Allelopathy as a potential strategy to improve microalgae cultivation

The need for smart microalgal bioprospecting

Microalgae's adaptability and resilience to Earth's diverse environments have evolved these photosynthetic microorganisms into a biotechnological source of industrially relevant physiological functions and biometabolites. Despite this, microalgae-based industries only exploit a handful of species. This lack of biodiversity hinders the expansion of the microalgal industry. Microalgal bioprospecting, searching for novel biological algal resources with new properties, remains a low throughput and time-consuming endeavour due to inefficient workflows that rely on non-selective sampling, monoalgal culture status and outdated, non-standardized characterization techniques. This review will highlight the importance of microalgal bioprospecting and critically explore commonly employed methodologies. We will also explore current advances driving the next generation of smart algal bioprospecting focusing on novel workflows and transdisciplinary methodologies with the potential to enable high-throughput microalgal biodiscoveries. Images adapted from (Addicted04 in Wikipedia File: Australia on the globe (Australia centered).svg. 2014.; Jin et al. in ACS Appl Bio Mater 4:5080-5089, 2021; Kim et al. in Microchim Acta 189:88, 2022; Tony et al. in Lab on a Chip 15, 19:3810-3810; Thermo Fisher Scientific INC. in CTS Rotea Brochure).

Monocultures vs. polyculture of microalgae: unveiling physiological changes to facilitate growth in ammonium rich-medium

Due to the increasing production of wastewater from human activities, the use of algal consortia for phytoremediation has become well-established over the past decade. Understanding how interspecific interactions and cultivation modes (monocultures vs. polyculture) influence algal growth and behaviour is a cutting-edge topic in both fundamental and applied science. Ammonium-rich growth media were used to challenge the monocultures of Auxenochlorella protothecoides, Chlamydomonas reinhardtii and Tetradesmus obliquus, as well as their polyculture; NO3 - was also used as the sole nitrogen chemical form in control cultures. The study primarily compared the growth, carbon and nitrogen metabolisms, and protein content of the green microalgae monocultures to those of their consortium. Overall, the cultivation mode significantly affected all the measured parameters. Notably, at 50 mM NH4 +, the assimilation rates of carbon and nitrogen were at least twice as high as those in the monoculture counterparts, and the protein content was three times more abundant.Additionally, the consortium's response to NH4 + toxicity was investigated by observing a linear relationship between the indicator of tolerance to NH4 + nutrition and the N isotopic signature. The study highlighted a high degree of acclimation through metabolic flexibility and diversity, as well as species abundance plasticity in the consortium, resulting in a functional resilience that would otherwise have been unattainable by the respective monocultures.

Microalgae and co-culture for polishing pollutants of anaerobically treated agro-processing industry wastewater: the case of slaughterhouse

Anaerobically treated slaughterhouse effluent is rich in nutrients, organic matter, and cause eutrophication if discharged to the environment without proper further treatment. Moreover, phosphorus and nitrogen in agro-processing industry wastewaters are mainly removed in the tertiary treatment phase. The objective of this study is to evaluate the pollutant removal efficiency of Chlorella and Scenedesmus species as well as their co-culture treating two-phase anaerobic digester effluent through microalgae biomass production. The dimensions of the rectangular photobioreactor used to conduct the experiment are 15 cm in height, 20 cm in width, and 30 cm in length. Removal efficiencies between 86.74-93.11%, 96.74-97.47%, 91.49-92.91%, 97.94-99.46%, 89.22-94.28%, and 91.08-95.31% were attained for chemical oxygen demand, total nitrogen, nitrate, ammonium, total phosphorous, and orthophosphate by Chlorella species, Scenedesmus species, and their co-culture, respectively. The average biomass productivity and biomass yield of Chlorella species, Scenedesmus species, and their co-culture were 1.4 ± 0.1, 1.17 ± 0.12, 1.5 ± 0.13 g/L, and 0.18, 0.21, and 0.23 g/L*day, respectively. The final effluent quality in terms of chemical oxygen demand, total nitrogen, and total phosphorous attained by Chlorella species and the co-culture were below the permissible discharge limit for slaughterhouse effluent standards in the country (Ethiopia). The results of the study showed that the use of microalgae as well as their co-culture for polishing the nutrients and residual organic matter in the anaerobically treated agro-processing industry effluent offers a promising result for wastewater remediation and biomass production. In general, Chlorella and Scenedesmus species microalgae and their co-culture can be applied as an alternative for nutrient removal from anaerobically treated slaughterhouse wastewater as well as biomass production that can be used for bioenergy.

Mixotrophy, a more promising culture mode: Multi-faceted elaboration of carbon and energy metabolism mechanisms to optimize microalgae culture

Some mixotrophic microalgae appear to exceed the sum of photoautotrophy and heterotrophy in terms of biomass production. This paper mainly reviews the carbon and energy metabolism of microalgae to reveal the synergistic mechanisms of the mixotrophic mode from multiple aspects. It explains the shortcomings of photoautotrophic and heterotrophic growth, highlighting that the mixotrophic mode is not simply the sum of photoautotrophy and heterotrophy. Specifically, microalgae in mixotrophic mode can be divided into separate parts of photoautotrophic and heterotrophic cultures, and the synergistic parts of photoautotrophic culture enhance aerobic respiration and heterotrophic culture enhance the Calvin cycle. Additionally, this review argues that current deficiencies in mixotrophic culture can be improved by uncovering the synergistic mechanism of the mixotrophic mode, aiming to increase biomass growth and improve quality. This approach will enable the full utilization of advantagesin various fields, and provide research directions for future microalgal culture.

Microalgae: A green eco-friendly agents for bioremediation of tannery wastewater with simultaneous production of value-added products

Tannery wastewater (TWW) has high BOD, COD, TS and variety of pollutants like chromium, formaldehydes, biocides, oils, chlorophenols, detergents and phthalates etc. Besides these pollutants, TWW also rich source of nutrients like nitrogen, phosphorus, carbon and sulphur etc. that can be utilized by microalgae during their growth. Direct disposal of TWW into the environment may lead severe environmental and health threats, therefore it needs to be treated adequately. Microalgae are considered as an efficient microorganisms (fast growing, adaptability and strain robustness, high surface to volume ratio, energy saving) for remediation of wastewaters with simultaneous biomass recovery and generation of value added products (VAPs) such as biofuels, biohydrogen, biopolymer, biofertilizer, pigments, bioethanol, bioactive compounds, nutraceutical etc. Most microalgae are photosynthetic and use CO₂ and light energy to synthesise carbohydrate and reduces the emission of greenhouse gasses. Microalgae are also reported to remove heavy metals and antibiotics from wastewaters by bioaccumulation, biodegradation and biosorption. Microalgal treatment can be an alternative of conventional processes with generation of VAPs. The use of biotechnology in wastewater remediation with simultaneous generation of VAPs is trending. The validation of economic viability and environmental sustainability, life cycle assessment studies and techno-economic analysis is undergoing. Thus, in this review, the characteristics of TWW and microalgae are summarized, which manifest microalgae as potential candidates for wastewater remediation with simultaneous production of VAPs. Further, the treatment mechanisms, various factors (physical, chemical, mechanical and biological etc.) affecting treatment efficiency as well as challenges associated with microalgal remediation are also discussed.

