Bacterial intervention on the growth, nutrient removal and lipid production of filamentous oleaginous microalgae Tribonema sp

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

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

Development of a new sterilization method for microalgae media using calcium hypochlorite as the sterilant

Calcium hypochlorite (Ca(ClO)2), which can be stably stored in powder form for a long period, is widely used as a disinfectant in various fields. A new sterilization process was developed in the present study, where a microalgal medium was sterilized using 0.02% Ca(ClO)2, followed by complete neutralization of the Ca(ClO)2 within 8 h through catalytic reaction of an MnCl2-Na2EDTA complex and a synergistic effect of glucose. When comparing the growth of Chlorella vulgaris in the autoclaved medium, a 2.65 times greater maximum cell growth was observed in cells grown in the medium prepared by treatment of Ca(ClO)2. This result indicates that denaturation of the medium by heat can hinder the growth of some microorganisms. In the case of cultivation of Euglena gracilis, successful culture growth was achieved without growth inhibition or contamination on a medium prepared in the same manner.

Effects of Silybum marianum L. Seed Extracts on Multi Drug Resistant (MDR) Bacteria

Wound infections became a great challenge, especially after the emergence of bacterial resistance to commonly used antibiotics. Medicinal plants can be the source of alternative antibacterial agents effective against multi drug resistant (MDR) bacteria. This research aimed to evaluate the effectiveness of different Silybum marianum seed extracts in fighting MDR bacteria that infect wounds. First, thirty purified bacterial cultures obtained from superficial, infected wounds were subjected to antibiotic sensitivity tests. The selected MDR isolates were then used to test the antimicrobial effects of different S. marianum seed extracts. The most potent extract was evaluated for its impact on the ultrastructure of the cells of sensitive bacterial isolates using transmission electron microscopy (TEM). The bioactive ingredients of this extract were analyzed by means of gas chromatography-mass spectroscopy (GC-MS). Then, in-silico absorption, distribution, metabolism, excretion, and toxicity (ADMET) properties were predicted for the main components. The results indicated that four out of 30 bacterial isolates were considered MDR bacteria. Primary morphological features of colonies, secondary (automatic) identification using the Biomerieux Vitek 2 System, and 16S rRNA sequencing of the four isolates confirmed that they represent Staphylococcus aureus, Stenotrophomonas maltophilia, Klebsiella pneumoniae, and Escherichia coli. Among different extracts of S. marianum seeds, ethanol extract showed the strongest inhibitory effect on both Gram-positive and Gram-negative bacteria, with minimum inhibitory concentration (MIC) values between 9.375 and 1.172 mg/mL. However, at concentrations four times higher, this extract was unable to kill bacterial cells, indicating that it had a bacteriostatic effect on the tested MDR strains. TEM revealed denaturation and distorted cell ultrastructure in S. aureus and S. maltophilia after exposure to ethanol extract. In addition, GC-MS analysis of the ethanol extract identified nine compounds known to have important biological activities, and ADMET analysis showed good drug-likeness for two of these compounds. Consequently, S. marianum seeds could be a good source of alternative bacteriostatic agents effective against MDR bacterial strains that cause wound infections.

Advanced treatment and Resource recovery of brewery wastewater by Co-cultivation of filamentous microalga Tribonema aequale and autochthonous Bacteria

To use unicellular microalgae to remove waste nutrients from brewery wastewater while converting them into algal biomass has been explored but high-cost treatment and low-value biomass associated with current technologies have prevented this concept from further attempts. In this study, a filamentous microalga Tribonema aequale was introduced and the alga can grow vigorously in brewery wastewater and algal biomass concentration could be as high as 6.45 g L-1 which can be harvested by a cost-effective filtration method. The alga together with autochthonous bacteria removed majority of waste nutrients from brewery wastewater. Specifically, 85.39% total organic carbon (TOC), 79.53% total dissolved nitrogen (TN), 93.38% ammonia nitrogen (NH3-N) and 71.33% total dissolved phosphorus (TP) in brewery wastewater were rapidly removed by co-cultivation of T. aequale and autochthonous bacteria. Treated wastewater met the national wastewater discharge quality, and resulting algal biomass contained large amounts of high-value products chrysolaminarin, palmitoleic acid (PLA) and eicosapentaenoic acid (EPA). It is anticipated that reduced cost of algal harvesting coupled with value-added biomass could make T. aequale as a promising candidate for brewery wastewater treatment and resource utilization.

