Heterotrophic microalgae cultivation to synergize biodiesel production with waste remediation: progress and perspectives

Advancements in sustainable production of biofuel by microalgae: Recent insights and future directions

Microalgae is considered as sustainable and viable feedstock for biofuel production due to its significant advantages over terrestrial plants. Algal biofuels have received significant attention among researchers and energy experts owing to an upsurge in global energy issues emanating from depletion in fossil fuel reserves increasing greenhouse gases emission conflict among agricultural crops, traditional biomass feedstock, and potential futuristic energy security. Further, the exploration of value-added microalgae as sustainable and viable feedstock for the production of variety of biofuels such as biogas, bio-hydrogen, bioethanol, and biodiesel are addressed. Moreover, the assessment of life-cycle, energy balance, and environmental impacts of biofuel production from microalgae are briefly discussed. The present study focused on recent advancements in synthetic biology, metabolic engineering tools, algal bio refinery, and the optimization of algae growth conditions. This paper also elucidates the function of microalgae as bio refineries, the conditions of algae-based cultures, and other operational factors that must be adjusted to produce biofuels that are price-competitive with fossil fuels.

Biowaste to bioenergy nexus: Fostering sustainability and circular economy

Existing fossil-based commercial products present a significant threat to the depletion of global natural resources and the conservation of the natural environment. Also, the ongoing generation of waste is giving rise to challenges in waste management. Conventional practices for the management of waste, for instance, incineration and landfilling, emit gases that contribute to global warming. Additionally, the need for energy is escalating rapidly due to the growing populace and industrialization. To address this escalating desire in a sustainable manner, access to clean and renewable sources of energy is imperative for long-term development of mankind. These interrelated challenges can be effectively tackled through the scientific application of biowaste-to-bioenergy technologies. The current article states an overview of the strategies and current status of these technologies, including anaerobic digestion, transesterification, photobiological hydrogen production, and alcoholic fermentation which are utilized to convert diverse biowastes such as agricultural and forest residues, animal waste, and municipal waste into bioenergy forms like bioelectricity, biodiesel, bio alcohol, and biogas. The successful implementation of these technologies requires the collaborative efforts of government, stakeholders, researchers, and scientists to enhance their practicability and widespread adoption.

Effect of microalgae and bacteria inoculation on the startup of bioreactors for paper pulp wastewater and biofuel production

The use of microalgae and bacteria as a strategy for the startup of bioreactors for the treatment of industrial wastewater can be a sustainable and economically viable alternative. This technology model provides satisfactory results in the nitrification and denitrification process for nitrogen removal, organic matter removal, biomass growth, sedimentation, and byproducts recovery for added-value product production. The objective of this work was to evaluate the performance of microalgae and bacteria in their symbiotic process when used in the treatment of paper pulp industry wastewater. The experiment, lasting fourteen days, utilized four bioreactors with varying concentrations in mgVSS/L of microalgae to bacteria ratio (R1-100:100, R2-100:300, R3-100:500, R4-300:100) in the startup process. Regarding the sludge volumetric index (SVI), the results show that the R1 and R2 reactors developed SVI30/SVI10 biomass in the range of 85.57 ± 7.33% and 84.72 ± 8.19%, respectively. The lipid content in the biomass of reactors R1, R2, R3 e R4 was 13%, 7%, 19%, and 22%, respectively. This high oil content at the end of the batch, may be related to the nutritional stress that the species underwent during this feeding regime. In terms of chlorophyll, the bioreactor with an initial inoculation of 100:100 showed better symbiotic growth of microalgae and bacteria, allowing exponential growth of microalgae. The total chlorophyll value for this bioreactor was 801.46 ± 196.96 μg/L. Biological removal of nitrogen from wastewater from the paper pulp industry is a challenge due to the characteristics of the effluent, but the four reactors operated in a single batch obtained good nitrogen removal. Ammonia nitrogen removal performances were 91.55 ± 9.99%, 72.13 ± 19.18%, 64.04 ± 21.34%, and 86.15 ± 30.10% in R1, R2, R3, and R4, respectively.

Modulating cultivation regimes of Messastrum gracile SVMIICT7 for biomass productivity integrated with resource recovery via hydrothermal liquefaction

The present study was designed to assess Messastrum gracile SVMIICT7 potential in treating dairy wastewater (autoclaved (ADWW) and raw (DWW)) with relation to nutrient removal, in-vivo Chl-a-based biomass, and bio-oil synthesis. Chlorophyll a fluorescence kinetics revealed improved photochemical efficiency (0.639, Fv/Fm) in M. gracile when grown with DWW. This may be owing to enhanced electron transport being mediated by an effective water-splitting complex at photosystem (PSII) of thylakoids. The increase in ABS/RC observed in DWW can be attributed to the elevated chlorophyll content and reduced light dissipation, as evident by higher values of ETo/RC and a decrease in non-photochemical quenching (NPQ). M. gracile inoculated in DWW had the highest Chl-a-biomass yield (1.8 g L-1) and biomolecules while maximum nutrient removal efficiency was observed in ADWW (83.7% TN and 60.07% TP). M. gracile exhibited substantial bio-oil yield of 29.6% and high calorific value of 37.19 MJ kg-1, predominantly composed of hydrocarbons along with nitrogen and oxygen cyclic compounds. This research offers a thorough investigation into wastewater treatment, illustrating the conversion of algal biomass into valuable energy sources and chemical intermediates within the framework of a biorefinery.

Ephedra alte extracts' GC-MS profiles and antimicrobial activity against multidrug-resistant pathogens (MRSA)

The extracts of E. alte offer promising potential as renewable resources for various chemical derivative products aimed at addressing antibiotic resistance. These extracts exhibited significant activity against methicillin-resistant Staphylococcus aureus (MRSA), a strain known for its resistance to multiple antibiotics. The extracts were found to be effective against several common antibiotics, including Imipenem, Ampicillin, Penicillin G, Oxacillin, and Amoxicillin-clavulanate. GC-MS analysis revealed that the phytoconstituents of E. alte extracts, obtained using both methanol and ethyl acetate, consist of a diverse range of 83 and 160 phytocompounds, respectively. These organic compounds serve as important biochemical precursors for the synthesis of vitamins E and K1, and exhibit antioxidant, antimicrobial, and anti-inflammatory properties in both plants and microorganisms. Notable compounds identified include fatty acids (such as palmitic acid, dodecanoic acid, sebacic acid, pentadecanoic acid, myristic acid, stearic acid, behenic acid, and linoelaidic acid), phytosterols (Campesterol, β-sitosterol, Stigmast-5-ene), sugars (D-fructose, Fructofuranans), terpenoids (Phytol, citronellol), and phenolic acids (Protocatechoic acid, shikimic acid). The antimicrobial activity of all E. alte extracts was found to be superior to that of mupirocin and ciprofloxacin, as observed in susceptibility testing against MRSA ATCC 43300 and other pathogenic bacteria and fungi. It is likely that the combined action of the antimicrobial components within the E. alte extract bypasses the mechanisms employed by MRSA to protect itself from antibiotics. Further experiments are needed to investigate the individual effects of each pure compound and their potential synergistic interactions, which may enhance their overall performance.

