeldahl nitrogen (TKN) and phosphate phosphorous (PO43- -P), respectively. In the following step, the hydrothermal pretreatment of Scenedesmus sp. biomass was carried out at 120, 150 and 170 °C and retention time of 0, 30 and 60 min to evaluate its solubilization and biogas production through AD in batch test. Soluble chemical oxygen demand (sCOD) increased by 260% compared to untreated microalgae at 170 °C for 60 min. In comparison to untreated microalgae, the highest increase in biogas (70%) and methane yield (100%) was observed for 150 °C and 60 min pretreated microalgae as a consequence of hydrothermal pretreatment. Hydrothermal pretreatment has shown effectiveness in enhancing biomass solubilization and increasing biogas yield. Nevertheless, further research at the pilot scale is necessary to thoroughly evaluate the potential and feasibility of hydrothermal pretreatment for full-scale implementation.

Microalgae production in olive mill wastewater fractions and cattle digestate slurry: Bioremediation effects and suitability for energy and feed uses.

The possibility of obtaining energy or nutritive streams and bioremediation as an add-on opens new perspectives for the massive culturing of microalgal biomass on waste waters generated by the agro-food sector. Ordinary revenue streams are fully preserved, or even boosted, if they are used in microalgal cultivation; however, the suitability of wastewaters depends on multiple nutritional and toxic factors. Here, the effect of modulating the Olive Mill Wastewater (OMW) and cattle digestate (CD) fraction in the formulation of a growth medium on biomass accumulation and productivity of selected biomass fractions and their relevance for biofuel and/or feed production were tested for the microalga Scenedesmus dimorphus and for the cyanobacterium Arthrospira platensis (Spirulina). Tests highlighted the strong S. dimorphus adaptability to digestate, as on OMW, compared to A. platensis, with the maximum lipid storage (48 %) when culture medium was composed by 50 % of cattle digestate.

Competence of algal consortia under municipal wastewater: remediation efficiency, photosynthetic performance, antioxidant defense mechanisms and biofuel production.

Utilizing monoalgal species for wastewater treatment is facing tremendous challenges owing to changing wastewater complexity in terms of physico-chemical characteristic, nutrient and metal concentration. The environmental conditions are also fluctuating therefore, the formation of robust system is of utmost importance for concomitant sustainable wastewater treatment and bioenergy production. In the present study, the tolerance and adaptability potential of algal consortia-1 (Chlorococcum humicola and Tetradesmus sp.) and consortia-2 (Chlorococcum humicola, Scenedesmus vacuolatus and Tetradesmus sp.) treated with municipal wastewater were examined under natural environmental conditions. The results exhibited that consortia-2 was more competent in recovering nitrate-nitrogen (82.92%), phosphorus (70.47%), and heavy metals (31-73.70%) from municipal wastewater (100%) than consortia-1. The results further depicted that total chlorophyll, carbohydrate, and protein content decreased significantly in wastewater-treated consortia-1 as compared to consortia-2. However, lipid content was increased by 4.01 and 1.17 folds in algal consortia-1 and consortia-2 compared to their respective controls. Moreover, absorption peak at 1740.6 cm-1 reflected higher biofuel-producing potential of consortia-1 as compared to consortia-2 as confirmed through FTIR spectroscopy. The results also revealed that consortia-2 showed the highest photosynthetic performance which was evident from the increment in the active photosystem-II reaction center (1.724 ± 0.068), quantum efficiency (0.633 ± 0.038), and performance index (3.752 ± 0.356). Further, a significant increase in photosynthetic parameters was observed in selected consortia at lag phase, while a noteworthy decline was observed at exponential and stationary phases in consortia-1 than consortia-2. The results also showed the maximum enhancement in ascorbic acid (2.43 folds), proline (3.34 folds), and cysteine (1.29 folds) in consortia-2, while SOD (1.75 folds), catalase (2.64 folds), and GR (1.19 folds) activity in consortia-1. Therefore, it can be concluded that due to remarkable flexibility and photosynthetic performance, consortia-2 could serve as a potential candidate for sustainable nutrient resource recovery and wastewater treatment, while consortia-1 for bio-fuel production in a natural environment. Thus, formation of algal consortia as the robust biosystem tolerates diverse environmental fluctuations together with wastewater complexity and ultimately can serve appropriate approach for environmental-friendly wastewater treatment and bioenergy production.

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 0.5 g/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.

Comprehensive Analysis of Lutein and Loroxanthin in Scenedesmus obliquus: From Quantification to Isolation.