Effects of sodium selenite on the growth, biochemical composition and selenium biotransformation of the filamentous microalga Tribonema minus

This study aimed to investigate the physiological and biochemical responses of filamentous microalga Tribonema minus to different Na₂SeO₃ concentrations and its selenium absorption and metabolism to evaluate the potential in treating selenium-containing wastewater. The results showed that low Na₂SeO₃ concentrations promoted growth by increasing chlorophyll content and antioxidant capacity, whereas high concentrations caused oxidative damage. Although Na₂SeO₃ exposure reduced lipid accumulation compared with the control, it significantly increased carbohydrate, soluble sugar, and protein contents, with the highest carbohydrate productivity of 117.97 mg/L/d at 0.5 mg/L Na₂SeO₃. Furthermore, this alga effectively absorbed Na₂SeO₃ in the growth medium and converted most of it into volatile selenium and a small part into organic selenium (predominantly as selenocysteine), showing strong selenite removal efficacy. This is the first report on the potential of T. minus to produce valuable biomass while removing selenite, providing new insights into the economic feasibility of bioremediation of selenium-containing wastewater.

Coupling wastewater treatment, biomass, lipids, and biodiesel production of some green microalgae

This study demonstrates the combination of wastewater treatment and green microalgae cultivation for the low-cost production of lipids as a feedstock for biodiesel production. Three green microalgal species were used: Chlamydomonas reinhardtii, Monoraphidium braunii, and Scenedesmus obliquus. Nutrient, heavy metals and minerals removal, biomass productivity, carbohydrate, protein, proline, lipid, and fatty acids methyl ester (FAMEs) contents besides biodiesel properties were evaluated. The results showed that all algal species were highly efficient and had the potential to reduce nitrate, ammonia, phosphate, sulfate, heavy metals (Zn²⁺, Cu²⁺, Mn²⁺, and Fe²⁺), calcium, magnesium, sodium, and potassium after 10 days of algal treatment compared to initial concentrations. The removal efficiency of these parameters ranged from 12 to 100%. The growth rates of M. braunii and S. obliquus cultivated in wastewater were significantly decreased compared to the control (synthetic medium). In contrast, C. reinhardtii showed the highest growth rate when cultivated in sewage water. Wastewater could decrease the soluble carbohydrates and protein content in all tested algae and increase the proline content in M. braunii and S. obliquus. In wastewater culture, M. braunii had the highest lipid productivity of 5.26 mg L^-1 day^-1. The fatty acid profiles of two studied species (C. reinhardtii and M. braunii) revealed their suitability as a feedstock for biodiesel production due to their high content of saturated fatty acids, representing 80.91% and 68.62% of the total fatty acid content, respectively, when cultivated in wastewater. This study indicated that wastewater could be used to modify biomass productivity, lipid productivity, and the quantity of individual fatty acids in some algae that affect biodiesel quality to achieve international biodiesel standards.

Application of a novel biological-nanoparticle pretreatment to Oscillatoria acuminata biomass and coculture dark fermentation for improving hydrogen production

BACKGROUND

Energy is the basis and assurance for a world's stable development; however, as traditional non-renewable energy sources deplete, the development and study of renewable clean energy have emerged. Using microalgae as a carbon source for anaerobic bacteria to generate biohydrogen is a clean energy generation system that both local and global peers see as promising.

RESULTS

Klebsiella pneumonia, Enterobacter cloacae, and their coculture were used to synthesize biohydrogen using Oscillatoria acuminata biomass via dark fermentation. The total carbohydrate content in O. acuminata was 237.39 mg/L. To enhance the content of fermentable reducing sugars, thermochemical, biological, and biological with magnesium zinc ferrite nanoparticles (Mg-Zn Fe₂O₄-NPs) pretreatments were applied. Crude hydrolytic enzymes extracted from Trichoderma harzianum of biological pretreatment were enhanced by Mg-Zn Fe₂O₄-NPs and significantly increased reducing sugars (230.48 mg/g) four times than thermochemical pretreatment (45.34 mg/g). K. pneumonia demonstrated a greater accumulated hydrogen level (1022 mLH₂/L) than E. cloacae (813 mLH₂/L), while their coculture showed superior results (1520 mLH₂/L) and shortened the production time to 48 h instead of 72 h in single culture pretreatments. Biological pretreatment + Mg-Zn Fe₂O₄ NPs using coculture significantly stimulated hydrogen yield (3254 mLH₂/L), hydrogen efficiency)216.9 mL H₂/g reducing sugar( and hydrogen production rate (67.7 mL/L/h) to the maximum among all pretreatments.

CONCLUSION

These results confirm the effectiveness of biological treatments + Mg-Zn Fe₂O₄-NPs and coculture dark fermentation in upregulating biohydrogen production.