Cultivation of microalgae-bacteria consortium by waste gas-waste water to achieve CO2 fixation, wastewater purification and bioproducts production

The cultivation of microalgae and microalgae-bacteria consortia provide a potential efficient strategy to fix CO2 from waste gas, treat wastewater and produce value-added products subsequently. This paper reviews recent developments in CO2 fixation and wastewater treatment by single microalgae, mixed microalgae and microalgae-bacteria consortia, as well as compares and summarizes the differences in utilizing different microorganisms from different aspects. Compared to monoculture of microalgae, a mixed microalgae and microalgae-bacteria consortium may mitigate environmental risk, obtain high biomass, and improve the efficiency of nutrient removal. The applied microalgae include Chlorella sp., Scenedesmus sp., Pediastrum sp., and Phormidium sp. among others, and most strains belong to Chlorophyta and Cyanophyta. The bacteria in microalgae-bacteria consortia are mainly from activated sludge and specific sewage sources. Bioengineer in CBB cycle in microalgae cells provide effective strategy to achieve improvement of CO2 fixation or a high yield of high-value products. The mechanisms of CO2 fixation and nutrient removal by different microbial systems are also explored and concluded, the importance of microalgae in the technology is proven. After cultivation, microalgae biomass can be harvested through physical, chemical, biological and magnetic separation methods and used to produce high-value by-products, such as biofuel, feed, food, biochar, fertilizer, and pharmaceutical bio-compounds. Although this technology has brought many benefits, some challenging obstacles and limitation remain for industrialization and commercializing.

Applications of Microalgae in Foods, Pharma and Feeds and Their Use as Fertilizers and Biostimulants: Legislation and Regulatory Aspects for Consideration

Microalgae are a rich resource of lipids, proteins, carbohydrates and pigments with nutritional and health benefits. They increasingly find use as ingredients in functional foods and feeds as well as in cosmetics and agricultural products including biostimulants. One of their distinct advantages is their ability to grow on wastewaters and other waste streams, and they are considered an environmentally friendly and cheap method to recover nutrients and remove pollutants from the environment. However, there are limits concerning their applications if grown on certain waste streams. Within, we collate an overview of existing algal applications and current market scenarios for microalgal products as foods and feeds along with relevant legislative requirements concerning their use in Europe and the United States. Microalgal compounds of interest and their extraction and processing methodologies are summarized, and the benefits and caveats of microalgae cultivated in various waste streams and their applications are discussed.

Wastewater treatment by using microalgae: Insights into fate, transport, and associated challenges

The remediation of wastewater with microalgae is a new topic that concentrates on devising a cost-effective and environmentally beneficial method. Multiple microalgae and bacterial consortiums have recently been evaluated to determine if they can purify effluent from various sources. Critical to a system's efficacy is its ability to remove nutrients such as nitrogen (N) and phosphorus (P) and heavy metals such as arsenic (As), lead (Pb), and copper (Cu). This study compared traditional wastewater treatment systems to microalgae-based systems for treating different types of wastewater. The research investigates the potential for microalgae to cleanse wastewater. The research also evaluates wastewater parameters, methods, and scientific techniques for extracting nutrients and heavy metals from polluted water. According to the literature, Microalgae can remove between 98.7% and 100% of nitrogen (N), phosphorous (P), and heavy metals from various effluents. The paper concludes by discussing the difficulties of using microalgae to remediate wastewater. The elimination of nutrients from the effluent is influenced by biomass production, osmotic capacity, temperature, pH, and O2 concentration. Therefore, a "pilot" study is recommended to investigate contaminants.

Production and use of Scenedesmus acuminatus biomass in synthetic municipal wastewater for integrated biorefineries

Bioethanol production from algal biomass is a promising alternative for sustainable biofuel production. Algae possess a high photosynthetic capacity and an adaptive ability to thrive under harsh environmental conditions. The potential properties of Scenedesmus acuminatus CCALA 436 were assessed in this research for its bioethanol efficiency, and the effects of growing the algae in wastewater and at different concentrations of mepiquat chloride were studied. Also, pre-treatment efficiencies of different concentrations of calcium oxide were carried out on microalgae biomass. Superoxide dismutase, catalase activity, glutathione, and malondialdehyde contents of microalgae were examined, and the changes in chlorophyll, photoprotective carotenoid contents, and protein concentrations were determined. The results revealed that the maximum sugar and ethanol contents of Scenedesmus acuminatus CCALA 436 were 44.7 ± 1.5% and 20.32 g/L, respectively, for 50% wastewater and mepiquat chloride (2.5 mg/L) after pre-treatment with calcium oxide (0.08%). Additionally, the levels of oxidative enzymes varied depending on the wastewater concentrations. These findings indicate Scenedesmus acuminatus CCALA 436 grown in wastewater and mepiquat chloride can be used for the treatment of wastewater and the production of ethanol and high-value products such as carotenoid.

A Review on a Hidden Gem: Phycoerythrin from Blue-Green Algae

Phycoerythrin (PE) is a pink/red-colored pigment found in rhodophytes, cryptophytes, and blue-green algae (cyanobacteria). The interest in PE is emerging from its role in delivering health benefits. Unfortunately, the current cyanobacterial-PE (C-PE) knowledge is still in the infant stage. It is essential to acquire a more comprehensive understanding of C-PE. This study aimed to review the C-PE structure, up and downstream processes of C-PE, application of C-PE, and strategies to enhance its stability and market value. In addition, this study also presented a strengths, weaknesses, opportunities, and threats (SWOT) analysis on C-PE. Cyanobacteria appeared to be the more promising PE producers compared to rhodophytes, cryptophytes, and macroalgae. Green/blue light is preferred to accumulate higher PE content in cyanobacteria. Currently, the prominent C-PE extraction method is repeated freezing-thawing. A combination of precipitation and chromatography approaches is proposed to obtain greater purity of C-PE. C-PE has been widely exploited in various fields, such as nutraceuticals, pharmaceuticals, therapeutics, cosmetics, biotechnology, food, and feed, owing to its bioactivities and fluorescent properties. This review provides insight into the state-of-art nature of C-PE and advances a step further in commercializing this prospective pigment.