The Potential of Allelochemicals from Microalgae for Biopesticides

Improvements in agricultural productivity are required to meet the demand of a growing world population. Phytopathogens, weeds, and insects are challenges to agricultural production. The toxicity and widespread application of persistent synthetic pesticides poses a major threat to human and ecosystem health. Therefore, sustainable strategies to control pests are essential for agricultural systems to enhance productivity within a green paradigm. Allelochemicals are a less persistent, safer, and friendly alternative to efficient pest management, as they tend to be less toxic to non-target organisms and more easily degradable. Microalgae produce a great variety of allelopathic substances whose biocontrol potential against weeds, insects, and phytopathogenic fungi and bacteria has received much attention. This review provides up-to-date information and a critical perspective on allelochemicals from microalgae and their potential as biopesticides.

Cytogenotoxic, insecticidal, and phytotoxic activity from biomass extracts of the freshwater algae Nitella furcata

Agroecology, the application of ecological concepts to agricultural production, has been developing over the last years with consequent promotion for discovery of bioactive compounds to control pests and abolish crop diseases. In this context, algae from Nitella genus are characterized by high potential for bioeconomic applications due to (1) available biomass for harvesting or cultivation and (2) production of allelochemicals, which present a potential to protect field crops from insect infestation. Therefore, this study aimed to determine primary and secondary metabolites derived from aqueous and hydroethanolic extracts of Nitella furcata and to evaluate phytotoxic, cytogenotoxic, insecticidal, and pro-oxidative activities of these extracts. Determination of metabolites showed the presence predominantly of carbohydrates, proteins, phenols, and flavonoids in hydroethanolic extract. Both extracts of N. furcata interfered in the germination of seeds and development of seedlings of Lactuca sativa, with hydroethanolic extract exhibiting greater inhibition. Both extracts also interfered with meristematic cells of Allium cepa as evidenced by chromosomal alterations and higher pro-oxidative activity. Aqueous extract at 5 and 0 mg/ml produced 100% insect mortality. Further, hydroethanolic extract at 0 mg/ml was lethal immediately upon exposure. Therefore, results demonstrate that N. furcata is potential algae species to be considered for development of environmental and ecotoxicological studies as a source of compounds with potential use in agroecological strategies.

Allelopathic effect of benzoic acid (hydroponics root exudate) on microalgae growth

Hydroponic effluent (HE) contains a reasonable amount of residual nutrients. Therefore, HE could be used as a low-cost growth media for microalgae mediated resource recovery and water recycling. However, the presence of root exudates (particularly, benzoic acid) may lead to toxicity in microalgae.In the present study, the allelopathic effects of benzoic acid on microalgal growth was tested. During 96 h batch growth, Chlorella pyrenoidosa showed the highest biomass concentration (0.064-0.037 g.L^-1) compared to Chlorella sorokiniana (0.09-0.26 g.L^-1) at the tested benzoic acid doses. Moreover, both the species showed growth stimulation and growth inhibition up to certain benzoic acid doses. Hence, both the microalgal species showed allelopathic behaviour at different doses of benzoic acid. Further, the observed half effective concentration (96 h EC₅₀) were 65.10 mg.L^-1 and 105.27 mg.L^-1, respectively, for Chlorella pyrenoidosa and C. sorokiniana with 95% confidence limits. Further, Haldane's model best fitted with experimental data of both the microalgae (r ∼ 0.99). Overall, the study reveals that the HE with low benzoic acid dose may serve as a suitable growth media for microalgae. However, further in-depth research interventions using real HE are desirable to determine its real-world applicability.

Volatile organic compounds in aquatic ecosystems - Detection, origin, significance and applications

Volatile organic compounds (VOCs) include a broad range of compounds. Their production influences a large number of processes, having direct and secondary effects on different fields, such as climate change, economy and ecology. Although our planet is primarily covered with water (~70% of the globe surface), the information on aquatic VOCs, compared to the data available for the terrestrial environments, is still limited. Regardless of the difficulty in collecting and analysing data, because of their extreme complexity, diversification and important spatial-temporal emission variation, it was demonstrated that aquatic organisms are able to produce a variety of bioactive compounds. This production happens in response to abiotic and biotic stresses, evidencing the fundamental role of these metabolites, both in terms of composition and amount, in providing important ecological information and possible non-invasive tools to monitor different biological systems. The study of these compounds is an important and productive task with possible and interesting impacts in future practical applications in different fields. This review aims to summarize the knowledge on the aquatic VOCs, the recent advances in understanding their diverse roles and ecological impacts, the generally used methodology for their sampling and analysis, and their enormous potential as non-invasive, non-destructive and financeable affordable real-time biomonitoring tool, both in natural habitats and in controlled industrial situations. Finally, the possible future technical applications, highlighting their economic and social potential, such as the possibility to use VOCs as valuable alternative source of chemicals and as biocontrol and bioregulation agents, are emphasized.

Periphytic biofilms-mediated microbial interactions and their impact on the nitrogen cycle in rice paddies

Rice paddies are unique waterlogged wetlands artificially constructed for agricultural production. Periphytic biofilms (PBs) at the soil-water interface play an important role in rice paddies characterized by high nutrient input but low utilization efficiency. PBs are composed of microbial aggregates, including a wide variety of microorganisms (algae, bacteria, fungi, protozoa, and metazoa), extracellular polymeric substances and minerals (iron, aluminum, and calcium), which form an integrated food web and energy flux within a relatively stable micro-ecosystem. PBs are crucial to regulate and streamline the nitrogen cycle by neutralizing nitrogen losses and improving rice production since PBs can serve as both a sink by capturing surplus nitrogen and a source by slowly re-releasing this nitrogen for reutilization. Here the ecological advantages of PBs in regulating the nitrogen cycle in rice paddies are illustrated. We summarize the key functional importance of PBs, including the intricate and delicate community structure, microbial interactions among individual phylotypes, a wide diversity of self-produced organics, the active adaptation of PBs to constantly changing environments, and the intricate mechanisms by which PBs regulate the nitrogen cycle. We also identify the future challenges of microbial interspecific cooperation in PBs and their quantitative contributions to agricultural sustainability, optimizing nitrogen utilization and crop yields in rice paddies.

