Marine microalgae for production of biofuels and chemicals

Role of cultivation parameters in carbohydrate accretion for production of bioethanol and C-phycocyanin from a marine cyanobacterium Leptolyngbya valderiana BDU 41001: A sustainable approach

The investigation aimed to augment carbohydrate accumulation in the marine cyanobacterium Leptolyngbya valderiana BDU 41001 to facilitate bioethanol production. Under the standardised physiochemical condition (SPC), i.e. 90 µmol photon m-2 s-1 light intensity, initial culture pH 8.5, 35 °C temperature and mixing at 150 rpm increased the carbohydrate productivity ∼70 % than the control, while a 47 % rise in content was obtained under the nitrate (N)-starved condition. Therefore, a two-stage cultivation strategy was implemented, combining SPC at the 1st stage and N starvation at the 2nd stage, resulting in 80 % augmentation of carbohydrate yield, which enhanced the bioethanol yield by ∼86 % as compared to the control employing immobilised yeast fermentation. Moreover, biomass utilisation was maximised by extracting C-phycocyanin, where a ∼77 % rise in productivity was recorded under the SPC. This study highlights the potential of L. valderiana for pilot-scale biorefinery applications, advancing the understanding of sustainable biofuel production.

Microfluidics for macrofluidics: addressing marine-ecosystem challenges in an era of climate change

Climate change presents a mounting challenge with profound impacts on ocean and marine ecosystems, leading to significant environmental, health, and economic consequences. Microfluidic technologies, with their unique capabilities, play a crucial role in understanding and addressing the marine aspects of the climate crisis. These technologies leverage quantitative, precise, and miniaturized formats that enhance the capabilities of sensing, imaging, and molecular tools. Such advancements are critical for monitoring marine systems under the stress of climate change and elucidating their response mechanisms. This review explores microfluidic technologies employed both in laboratory settings for testing and in the field for monitoring purposes. We delve into the application of miniaturized tools in evaluating ocean-based solutions to climate change, thus offering fresh perspectives from the solution-oriented end of the spectrum. We further aim to synthesize recent developments in technology around critical questions concerning the ocean environment and marine ecosystems, while discussing the potential for future innovations in microfluidic technology. The purpose of this review is to enhance understanding of current capabilities and assist researchers interested in mitigating the effects of climate change to identify new avenues for tackling the pressing issues posed by climate change in marine ecosystems.

Towards cleaner environment: recycling microalgal co-product to reduce emissions and impacts while eliminating fishmeal in rainbow trout feed for sustainable aquaculture

The rapid increase in aquaculture over the last several decades has led to concerns about the environmental impact of fish feeds relying on marine resources for fishmeal (FM). We aim to assess Nannochloropsis sp. QH25 co-product as a viable and sustainable replacement for FM in juvenile rainbow trout, Oncorhynchus mykiss, feeds. We formulated four experimental diets: a reference (FM based), 33N, 66N, and 100N diet (33%, 66%, and 100% co-product replacement). Rainbow trout were randomly assigned to one of 16 tanks and randomly assigned an experimental diet to consume throughout the experiment (64 days total), with four replicate tanks per diet. We compared the phosphorus (P) and nitrogen (N) digestibility, emissions, and growth between diets and, compared six environmental impacts (biotic resource use (BRU), global warming potential (GWP), water use, land use, marine eutrophication potential (MEP), and freshwater eutrophication potential (FEP)) of each diet. Our results indicate that replacing FM with co-product did not significantly alter growth. P digestibility of the experimental and reference diets was comparable. BRU conversion ratio was significantly lower in the experimental diets. However, there were significantly higher water and land use conversion ratios but insignificantly higher results in GWP, MEP, and FEP between the reference and 100N diet.

Microalgae biofuels: illuminating the path to a sustainable future amidst challenges and opportunities

The development of microalgal biofuels is of significant importance in advancing the energy transition, alleviating food pressure, preserving the natural environment, and addressing climate change. Numerous countries and regions across the globe have conducted extensive research and strategic planning on microalgal bioenergy, investing significant funds and manpower into this field. However, the microalgae biofuel industry has faced a downturn due to the constraints of high costs. In the past decade, with the development of new strains, technologies, and equipment, the feasibility of large-scale production of microalgae biofuel should be re-evaluated. Here, we have gathered research results from the past decade regarding microalgae biofuel production, providing insights into the opportunities and challenges faced by this industry from the perspectives of microalgae selection, modification, and cultivation. In this review, we suggest that highly adaptable microalgae are the preferred choice for large-scale biofuel production, especially strains that can utilize high concentrations of inorganic carbon sources and possess stress resistance. The use of omics technologies and genetic editing has greatly enhanced lipid accumulation in microalgae. However, the associated risks have constrained the feasibility of large-scale outdoor cultivation. Therefore, the relatively controllable cultivation method of photobioreactors (PBRs) has made it the mainstream approach for microalgae biofuel production. Moreover, adjusting the performance and parameters of PBRs can also enhance lipid accumulation in microalgae. In the future, given the relentless escalation in demand for sustainable energy sources, microalgae biofuels should be deemed a pivotal constituent of national energy planning, particularly in the case of China. The advancement of synthetic biology helps reduce the risks associated with genetically modified (GM) microalgae and enhances the economic viability of their biofuel production.