Sustainable production of biofuels from the algae-derived biomass

The worldwide fossil fuel reserves are rapidly and continually being depleted as a result of the rapid increase in global population and rising energy sector needs. Fossil fuels should not be used carelessly since they produce greenhouse gases, air pollution, and global warming, which leads to ecological imbalance and health risks. The study aims to discuss the alternative renewable energy source that is necessary to meet the needs of the global energy industry in the future. Both microalgae and macroalgae have great potential for several industrial applications. Algae-based biofuels can surmount the inadequacies presented by conventional fuels, thereby reducing the ‘food versus fuel’ debate. Cultivation of algae can be performed in all three systems; closed, open, and hybrid frameworks from which algal biomass is harvested, treated and converted into the desired biofuels. Among these, closed photobioreactors are considered the most efficient system for the cultivation of algae. Different types of closed systems can be employed for the cultivation of algae such as stirred tank photobioreactor, flat panel photobioreactor, vertical column photobioreactor, bubble column photobioreactor, and horizontal tubular photobioreactor. The type of cultivation system along with various factors, such as light, temperature, nutrients, carbon dioxide, and pH affect the yield of algal biomass and hence the biofuel production. Algae-based biofuels present numerous benefits in terms of economic growth. Developing a biofuel industry based on algal cultivation can provide us with a lot of socio-economic advantages contributing to a publicly maintainable result. This article outlines the third-generation biofuels, how they are cultivated in different systems, different influencing factors, and the technologies for the conversion of biomass. The benefits provided by these new generation biofuels are also discussed. The development of algae-based biofuel would not only change environmental pollution control but also benefit producers' economic and social advancement.

Graphical abstract

Cultivation of microalgae on food waste: Recent advances and way forward

Microalgae are photosynthetic microbes that can synthesize compounds of therapeutic potential with wide applications in the food, bioprocessing and pharmaceutical sector. Recent research advances have therefore, focused on finding suitable economic substrates for the sustainable cultivation of microalgae. Among such substrates, food derived waste specifically from the starch, meat, dairy, brewery, oil and fruit and vegetable processing industries has gained popularity but poses numerous challenges. Pretreatment, dilution of waste water supernatants, mixing of different food waste streams, utilizing two-stage cultivation and other biorefinery approaches have been intensively explored for multifold improvement in microalgal biomass recovery from food waste. This review discusses the advances and challenges associated with cultivation of microalgae on food waste. The review suggests that there is a need to standardize different waste substrates in terms of general composition, genetically engineered microalgal strains, tackling process scalability issues, controlling wastewater toxicity and establishing a waste transportation chain.

Current perspectives, future challenges and key technologies of biohydrogen production for building a carbon-neutral future: A review

The ever-increasing quantity of greenhouse gases in the atmosphere can be attributed to the rapid increase in the world population as well as the expansion of globalization. Hence, achieving carbon neutrality by 2050 stands as a challenging task to accomplish. Global industrialization had necessitated the need to enhance the current production systems to reduce greenhouse gases emission, whilst promoting the capture of carbon dioxide from atmosphere. Hydrogen is often touted as the fuel of future via substituting fossil-based fuels. In this regard, renewable hydrogen happens to be a niche sector of novel technologies in achieving carbon neutrality. Microalgae-based biohydrogen technologies could be a sustainable and economical approach to produce hydrogen from a renewable source, while simultaneously promoting the absorption of carbon dioxide. This review highlights the current perspectives of biohydrogen production as an alternate source of energy. In addition, future challenges associated with biohydrogen production at large-scale application, storage and transportation are included. Key technologies in producing biohydrogen are finally described in building a carbon-neutral future.

Algal biorefinery culminating multiple value-added products: recent advances, emerging trends, opportunities, and challenges

Algal biorefinery is rising as a prominent solution to economically fulfill the escalating global requirement for nutrition, feed, fuel, and medicines. In recent years, scientific productiveness associated with microalgae-based studies has elaborated in multiplied aspects, while translation to the commercial level continues to be missing. The present microalgal biorefinery has a challenge in long-term viability due to escalated market price of algal-mediated biofuels and bioproducts. Advancements are required in a few aspects like improvement in algae processing, energy investment, and cost analysis of microalgae biorefinery. Therefore, it is essential to recognize the modern work by understanding the knowledge gaps and hotspots driving business scale up. The microalgae biorefinery integrated with energy-based products, bioactive and green compounds, focusing on a circular bioeconomy, is urgently needed. A detailed investigation of techno-economic analysis (TEA) and life cycle assessment (LCA) is important to increase the market value of algal products. This review discusses the valorization of algal biomass for the value-added application that holds a sustainable approach and cost-competitive algal biorefinery. The current industries, policies, technology transfer trends, challenges, and future economic outlook are discussed. This study is an overview through scientometric investigation attempt to describe the research development contributing to this rising field.

Sustainable Microalgae and Cyanobacteria Biotechnology

Marine organisms are a valuable source of new compounds, many of which have remarkable biotechnological properties, such as microalgae and cyanobacteria, which have attracted special attention to develop new industrial production routes. These organisms are a source of many biologically active molecules in nature, including antioxidants, immunostimulants, antivirals, antibiotics, hemagglutinates, polyunsaturated fatty acids, peptides, proteins, biofuels, and pigments. The use of several technologies to improve biomass production, in the first step, industrial processes schemes have been addressed with different accomplishments. It is critical to consider all steps involved in producing a bioactive valuable compound, such as species and strain selection, nutrient supply required to support productivity, type of photobioreactor, downstream processes, namely extraction, recovery, and purification. In general, two product production schemes can be mentioned; one for large amounts of product, such as biodiesel or any other biofuel and the biomass for feeding purposes; the other for when the product will be used in the human health domain, such as antivirals, antibiotics, antioxidants, etc. Several applications for microalgae have been documented. In general, the usefulness of an application for each species of microalgae is determined by growth and product production. Furthermore, the use of OMICS technologies enabled the development of a new design for human therapeutic recombinant proteins, including strain selection based on previous proteomic profiles, gene cloning, and the development of expression networks. Microalgal expression systems have an advantage over traditional microbial, plant, and mammalian expression systems for new and sustainable microalga applications, for responsible production and consumption.

Progress towards a targeted biorefinery of Chromochloris zofingiensis: a review

Biorefinery approaches offer the potential to improve the economics of the microalgae industry by producing multiple products from a single source of biomass. Chromochloris zofingiensis shows great promise for biorefinery due to high biomass productivity and a diverse range of products including secondary carotenoids, predominantly astaxanthin; lipids such as TAGs; carbohydrates including starch; and proteins and essential amino acids. Whilst this species has been demonstrated to accumulate multiple products, the development of an integrated downstream process to obtain these is lacking. The objective of this review paper is to assess the research that has taken place and to identify the steps that must be taken to establish a biorefinery approach for C. zofingiensis. In particular, the reasons why C. zofingiensis is a promising species to target for biorefinery are discussed in terms of cellular structure, potential products, and means to accumulate desirable components via the alteration of culture conditions. Future advances and the challenges that lie ahead for successful biorefinery of this species are also reviewed along with potential solutions to address them.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13399-022-02955-7.