Profiling of grazed cultures of the chlorophyte alga Dunaliella tertiolecta using an untargeted LC-MS approach

Extracellular signals are reported to mediate chemical cross-talk among pelagic microbes, including microalgal prey and predators. Water-soluble mediator compounds play a crucial role in extracellular communication which is vital for prey recognition, attraction, capture, and predator deterrence. A range of exo-metabolites including oxylipins and vitamins are released by prey in response to grazing stress. The temporal dynamics of such exo-metabolites largely remains unknown, especially in large-scale cultivation of microalgae such as closed or open ponds. In open ponds, infestation of predators is almost inevitable but highly undesirable due to the imminent threat of culture collapse. The early production of exo-metabolites emitted by microalgal prey in response to predator attack could be leveraged as diagnostic markers of possible culture collapse. This study uses an untargeted approach for temporal profiling of Dunaliella tertiolecta-specific exo-metabolites under grazing pressure from Oxyrrhis marina. We report 24 putatively identified metabolites, belonging to various classes such as short peptides, lipids, indole-derivatives, and free amino acids, as potential markers of grazing-mediated stress. In addition, this study outlines a clear methodology for screening of exo-metabolites in marine algal samples, the analysis of which is frequently hindered by high salt concentrations. In future, a chemistry-based targeted detection of these metabolites could enable a quick and on-site screening of predators in microalgal cultures.

Cumulative Effects of Physical, Chemical, and Biological Measures on Algae Growth Inhibition

Measures based on concurrent alterations of an environment’s physical, chemical, and biological factors are commonly adopted to control harmful algal blooms (HABs). It was postulated that the combinations and interactions of multiple measures could exert cumulative effects (as the overall effect may or may not be equal to the additive sum for each measure individually). However, few studies have further assessed whether the cumulative effect is synergistic, additive, or antagonistic. This study proposed a framework to distinguish and quantify the cumulative effects. We also designed an experiment to investigate the cumulative effect of the combined utilization of physical (flow velocity), chemical (copper), and biological (propionamide) measures on algae growth inhibition. The results show that the cumulative effect of physical and chemical measures on algae growth inhibition was antagonistic; the cumulative effect of physical and biological measures was antagonistic; the cumulative effect of chemical and biological measures was synergistic, and the cumulative effect of all the measures together tended to be antagonistic. These results showed that the synergistic interactions between chemical and biological measures produced antagonistic effects when physical measures were added. Through response surface methodology analysis, we also found that the physical factor was the most significant factor affecting the cumulative effect, followed by the chemical factor and then the biological factor. Our results provide a more detailed understanding of the interaction patterns among multiple measures that affect algal growth. Importantly, this understanding can be further integrated into future strategy development to fully exploit the potential of the cumulative effect at its maximum performance.

Microalgae show a range of responses to exometabolites of foreign species

Studies on microalgae interspecific interactions have so far focused either on nutrient competition or allelopathic effects due to excreted substances from Harmful Algal Bloom (HAB) species. Evidence from plants, bacteria and specific microalgae groups, point to a range of responses mediated by sensing or direct chemical impact of exometabolites from foreign species. Such processes remain under-investigated, especially in non-HAB microalgae, despite the importance of such knowledge in ecology and industrial applications. Here, we study the directional effect of exometabolites of 4 "foreign" species Heterosigma akashiwo, Phaeocystis sp., Tetraselmis sp. and Thalassiosira sp. to each of three "target" species across a total of 12 treatments. We disentangle these effects from nutrient competition by adding cell free medium of each "foreign" species into our treatment cultures. We measured the biomass response, to the foreign exometabolites, as cell number and photosynthetic biomass (Chla), whereas nutrient use was measured as residual phosphorus (PO4) and intracellular phosphorus (P). Exometabolites from filtrate of foreign species were putatively annotated by untargeted metabolomics analysis and were discussed in association to observed responses of target species. Among others, these metabolites included L-histidinal, Tiliacorine and dimethylsulfoniopropionate (DMSP). Our findings show that species show a range of responses with the most common being biomass suppression, and less frequent biomass enhancement and intracellular P storage. Filtrate from the green microalgae Tetraselmis caused the most pronounced negative effects suggesting that non-HAB species can also cause negative chemical interference. A candidate metabolite inducing this response is L-histidinal which was measured in high abundance uniquely in Tetraselmis and its L-histidine form derived from bacteria was previously confirmed as a microalgal algicidal. H. akashiwo also induced biomass suppression on other microalgae and a candidate metabolite for this response is Tiliacorine, a plant-derived alkaloid with confirmed cytotoxic activity.

Treating agricultural non-point source pollutants using periphyton biofilms and biomass volarization

Untreated domestic wastewater and agricultural runoff are emerging as a potent cause of non-point source (NPS) pollutants which are a major threat to aquatic ecosystems. Periphyton biofilm-based technologies due to their high growth rate, energy efficiency and low input costs offer promising solutions for controlling nutrient pollution in agricultural systems. In this study we employed periphyton floway to treat NPS pollution from the agricultural watershed. The process performance of outdoor single pass algae floway (AFW) was evaluated. Steady state average biomass concentration of 11.73 g m^-2 d^-1 and removal rate of nitrogen: 0.60 g m^-2 d^-1, phosphorus: 0.27 g m^-2d^-1, arsenic: 9.26 mg m^-2 d^-1, chromium: 255.3 mg m^-2 d^-1 and lead: 238.6 mg m^-2 d^-1 was achieved. In addition, the microalgae and their associated bacterial diversity and dynamics were analyzed. The results revealed a high diversity and rapid variations in the microbiome structure with diatom and cyanobacteria dominance combined with high N fixing and P solubilizing bacteria during most of the operational period. Elemental analysis of periphyton biomass was done for its safe use as slow-release fertilizer. Biofuel feedstock potential and nanoparticle generation potential of the biomass were analyzed. This work highlights the potential use of periphyton biofilms in remediation and recycling of NPS pollutants with simultaneous resource recovery.

Pathogens and predators impacting commercial production of microalgae and cyanobacteria

Production of phytoplankton (microalgae and cyanobacteria) in commercial raceway ponds and other systems is adversely impacted by phytoplankton pathogens, including bacteria, fungi and viruses. In addition, cultures are susceptible to productivity loss, or crash, through grazing by contaminating zooplankton such as protozoa, rotifers and copepods. Productivity loss and product contamination are also caused by otherwise innocuous invading phytoplankton that consume resources in competition with the species being cultured. This review is focused on phytoplankton competitors, pathogens and grazers of significance in commercial culture of microalgae and cyanobacteria. Detection and identification of these biological contaminants are discussed. Operational protocols for minimizing contamination, and methods of managing it, are discussed.