Development of sustainable downstream processing for nutritional oil production

Nutritional oils (mainly omega-3 fatty acids) are receiving increased attention as critical supplementary compounds for the improvement and maintenance of human health and wellbeing. However, the predominant sources of these oils have historically shown numerous limitations relating to desirability and sustainability; hence the crucial focus is now on developing smarter, greener, and more environmentally favourable alternatives. This study was undertaken to consider and assess the numerous prevailing and emerging techniques implicated across the stages of fatty acid downstream processing. A structured and critical comparison of the major classes of disruption methodology (physical, chemical, thermal, and biological) is presented, with discussion and consideration of the viability of new extraction techniques. Owing to a greater desire for sustainable industrial practices, and a desperate need to make nutritional oils more available; great emphasis has been placed on the discovery and adoption of highly sought-after 'green' alternatives, which demonstrate improved efficiency and reduced toxicity compared to conventional practices. Based on these findings, this review also advocates new forays into application of novel nanomaterials in fatty acid separation to improve the sustainability of nutritional oil downstream processing. In summary, this review provides a detailed overview of the current and developing landscape of nutritional oil; and concludes that adoption and refinement of these sustainable alternatives could promptly allow for development of a more complete 'green' process for nutritional oil extraction; allowing us to better meet worldwide needs without costing the environment.

Different Responses of Photosynthesis to Nitrogen Starvation Between Highly Oil-Accumulative Diatoms, Fistulifera solaris and Mayamaea sp. JPCC CTDA0820

Highly oil-accumulative diatoms are expected to be a promising biomass for the production of biofuel. To harvest the diatom oils at high yields, it is critical to elucidate the relationship of oil accumulation with photosynthesis under fluctuating environmental conditions. Here, we characterized the physiological responses of the growth and photosynthesis in the mesophilic diatom Fistulifera solaris and the cold-tolerant one Mayamaea sp. JPCC CTDA0820 to nitrogen starvation, one of the most notable abiotic stresses, where most eukaryotic algae decrease their photosynthetic activity and accumulate oil in the cells. While F. solaris started showing growth retardation at NaNO₃ levels less than 50% of a normal F/2 artificial seawater (ASW) medium, Mayamaea sp. sustained normal growth even at a NaNO₃ level 10% of normal F/2ASW, indicating the sharp contrast of nitrogen requirement between these two diatom species. In the transition from 100 to 0% nitrogen conditions in the modified F/2ASW, F. solaris showed a clear suppression of chlorophyll (Chl)-based photosynthetic O₂ evolution rate and relative electron transport rate at photosystem II, which were negatively correlated to the capacity of non-photochemical quenching. Meanwhile, there was no change in these Chl-based parameters observed in nitrogen-starved Mayamaea sp. Instead, Mayamaea sp. showed a significant decrease in the Chl a amount per cells. These data suggested the occurrence of two types of photosynthetic responses to nitrogen starvation in oleaginous diatoms; that is, (1) suppression of photosynthetic activity per Chl with enhancing heat dissipation of excess light energy and (2) synchronous suppression of cellular photosynthetic activity with Chl amounts.

Bioprospecting for fungal enzymes for applications in microalgal biomass biorefineries

Microalgal biomass is a promising feedstock for biofuels, feed/food, and biomaterials. However, while production and commercialization of single-product commodities are still not economically viable, obtaining multiple products in a biomass biorefinery faces several techno-economic challenges. The aim of this study was to identify a suitable source of hydrolytic enzymes for algal biomass saccharification. Screening of twenty-six fungal isolates for secreted enzymes activity on Chlamydomonas reinhardtii biomass resulted in the identification of Aspergillus niger IB-34 as a candidate strain. Solid-state fermentation on wheat bran produced the most active enzyme preparations. From sixty-five proteins identified by liquid chromatography coupled to mass spectrometry (LC-MS) (ProteomeXchange, identifier PXD034998) from A. niger IB-34, the majority corresponded to predicted secreted proteins belonging to the Gene Ontology categories of catalytic activity/hydrolase activity on glycosyl and O-glycosyl compounds. Skimmed biomass of biotechnologically relevant strains towards the production of commodities, Chlorella sorokiniana and Scenedesmus obliquus, was fully saccharified after a mild pretreatment at 80 °C for 10 min, at a high biomass load of 10% (w/v). The soluble liquid stream, after skimming and saccharification of biomass of both strains, was further converted into ethanol by fermentation with Saccharomyces cerevisiae at a theoretical maximum efficiency, in a separated saccharification and fermentation assays. The resulting insoluble protein, after biomass skimming with an organic solvent and enzymatic saccharification, was highly digestible in an in vitro digestion assay. Proof of concept is presented for an enzyme-assisted biomass biorefinery recovering 81% of the main biomass fractions in a likely suitable form for the conversion of lipids and carbohydrates into biofuels and proteins into feed/food. KEY POINTS: • Twenty-six fungal extracts were analyzed for saccharification of microalgal biomass. • Skimmed biomass was fully enzymatically saccharified and fermented into ethanol. • Up to 81% recovery of biomass fractions suitable for biofuels and feed/food.

Food Waste Utilization for Reducing Carbon Footprints towards Sustainable and Cleaner Environment: A Review

There is world-wide generation of food waste daily in significant amounts, leading to depletion of natural resources and deteriorating air quality. One-third of global food produced is wasted laterally with the food value chain. Carbon footprint is an efficient way of communicating the issues related to climate change and the necessity of changing behavior. Valorization or utilization of food wastes helps in resolving issues related to environment pollution. Reduction in the carbon footprint throughout the chain of food supply makes the whole process eco-friendly. Prevailing food waste disposal systems focus on their economic and environmental viability and are putting efforts into using food waste as a resource input to agriculture. Effective and advanced waste management systems are adopted to deal with massive waste production so as to fill the gap between the production and management of waste disposal. Food waste biorefineries are a sustainable, eco-friendly, and cost-effective approach for the production of platform chemicals, biofuels, and other bio-based materials. These materials not only provide sustainable resources for producing various chemicals and materials but have the potential to reduce this huge environmental burden significantly. In this regard, technological advancement has occurred in past few years that has proven suitable for tackling this problem.