A cheap two-step cultivation of Phaeodactylum tricornutum for increased TAG production and differential expression of TAG biosynthesis associated genes

A cheap cultivation of microalgae greatly reduces the biodiesel production cost. Subsequently in this study, citric acid and effluents from sugar and tannery industries were used as the nutritional supplements for the improvement of biomass and TAG production in Phaeodactylum tricornutum using two-step cultivation. When compared to control (media without supplementation), a considerable increase in biomass and chlorophyll a was obtained with citric acid (CA) and sugar industry effluent (SIE) supplemented media. In the two-step cultivation method, biomass raised from CA (100mg·L^-1) and SIE (1.5mL·L^-1) supplementations in the first step, viz. biomass production (BP) step was allowed for lipid accumulation in the second step, viz. lipid production (LP) step, and thus yielded enhanced lipids of 11.5 ± 0.7mg·L^-1·day^-1 and 13.5 ± 1.9mg·L^-1·day^-1 respectively, with improved TAG synthesis. Further, differential expression analysis of TAG biosynthetic genes of P. tricornutum under single-step and two-step cultivation modes were performed, and the gene expression patterns were studied.

Optimization of Microalgae–Bacteria Consortium in the Treatment of Paper Pulp Wastewater

The microalgae–bacteria consortium is a promising and sustainable alternative for industrial wastewater treatment, since it may allow good removal of organic matter and nutrients, as well as the possibility of producing products with added value from the algae biomass. This research investigated the best bacterial and microalgae inoculation ratio for system start-up and evaluation of removing organic matter (as chemical oxygen demand (COD)), ammoniacal nitrogen (NH4+–N), nitrite nitrogen (NO2−–N), nitrate nitrogen (NO3−–N), phosphate phosphorus (PO43−–P) and biomass formation parameters in six photobioreactors with a total volume of 1000 mL. Reactors were operated for 14 days with the following ratios of pulp mill biomass aerobic (BA) and Scenedesmus sp. microalgae (MA): 0:1 (PBR1), 1:0 (PBR2), 1:1 (PBR3), 3:1 (PBR4), 5:1 (PBR5), and 1:3 (PBR6). Results show that COD removal was observed in just two days of operation in PBR4, PBR5, and PBR6, whereas for the other reactors (with a lower rate of initial inoculation) it took five days. The PBR5 and PBR6 performed better in terms of NH4+–N removal, with 86.81% and 77.11%, respectively, which can be attributed to assimilation by microalgae and nitrification by bacteria. PBR6, with the highest concentration of microalgae, had the higher PO43−–P removal (86%), showing the advantage of algae in consortium with bacteria for phosphorus uptake. PBR4 and PBR5, with the highest BA, led to a better biomass production and sedimentability on the second day of operation, with flocculation efficiencies values over 90%. Regarding the formation of extracellular polymeric substances (EPS), protein production was substantially higher in PBR4 and PBR5, with more BA, with average concentrations of 49.90 mg/L and 49.05 mg/L, respectively. The presence of cyanobacteria and Chlorophyceae was identified in all reactors except PBR1 (only MA), which may indicate a good formation and structuring of the microalgae–bacteria consortium. Scanning electron microscopy (SEM) analysis revealed that filamentous microalgae were employed as a foundation for the fixation of bacteria and other algae colonies.

Bacterial Outer Membrane Permeability Increase Underlies the Bactericidal Effect of Fatty Acids From Hermetia illucens (Black Soldier Fly) Larvae Fat Against Hypermucoviscous Isolates of Klebsiella pneumoniae

Behind expensive treatments, Klebsiella pneumoniae infections account for extended hospitalization’s high mortality rates. This study aimed to evaluate the activity and mechanism of the antimicrobial action of a fatty acid-containing extract (AWME3) isolated from Hermetia illucens (HI) larvae fat against K. pneumoniae subsp. pneumoniae standard NDM-1 carbapenemase-producing ATCC BAA-2473 strain, along with a wild-type hypermucoviscous clinical isolate, strain K. pneumoniae subsp. pneumoniae KPi1627, and an environmental isolate, strain K. pneumoniae subsp. pneumoniae KPM9. We classified these strains as extensive multidrug-resistant (XDR) or multiple antibiotic-resistant (MDR) demonstrated by a susceptibility assay against 14 antibiotics belonging to ten classes of antibiotics. Antibacterial properties of fatty acids extracted from the HI larvae fat were evaluated using disk diffusion method, microdilution, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), half of the inhibitory concentration (MIC50), and bactericidal assays. In addition, the cytotoxocity of AWME3 was tested on human HEK293 cells, and AWME3 lipid profile was determined by gas chromatography-mass spectrometry (GC-MS) analysis. For the first time, we demonstrated that the inhibition zone diameter (IZD) of fatty acid-containing extract (AWME3) of the HI larvae fat tested at 20 mg/ml was 16.52 ± 0.74 and 14.23 ± 0.35 mm against colistin-resistant KPi1627 and KPM9, respectively. It was 19.72 ± 0.51 mm against the colistin-susceptible K. pneumoniae ATCC BAA-2473 strain. The MIC and MBC were 250 μg/ml for all the tested bacteria strains, indicating the bactericidal effect of AWME3. The MIC50 values were 155.6 ± 0.009 and 160.1 ± 0.008 μg/ml against the KPi1627 and KPM9 isolates, respectively, and 149.5 ± 0.013 μg/ml against the ATCC BAA-2473 strain in the micro-dilution assay. For the first time, we demonstrated that AWME3 dose-dependently increased bacterial cell membrane permeability as determined by the relative electric conductivity (REC) of the K. pneumoniae ATCC BAA-2473 suspension, and that none of the strains did not build up resistance to extended AWME3 treatment using the antibiotic resistance assay. Cytotoxicity assay showed that AWME3 is safe for human HEK293 cells at IC₅₀ 266.1 μg/ml, while bactericidal for all the strains of bacteria at the same concentration. Free fatty acids (FFAs) and their derivatives were the significant substances among 33 compounds identified by the GC-MS analysis of AWME3. Cis-oleic and palmitoleic acids represent the most abundant unsaturated FAs (UFAs), while palmitic, lauric, stearic, and myristic acids were the most abundant saturated FAs (SFAs) of the AWME3 content. Bactericidal resistant-free AWM3 mechanism of action provides a rationale interpretations and the utility of HI larvae fat to develop natural biocidal resistance-free formulations that might be promising therapeutic against Gram-negative MDR bacteria causing nosocomial infections.

Cultivation of Microalgae in Unsterile Malting Effluent for Biomass Production and Lipid Productivity Improvement

Microalgae have the potential to grow in nutrient-rich environments and have the ability to accumulate nutrients from wastewater. The nutrients in malting wastewater are ideal for microalgae cultivation. However, there is limited published work on the growth characteristics of freshwater microalgae grown in malting effluent. This study examined the potential of diluted malting effluent for the growth of freshwater green algae Chlorella sp. and Chlamydomonas sp. isolated from northern Ontario and subsequent biomass and lipid production. Under the 18:6 h light/dark cultivation cycle, the highest cell number counted (540 × 104 cell·mL−1 on day 20) and total chlorophyll content were found in 50% diluted malting effluents for Chlorella sp., whereas the 70% dilution concentration was the most productive for Chlamydomonas (386 × 104 cell·mL−1 on day 16). The total lipid content was higher in the 50% dilution concentration of malting effluent in both Chlorella sp. (maximum 20.5%–minimum 11.5% of dry weight) and Chlamydomonas sp. (max 39.3%–min 25.9% of dry weight). These results emphasize the suitability of using unsterile diluted malting effluent for microalgae cultivation.