Using different cultivation strategies and methods for the production of microalgal biomass as a raw material for the generation of bioproducts

Microalgal biomass and its fine chemical production from microalgae have pioneered algal bioprocess technology with few limitations such as lab-to-industry. However, laboratory-scale transitions and industrial applications are hindered by a plethora of limitations comprising expensive in culturing methods. Therefore, to emphasize the profitable benefits, the algal culturing techniques appropriately employed for large-scale microalgal biomass yield necessitates intricate assessment to emphasize the profitable benefits. The present review holistically compiles the culturing strategies for improving microalgal biomass production based on appropriate factors like designing better bioreactor designs. On the other hand, synthetic biology approaches for abridging the effective industrial transition success explored recently. Prospects in synthetic biology for enhanced microalgal biomass production based on cultivation strategies and various mechanistic modes approach to enrich cost-effective and viable output are discussed. The State-of-the-art culturing techniques encompassing enhancement of photosynthetic activity, designing bioreactor design, and potential augmenting protocols for biomass yield employing indoor cultivation in both (Open and or/closed) methods are enumerated. Further, limitations hindering the microalgal bioproducts development are critically evaluated for improving culturing techniques for microalgal cell factories, subsequently escalating the cost-benefit ratio in bioproducts synthesis from microalgae. The comprehensive analysis could provide a rational and deeper detailed insight for microalgal entrepreneurs through alternative culturing technology viz., synthetic biology and genome engineering in an Industrial perspective arena.

Potential to resist biological contamination in marine microalgae culture: Effect of extracellular substances of Nannochloropsis oceanica on population growth of Euplotes vannus and other protozoa

The commercially important marine microalgae Nannochloropsis oceanica is easily ingested by protozoan predators during large-scale cultivation. However, investigations into the effect of microalgae on the growth of protozoa are scant. A feeding experiment was conducted with Euplotes vannus grazing on different concentrations of N. oceanica. The ciliate population was significantly lower in the high concentration of algae than that in the low or medium algal concentration treatments. The density of ciliates cultured in algae filtrate media was significantly lower than that in lysate media and the blank control. Furthermore, the algal cell filtrate was added to three other protozoan populations, and they all gradually lost their ability to move and their body shape changed. This study investigated the interactions between N. oceanica and protozoan predators and provides insight on using microalgal extracellular substances to control biological contamination in the future.

Microalgae as Sustainable Biofactories to Produce High-Value Lipids: Biodiversity, Exploitation, and Biotechnological Applications

Microalgae are often called “sustainable biofactories” due to their dual potential to mitigate atmospheric carbon dioxide and produce a great diversity of high-value compounds. Nevertheless, the successful exploitation of microalgae as biofactories for industrial scale is dependent on choosing the right microalga and optimum growth conditions. Due to the rich biodiversity of microalgae, a screening pipeline should be developed to perform microalgal strain selection exploring their growth, robustness, and metabolite production. Current prospects in microalgal biotechnology are turning their focus to high-value lipids for pharmaceutic, nutraceutic, and cosmetic products. Within microalgal lipid fraction, polyunsaturated fatty acids and carotenoids are broadly recognized for their vital functions in human organisms. Microalgal-derived phytosterols are still an underexploited lipid resource despite presenting promising biological activities, including neuroprotective, anti-inflammatory, anti-cancer, neuromodulatory, immunomodulatory, and apoptosis inductive effects. To modulate microalgal biochemical composition, according to the intended field of application, it is important to know the contribution of each cultivation factor, or their combined effects, for the wanted product accumulation. Microalgae have a vital role to play in future low-carbon economy. Since microalgal biodiesel is still costly, it is desirable to explore the potential of oleaginous species for its high-value lipids which present great global market prospects.

Optimization of a novel lipid extraction process from microalgae

Previous study found that the solvent extraction efficiency of lipid in microalgae could be greatly improved by washing algae cells before the second time extraction. Based on the "organic solvents-water-organic solvents" method, this research further studied the effect of four solvent systems (acetone, chloroform/methanol, chloroform/methanol/water, dichloromethane/methanol), two types of water treatment (vortex and ultrasonic), three water treatment time gradient (0 s, 30 s, 120 s) on the lipid extraction at three different microalgae growth stages (3rd day, 5th day, 9th day). The results show that the combination of water treatment type, treatment time and solvent is very important to the efficiency of lipid extraction. The total lipid extracted was generally increased by 10-30% after water treatment. Especially under the condition of 120 s vortex water treatment with dichloromethane/methanol as extraction solvent, the total lipid extracted increased by 61.14%. In addition, microalgae cells at different culture stages had different sensitivity to water treatment. In this study, under the combination of chloroform/methanol/water as extraction solvent and vortex water treatment for 120 s, the highest lipid yield was obtained on the ninth day of cell culture, which accounts 47.88% of the cell dry weight (478 mg/g cell dry weight). The changes of cell morphology and structure after water treatment were studied by scanning electron microscope, and it was found that water treatment could seriously destroy the cell membrane damaged by solvent, thus promoting the release of lipids. This study further optimizes the "solvent-water-solvent" lipid extraction method, which neither produces impurities nor damages the lipid quality, and can reduce the amount of organic solvent applied in the classical lipid extraction method with the same lipid yield, so it has a broad application prospect.

Microalgae-based technology for antibiotics removal: From mechanisms to application of innovational hybrid systems

Antibiotics contamination is an emerging environmental concern, owing to its potential risks to ecosystems and human health. Microalgae-based technology has been widely reported as a promising alternative to conventional wastewater treatment, since it is a solar-power driven, ecologically friendly, cost-effective, and sustainable reclamation strategy. This review provides fundamental insights into the major mechanisms underpinning microalgae-based antibiotics removal, including bioadsorption, bioaccumulation, and biodegradation. The critical role of extracellular polymeric substances on bioadsorption and extracellular biodegradation of antibiotics are also covered. Moreover, this review sheds light on the important factors affecting the removal of antibiotics by microalgae, and summarizes several novel approaches to improve the removal efficiency, including acclimation, co-metabolism and microbial consortium. Besides, hybrid systems (such as, microalgae-based technologies combined with the conventional activated sludge, advanced oxidation processes, constructed wetlands, and microbial fuel cells), and genetic engineering are also recommended, which will be feasible for enhanced removal of antibiotics. Finally, this review also highlights the need for further studies aimed at optimizing microalgae-based technology, with emphasis on improving performance and expanding its application in large-scale settings, especially in terms of technical, environmental-friendly and economically competitiveness. Overall, this review summarizes current understanding on microalgae-based technologies for removal of antibiotics and outlines future research directions.