Chemical characterization and biological activities of ulvan extracted from Ulva fasciata (Chlorophyta)

Ulvan is a sulfated heteropolysaccharide present in the cell wall of Ulva species with a unique structure and biological potential used in various fields. Chemical characterization was carried out to determine the structure of ulvan from Ulva fasciata Delile collected from Eastern Harbor, Alexandria coast, Egypt. Ulva contains 31.5% carbohydrate with a total ulvan content of 43.66% of total carbohydrate (13.75 g/100 g DW) and sulfate content of 20.45% of ulvan. FTIR spectrum presented signals of the sulfate ester (C–O–S) and sulfate groups (S=O), typical for ulvan. GC–MS revealed that ulvan was mainly composed of rhamnose and fucose. 1H-NMR spectra of ulvan showed identical behavior of monosaccharides nature with peaks characteristic of sulfated polysaccharides at 3.2–5.3 ppm region. Scanning electron micrographs (SEM) demonstrated amorphous architecture, and the sulfated nature of polysaccharides was emphasized by EDX analysis. The extracted ulvan showed significant antimicrobial activity against human and fish pathogens as well as antifouling bacteria with minimum inhibitory concentrations (MIC) of 8 µg/mL. The extracted ulvan exhibited potent antioxidant activity with a scavenging effect of 84.93% for 2,2-diphenyl-1-picrylhydrazy free radical (DPPH). Moreover, it showed anti-arthritic properties for the first time with a maximum inhibition of 86.04% with IC50 of 43.21%, indicating their potential value for the health and food industry.

Enhancing biomass and lipid productivity of a green microalga Parachlorella kessleri for biodiesel production using rapid mutation of atmospheric and room temperature plasma

BACKGROUND

Microalgae, with their high adaptability to various stress conditions and rapid growth, are considered excellent biomass resources for lipid production and biodiesel feedstocks. However, lipid yield and productivity of the natural strains are common bottlenecks in their large-scale use for lipid production, which can be overcome by evolving new strains using conventional and advanced mutagenic techniques. It is challenging to generate microalgae strains capable of high lipid synthesis through natural selection. As a result, random mutagenesis is currently considered a viable option in many scenarios. The objective of this study was to explore atmospheric and room temperature plasma (ARTP) as a random mutagenesis technique to obtain high lipid-accumulating mutants of a green microalga for improved biodiesel production.

RESULTS

A green microalgal species was isolated from the Chinese Yellow Sea and identified as Parachlorella kessleri (OM758328). The isolated microalga was subsequently mutated by ARTP to obtain high lipid-accumulating mutants. Based on the growth rate and lipid content, 5 mutants (named M1, M2, M4, M5, and M8) were selected from 15 pre-selected mutants. These five mutants varied in their growth rate from 0.33 to 0.68 day^-1, with the lipid content varying between 0.25 g/L in M2 to 0.30 g/L in M8 at 10th day of cultivation. Among the mutants, M8 showed the maximum biomass productivity (0.046 g/L/day) and lipid productivity (20.19 mg/L/day), which were 75% and 44% higher than the wild strain, respectively. The triglyceride (TAG) content of M8 was found to be 0.56 g/L at 16th day of cultivation, which was 1.77-fold higher than that of the wild strain. Furthermore, M8 had the highest saturated fatty acids (C16-18) with the lowermost polyunsaturated fatty acid content, which are favorable properties of a biodiesel feedstock according to international standards.

CONCLUSION

The mutant strain of P. kessleri developed by the ARTP technique exhibited significant improvements in biomass productivity, lipid content, and biodiesel quality. Therefore, the biomass of this mutant microalga could be a potential feedstock for biodiesel production.

Equilibrium and Kinetic Modeling of Crystal Violet Dye Adsorption by a Marine Diatom, Skeletonema costatum

Significant efforts have been made to improve adsorbents capable of eliminating pollutants from aqueous solutions, making it simple and quick to separate from the treated solution. In the current study, the removal of Crystal Violet Dye (CVD) from an aqueous synthetic solution onto a marine diatom alga, Skeletonema costatum, was investigated. Different experiments were conducted as a function of different pH, contact time, adsorbent dosage, temperature, and initial CVD concentration. The highest adsorption efficiency (98%) was obtained at 0.4 g of S. costatum, pH 3, and a contact time of 120 min, at 25 °C. Furthermore, Fourier-transform infrared spectroscopy (FTIR) results display that binding of CVD on S. costatum may occur by electrostatic and complexation reactions. Moreover, the Brunauer-Emmett-Teller surface area analysis (BET) obtained was 87.17 m² g^-1, which, in addition to a scanning electron microscope (SEM), reveals large pores that could enhance the uptake of large molecules. However, the equilibrium adsorption models were conducted by Halsey, Langmuir, Freundlich, Henderson, and Tempkin isotherm. In addition, multilayer adsorption isotherm best described the uptake of CVD onto S. costatum. The maximum monolayer adsorption capacity (q_max) was 6.410 mg g^-1. Moreover, thermodynamic parameters of the adsorption studies suggested that the uptake of CVD onto S. costatum was endothermic and spontaneous. The pseudo-first-order, pseudo-second-order, and intra-particle diffusion kinetic equations were applied to model the adsorption kinetic data. It was seen that the kinetics of the adsorption may be described using pseudo-second-order kinetic equations. Finally, the present work concluded that the marine diatom alga S. costatum is suitable as a natural material for the adsorption of CVD.