A comprehensive review on the use of algal-bacterial systems for wastewater treatment with emphasis on nutrient and micropollutant removal

The scarcity of water resources and environmental pollution have highlighted the need for sustainable wastewater treatment. Existing conventional treatment systems are energy-intensive and not always able to meet stringent disposal standards. Recently, algal-bacterial systems have emerged as environmentally friendly sustainable processes for wastewater treatment and resource recovery. The algal-bacterial systems work on the principle of the symbiotic relationship between algae and bacteria. This paper comprehensively discusses the most recent studies on algal-bacterial systems for wastewater treatment, factors affecting the treatment, and aspects of resource recovery from the biomass. The algal-bacterial interaction includes cell-to-cell communication, substrate exchange, and horizontal gene transfer. The quorum sensing (QS) molecules and their effects on algal-bacterial interactions are briefly discussed. The effect of the factors such as pH, temperature, C/N/P ratio, light intensity, and external aeration on the algal-bacterial systems have been discussed. An overview of the modeling aspects of algal-bacterial systems has been provided. The algal-bacterial systems have the potential for removing micropollutants because of the diverse possible interactions between algae-bacteria. The removal mechanisms of micropollutants - sorption, biodegradation, and photodegradation, have been reviewed. The harvesting methods and resource recovery aspects have been presented. The major challenges associated with algal-bacterial systems for real scale implementation and future perspectives have been discussed. Integrating wastewater treatment with the algal biorefinery concept reduces the overall waste component in a wastewater treatment system by converting the biomass into a useful product, resulting in a sustainable system that contributes to the circular bioeconomy.

Removal of levofloxacin by an oleaginous microalgae Chromochloris zofingiensis in the heterotrophic mode of cultivation: Removal performance and mechanism

Microalgae-based technology is an environmental-friendly and cost-effective method for treating antibiotics-contaminated wastewater. This work investigated the removal of levofloxacin (LEV) by an oleaginous microalgae Chromochloris zofingiensis under photoautotrophic and heterotrophic conditions. The results showed that the significantly higher biomass production, accumulation of extracellular polymeric substance and LEV removal efficiency were achieved in heterotrophic C. zofingiensis compared with the photoautotrophic ones. The removal efficiencies under the heterotrophic condition were 97%, 88% and 76% at 1, 10, and 100 mg/L LEV, respectively. HPLC-MS/MS and RNA-Seq analyses suggested that LEV could be bioaccumulated and biodegraded by heterotrophic C. zofingiensis through the reactions of defluorination, hydroxylation, demethylation, ring cleavage, oxidation, dehydrogenation, denitrification, and decarboxylation. The chemical composition of the algal biomass obtained after LEV treatment indicated the potential of this alga for removing LEV from wastewaters and simultaneously producing biodiesel, astaxanthin, and other products. Collectively, this research shows that the heterotrophic C. zofingiensis can be identified as a promising candidate for removing LEV in wastewater remediation.

Algal Metabolites Can Be an Immune Booster against COVID-19 Pandemic

The world has faced the challenges of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) for the last two years, first diagnosed at the end of 2019 in Wuhan and widely distributed worldwide. As a result, the WHO has proclaimed the illness brought on by this virus to be a global pandemic. To combat COVID-19, researcher communities continuously develop and implement rapid diagnoses, safe and effective vaccinations and other alternative therapeutic procedures. However, synthetic drug-related side effects and high costs have piqued scientists’ interest in natural product-based therapies and medicines. In this regard, antiviral substances derived from natural resources and some medicines have seen a boom in popularity. For instance, algae are a rich source of compounds such as lectins and sulfated polysaccharides, which have potent antiviral and immunity-boosting properties. Moreover, Algae-derived compounds or metabolites can be used as antibodies and vaccine raw materials against COVID-19. Furthermore, some algal species can boost immunity, reduce viral activity in humans and be recommended for usage as a COVID-19 preventative measure. However, this field of study is still in its early stages of development. Therefore, this review addresses critical characteristics of algal metabolites, their antioxidant potential and therapeutic potential in COVID-19.

Utilization of the microalga Scenedesmus quadricauda for hexavalent chromium bioremediation and biodiesel production

The purpose of this study was to evaluate the bioremediation potential of the microalga Scenedesmus quadricauda in removing hexavalent chromium (Cr (VI)) from synthetic wastewater, under autotrophic and heterotrophic conditions and different inoculum concentrations. In both cultivation modes, the highest inoculum density of 0.8 g L^-1 led to the highest Cr (VI) removal efficiency. In addition, Cr (VI) stress was more severe in 10 ppm compared to 5 ppm, while heavy metal effects were alleviated under heterotrophic conditions. Concurrently, Cr (VI) stress affected biomass quality, resulting in an increase in lipid and carbohydrate production and decreased proteins. Furthermore, under higher Cr (VI) concentration more saturated and monounsaturated fatty acids were produced, while monounsaturated fatty acids content was also greater under heterotrophic conditions. In total, the findings of this study highlight the advantages of heterotrophic cultivation of microalgae for concomitant industrial wastewater treatment and biofuel production.

Microalgal transformation of food processing byproducts into functional food ingredients

Large amounts of food processing byproducts (FPBs) are generated from food manufacturing industries, the second-largest portion of food waste generation. FPBs may require additional cost for post-treatment otherwise cause environmental contamination. Valorization of FPBs into food ingredients by microalgae cultivation can save a high cost for organic carbon sources and nutrients from medium cost. This study reviews FPBs generation categorized by industry and traditional disposal. In contrast with the low-value production, FPBs utilization as the nutrient-abundant medium for microalgae can lead to high-value production. Due to the complex composition in FPBs, various pretreatment methods have been applied to extract the desired compounds and medium preparation. Using the FPB-based medium resulted in cost reduction and a productivity enhancement in previous literature. Although there are still challenges to overcome to achieve economic viability and environmental sustainability, the microalgal transformation of FPBs is attractive for functional food ingredients production.

Recent advances in microalgae-based remediation of industrial and non-industrial wastewaters with simultaneous recovery of value-added products

The ability of microalgae to grow in a broad spectrum of wastewaters manifests great potentials for removing contaminants from effluents of industries and urban areas. Since the post-treatment microalgae biomass is also a significant source of high-value products, microalgae-based wastewater treatment is an economical and sustainable solution to wastewater management. Adding more value, the integration of microalgae with living/non-living materials looks more promising. Microalgae-based treatment technology has certain limitations like high operational costs, problematic harvesting, large land requirements, and hindrance in photosynthesis due to turbid wastewater. These challenges need to be essentially addressed to achieve enhanced wastewater remediation. This review has highlighted the potential applications of microalgae in contaminant removal from wastewaters, simultaneous resource recovery, efficient microalgae-based hybrid systems along with bottlenecks and prospects. This state-of-the-art article will edify the role of microalgae in wastewater remediation, biomass valorization for bio-based products, and present numerous possibilities in strengthening the circular bioeconomy.