Microalgal Co-Cultivation Prospecting to Modulate Vitamin and Bioactive Compounds Production

Microalgal biotechnology is gaining importance. However, key issues in the pipeline from species selection towards large biomass production still require improvements to maximize the yield and lower the microalgal production costs. This study explores a co-cultivation strategy to improve the bioactive compounds richness of the harvested microalgal biomass. Based on their biotechnological potential, two diatoms (Skeletonema marinoi, Cyclotella cryptica) and one eustigmatophyte (Nannochloropsis oceanica) were grown alone or in combination. Concentrations of ten vitamins (A, B₁, B₂, B₆, B₁₂, C, D₂, D₃, E and H), carotenoids and polyphenols, together with total flavonoids, sterols, lipids, proteins and carbohydrates, were compared. Moreover, antioxidant capacity and chemopreventive potential in terms inhibiting four human tumor-derived and normal cell lines proliferation were evaluated. Co-cultivation can engender biomass with emergent properties regarding bioactivity or bioactive chemical profile, depending on the combined species. The high vitamin content of C. cryptica or N. oceanica further enhanced (until 10% more) when co-cultivated, explaining the two-fold increase of the antioxidant capacity of the combined C. cryptica and N. oceanica biomass. Differently, the chemopreventive activity was valuably enhanced when coupling the two diatoms C. cryptica and S. marinoi. The results obtained in this pilot study promote microalgal co-cultivation as a valuable strategy aiming to boost their application in eco-sustainable biotechnology.

Glucosidase Inhibitors Screening in Microalgae and Cyanobacteria Isolated from the Amazon and Proteomic Analysis of Inhibitor Producing Synechococcus sp. GFB01

Microalgae and cyanobacteria are good sources for prospecting metabolites of biotechnological interest, including glucosidase inhibitors. These inhibitors act on enzymes related to various biochemical processes; they are involved in metabolic diseases, such as diabetes and Gaucher disease, tumors and viral infections, thus, they are interesting hubs for the development of new drugs and therapies. In this work, the screening of 63 environmental samples collected in the Brazilian Amazon found activity against β-glucosidase, of at least 60 min, in 13.85% of the tested extracts, with Synechococcus sp. GFB01 showing inhibitory activity of 90.2% for α-glucosidase and 96.9% against β-glucosidase. It was found that the nutritional limitation due to a reduction in the concentration of sodium nitrate, despite not being sufficient to cause changes in cell growth and photosynthetic apparatus, resulted in reduced production of α and β-glucosidase inhibitors and differential protein expression. The proteomic analysis of cyanobacteria isolated from the Amazon is unprecedented, with this being the first work to evaluate the protein expression of Synechococcus sp. GFB01 subjected to nutritional stress. This evaluation helps to better understand the metabolic responses of this organism, especially related to the production of inhibitors, adding knowledge to the industrial potential of these cyanobacterial compounds.

The current state of knowledge on taxonomy, modulating factors, ecological roles, and mode of action of phytoplankton allelochemicals

Allelopathy is widespread in marine, brackish, and freshwater habitats. Literature data indicate that allelopathy could offer a competitive advantage for some phytoplankton species by reducing the growth of competitors. It is also believed that allelopathy may affect species succession. Thus, allelopathy may play a role in the development of blooms. Over the past few decades, the world's coastal waters have experienced increases in the numbers of cyanobacterial and microalgal blooming events. Understanding how allelopathy is implicated with other biological and environmental factors as a bloom-development mechanism is an important topic for future research. This review focuses on a taxonomic overview of allelopathic cyanobacteria and microalgae, the biological and environmental factors that affect allelochemical production, their role in ecological dynamics, and their physiological modes of action, as well as potential industrial applications of allelopathic compounds.

Current perspectives on integrated approaches to enhance lipid accumulation in microalgae

In recent years, research initiatives on renewable bioenergy or biofuels have been gaining momentum, not only due to fast depletion of finite reserves of fossil fuels but also because of the associated concerns for the environment and future energy security. In the last few decades, interest is growing concerning microalgae as the third-generation biofuel feedstock. The CO₂ fixation ability and conversion of it into value-added compounds, devoid of challenging food and feed crops, make these photosynthetic microorganisms an optimistic producer of biofuel from an environmental point of view. Microalgal-derived fuels are currently being considered as clean, renewable, and promising sustainable biofuel. Therefore, most research targets to obtain strains with the highest lipid productivity and a high growth rate at the lowest cultivation costs. Different methods and strategies to attain higher biomass and lipid accumulation in microalgae have been extensively reported in the previous research, but there are fewer inclusive reports that summarize the conventional methods with the modern techniques for lipid enhancement and biodiesel production from microalgae. Therefore, the current review focuses on the latest techniques and advances in different cultivation conditions, the effect of different abiotic and heavy metal stress, and the role of nanoparticles (NPs) in the stimulation of lipid accumulation in microalgae. Techniques such as genetic engineering, where particular genes associated with lipid metabolism, are modified to boost lipid synthesis within the microalgae, the contribution of "Omics" in metabolic pathway studies. Further, the contribution of CRISPR/Cas9 system technique to the production of microalgae biofuel is also briefly described.

Isolation of Industrial Important Bioactive Compounds from Microalgae

Microalgae are known as a rich source of bioactive compounds which exhibit different biological activities. Increased demand for sustainable biomass for production of important bioactive components with various potential especially therapeutic applications has resulted in noticeable interest in algae. Utilisation of microalgae in multiple scopes has been growing in various industries ranging from harnessing renewable energy to exploitation of high-value products. The focuses of this review are on production and the use of value-added components obtained from microalgae with current and potential application in the pharmaceutical, nutraceutical, cosmeceutical, energy and agri-food industries, as well as for bioremediation. Moreover, this work discusses the advantage, potential new beneficial strains, applications, limitations, research gaps and future prospect of microalgae in industry.

Removal of pharmaceutical and personal care products (PPCPs) from wastewater using microalgae: A review

Pharmaceuticals and personal care products (PPCPs) are a group of emerging micro-pollutants causing detrimental effects on living organisms even at low doses. Previous investigations have confirmed the presence of PPCPs in the environment at hazardous levels, mainly due to the inefficiency of conventional wastewater treatment plants (CWWTPs). Their stable structure induces longer persistence in the environment. Microalgae are currently used to bioremediate numerous pollutants of different characteristics and properties released from the domestic, industrial, agricultural, and farm sectors. CO₂ mitigation during culture and the use of biomass as feedstock for biodiesel or biofuel production are, briefly, other benefits of microalgae-mediated treatment over CWWTPs. This review provides a comprehensive summary of recent literature, an overview of approaches and treatment systems, and breakthrough in the field of algal-mediated removal of PPCPs in wastewater treatment processes. The mechanisms involved in phycoremediation, along with their experimental approaches, have been discussed in detail. Factors influencing the removal of PPCPs from aqueous media are comprehensively described and assessed. A comparative study on microalgal strains is analyzed for a more efficient implementation of future processes. The role of microalgae to mitigate the most severe environmental impacts of PPCPs and the generation of antibiotic-resistant bacteria is discussed. Also, a detailed assessment of recent research on potential toxic effects of PPCPs on microalgae was conducted. The current review highlights microalgae as a promising and sustainable approach to efficiently bio-transform or bio-adsorb PPCPs.