CO2 Levels Modulate Carbon Utilization, Energy Levels and Inositol Polyphosphate Profile in Chlorella

Microalgae have a growing recognition of generating biomass and capturing carbon in the form of CO₂. The genus Chlorella has especially attracted scientists' attention due to its versatility in algal mass cultivation systems and its potential in mitigating CO₂. However, some aspects of how these green microorganisms respond to increasing concentrations of CO₂ remain unclear. In this work, we analyzed Chlorella sorokiniana and Chlorella vulgaris cells under low and high CO₂ levels. We monitored different processes related to carbon flux from photosynthetic capacity to carbon sinks. Our data indicate that high concentration of CO₂ favors growth and photosynthetic capacity of the two Chlorella strains. Different metabolites related to the tricarboxylic acid cycle and ATP levels also increased under high CO₂ concentrations in Chlorella sorokiniana, reaching up to two-fold compared to low CO₂ conditions. The signaling molecules, inositol polyphosphates, that regulate photosynthetic capacity in green microalgae were also affected by the CO₂ levels, showing a deep profile modification of the inositol polyphosphates that over-accumulated by up to 50% in high CO₂ versus low CO₂ conditions. InsP₄ and InsP₆ increased 3- and 0.8-fold, respectively, in Chlorella sorokiniana after being subjected to 5% CO₂ condition. These data indicate that the availability of CO₂ could control carbon flux from photosynthesis to carbon storage and impact cell signaling integration and energy levels in these green cells. The presented results support the importance of further investigating the connections between carbon assimilation and cell signaling by polyphosphate inositols in microalgae to optimize their biotechnological applications.

Chromosome-Scale Genome Assembly of the Marine Oleaginous Diatom Fistulifera solaris

Microalgae including diatoms are of interest for environmentally friendly manufacturing such as production of biofuels, chemicals, and materials. The highly oil-accumulating marine diatom Fistulifera solaris has been studied as a promising host organism to be employed for these applications. Recently reported large-scale genetic engineering based on episomal vectors for diatoms could be useful to further enhance the potential of F. solaris, whereas we need to understand more the mode-of-action of diatom centromeres to rationally design the episomal vectors for stable extrachromosomal maintenance. Our previous genome analysis with pyrosequencing (short read sequencing) had generated the fragmented scaffolds which were not useful to predict centromeres on each chromosome. Here, we report the almost complete chromosomal structure of the genome of F. solaris using a long-read nanopore sequencing platform MinION. From just one single run using a MinION flow-cell, the chromosome-scale assembly with telomere-to-telomere resolution was achieved for 41 out of 44 chromosomes. Putative centromere regions were predicted from the 16 chromosomes, and we discovered putative consensus motifs in the predicted centromeres. Similar motif search had been performed in model diatoms, but no consensus motif was found. Therefore, this is the first study to successfully estimate consensus motifs in diatom centromeres. The chromosome-scale assembly also suggests the potential existence of multi-copy mini-chromosomes and tandemly repeated lipogenesis genes related to the oleaginous phenotype of F. solaris. Findings of this study are useful to understand and further engineer the oleaginous phenotype of F. solaris.

Bioactive Compounds for Quorum Sensing Signal-Response Systems in Marine Phycosphere

Quorum sensing in the phycosphere refers to a sensor system in which bacteria secrete bioactive compounds to coordinate group behavior relying on cell density. It is an important way for algae and bacteria to communicate with each other and achieve interactions. It has been determined that quorum sensing is widely presented in the marine phycosphere, which involves a variety of bioactive compounds. Focused on these compounds in marine phycosphere, this review summarizes the types and structures of the compounds, describes the methods in detection and functional evaluation, discusses the ecological functions regulated by the compounds, such as modulating microbial colonization, achieving algae–bacteria mutualism or competition and contributing to marine biogeochemical cycles. Meanwhile, the application prospects of the compounds are also proposed, including controlling harmful algal blooms and producing biofuel. Future research should focus on improving detection techniques, developing more model systems and investigating the effects of climate change on the quorum-sensing pathway to further understand the mechanism and application potential of quorum sensing compounds. This review aims to present an overview of current research carried out in order to provide the reader with perspective on bioactive compounds involved in quorum sensing.

Marine microbial bioprospecting: Exploitation of marine biodiversity towards biotechnological applications-a review

The increase in the human population causes an increase in the demand for nutritional supplies and energy resources. Thus, the novel, natural, and renewable resources became of great interest. Here comes the optimistic role of bioprospecting as a promising tool to isolate novel and interesting molecules and microorganisms from the marine environment as alternatives to the existing resources. Bioprospecting of marine metabolites and microorganisms with high biotechnological potentials has gained wide interest due to the variability and richness of the marine environment. Indeed, the existence of extreme conditions that increases the adaptability of marine organisms, especially planktons, allow the presence of interesting biological species that are able to produce novel compounds with multiple health benefits and high economical value. This review aims to provide a comprehensive overview of marine microbial bioprospecting as a growing field of interest. It emphasizes functional bioprospecting that facilitates the discovery of interesting metabolites. Marine bioprospecting was also discussed from a legal aspect for the first time, focusing on the shortcomings of international law. We also summarized the challenges facing bioprospecting in the marine environment including economic feasibility issues.

Integrated marine microalgae biorefineries for improved bioactive compounds: A review

Marine microalgae offer a promising feedstock for biofuels and other valuable compounds for biorefining and carry immense potential to contribute to a clean energy and environment future. However, it is currently not economically feasible to use marine algae to produce biofuels, and the potential bioactive chemicals account for only a small market share. The production of algal biomass with multiple valuable chemicals is closely related to the algal species, cultivation conditions, culture systems, and production modes. Thus, higher requirements for screening of dominant algal strains, developing integrated technologies with the optimum culture conditions, efficient cultivation systems, and production modes to exploit algal biomass for biorefinery applications, are all needed. This review summarizes the screening of dominant microalgae, discusses the environmental conditions that may affect the growth, as well as the culture systems and production modes, and further emphasizes the valorization options of the algal biomass, which should help to offer a sustainable approach to run a profitable marine algae production system.