Mass cultivation and harvesting of microalgal biomass: Current trends and future perspectives

Microalgae are unicellular photosynthetic organisms capable of producing high-value metabolites like carbohydrates, lipids, proteins, polyunsaturated fatty acids, vitamins, pigments, and other high-value metabolites. Microalgal biomass gained more interest for the production of nutraceuticals, pharmaceuticals, therapeutics, food supplements, feed, biofuel, bio-fertilizers, etc. due to its high lipid and other high-value metabolite content. Microalgal biomass has the potential to convert trapped solar energy to organic materials and potential metabolites of nutraceutical and industrial interest. They have higher efficiency to fix carbon dioxide (CO₂) and subsequently convert it into biomass and compounds of potential interest. However, to make microalgae a potential industrial candidate, cost-effective cultivation systems and harvesting methods for increasing biomass yield and reducing the cost of downstream processing have become extremely urgent and important. In this review, the current development in different microalgal cultivation systems and harvesting methods has been discussed.

Progress and challenges of contaminate removal from wastewater using microalgae biomass

The utilization of microalgae in treating wastewater has been an emerging topic focussed on finding an economically sustainable and environmentally friendly approach to treating wastewater. Over the last several years, different types of con microalgae and bacteria consortia have been experimented with to explore their potential in effectively treating wastewater from different sources. The basic features considered while determining efficiency is their capacity to remove nutrients including nitrogen (N) and phosphorus (P) and heavy metals like arsenic (As), lead (Pb), and copper (Cu). This paper reviews the efficiency of microalgae as an approach to treating wastewater from different sources and compares conventional and microalgae-based treatment systems. The paper also discusses the characteristics of wastewater, conventional methods of wastewater treatment that have been used so far, and the technological mechanisms for removing nutrients and heavy metals from contaminated water. Microalgae can successfully eliminate the suspended nutrients and have been reported to successfully remove N, P, and heavy metals by up to 99.6 %, 100 %, and 13%-100 % from different types of wastewater. However, although a microalgae-based wastewater treatment system offers some benefits, it also presents some challenges as outlined in the last section of this paper. Performance in eliminating nutrients from wastewater is affected by different parameters such as temperature, biomass productivity, osmotic ability, pH, O₂ concentration. Therefore, the conducting of pilot-scale studies and exploration of the complexities of contaminants under complex environmental conditions is recommended.

Improving microalgae for biotechnology - From genetics to synthetic biology - Moving forward but not there yet

Microalgae are a diverse group of photosynthetic organisms that can be exploited for the production of different compounds, ranging from crude biomass and biofuels to high value-added biochemicals and synthetic proteins. Traditionally, algal biotechnology relies on bioprospecting to identify new highly productive strains and more recently, on forward genetics to further enhance productivity. However, it has become clear that further improvements in algal productivity for biotechnology is impossible without combining traditional tools with the arising molecular genetics toolkit. We review recent advantages in developing high throughput screening methods, preparing genome-wide mutant libraries, and establishing genome editing techniques. We discuss how algae can be improved in terms of photosynthetic efficiency, biofuel and high value-added compound production. Finally, we critically evaluate developments over recent years and explore future potential in the field.

Resource recovery through bioremediation of wastewaters and waste carbon by microalgae: a circular bioeconomy approach

Microalgal biomass-based biofuels are a promising alternative to fossil fuels. Microalgal biofuels' major obstacles are the water and carbon sources for their cultivation and biomass harvest from the liquid medium. To date, an economically viable process is not available for algal based biofuels. The circular bioeconomy is an attractive concept for reuse, reduce, and recycle resources. The recovery of nutrients from waste and effluents by microalgae could significantly impact the escalating demands of energy and nutraceutical source to the growing population. Wastewaters from different sources are enriched with nutrients and carbon, and these resources can be recovered and utilized for the circular bioeconomy approach. However, the utilization of wastewaters and waste seems to be an essential strategy for mass cultivation of microalgae to minimizing freshwater consumption, carbon, nutrients cost, nitrogen, phosphorus removal, and other pollutants loads from wastewater and generating sustainable biomass for value addition for either biofuels or other chemicals. Hence, the amalgamation of wastewater treatment with the mass cultivation of microalgae improved the conventional treatment process and environmental impacts. This review provides complete information on the latest progress and developments of microalgae as potential biocatalyst for the remediation of wastewaters and waste carbon to recover resources through biomass with metabolites for various industrial applications and large-scale cultivation in wastewaters, and future perspectives are discussed.

Photosynthetic transients in Chlorella sorokiniana during phycoremediation of dairy wastewater under distinct light intensities

The present study is aimed to understand the photosynthetic transients of Chlorella sorokiniana SVMBIOEN2 during treatment of dairy wastewater under different light intensities (100, 150, and 200 µmol m^-2s^-1) in mixotrophic mode. Light intensities showed marked influence on photosystem behavior, lipid profile, and organic pollutant removal. Analysis of Chlorophyll a fluorescence transient including Fv/Fm, ETo/RC, TRo/RC, and Abs/RC showed better photosystem efficiency at 100 µmol m^-2s^-1 operations. OJIP curve fitting depicted a positive L-band at 150 µmol m^-2s^-1 indicating lower kinetic energy of photosystem II (PSII) reaction centres at high light intensities. Better photosynthetic activity at 100 µmol m^-2s^-1 operations resulted in good assimilation of biomass (2.3 g L^-1), carbohydrates (10.2 mg g^-1), and proteins (14 mg g^-1) with a significant reduction in chemical oxygen demand (85%). Phycoremediation of dairy wastewater accumulates predominantly monounsaturated fatty acids followed by polyunsaturated fatty acids showing the application of C. sorokiniana in nutraceutical and food industries.

Effects of Nitrogen and Phosphorus Limitation on Fatty Acid Contents in Aspergillus oryzae

Aspergillus oryzae, commonly known as koji mold, has been widely used for the large-scale production of food products (sake, makgeolli, and soy sauce) and can accumulate a high level of lipids. In the present study, we showed the dynamic changes in A. oryzae mycelium growth and conidia formation under nitrogen and phosphorus nutrient stress. The fatty acid profile of A. oryzae was determined and the content of unsaturated fatty acid was found increased under nitrogen and phosphorus limitation. Oleic acid (C18:1), linoleic acid (C18:2), and γ-linolenic acid (C18:3) production were increased on five nitrogen and phosphorus limitation media, especially on nitrogen deep limitation and phosphorus limitation group, showing a 1. 2-, 1. 6-, and 2.4-fold increment, respectively, compared with the control. Transcriptomic analysis showed the expression profile of genes related to nitrogen metabolism, citrate cycle, and linoleic acid synthesis, resulting in the accumulation of unsaturated fatty acid. qRT-PCR results further confirmed the reliability and availability of the differentially expressed genes obtained from the transcriptome analysis. Our study provides a global transcriptome characterization of the nitrogen and phosphorus nutrient stress adaptation process in A. oryzae. It also revealed that the molecular mechanisms of A. oryzae respond to nitrogen and phosphorus stress. Our finding facilitates the construction of industrial strains with a nutrient-limited tolerance.