Extracellular and intracellular phenol production by microalgae during photoautotrophic batch cultivation

Understanding the mechanisms of phenol production by microalgae can contribute to the development of microalgal biorefinery processes with higher economic and environmental sustainability. However, little is known about how phenols are produced and accumulate during microalgal cultivation. In this study, both extracellular and intracellular phenol production by two microalgal strains (Tetradesmus obliquus and Chlorella sp.) were investigated throughout a conventional photoautotrophic batch cultivation. The highest intracellular phenol content (10-25 mg g^-1) and productivity (12-18 mg L^-1 d^-1) were attained for both strains in the first part of the batch, indicating a positive relation with nutrient availability and biomass productivity. Extracellular phenol production was 2-20 fold lower than intracellular phenols, but reached up to 27 mg L^-1 for T. obliquus and 13 mg L^-1 for Chlorella sp. The latter finding highlights relevant issues about the management of the exhausted culture medium, due to likely antimicrobial effects.

Removal of pollutants from biogas slurry and CO2 capture in biogas by microalgae-based technology: a systematic review

Recent research interest has focused on microalgae cultivation for biogas slurry purification and biogas upgrading due to the requirement of high efficiency for nutrient uptake and CO₂ capture, with economic feasibility and environmental benefits. Numerous studies have suggested that biogas slurry purification and biogas upgrading can occur simultaneously via microalgae-based technology. However, there is no comprehensive review on this technology with respect to the nutrient removal from biogas slurry and biogas upgrading. This article summarizes microalgal cultivation with biogas slurry and biogas from anaerobic digestion. The parameters, techniques, and modes of microalgae cultivation have been discussed in detail to achieve high efficiency in biogas slurry purification and biogas upgrading. In addition, the evaluation of energy efficiency and safety has also been explored. Compared with mono-cultivation of microalgae and co-cultivation of microalgae and bacteria, microalgae-fungi symbiosis has demonstrated greater development prospect and higher energy efficiency and the energy consumption for pollutants and CO₂ removal were 14.2-39.0% · USD^-1 and 19.9-23.3% · USD^-1, respectively. Further, a sustainable recycling scheme is proposed for the purification of biogas slurry from anaerobic digestion process and biogas upgrading via microalgae-based technology.

Bioactive molecules from protists: Perspectives in biotechnology

For hundreds of years, mankind has benefited from the natural metabolic processes of microorganisms to obtain basic products such as fermented foods and alcoholic beverages. More recently, microorganisms have been exploited for the production of antibiotics, vitamins and enzymes to be used in medicine and chemical industries. Additionally, several modern drugs, including those for cancer therapy, are natural products or their derivatives. Protists are a still underexplored source of natural products potentially of interest for biotechnological and biomedical applications. This paper focuses on some examples of bioactive molecules from protists and associated bacteria and their possible use in biotechnology.

Application of computational fluid dynamics (CFD) on the raceway design for the cultivation of microalgae: a review

Microalgae are a potential solution to supersede fossil fuels and produce renewable energy. The major obstacle to the commercialization of microalgae-based biofuels is the high production cost, including nutritional requirements, photobioreactor design, and downstream processes. As for the photobioreactor design, open ponds have been adopted by major commercial plants for their economic advantages. Raceway is a popular type among open ponds. Nevertheless, the fluid dynamics of the raceway operation is quite complex. Software simulation based on Computational Fluid Dynamics is an upcoming strategy for optimizing raceway design. The optimization intends to affect light penetration, particle distribution, mass transfer, and biological kinetics. This review discusses how this strategy can be helpful to design a highly productive raceway pond-based microalgal culture system.

High density long-term cultivation of Chlorella vulgaris SAG 211-12 in a novel microgravity-capable membrane raceway photobioreactor for future bioregenerative life support in SPACE

Hybrid life support systems are of great interest for future far-distant space exploration missions to planetary surfaces, e.g. Mars, planned until 2050. By synergistically combining physicochemical and biotechnological algae-based subsystems, an essential step towards the closure of the carbon loop in environmental control and life support systems (ECLSS) shall be accomplished, offering a wide beneficial potential for ECLSS through the utilization of oxygenic photosynthesis: O₂ and potential human food can be formed in-situ from CO₂ and water. The wild type green alga Chlorella vulgaris strain SAG 211-12 was selected as model microorganism due to its photoautotrophic growth, high biomass yield, cultivation flexibility and long-term cultivation robustness. The current study presents for the first time a stable xenic long-term processing of microalgae in a novel microgravity capable membrane raceway photobioreactor for 188 days with the focus on algal growth kinetics and gas evolution. In particular, culture homogeneity and viability were monitored and evaluated during the whole cultivation process due to their putative crucial impact on long-term functionality and efficiency of a closed cultivation system. Based on a specially designed cyclic batch cultivation process for SAG 211-12, a successive biomass growth up to a maximum of 12.2 g l^-1 with a max. global volumetric productivity of 1.3 g l^-1 d^-1 was reached within the closed loop system. The photosynthetic capacity was assessed to a global molar photosynthetic quotient of 0.31. Furthermore, cultivation parameters for a change from batch to continuous processing at high biomass densities and proliferation rates are introduced. The presented µgPBR miniature plant and the developed high throughput cultivation process are planned to be tested under real space conditions within the PBR@LSR project (microgravity and cosmic radiation) aboard the International Space Station with an operation period of up to 180 days to investigate the impact on long-term system stability.

Biostimulant Effect and Biochemical Response in Lettuce Seedlings Treated with A Scenedesmus quadricauda Extract

The use of natural biostimulants is becoming an attractive option in order to reduce the use of fertilizer and increase the yield of crops. In particular, algal extracts are suitable candidates as they positively affect plant physiology. Among crops, lettuce often requires the use of biostimulants to improve both the quality and quantity of production. The aim of this work is to investigate the potential use of a Scenedesmus quadricauda extract as a biostimulant in order to obtain sustainable cultivation and a reduction in the cost of chemical fertilizers in lettuce cultivation. Therefore, the effect of S. quadricauda extract on lettuce seedlings was explored by evaluating the physiological parameters, chlorophyll, carotenoid, and total protein contents as well as several plant enzymatic activities involved in primary and secondary metabolisms. The experiment was performed by growing plants on inert substrate (pumice) with a 16-h photoperiod, by carrying out two consecutive radical treatments, one week apart, using a concentration of the extract corresponding to 1 mg Corg L⁻¹. Lettuce plants were sampled at 1, 4, and 7 days from the first treatment and 7 days from the second treatment. The results showed that the S. quadricauda extract positively affected the growth of lettuce seedlings, mainly acting at the shoot level, determining an increase in dry matter, chlorophylls, carotenoids, proteins, and influencing the activities of several enzymes involved in the primary metabolism.

Metabolic engineering of phosphite metabolism in Synechococcus elongatus PCC 7942 as an effective measure to control biological contaminants in outdoor raceway ponds

BACKGROUND

The use of cyanobacteria and microalgae as cell factories to produce biofuels and added-value bioproducts has received great attention during the last two decades. Important investments have been made by public and private sectors to develop this field. However, it has been a challenge to develop a viable and cost-effective platform for cultivation of cyanobacteria and microalgae under outdoor conditions. Dealing with contamination caused by bacteria, weedy algae/cyanobacteria and other organisms is a major constraint to establish effective cultivation processes.