Fourth generation biofuel from genetically modified algal biomass: Challenges and future directions

Genetic engineering applications in the field of biofuel are rapidly expanding due to their potential to boost biomass productivity while lowering its cost and enhancing its quality. Recently, fourth-generation biofuel (FGB), which is biofuel obtained from genetically modified (GM) algae biomass, has gained considerable attention from academic and industrial communities. However, replacing fossil resources with FGB is still beset with many challenges. Most notably, technical aspects of genetic modification operations need to be more fully articulated and elaborated. However, relatively little attention has been paid to GM algal biomass. There is a limited number of reviews on the progress and challenges faced in the algal genetics of FGB. Therefore, the present review aims to fill this gap in the literature by recapitulating the findings of recent studies and achievements on safe and efficient genetic manipulation in the production of FGB. Then, the essential issues and parameters related to genome editing in algal strains are highlighted. Finally, the main challenges to FGB pertaining to the diffusion risk and regulatory frameworks are addressed. This review concluded that the technical and biosafety aspects of FGB, as well as the complexity and diversity of the related regulations, legitimacy concerns, and health and environmental risks, are among the most important challenges that require a strong commitment at the national/international levels to reach a global consensus.

Role of Biofuels in Energy Transition, Green Economy and Carbon Neutrality

Modern civilization is heavily reliant on petroleum-based fuels to meet the energy demand of the transportation sector. However, burning fossil fuels in engines emits greenhouse gas emissions that harm the environment. Biofuels are commonly regarded as an alternative for sustainable transportation and economic development. Algal-based fuels, solar fuels, e-fuels, and CO2-to-fuels are marketed as next-generation sources that address the shortcomings of first-generation and second-generation biofuels. This article investigates the benefits, limitations, and trends in different generations of biofuels through a review of the literature. The study also addresses the newer generation of biofuels highlighting the social, economic, and environmental aspects, providing the reader with information on long-term sustainability. The use of nanoparticles in the commercialization of biofuel is also highlighted. Finally, the paper discusses the recent advancements that potentially enable a sustainable energy transition, green economy, and carbon neutrality in the biofuel sector.

Algal biomass production by phosphorus recovery and recycling from wastewater using amorphous calcium silicate hydrates

The phosphorous supply crisis is a major challenge for a sustainable society, and the algal industry is not unrelated to this crisis. Recycling phosphorus from sewage wastewater is a potential way to address this issue. We previously developed amorphous calcium silicate hydrates (aCSH) as excellent phosphorus recovery materials. In this study, we designed a phosphorus recovery process using aCSH in a pilot-scale facility connected to a sewage wastewater treatment plant, and demonstrated the production of microalgal biomass using phosphorous-containing aCSH (P_aCSH). As a result, high phosphorous recovery rates (>80%) were obtained throughout the year. The carbohydrate-rich microalga Pseudoneochloris sp. NKY372003 was cultivable with P_aCSH. The biomass and carbohydrate productivity of this microalga with P_aCSH was comparable to that with conventional media. Approximately 94% of the phosphorus in P_aCSH was recycled into the biomass. This study successfully demonstrated the recycling the phosphorus recovered from wastewater for microalgal cultivation by aCSH.

Marine bioactives: from energy to nutrition

Microalgae have been evaluated as promising resource for biodiesel production, but algal biofuel production is not yet commercially viable, which reflects the high energy costs linked with cultivation, harvesting, and dewatering of algae. As crude oil processing declines, microalgae biorefineries are being considered for producing bioactives such as enzymes, proteins, omega-3 oils, pigments, recombinant products, and vitamins, to offset the costs of biofuel production. We believe that producing algal bioactives through advanced manufacturing pathways, encompassing a biorefinery approach, would be effective, profitable, and economical.

Blue Economy and Blue Activities: Opportunities, Challenges, and Recommendations for The Bahamas

Following the global shutdown of tourism at the onset of the COVID-19 pandemic, small island developing states such as The Bahamas had their economies immobilized due to their heavy dependence on the industry. Beyond economic recovery in a post COVID-19 paradigm, the blue economy, blue growth, and associated activities offer pathways for a more resilient economy and is well-suited for The Bahamas. This paper suggests conduits for economic development using a traditional strength, coastal and marine tourism, in conjunction with the emerging fields of ocean renewable energy, offshore aquaculture, marine biotechnology, and bioprospecting. The interlinkages between each activity are discussed. Knowledge gaps in offshore aquaculture, ocean renewable energy, marine biotechnology, and marine environment monitoring are identified. In each sector case, strategic and tactical decision-making can be achieved through the exploitation of ocean numerical modeling and observations, and consequently should be invested in and developed alongside the requisite computational resources. Blue growth is encouraged, but instances of blue injustice are also highlighted. Crucially, pursuing blue economy activities should be given top national priority for economic recovery and prosperity.

Evaluation of co-culturing a diatom and a coccolithophore using different silicate concentrations

Globally, the demand for sustainable energy production and high-value biological compounds have become intertwined in an attempt to improve the feasibility of sustainable algal cultivation. Marine microalgae, especially diatoms and coccolithophores, represent viable cultures that can produce biofuels and high-value compounds. Growing them in co-culture offers the potential to produce lipids and pigments, while also generating CaCO₃ for C sequestration. The main objective of this work was to investigate competition or co-existence of the diatom Chaetoceros gracilis and the coccolithophore Pleurochrysis Carterae. The focus was on the effects of silicate and co-culturing on the growth rate, productivity, pigment production, and ash production for C. gracilis and P. carterae in laboratory conditions. The results showed that, in monoculture, 2-mM Si enhanced the specific growth rate of C. gracilis, but did not affect P. carterae. Regardless of silicate concentration, C. gracilis was more productive than P. carterae. In co-culture, P. carterae had a slower growth rate, indicating an inhibitory effect of C. gracilis on P. carterae. Neither silicate concentration nor co-culturing had an impact on the contents of pigments fucoxanthin, chlorophyll-a, and chlorophyll-c, which means that pigment productivity was proportional to biomass productivity. Finally, the ash content increased in all cultures with the lower silicate concentration (0.2 mM) in the medium. With one exception, the ash content was dominated by SiO₂ regardless of silicate amount, and CaCO₃ was a major part of the ash only when P. carterae was grown separately with the higher silicate level. These results highlight that co-culturing did not provide an advantage for improving biomass, pigments, or CaCO₃ productivity.