Carotenoids are hydrophobic pigments produced exclusively by plants, fungi, and specific microbes. Microalgae are well suited for the production of valuable carotenoids due to their rapid growth, efficient isoprenoid production pathway, and ability to store these compounds within their cells. The possible markets for bio-products range from feed additives in aquaculture and agriculture to pharmaceutical uses. The production of carotenoids in microalgae is affected by several environmental conditions, which can be utilized to enhance productivity. The current study focused on optimizing the extraction parameters (time, temperature, and extraction number) to maximize the yield of carotenoids. Additionally, the impact of various nitrogen sources (ammonia, nitrate, nitrite, and urea) on the production of lutein and loroxanthin in Scenedesmus obliquus was examined. To isolate the carotenoids, 0.20 g of biomass was added to 0.20 g of CaCO3 and 10.0 mL of ethanol solution containing 0.01% (w/v) pyrogallol. Subsequently, the extraction was performed using an ultrasonic bath for a duration of 10 min at a temperature of 30 °C. This was followed by a four-hour saponification process using a 10% methanolic KOH solution. The concentration of lutein and loroxanthin was measured using HPLC-DAD at 446 nm, with a flow rate of 1.0 mL/min using a Waters YMC C30 Carotenoid column (4.6 × 250 mm, 5 µm). The confirmation of carotenoids after their isolation using preparative chromatography was achieved using liquid chromatography-tandem mass spectrometry (LC-MS/MS) with an atmospheric pressure chemical ionization (APCI) probe and UV-vis spectroscopy. In summary, S. obliquus shows significant promise for the large-scale extraction of lutein and loroxanthin. The findings of this study provide strong support for the application of this technology to other species.

Chemotactic Interactions of Scenedesmus sp. and Azospirillum brasilense Investigated by Microfluidic Methods.

The use of algae for industrial, biotechnological, and agricultural purposes is spreading globally. Scenedesmus species can play an essential role in the food industry and agriculture due to their favorable nutrient content and plant-stimulating properties. Previous research and the development of Scenedesmus-based foliar fertilizers raised several questions about the effectiveness of large-scale algal cultivation and the potential effects of algae on associative rhizobacteria. In the microbiological practice applied in agriculture, bacteria from the genus Azospirillum are one of the most studied plant growth-promoting, associative, nitrogen-fixing bacteria. Co-cultivation with Azospirillum species may be a new way of optimizing Scenedesmus culturing, but the functioning of the co-culture system still needs to be fully understood. It is known that Azospirillum brasilense can produce indole-3-acetic acid, which could stimulate algae growth as a plant hormone. However, the effect of microalgae on Azospirillum bacteria is unclear. In this study, we investigated the behavior of Azospirillum brasilense bacteria in the vicinity of Scenedesmus sp. or its supernatant using a microfluidic device consisting of physically separated but chemically coupled microchambers. Following the spatial distribution of bacteria within the device, we detected a positive chemotactic response toward the microalgae culture. To identify the metabolites responsible for this behavior, we tested the chemoeffector potential of citric acid and oxaloacetic acid, which, according to our HPLC analysis, were present in the algae supernatant in 0.074 mg/ml and 0.116 mg/ml concentrations, respectively. We found that oxaloacetic acid acts as a chemoattractant for Azospirillum brasilense.

Comparative modeling of fluorescence and P700 induction kinetics for alga Scenedesmus sp. obliques and cyanobacterium Synechocystis sp. PCC 6803. Role of state 2-state 1 transitions and redox state of plastoquinone pool.

The model of thylakoid membrane system (T-M model) (Belyaeva et al. Photosynth Res 2019, 140:1-19) has been improved in order to analyze the induction data for dark-adapted samples of algal (Scenedesmus obliques) and cyanobacterial (Synechocystis sp. PCC 6803) cells. The fluorescence induction (FI) curves of Scenedesmus were measured at light exposures of 5 min, while FI and P700 redox transformations of Synechocystis were recorded in parallel for 100 s intervals. Kinetic data comprising the OJIP-SMT fluorescence induction and OABCDEF P700+ absorbance changes were used to study the processes underlying state transitions qT2→1 and qT1→2 associated with the increase/decrease in Chl fluorescence emission. A formula with the Hill kinetics (Ebenhöh et al. Philos Trans R Soc B 2014, 369:20130223) was introduced into the T-M model, with a new variable to imitate the flexible size of antenna AntM(t) associated with PSII. Simulations revealed that the light-harvesting capacity of PSII increases with a corresponding decrease for that of PSI upon the qT2→1 transition induced by plastoquinone (PQ) pool oxidation. The complete T-M model fittings were attained on Scenedesmus or Synechocystis fast waves OJIPS of FI, while SMT wave of FI was reproduced at intervals shorter than 5 min. Also the fast P700 redox transitions (OABC) for Synechocystis were fitted exactly. Reasonable sets of algal and cyanobacterial electron/proton transfer (ET/PT) parameters were found. In the case of Scenedesmus, ET/PT traits remained the same irrespective of modeling with or without qT2→1 transitions. Simulations indicated a high extent (20%) of the PQ pool reduction under dark conditions in Synechocystis compared to 2% in Scenedesmus.