A multicriteria decision analysis for the evaluation of microalgal growth and harvesting

Biomass obtained from microalgae research studies gained momentum in recent years because of their extensive application potential in multiple industries such as high-value nutraceuticals, bioproducts, cosmetics, animal feed industries, and biofuels while being a sustainable and environmentally friendly option. Although they have high biomass yields and rapid growth rates there are some limitations and challenges that remain for large-scale commercialized cultivation and harvesting methods of microalgae. Since there are multiple pathways related to efficient cultivation and harvesting methods to be viable, this study adopted, TOPSIS (Technique for Order Preference by Similarity to Ideal Solution), a multicriteria decision-making tool, to find the most acceptable alternative by using excel spreadsheets to evaluate the information that is derived from literature and pilot-scale studies. As a result, tubular (helical) and plate (flat panel) photobioreactors (PBRs) for cultivation and chemical harvesting (with chitosan) and bio-flocculation for harvesting were deemed suitable, while plastic bag PBR and suspended air flotation were deemed unsuitable.

Role of extracellular polymeric substances on nutrients storage and transfer in algal-bacteria symbiosis sludge system treating wastewater

This study reported the role and significance of extracellular polymeric substances (EPSs) on nutrients storage and transfer in an algal-bacteria symbiosis sludge (ABSS) system for wastewater treatment, and the novel algae-based sequencing batch suspended biofilm reactor (A-SBSBR, Ra) was selected as model of ABSS system. Results showed that compared to conventional SBSBR, the EPS of Ra performed better storage for NO₂^--N, NO₃^--N, total phosphorus and PO₄^3- -P, with increase ratios of 43.7%, 36.0%, 34.1% and 14.7% in sludge phase and 174.0%, 147.4%, 150.4% and 122.0% in biofilm phase, respectively. The analysis of mechanisms demonstrated that microalgae active transport and uptake for divalent cations could enhance their local concentrations around ABS flocs and partially neutralized negative charge of EPSs, and more anions related to nutrients were absorbed in EPSs. Moreover, O₂ produced by microalgae photosynthesis enhanced bacteria activity and improved the production of EPSs in both sludge and biofilm phases.

Exploitation of Marine Molecules to Manage Alzheimer's Disease

Neurodegenerative diseases are sociosanitary challenges of today, as a result of increased average life expectancy, with Alzheimer’s disease being one of the most prevalent. This pathology is characterized by brain impairment linked to a neurodegenerative process culminating in cognitive decline and behavioral disorders. Though the etiology of this pathology is still unknown, it is usually associated with the appearance of senile plaques and neurofibrillary tangles. The most used prophylaxis relies on anticholinesterase drugs and NMDA receptor antagonists, whose main action is to relieve symptoms and not to treat or prevent the disease. Currently, the scientific community is gathering efforts to disclose new natural compounds effective against Alzheimer’s disease and other neurodegenerative pathologies. Marine natural products have been shown to be promising candidates, and some have been proven to exert a high neuroprotection effect, constituting a large reservoir of potential drugs and nutraceutical agents. The present article attempts to describe the processes of extraction and isolation of bioactive compounds derived from sponges, algae, marine bacteria, invertebrates, crustaceans, and tunicates as drug candidates against AD, with a focus on the success of pharmacological activity in the process of finding new and effective drug compounds.

Metabolomic Study of Heterotrophically Grown Chlorella sp. Isolated from Wastewater in Northern Sweden

There are numerous strains of Chlorella with a corresponding variety of metabolic pathways. A strain we previously isolated from wastewater in northern Sweden can grow heterotrophically as well as autotrophically in light and has higher lipid contents under heterotrophic growth conditions. The aims of the present study were to characterize metabolic changes associated with the higher lipid contents in order to enhance our understanding of lipid production in microalgae and potentially identify new compounds with utility in sustainable development. Inter alia, the amino acids glutamine and lysine were 7-fold more abundant under heterotrophic conditions, the key metabolic intermediate alpha-ketoglutarate was more abundant under heterotrophic conditions with glucose, and maltose was more abundant under heterotrophic conditions with glycerol than under autotrophic conditions. The metabolite 3-hydroxy-butyric acid, the direct precursor of the biodegradable plastic PHB (poly-3-hydroxy-butyric acid), was also more abundant under heterotrophic conditions. Our metabolomic analysis has provided new insights into the alga's lipid production pathways and identified metabolites with potential use in sustainable development, such as the production of renewable, biodegradable plastics, cosmetics, and nutraceuticals, with reduced pollution and improvements in both ecological and human health.

Bioprospecting of wild type ethanologenic yeast for ethanol fuel production from wastewater-grown microalgae

BACKGROUND

Wild-type yeasts have been successfully used to obtain food products, yet their full potential as fermenting microorganisms for large-scale ethanol fuel production has to be determined. In this study, wild-type ethanologenic yeasts isolated from a secondary effluent were assessed for their capability to ferment saccharified microalgae sugars.

RESULTS

Yeast species in wastewater were identified sequencing the Internal Transcribed Spacers 1 and 2 regions of the ribosomal cluster. Concurrently, microalgae biomass sugars were saccharified via acid hydrolysis, producing 5.0 ± 0.3 g L^-1 of fermentable sugars. Glucose consumption and ethanol production of yeasts in hydrolyzed-microalgae liquor were tested at different initial sugar concentrations and fermentation time. The predominant ethanologenic yeast species was identified as Candida sp., and glucose consumption for this strain and S. cerevisiae achieved 75% and 87% of the initial concentration at optimal conditions, respectively. Relatively similar ethanol yields were determined for both species, achieving 0.45 ± 0.05 (S. cerevisiae) and 0.46 ± 0.05 g ethanol per g glucose (Candida sp.).

CONCLUSION

Overall, the results provide a first insight of the fermentation capacities of specific wild-type Candida species, and their potential role in ethanol industries seeking to improve their cost-efficiency.

Synergistic effect of growth conditions and organic carbon sources for improving biomass production and biodiesel quality by the microalga Choricystis minor var. minor

In the search for microalgae species with potential for biodiesel production, Choricystis minor var. minor has been seen as a promising source of biomass due to its high lipid content and the satisfactory characteristics of its fatty acid methyl esters (FAMEs). For this reason, the objective of this study was to investigate the synergistic effect of growth conditions and organic carbon sources on cultivation of this microalga. To do so, experimental cultivations were conducted in photoautotrophic, heterotrophic and mixotrophic metabolisms using glucose, fructose, glycerol or sucrose - in growth conditions that use organic carbon. Thus, growth parameters of the cultures were evaluated and at the end of the cultivations, FAMEs yield and profile were determined by gas chromatography, the efficiency of carbon conversion into biomass was evaluated and a microbial analysis was conducted. Regarding growth conditions, the findings have confirmed that, regardless of the organic carbon source used, the heterotrophic and mixotrophic metabolisms can present advantages over the photoautotrophic one. In addition, biomass production was higher with the use of glucose than with other organic carbon sources, regardless of growth condition (heterotrophic or mixotrophic). Moreover, cultivations with the addition of CO₂ have converted carbon into biomass less efficiently. On the other hand, photoautotrophic cultures presented the lowest bacterial load. In comparison to photoautotrophic and mixotrophic, heterotrophic cultures have led to lower FAMEs content and higher yields of unsaturated fatty acids. The most satisfactory FAMEs profile for biodiesel production was obtained with mixotrophic growth using fructose.