Marine Microalgae Contribution to Sustainable Development

The burning of fossil fuels is an unsustainable activity, which is leading to an increase in greenhouse gases (GHGs) emissions and related global warming. Among sustainable energy sources, microalgae represent a promising alternative to fossil fuel and contribute to the achievement of important Sustainable Development Goals (SDGs). In particular, the potential contribution of marine microalgae to sustainable development is large as, among other benefits, they represent a carbon negative energy source and may be applied in many coastal areas around the world. Despite this, significant economic and technological improvements are needed in order to make microalgae biofuels viable on a large scale. This review aims to explore how and to what extent third-generation biofuels (marine microalgae, but also the latest advances in freshwater microalgae) can benefit the realization of these SDGs. From this study we concluded that the production of large-scale marine microalgae biofuels is not yet feasible from the economic perspective at a large scale. However, the cultivation of microalgae in seawater holds great potential for increasing the small to medium viability of this biofuel source. The possibilities for improvement along with the contributions to sustainable development lay the groundwork for continuing to study and apply the potential of sustainable production of microalgae bioenergy.

Engineered chlorophyll catabolism conferring predator resistance for microalgal biomass production

Production of valuable compounds including biofuels and pharmaceutical precursors derived from microalgae has garnered significant interest. Stable production of algal biomass is essential to make the microalgal industry commercially feasible. However, one of the largest issues is severe biological contamination by predators grazing the algal biomass, resulting in the crash of outdoor cultures. In the present study, we propose a novel engineering strategy for microalgae to cope with predators. The overexpression of plant chlorophyllase (CLH) in a microalga resulted in the enhancement of resistance to the predator. This result supported our hypothesis that CLH promotes chlorophyll breakdown in the chloroplasts of the microalgae when they are digested by the predator, generating the phototoxic catabolite chlorophyllide that damages the predator. To the best of our knowledge, this is the first study to establish predator-resistant microalgae by enhancing the CLH activity.

Structural insight into a GH1 β-glucosidase from the oleaginous microalga, Nannochloropsis oceanica

Marine microalgae are promising sources of novel glycoside hydrolases (GHs), which have great value in biotechnical and industrial applications. Although many GH1 family β-glucosidases have been extensively studied, studies on β-glucosidases from microalgae are rare, and no structure of algal GH1 β-glucosidase has been reported. Here, we report the biochemical and structural study of a GH1 β-glucosidase BGLN1 from Nannochloropsis oceanica, an oleaginous microalga. Phylogenetic analysis of BGLN1, together with the known structures of GH1 β-glucosidases, has indicated that BGLN1 is branched at the root of the eukaryotic part of the phylogenetic tree. BGLN1 showed higher activity against laminaribiose compared to cello-oligosaccharides. Unlike most of the other GH1 β-glucosidases, BGLN1 is partially inhibited by metal ions. The crystal structure of BGLN1 revealed that BGLN1 adopts a typical (α/β)₈-barrel fold with variations in loops and N-terminal regions. BGLN1 contains extra residues at the N-terminus, which are essential for maintaining protein stability. BGLN1 has a more acidic substrate-binding pocket than other β-glucosidases, and the variations beyond the conserved -1 site determine the substrate specificity. These results indicate that GH enzymes from microalgae may have unique structural and functional features, which will provide new insight into carbohydrate synthesis and metabolism in marine microalgae.

Sustainable lipid and lutein production from Chlorella mixotrophic fermentation by food waste hydrolysate

Bioconversion of food waste into value-added products is a promising way to tackle the global food waste management problem. In this study, a novel valorisation strategy for bioenergy and lutein production via microalgal fermentation was investigated. Significant amount of glucose was recovered from enzymatic hydrolysis of food waste. The resultant hydrolysate was then utilised as culture medium in mixotrophic cultivation of Chlorella sp. to obtain high levels of lipid and lutein, whose accumulation patterns were consistent with molecular analyses. The resultant algal lipid derived from microalgal biomass using food hydrolysate was at high quality in terms of biodiesel properties. Further, in semi-continuous fermentation, the average algal biomass was 6.1 g L^-1 with 2.5 g L^-1 lipid and 38.5 mg L^-1 lutein using hydrolysate with an initial glucose concentration of 10 g L^-1. Meanwhile, the resultant algal biomass was 6.9 g L^-1 with 1.8 g L^-1 lipid and 63.0 mg L^-1 lutein using hydrolysate with an initial glucose concentration of 20 g L^-1, which suggests food waste hydrolysate could trigger algal products preferences. The experimental results of this study suggested the potential of microalgae as a platform for bioconversion of food waste into high-value products, especially sustainable bioenergy.

Human Health and Ocean Pollution

Background

Pollution - unwanted waste released to air, water, and land by human activity - is the largest environmental cause of disease in the world today. It is responsible for an estimated nine million premature deaths per year, enormous economic losses, erosion of human capital, and degradation of ecosystems. Ocean pollution is an important, but insufficiently recognized and inadequately controlled component of global pollution. It poses serious threats to human health and well-being. The nature and magnitude of these impacts are only beginning to be understood.

Goals

(1) Broadly examine the known and potential impacts of ocean pollution on human health. (2) Inform policy makers, government leaders, international organizations, civil society, and the global public of these threats. (3) Propose priorities for interventions to control and prevent pollution of the seas and safeguard human health.

Methods

Topic-focused reviews that examine the effects of ocean pollution on human health, identify gaps in knowledge, project future trends, and offer evidence-based guidance for effective intervention.