Catalytic flash pyrolysis of Scenedesmus sp. post-extraction residue using low-cost HZSM-5 catalyst with the perspective to produce renewable aromatic hydrocarbons.

Recovering renewable chemicals from de-fatted microalgal residue derived from lipid extraction within the algal-derived biofuel sector is crucial, given the rising significance of microalgal-derived biodiesel as a potential substitute for petroleum-based liquid fuels. As a circular economy strategy, effective valorization of de-fatted biomass significantly improves the energetic and economic facets of establishing a sustainable algal-derived biofuel industry. In this scenario, this study investigates flash catalytic pyrolysis as a sustainable pathway for valorizing Scenedesmus sp. post-extraction residue (SPR), potentially yielding a bio-oil enriched with upgraded characteristics, especially renewable aromatic hydrocarbons. In the scope of this study, volatile products from catalytic and non-catalytic flash pyrolysis were characterized using a micro-furnace type temperature programmable pyrolyzer coupled with gas chromatographic separation and mass spectrometry detection (Py-GC/MS). Flash pyrolysis of SPR resulted in volatile products with elevated oxygen and nitrogen compounds with concentrations of 46.4% and 26.4%, respectively. In contrast, flash pyrolysis of lyophilized microalgal biomass resulted in lower concentrations of these compounds, with 40.9% oxygen and 17.3% nitrogen. Upgrading volatile pyrolysis products from SPR led to volatile products comprised of only hydrocarbons, while completely removing oxygen and nitrogen-containing compounds. This was achieved by utilizing a low-cost HZSM-5 catalyst within a catalytic bed at 500 °C. Catalytic experiments also indicate the potential conversion of SPR into a bio-oil rich in monocyclic aromatic hydrocarbons, primarily BETX, with toluene comprising over one-third of its composition, thus presenting a sustainable pathway for producing an aromatic hydrocarbon-rich bio-oil derived from SPR. Another significant finding was that 97.8% of the hydrocarbon fraction fell within the gasoline range (C5-C12), and 35.5% fell within the jet fuel range (C8-C16). Thus, flash catalytic pyrolysis of SPR exhibits significant promise for application in drop-in biofuel production, including green gasoline and bio-jet fuel, aligning with the principles of the circular economy, green chemistry, and bio-refinery.

Enhancing bioremediation potential of microalgae Chlorella vulgaris and Scenedesmus acutus by NaCl for pyrene degradation.

Microalgae are increasingly recognized as promising organisms for bioremediation of organic pollutants. This study investigates the potential of enhancing the bioremediation efficiency of pyrene (PYR), a polycyclic aromatic hydrocarbon (PAH), through NaCl induced physiological and biochemical alterations in two microalgae species, Chlorella vulgaris and Scenedesmus acutus. Our findings reveal significant improvement in PYR removal when these microalgae were cultivated in the presence of 0.1% NaCl where PYR removal increased from 54 to 74% for C. vulgaris and from 26 to 75% for S. acutus. However, it was observed that NaCl induced stress had varying effects on the two species. While C. vulgaris exhibited increased PYR removal, it experienced reduced growth and biomass production, as well as lower photosynthetic efficiency when exposed to PYR and PYR + NaCl. In contrast, S. acutus displayed better growth and biomass accumulation under PYR + NaCl conditions, making it a more efficient candidate for enhancing PYR bioremediation in the presence of NaCl. In addition to assessing growth and biochemical content, we also investigated stress biomarkers, such as lipid peroxidation, polyphenol and proline contents. These findings suggest that S. acutus holds promise as an alternative microalgae species for PYR removal in the presence of NaCl, offering potential advantages in terms of bioremediation efficiency and ecological sustainability. This study highlights the importance of understanding the physiological and biochemical responses of microalgae to environmental stressors, which can be harnessed to optimize bioremediation strategies for the removal of organic pollutants like PYR.