RESULTS

Here, we describe the implementation in the cyanobacterium Synechococcus elongatus PCC 7942 of a phosphorus selective nutrition system to control biological contamination during cultivation. The system is based on metabolic engineering of S. elongatus to metabolize phosphite, a phosphorus source not normally metabolized by most organisms, by expressing a bacterial phosphite oxidoreductase (PtxD). Engineered S. elongatus strains expressing PtxD grow at a similar rate on media supplemented with phosphite as the non-transformed control supplemented with phosphate. We show that when grown in media containing phosphite as the sole phosphorus source in glass flasks, the engineered strain was able to grow and outcompete biological contaminants even when the system was intentionally inoculated with natural competitors isolated from an irrigation canal. The PtxD/phosphite system was successfully used for outdoor cultivation of engineered S. elongatus in 100-L cylindrical reactors and 1000-L raceway ponds, under non-axenic conditions and without the need of sterilizing containers and media. Finally, we also show that the PtxD/phosphite system can be used as selectable marker for S. elongatus PCC 7942 transgenic strains selection, eliminating the need of antibiotic resistance genes.

CONCLUSIONS

Our results suggest that the PtxD/phosphite system is a stable and sufficiently robust strategy to control biological contaminants without the need of sterilization or other complex aseptic procedures. Our data show that the PtxD/phosphite system can be used as selectable marker and allows production of the cyanobacterium S. elongatus PCC 7942 in non-axenic outdoor reactors at lower cost, which in principle should be applicable to other cyanobacteria and microalgae engineered to metabolize phosphite.

The phosphite oxidoreductase gene, ptxD as a bio-contained chloroplast marker and crop-protection tool for algal biotechnology using Chlamydomonas

Edible microalgae have potential as low-cost cell factories for the production and oral delivery of recombinant proteins such as vaccines, anti-bacterials and gut-active enzymes that are beneficial to farmed animals including livestock, poultry and fish. However, a major economic and technical problem associated with large-scale cultivation of microalgae, even in closed photobioreactors, is invasion by contaminating microorganisms. Avoiding this requires costly media sterilisation, aseptic techniques during set-up and implementation of 'crop-protection' strategies during cultivation. Here, we report a strain improvement approach in which the chloroplast of Chlamydomonas reinhardtii is engineered to allow oxidation of phosphite to its bio-available form: phosphate. We have designed a synthetic version of the bacterial gene (ptxD)-encoding phosphite oxidoreductase such that it is highly expressed in the chloroplast but has a Trp→Opal codon reassignment for bio-containment of the transgene. Under mixotrophic conditions, the growth rate of the engineered alga is unaffected when phosphate is replaced with phosphite in the medium. Furthermore, under non-sterile conditions, growth of contaminating microorganisms is severely impeded in phosphite medium. This, therefore, offers the possibility of producing algal biomass under non-sterile conditions. The ptxD gene can also serve as a dominant marker for genetic engineering of any C. reinhardtii strain, thereby avoiding the use of antibiotic resistance genes as markers and allowing the 'retro-fitting' of existing engineered strains. As a proof of concept, we demonstrate the application of our ptxD technology to a strain expressing a subunit vaccine targeting a major viral pathogen of farmed fish.

Current practices and challenges in using microalgae for treatment of nutrient rich wastewater from agro-based industries

Considerable research activities are underway involving microalgae species in order to treat industrial wastewater to address the waste-to-bioenergy economy. Several studies of wastewater treatment using microalgae have been primarily focused on removal of key nutrients such as nitrogen and phosphorus. Although the use of wastewater would provide nutrients and water for microalgae growth, the whole process is even more complex than the conventional microalgae cultivation on freshwater media. The former one adds several gridlocks to the system. These gridlocks are surplus organic and inorganic nutrients concentration, pH of wastewater, wastewater color, total dissolved solids (TDS), microbial contaminants, the scale of photobioreactor, batch versus continuous system, harvesting of microalgae biomass etc. The present review discusses, analyses, and summarizes key aspects involved in the treatment of wastewaters from distillery, food/snacks product processing, and dairy processing industry using microalgae along with sustainable production of its biomass. This review further evaluates the bottlenecks for individual steps involved in the process such as pretreatment of wastewater for contaminants removal, concentration tolerance/dilutions, harvesting of microalgae biomass, and outdoor scale-up. The review also describes various strategies to optimize algal biomass and lipid productivities for various wastewater and photobioreactor type. Moreover, the review emphasizes the potential of co-cultivation of microorganism such as yeast and bacteria along with microalgae in the treatment of industrial wastewater.

NMR Metabolomics as an Effective Tool To Unravel the Effect of Light Intensity and Temperature on the Composition of the Marine Microalgae Isochrysis galbana

NMR spectroscopy coupled with multivariate data analysis techniques was applied to obtain meaningful information about nontargeted metabolic changes on  Isochrysis galbana upon acclimation to different environmental conditions at indoor lab-scale. The effects of temperature (from 15 to 30 °C) and incident irradiance (from 250 to 1600 μmol m^-2 s^-1) at a constant dilution rate of 0.3 h^-1 were evaluated. High irradiances stimulated a decrease of chlorophyll a, fucoxanthin and amino acids content, and the conversion of polar fatty acids (PLs, GLs, DGDGs, SGDGs) to neutral fatty acids (saturated and unsaturated). High temperatures together with high irradiances decreased PUFAs concentration, including omega-3 fatty acids. Under low irradiance and temperature organic osmolytes (homarine, DMSP, GBT, and glycerol), and sugars (glucose, trehalose, and galactose) were also reduced.

Producing Oleaginous Microorganisms Using Wastewater: Methods and Guidelines for Lab- and Industrial-Scale Production

Cultivation of oleaginous microorganisms on wastewater provides alternative biofuel options while also acting as a remediation technique for alternative wastewater treatment. This chapter describes guidelines and methods for the production of oleaginous microorganisms-with a focus on microalgae-using wastewater as a growth medium while considering a variety of general challenges for both lab- and industrial-scale production. Cultivation techniques described here range in scale from microplates with 10-mL working volumes, up to multigallon, industrial-scale microorganism cultivation, with a focus on microalgae. This chapter includes guidelines for the preparation of wastewater and selection of oleaginous microorganisms combined with methods for the production of oleaginous microorganisms cultivated using wastewater.