Environmental Findings

Pollution of the oceans is widespread, worsening, and in most countries poorly controlled. It is a complex mixture of toxic metals, plastics, manufactured chemicals, petroleum, urban and industrial wastes, pesticides, fertilizers, pharmaceutical chemicals, agricultural runoff, and sewage. More than 80% arises from land-based sources. It reaches the oceans through rivers, runoff, atmospheric deposition and direct discharges. It is often heaviest near the coasts and most highly concentrated along the coasts of low- and middle-income countries. Plastic is a rapidly increasing and highly visible component of ocean pollution, and an estimated 10 million metric tons of plastic waste enter the seas each year. Mercury is the metal pollutant of greatest concern in the oceans; it is released from two main sources - coal combustion and small-scale gold mining. Global spread of industrialized agriculture with increasing use of chemical fertilizer leads to extension of Harmful Algal Blooms (HABs) to previously unaffected regions. Chemical pollutants are ubiquitous and contaminate seas and marine organisms from the high Arctic to the abyssal depths.

Ecosystem Findings

Ocean pollution has multiple negative impacts on marine ecosystems, and these impacts are exacerbated by global climate change. Petroleum-based pollutants reduce photosynthesis in marine microorganisms that generate oxygen. Increasing absorption of carbon dioxide into the seas causes ocean acidification, which destroys coral reefs, impairs shellfish development, dissolves calcium-containing microorganisms at the base of the marine food web, and increases the toxicity of some pollutants. Plastic pollution threatens marine mammals, fish, and seabirds and accumulates in large mid-ocean gyres. It breaks down into microplastic and nanoplastic particles containing multiple manufactured chemicals that can enter the tissues of marine organisms, including species consumed by humans. Industrial releases, runoff, and sewage increase frequency and severity of HABs, bacterial pollution, and anti-microbial resistance. Pollution and sea surface warming are triggering poleward migration of dangerous pathogens such as the Vibrio species. Industrial discharges, pharmaceutical wastes, pesticides, and sewage contribute to global declines in fish stocks.

Human Health Findings

Methylmercury and PCBs are the ocean pollutants whose human health effects are best understood. Exposures of infants in utero to these pollutants through maternal consumption of contaminated seafood can damage developing brains, reduce IQ and increase children's risks for autism, ADHD and learning disorders. Adult exposures to methylmercury increase risks for cardiovascular disease and dementia. Manufactured chemicals - phthalates, bisphenol A, flame retardants, and perfluorinated chemicals, many of them released into the seas from plastic waste - can disrupt endocrine signaling, reduce male fertility, damage the nervous system, and increase risk of cancer. HABs produce potent toxins that accumulate in fish and shellfish. When ingested, these toxins can cause severe neurological impairment and rapid death. HAB toxins can also become airborne and cause respiratory disease. Pathogenic marine bacteria cause gastrointestinal diseases and deep wound infections. With climate change and increasing pollution, risk is high that Vibrio infections, including cholera, will increase in frequency and extend to new areas. All of the health impacts of ocean pollution fall disproportionately on vulnerable populations in the Global South - environmental injustice on a planetary scale.

Conclusions

Ocean pollution is a global problem. It arises from multiple sources and crosses national boundaries. It is the consequence of reckless, shortsighted, and unsustainable exploitation of the earth's resources. It endangers marine ecosystems. It impedes the production of atmospheric oxygen. Its threats to human health are great and growing, but still incompletely understood. Its economic costs are only beginning to be counted.Ocean pollution can be prevented. Like all forms of pollution, ocean pollution can be controlled by deploying data-driven strategies based on law, policy, technology, and enforcement that target priority pollution sources. Many countries have used these tools to control air and water pollution and are now applying them to ocean pollution. Successes achieved to date demonstrate that broader control is feasible. Heavily polluted harbors have been cleaned, estuaries rejuvenated, and coral reefs restored.Prevention of ocean pollution creates many benefits. It boosts economies, increases tourism, helps restore fisheries, and improves human health and well-being. It advances the Sustainable Development Goals (SDG). These benefits will last for centuries.

Recommendations

World leaders who recognize the gravity of ocean pollution, acknowledge its growing dangers, engage civil society and the global public, and take bold, evidence-based action to stop pollution at source will be critical to preventing ocean pollution and safeguarding human health.Prevention of pollution from land-based sources is key. Eliminating coal combustion and banning all uses of mercury will reduce mercury pollution. Bans on single-use plastic and better management of plastic waste reduce plastic pollution. Bans on persistent organic pollutants (POPs) have reduced pollution by PCBs and DDT. Control of industrial discharges, treatment of sewage, and reduced applications of fertilizers have mitigated coastal pollution and are reducing frequency of HABs. National, regional and international marine pollution control programs that are adequately funded and backed by strong enforcement have been shown to be effective. Robust monitoring is essential to track progress.Further interventions that hold great promise include wide-scale transition to renewable fuels; transition to a circular economy that creates little waste and focuses on equity rather than on endless growth; embracing the principles of green chemistry; and building scientific capacity in all countries.Designation of Marine Protected Areas (MPAs) will safeguard critical ecosystems, protect vulnerable fish stocks, and enhance human health and well-being. Creation of MPAs is an important manifestation of national and international commitment to protecting the health of the seas.