Magnetic/electric field intervention on oil-rich filamentous algae production in the application of acrylonitrile butadiene styrene based wastewater treatment

Globally, the release of acrylonitrile-butadienestyrene (ABS) wastewater from numerous industries is a serious concern. Recently, oil-rich filamentous algae Tribonema sp has been grown utilizing toxic but nutrient-rich ABS effluent. Here, Tribonema sp. was cultivated under intervention of different magneto-electric combinatory fields (MCFs) (control, 0.6 V/cm, 1 h/d-1.2 V/cm, 1 h/d-0.6 V/cm, and 1 h/d-1.2 V/cm). Results showed MCF (1 h/d-0.6 V/cm) intervention increased the biomass by 9.7% (2.4 g/L) combined with high removal efficiencies (95% and 99%) of ammonium nitrogen and total phosphorus. The chemical oxygen demand (COD) removal rate increased to 82%, 6% higher than the control. Moreover, MCF of 1 h/d-0.6 V/cm significantly increased lipid and carbohydrate by 7.71% and 4.73% respectively. MCF increased premium fatty acid content such as palmitic acid (C16:0), myristic acid (C14: 0), and hexadecenoic acid (C16:1). MCF intervention also supported a diverse microbial flora, offering a favorable solution for ABS wastewater treatment.

Do Red Seaweed Nanoparticles Enhance Bioremediation Capacity of Toxic Dyes from Aqueous Solution?

Based on their functional groups, the use of various seaweed forms in phytoremediation has recently gained significant eco-friendly importance. The objective of this study was to determine whether a novel, sustainable, and ecologically acceptable adsorbent could be employed to remove toxic textile dye (Ismate Violet 2R (IV2R)) from an aqueous solution. The low-cost adsorbent was prepared from the nanoparticles form of the native red seaweed species, Pterocladia capillacea. Before and after the adsorption procedure, comprehensive characterization experiments on the bio-adsorbent were carried out, including BET, SEM, FTIR, UV, and dynamic light scattering (DLS) examination. The adsorption performance of the prepared nano-Pterocladia capillacea was optimized by adjusting operating parameters such as the initial dye concentration of 60 mg L⁻¹, pH of 2, and contact time of 15 min, all of which were obtained by batch experiments in the lab. At the optimum conditions, the prepared adsorbent had maximum removal effectiveness of 87.2%. Most typical kinetics and isotherm models were used to test the experimental results. The equilibrium data fit well with the Langmuir isotherm model, with comparatively higher R² values and fewer standard errors, while the pseudo-second-order kinetic model fits better with a decent correlation coefficient. Thermodynamic parameters revealed that the sorption process on nano-alga was exothermic and spontaneous.

A comprehensive review on carbon source effect of microalgae lipid accumulation for biofuel production

Energy is a major driving force for the economic development. Due to the scarcity of fossil fuels and negative impact on the environment, it is important to develop renewable and sustainable energy sources for humankind. Microalgae as the primary feedstock for biodiesel has shown great application potential. However, lipid yield from microalgae is limited by the upstream cost, which restrain the realization of large-scale biofuel production. The modification of lipid-rich microalgae cell has become the focus over the last few decades to improve the lipid content and productivity of microalgae. Carbon is a vital nutrient that regulates the growth and metabolism of microalgae. Different carbon sources are assimilated by microalgae cells via different pathways. Inorganic carbon sources are mainly used through the CO₂-concentrating mechanisms (CCMs), while organic carbon sources are absorbed by microalgae mainly through the Pentose Phosphate (PPP) Pathway and the Embden-Meyerhof-Pranas (EMP) pathway. Therefore, the addition of carbon source has a significant impact on the production of microalgae biomass and lipid accumulation. In this paper, mechanisms of lipid synthesis and carbon uptake of microalgae were introduced, and the effects of different carbon conditions (types, concentrations, and addition methods) on lipid accumulation in microalgal biomass production and biodiesel production were comprehensively discussed. This review also highlights the recent advances in microalgae lipid cultivation with large-scale commercialization and the development prospects of biodiesel production. Current challenges and constructive suggestions are proposed on cost-benefit concerns in large-scale production of microalgae biodiesel.