The effect of the algal microbiome on industrial production of microalgae

Microbes are ubiquitously distributed, and they are also present in algae production systems. The algal microbiome is a pivotal part of the alga holobiont and has a key role in modulating algal populations in nature. However, there is a lack of knowledge on the role of bacteria in artificial systems ranging from laboratory flasks to industrial ponds. Coexisting microorganisms, and predominantly bacteria, are often regarded as contaminants in algal research, but recent studies manifested that many algal symbionts not only promote algal growth but also offer advantages in downstream processing. Because of the high expectations for microalgae in a bio‐based economy, better understanding of benefits and risks of algal–microbial associations is important for the algae industry. Reducing production cost may be through applying specific bacteria to enhance algae growth at large scale as well as through preventing the growth of a broad spectrum of algal pathogens. In this review, we highlight the latest studies of algae–microbial interactions and their underlying mechanisms, discuss advantages of large‐scale algal–bacterial cocultivation and extend such knowledge to a broad range of biotechnological applications.

Pelagibaca bermudensis promotes biofuel competence of Tetraselmis striata in a broad range of abiotic stressors: dynamics of quorum-sensing precursors and strategic improvement in lipid productivity

BACKGROUND

Amelioration of biofuel feedstock of microalgae using sustainable means through synthetic ecology is a promising strategy. The co-cultivation model (Tetraselmis striata and Pelagibaca bermudensis) was evaluated for the robust biofuel production under varying stressors as well as with the selected two-stage cultivation modes. In addition, the role of metabolic exudates including the quorum-sensing precursors was assessed.

RESULTS

The co-cultivation model innovated in this study supported the biomass production of T. striata in a saline/marine medium at a broad range of pH, salinity, and temperature/light conditions, as well as nutrient limitation with a growth promotion of 1.2-3.6-fold. Hence, this developed model could contribute to abiotic stress mitigation of T. striata. The quorum-sensing precursor dynamics of the growth promoting bacteria P. bermudensis exhibited unique pattern under varying stressors as revealed through targeted metabolomics (using liquid chromatography-mass spectrometry, LC-MS). P. bermudensis and its metabolic exudates mutually promoted the growth of T. striata, which elevated the lipid productivity. Interestingly, hydroxy alkyl quinolones independently showed growth inhibition of T. striata on elevated concentration. Among two-stage cultivation modes (low pH, elevated salinity, and nitrate limitation), specifically, nitrate limitation induced a 1.5 times higher lipid content (30-31%) than control in both axenic and co-cultivated conditions.

CONCLUSION

Pelagibaca bermudensis is established as a potential growth promoting native phycospheric bacteria for robust biomass generation of T. striata in varying environment, and two-stage cultivation using nitrate limitation strategically maximized the biofuel precursors for both axenic and co-cultivation conditions (T and T-PB, respectively). Optimum metabolic exudate of P. bermudensis which act as a growth substrate to T. striata surpasses the antagonistic effect of excessive hydroxy alkyl quinolones [HHQ, 4-hydroxy-2-alkylquinolines and PQS (pseudomonas quorum signal), 2-heptyl-3-hydroxy-4(1H)-quinolone].

Eicosapentaenoic acid production from Nannochloropsis oceanica CY2 using deep sea water in outdoor plastic-bag type photobioreactors

In this study, Nannochloropsis oceanica CY2 was grown in deep-sea water (DSW)-based medium in 5-L plastic bag-type photobioreactors (PBRs) for the autotrophic production of Eicosapentaenoic acid (EPA, 20:5n-3). EPA production of N. oceanica CY2 was stimulated when it was grown in 100% DSW amended with 1.5 g L^-1 NaNO₃, achieving a EPA content of 3.1% and a biomass concentration of 3.3 g L^-1. An outdoor-simulated microalgae cultivation system was also conducted to validate the feasibility of outdoor cultivation of the CY2 strain in plastic bag-type PBRs. Using an inoculum size of 0.6 g/L, the biomass concentration in the PBR culture was 3.5 g L^-1, while the EPA content and productivity reached a maximal level of 4.12% and 7.49 mg L^-1 d^-1, respectively. When the PBRs were operated on semi-batch mode, the EPA productivity could further increase to 9.9 mg L^-1 d^-1 with a stable EPA content of 4.1%.

Microbial consortia: a critical look at microalgae co-cultures for enhanced biomanufacturing

Monocultures have been the preferred production route in the bio-industry, where contamination has been a major bottleneck. In nature, microorganisms usually exist as part of organized communities and consortia, gaining benefits from co-habitation, keeping invaders at bay. There is increasing interest in the use of co-cultures to tackle contamination issues, and simultaneously increase productivity and product diversity. The feasibility of extending the natural phenomenon of co-habitation to the biomanufacturing industry in the form of co-cultures requires careful and systematic consideration of several aspects. This article will critically examine and review current work on microbial co-cultures, with the intent of examining the concept and proposing a design pipeline that can be developed in a biomanufacturing context.

Autoinhibitory sterol sulfates mediate programmed cell death in a bloom-forming marine diatom

Cell mortality is a key mechanism that shapes phytoplankton blooms and species dynamics in aquatic environments. Here we show that sterol sulfates (StS) are regulatory molecules of a cell death program in Skeletonema marinoi, a marine diatom-blooming species in temperate coastal waters. The molecules trigger an oxidative burst and production of nitric oxide in a dose-dependent manner. The intracellular level of StS increases with cell ageing and ultimately leads to a mechanism of apoptosis-like death. Disrupting StS biosynthesis by inhibition of the sulfonation step significantly delays the onset of this fatal process and maintains steady growth in algal cells for several days. The autoinhibitory activity of StS demonstrates the functional significance of small metabolites in diatoms. The StS pathway provides another view on cell regulation during bloom dynamics in marine habitats and opens new opportunities for the biochemical control of mass-cultivation of microalgae.

Phytoplankton blooms are shaped by a period of rapid growth followed by massive cell death. Here the authors show that sterol sulfates accumulate in aging cells of a bloom-forming marine diatom and trigger an oxidative burst that leads to a mechanism of apoptosis-like death.

Volatile Metabolites Emission by In Vivo Microalgae-An Overlooked Opportunity?

Fragrances and malodors are ubiquitous in the environment, arising from natural and artificial processes, by the generation of volatile organic compounds (VOCs). Although VOCs constitute only a fraction of the metabolites produced by an organism, the detection of VOCs has a broad range of civilian, industrial, military, medical, and national security applications. The VOC metabolic profile of an organism has been referred to as its 'volatilome' (or 'volatome') and the study of volatilome/volatome is characterized as 'volatilomics', a relatively new category in the 'omics' arena. There is considerable literature on VOCs extracted destructively from microalgae for applications such as food, natural products chemistry, and biofuels. VOC emissions from living (in vivo) microalgae too are being increasingly appreciated as potential real-time indicators of the organism's state of health (SoH) along with their contributions to the environment and ecology. This review summarizes VOC emissions from in vivo microalgae; tools and techniques for the collection, storage, transport, detection, and pattern analysis of VOC emissions; linking certain VOCs to biosynthetic/metabolic pathways; and the role of VOCs in microalgae growth, infochemical activities, predator-prey interactions, and general SoH.