The effect of microplastics pollution in microalgal biomass production: A biochemical study

Microplastics (MPs) are widely spread throughout aquatic systems and water bodies. Given that water quality is one of the most important parameters in the microalgal-based industry, it is critical to assess the biochemical impact of short- and long-term exposure to MPs pollution. Here, the microalga Phaeodactylum tricornutum was exposed to water contaminated with 0.5 and 50 mg L^-1 of polystyrene (PS) and/or polymethyl methacrylate (PMMA). Results show that the microalgal cultures exposed to lower concentrations of PS displayed a growth enhancement of up to 73% in the first stage (days 3-9) of the exponential growth phase. Surprisingly, and despite the fact that long-term exposure to MPs contamination did not impair microalgal growth, a steep decrease in biomass production (of up to 82%) was observed. The production of photosynthetic pigments was shown to be pH-correlated during the full growth cycle, but cell density-independent in later stages of culturing. The extracellular carbohydrates production exhibited a major decrease during long-term exposure. Still, the production of extracellular proteins was not affected by the presence of MPs. This pilot laboratory-scale study shows that the microalgal exposure to water contaminated with MPs disturbs its biochemical equilibrium in a time-dependent manner, decreasing biomass production. Thus, microalgal industry-related consequences derived from the use of MPs-contaminated water are a plausible possibility.

Spirulina sp. LEB 18 cultivation in seawater and reduced nutrients: Bioprocess strategy for increasing carbohydrates in biomass

This study aimed to evaluate the growth and production of biomolecules by Spirulina sp. LEB 18 cultivated in seawater. The seawater was used without nutrient addition (SW0) and supplemented with 100% (SW100), 50% (SW50), and 25% (SW25) nitrogen, phosphorus, iron, and EDTA concentrations that make up the Zarrouk culture medium. When grown in SW0, Spirulina sp. LEB 18 showed maximum biomass concentration (2.17 g L^-1) on the 11th d of cultivation and an increase in the carbohydrate content and productivity by 203% and 52%, respectively, when compared to the control culture. This cultivation strategy demonstrated the feasibility of using seawater as an alternative to freshwater in cultures as well as reduced nutritional requirements for biomass and carbohydrate production.

Engineering of NADPH Supply Boosts Photosynthesis-Driven Biotransformations

Light-driven biocatalysis in recombinant cyanobacteria provides highly atom-efficient cofactor regeneration via photosynthesis, thereby remediating constraints associated with sacrificial cosubstrates. However, despite the remarkable specific activities of photobiocatalysts, self-shading at moderate-high cell densities limits efficient space-time-yields of heterologous enzymatic reactions. Moreover, efficient integration of an artificial electron sink into the tightly regulated network of cyanobacterial electron pathways can be highly challenging. Here, we used C=C bond reduction of 2-methylmaleimide by the NADPH-dependent ene-reductase YqjM as a model reaction for light-dependent biotransformations. Time-resolved NADPH fluorescence spectroscopy allowed direct monitoring of in-cell YqjM activity and revealed differences in NADPH steady-state levels and oxidation kinetics between different genetic constructs. This effect correlates with specific activities of whole-cells, which demonstrated conversions of >99%. Further channelling of electrons toward heterologous YqjM by inactivation of the flavodiiron proteins (Flv1/Flv3) led to a 2-fold improvement in specific activity at moderate cell densities, thereby elucidating the possibility of accelerating light-driven biotransformations by the removal of natural competing electron sinks. In the best case, an initial product formation rate of 18.3 mmol h^–1 L^–1 was reached, allowing the complete conversion of a 60 mM substrate solution within 4 h.

Seawater supplemented with bicarbonate for efficient marine microalgae production in floating photobioreactor on ocean: A case study of Chlorella sp

Cultivation of microalgae on ocean provides a promising way to produce massive biomass without utilizing limited land space, and using seawater as culture medium can avoid consumption of valuable fresh water. Bicarbonate is proved as a better approach for carbon supply in microalgae cultivation, but Ca²⁺ and Mg²⁺ in seawater is subjected to precipitate with carbonate derived from it. In this study, cultivation with this medium for a marine Chlorella sp. resulted in productivity of 0.470 g L^-1 day^-1, despite of continual precipitation caused by increased pH due to bicarbonate consumption. Actually, this precipitation is favorable, since it can work as a flocculation harvesting method for microalgae. The highest flocculation efficiency of 98.9 ± 0.0% was observed in cultures with 7.0 g L^-1 NaHCO₃, which was higher than that of cultures without bicarbonate (44.1 ± 0.2%). Additionally, the spent medium after flocculation supported better growth (1.60 ± 0.0 g L^-1) than the fresh medium (1.26 ± 0.0 g L^-1). Outdoor cultivation with floating photobioreactor on ocean resulted in the productivity of 0.190 g L^-1 day^-1, which was higher than that in land-based culture systems. The floating system also benefited from better temperature control with range from 20.6 to 37.2 °C, due to solar heating and surrounding water cooling. These results showed feasibility of efficient microalgae biomass production with fully utilizing of ocean resources, including culture medium preparation and temperature control with seawater, as well as wave energy for mixing, holding great potential to produce massive biomass to support sustainable development of human society.

Improvement of Bio-Oil and Nitrogen Recovery from Microalgae Using Two-Stage Hydrothermal Liquefaction with Solid Carbon and HCl Acid Catalysis

Bio-oil production from microalgae by using hydrothermal liquefaction (HTL) has been conducted extensively in the last decade. In this work, we conducted two-stage HTL of a microalga (Fistulifera solaris, JPCC DA0580) in the presence of 5.0 g/L carbon solid acid or a 0.02-0.50 M HCl catalyst to increase bio-oil yield and nitrogen recovery into the aqueous phase (AP). The first stage (HTL 1), to hydrolyze proteins, carbohydrates, and lipids and elute nitrogen components into the AP, was conducted at 100-250 °C for 30-120 min. The second stage (HTL 2), to produce the bio-oil, was conducted at 280-320 °C for 0-30 min. The best conditions to obtain a high bio-oil yield and NH₄ ⁺ recovery in the AP were 200 °C and 30 min of residence time for HTL 1 and 320 °C and 0 min residence time for HTL 2. We found that 0.50 M HCl decreased the bio-oil yield while greatly increasing NH₄ ⁺ in the AP and decreasing the nitrogen content in the bio-oil. This was probably due to the catalytic effect of HCl promoting hydrolysis of protein and deamination of amino acids during HTL 1. The fractions of water-soluble products were greatly increased by performing HTL 2 in neutral conditions while this maintained low nitrogen content in the bio-oil. From GC-MS analyses of the bio-oil, it was observed that, by using 0.50 M HCl, peak intensities of all the GC peaks decreased and MS spectra of amines decreased. The carbon solid acid had an insignificant influence on bio-oil and NH₄ ⁺ yields.