Overexpression of the Transcription Factor AtLEC1 Significantly Improved the Lipid Content of Chlorella ellipsoidea

Microalgae are considered to be a highly promising source for the production of biodiesel. However, the regulatory mechanism governing lipid biosynthesis has not been fully elucidated to date, and the improvement of lipid accumulation in microalgae is essential for the effective production of biodiesel. In this study, LEAFY COTYLEDON1 (LEC1) from Arabidopsis thaliana, a transcription factor (TF) that affects lipid content, was transferred into Chlorella ellipsoidea. Compared with wild-type (WT) strains, the total fatty acid content and total lipid content of AtLEC1 transgenic strains were significantly increased by 24.20–32.65 and 22.14–29.91%, respectively, under mixotrophic culture conditions and increased by 24.4–28.87 and 21.69–30.45%, respectively, under autotrophic conditions, while the protein content of the transgenic strains was significantly decreased by 18.23–21.44 and 12.28–18.66%, respectively, under mixotrophic and autotrophic conditions. Fortunately, the lipid and protein content variation did not affect the growth rate and biomass of transgenic strains under the two culture conditions. According to the transcriptomic data, the expression of 924 genes was significantly changed in the transgenic strain (LEC1-1). Of the 924 genes, 360 were upregulated, and 564 were downregulated. Based on qRT-PCR results, the expression profiles of key genes in the lipid synthesis pathway, such as ACCase, GPDH, PDAT1, and DGAT1, were significantly changed. By comparing the differentially expressed genes (DEGs) regulated by AtLEC1 in C. ellipsoidea and Arabidopsis, we observed that approximately 59% (95/160) of the genes related to lipid metabolism were upregulated in AtLEC1 transgenic Chlorella. Our research provides a means of increasing lipid content by introducing exogenous TF and presents a possible mechanism of AtLEC1 regulation of lipid accumulation in C. ellipsoidea.

Antibacterial fatty acids: An update of possible mechanisms of action and implications in the development of the next-generation of antibacterial agents

The antibacterial activity of fatty acids (FA) is well known in the literature and represents a promising option for developing the next-generation of antibacterial agents to treat a broad spectrum of bacterial infections. FA are highly involved in living organisms' defense system against numerous pathogens, including multidrug-resistant bacteria. When combined with other antibacterial agents, the remarkable ability of FA to enhance their bactericidal properties is a critical feature that is not commonly observed in other naturally-occurring compounds. More reviews focusing on FA antibacterial activity, traditional and non-traditional mechanisms and biomedical applications are needed. This review is intended to update the reader on the antibacterial properties of recent FA and how their chemical structures influence their antibacterial activity. This review also aims to better understand both traditional and non-traditional mechanisms involved in these recently explored FA antibacterial activities.

Microalgae: A Promising Source of Valuable Bioproducts

Microalgae are a group of autotrophic microorganisms that live in marine, freshwater and soil ecosystems and produce organic substances in the process of photosynthesis. Due to their high metabolic flexibility, adaptation to various cultivation conditions as well as the possibility of rapid growth, the number of studies on their use as a source of biologically valuable products is growing rapidly. Currently, integrated technologies for the cultivation of microalgae aiming to isolate various biologically active substances from biomass to increase the profitability of algae production are being sought. To implement this kind of development, the high productivity of industrial cultivation systems must be accompanied by the ability to control the biosynthesis of biologically valuable compounds in conditions of intensive culture growth. The review considers the main factors (temperature, pH, component composition, etc.) that affect the biomass growth process and the biologically active substance synthesis in microalgae. The advantages and disadvantages of existing cultivation methods are outlined. An analysis of various methods for the isolation and overproduction of the main biologically active substances of microalgae (proteins, lipids, polysaccharides, pigments and vitamins) is presented and new technologies and approaches aimed at using microalgae as promising ingredients in value-added products are considered.

Organic waste biorefineries: Looking towards implementation

The concept of biorefinery expands the possibilities to extract value from organic matter in form of either bespoke crops or organic waste. The viability of biorefinery schemes depends on the recovery of higher-value chemicals with potential for a wide distribution and an untapped marketability. The feasibility of biorefining organic waste is enhanced by the fact that the biorefinery will typically receive a waste management fee for accepting organic waste. The development and implementation of waste biorefinery concepts can open up a wide array of possibilities to shift waste management towards higher sustainability. However, barriers encompassing environmental, technical, economic, logistic, social and legislative aspects need to be overcome. For instance, waste biorefineries are likely to be complex systems due to the variability, heterogeneity and low purity of waste materials as opposed to dedicated biomasses. This article discusses the drivers that can make the biorefinery concept applicable to waste management and the possibilities for its development to full scale. Technological, strategic and market constraints affect the successful implementations of these systems. Fluctuations in waste characteristics, the level of contamination in the organic waste fraction, the proximity of the organic waste resource, the markets for the biorefinery products, the potential for integration with other industrial processes and disposal of final residues are all critical aspects requiring detailed analysis. Furthermore, interventions from policy makers are necessary to foster sustainable bio-based solutions for waste management.

Development and cost-benefit analysis of a novel process for biofuel production from microalgae using pre-treated high-strength fresh cheese whey wastewater

In this study, a novel two-step integrated process is proposed to facilitate the microalgae biofuel production as well as fresh cheese whey wastewater (FCWW) treatment simultaneously. The pre- and post-treatment of high-strength FCWW were performed by means of coagulation and algal cultivation, respectively. The pre-treatment of FCWW for maximum removal of chemical oxygen demand (COD), turbidity (TUR) and total solids (TS) as responses was obtained by statistical optimization of coagulation parameters. The maximum removal of COD, TUR and TS at the optimum level of variables was obtained as 68.09%, 47.80% and 73.63%, respectively. The pre-treated FCWW was further treated by Chlorella pyrenoidosa and observed a significant reduction in the above-mentioned responses (87-94%). The maximum algal biomass yield and lipid productivity were observed as 2.44 g L^-1 and 77.41 mg L^-1 day^-1, respectively. Based on promising results of FCWW treatment and its use as a third-generation biodiesel feedstock, a cost-benefit analysis of the developed process was assessed for microalgal oil production. The total profit earned by the integrated process model was $9.59 million year^-1. Accordingly, the estimated production cost of algal oil (TAG) from the developed system was estimated to be $79.03 per barrel.