Effects of ocean acidification on the growth and biochemical composition of a green alga (Ulva fasciata) and its associated microbiota

In marine ecosystems, fluctuations in surface-seawater carbon dioxide (CO₂), significantly influence the whole metabolism of marine algae, especially during the early stages of macroalgal development. In this study, the response of the green alga Ulva fasciata for elevating ocean acidification was investigated using four levels of pCO₂ ~ 280, 550, 750 and 1050 µatm. Maximum growth rate (6.6% day^-1), protein (32.43 %DW) and pigment (2.9 mg/g) accumulation were observed at pCO₂-550 with an increase of ~2-fold compared to control. On the other hand, lipid and carbohydrate contents recorded their maximum production (4.23 and 46.96 %DW, respectively) at pCO₂-750 while control showed 3.70 and 42.37 %DW, respectively. SDS-PAGE showed the presence of unique bands in response to pCO_2, especially at 550 µatm. Dominant associated bacteria was shifted from Halomonas hydrothermalis of control to Vibrio toranzoniae at pCO₂-1050. These findings suggest that ocean acidification at 550 µatm might impose noticeable effects on growth, protein, pigments, and protein profile of U. fasciata, which could be a good source for fish farming. While, pCO₂-750 was recommended for energetic purpose, due to its high lipid and carbohydrate contents.

Influence of Nutrient Manipulation on Growth and Biochemical Constituent in Anabaena variabilis and Nostoc muscorum to Enhance Biodiesel Production

The present study aims to improve biomass and biochemical constituents, especially lipid production of Anabaena variabilis and Nostoc muscorum by formulating an optimal growth condition using various concentrations of nutrients (NO3−, PO43− and CO32−) for biodiesel production. The supplementation of the three nutrients by +50% showed the maximum dry weight and biomass productivity, while the macromolecule contents were varied. The depletion of N-NO3− by 50% N-NO3− showed the maximum lipid yield (146.67 mg L−1) in A. variabilis and the maximum carbohydrate contents (285.33 mg L−1) in N. muscorum with an increase of 35% and 30% over control of the synthetic medium, respectively. However, variation in P-PO43− and C-CO32− showed insignificant improving results for all biochemical compositions in both cyanobacteria. A. variabilis was the superior species for lipid and protein accumulation; however, N. muscorum showed the maximum carbohydrate content. Accordingly, A. variabilis was selected for biodiesel production. In A. variabilis, −50% N-NO3− resulted in 35% higher lipid productivity compared to the control. Furthermore, the fatty acid profile and biodiesel quality-related parameters have improved under this condition. This study has revealed the strategies to improve A. variabilis lipid productivity for biodiesel production for small-scale in vitro application in terms of fuel quality under low nitrate levels.

Bioactive Lipids of Marine Microalga Chlorococcum sp. SABC 012504 with Anti-Inflammatory and Anti-Thrombotic Activities

Microalgae are at the start of the food chain, and many are known producers of a significant amount of lipids with essential fatty acids. However, the bioactivity of microalgal lipids for anti-inflammatory and antithrombotic activities have rarely been investigated. Therefore, for a sustainable source of the above bioactive lipids, the present study was undertaken. The total lipids of microalga Chlorococcum sp., isolated from the Irish coast, were fractionated into neutral-, glyco-, and phospho-lipids, and were tested in vitro for their anti-inflammatory and antithrombotic activities. All tested lipid fractions showed strong anti-platelet-activating factor (PAF) and antithrombin activities in human platelets (half maximal inhibitory concentration (IC₅₀) values ranging ~25–200 μg of lipid) with the highest activities in glyco- and phospho-lipid fractions. The structural analysis of the bioactive lipid fraction-2 revealed the presence of specific sulfoquinovosyl diacylglycerols (SQDG) bioactive molecules and the HexCer-t36:2 (t18:1/18:1 and 18:2/18:0) cerebrosides with a phytosphingosine (4-hydrosphinganine) base, while fraction-3 contained bioactive phosphatidylcholine (PC) and phosphatidylethanolamine (PE) molecules. These novel bioactive lipids of Chlorococcum sp. with putative health benefits may indicate that marine microalgae can be a sustainable alternative source for bioactive lipids production for food supplements and nutraceutical applications. However, further studies are required towards the commercial technology pathways development and biosafety analysis for the use of the microalga.