Light-Emitting Diode Power Conversion Capability and CO2 Fixation Rate of Microalgae Biofilm Cultured Under Different Light Spectra

Microalgae biofilm-based culture has attracted much interest due to its high harvest efficiency and low energy requirements. Using light-emitting diodes (LEDs) as light source for microalgae culture has been considered as a promising choice to enhance the economic feasibility of microalgae-based commodities. In this work, the LED power conversion capability and CO2 fixation rate of microalgae biofilms (Chlorella ellipsoidea and Chlorella pyrenoidosa) cultured under different light spectra (white, blue, green and red) were studied. The results indicated that the power-to-biomass conversion capabilities of these two microalgae biofilms cultured under blue and white LEDs were much higher than those under green and red LEDs (C. ellipsoidea: 32%–33% higher, C. pyrenoidosa: 34%–46% higher), and their power-to-lipid conversion capabilities cultured under blue LEDs were 61%–66% higher than those under green LEDs. The CO2 fixation rates of these two biofilms cultured under blue LEDs were 13% and 31% higher, respectively, than those under green LEDs. The results of this study have important implications for selecting the optimal energy-efficient LEDs using in microalgae biofilm-based culture systems.

Emerging Technologies in Algal Biotechnology: Toward the Establishment of a Sustainable, Algae-Based Bioeconomy

Mankind has recognized the value of land plants as renewable sources of food, medicine, and materials for millennia. Throughout human history, agricultural methods were continuously modified and improved to meet the changing needs of civilization. Today, our rapidly growing population requires further innovation to address the practical limitations and serious environmental concerns associated with current industrial and agricultural practices. Microalgae are a diverse group of unicellular photosynthetic organisms that are emerging as next-generation resources with the potential to address urgent industrial and agricultural demands. The extensive biological diversity of algae can be leveraged to produce a wealth of valuable bioproducts, either naturally or via genetic manipulation. Microalgae additionally possess a set of intrinsic advantages, such as low production costs, no requirement for arable land, and the capacity to grow rapidly in both large-scale outdoor systems and scalable, fully contained photobioreactors. Here, we review technical advancements, novel fields of application, and products in the field of algal biotechnology to illustrate how algae could present high-tech, low-cost, and environmentally friendly solutions to many current and future needs of our society. We discuss how emerging technologies such as synthetic biology, high-throughput phenomics, and the application of internet of things (IoT) automation to algal manufacturing technology can advance the understanding of algal biology and, ultimately, drive the establishment of an algal-based bioeconomy.

Biomass accumulation-influencing factors in microalgae farms

ABSTRACT Due to the emergence of large microalgae farms and increased competition in this sector, the search for higher productivity is common. One way to achieve this goal in microalgae production is to optimize the factors that influence their growth during the cultivation stage to increase the accumulation of bio-compounds of interest. In this stage, the factors that most influence are: nutrition, gas diffusion, light intensity and quality and, finally, stirring, which directly affects all other factors. Thus, a review and an evaluation of the influence and importance of stirring were performed in the present study. The nutrients that most influence biomass accumulation are carbon, nitrogen and phosphorus, but their proportion is directly related to the proposed objective for microalgae. In the diffusion of gases, it is essential to supply adequate CO2 for the growth of microalgae, and flue gases can be used. Also, it is necessary to ensure proper removal of photosynthetic O2, which could inhibit microalgae metabolism and slow their growth rate. It is important to provide the appropriate light intensity for photosynthesis, but excess may cause photoinhibition in cultivation. Stirring is of paramount importance to ensure nutrient distribution in the medium, gas diffusion (incorporation of CO2 and removal of O2) and adequate exposure of microalgae to light, reducing the effects of photoinhibition and self-shading.

Biotechnological Advances in the Design of Algae-Based Biosensors

In addition to their use in biomass production and bioremediation, algae have been extensively exploited in biosensing applications. Algae-based biosensors have demonstrated potential for sensitive, sustainable, and multiplexed detection of analytes of agroenvironmental and security interest. Their advantages include the availability of different algal bioreceptors including whole cells and their photosynthetic subcomponents, their potential to be integrated into dual transduction miniaturized devices, and the opportunity for continuous environmental monitoring. Despite obstacles including limited stability and selectivity, algae-based biosensing is a realistic prospect that has some recent effective applications. Strategic exploitation of cutting-edge technologies including materials science, nanotechnology, microfluidics, and genome editing will help to achieve the full potential of algae-based sensors.

Bioinformatics for Marine Products: An Overview of Resources, Bottlenecks, and Perspectives

The sea represents a major source of biodiversity. It exhibits many different ecosystems in a huge variety of environmental conditions where marine organisms have evolved with extensive diversification of structures and functions, making the marine environment a treasure trove of molecules with potential for biotechnological applications and innovation in many different areas. Rapid progress of the omics sciences has revealed novel opportunities to advance the knowledge of biological systems, paving the way for an unprecedented revolution in the field and expanding marine research from model organisms to an increasing number of marine species. Multi-level approaches based on molecular investigations at genomic, metagenomic, transcriptomic, metatranscriptomic, proteomic, and metabolomic levels are essential to discover marine resources and further explore key molecular processes involved in their production and action. As a consequence, omics approaches, accompanied by the associated bioinformatic resources and computational tools for molecular analyses and modeling, are boosting the rapid advancement of biotechnologies. In this review, we provide an overview of the most relevant bioinformatic resources and major approaches, highlighting perspectives and bottlenecks for an appropriate exploitation of these opportunities for biotechnology applications from marine resources.