Optimization of Heterotrophic Culture Conditions for the Microalgae Euglena gracilis to Produce Proteins

Cultivation of high-protein Euglena gracilis for enhanced protein production under inorganic nitrogen sources: mechanisms revealed by proteomics

Amid global food shortage, alternative cost-effective protein sources are urgently needed for aquaculture and animal feed. Without a rigid cell wall, Euglena gracilis provides extractable, digestible proteins, and its high productivity makes it an ideal feed source. This study investigates the effects of different inorganic nitrogen sources on the biomass and biochemical composition of E. gracilis, and discusses the mechanisms of its nutrient transformation via proteomics. Results show ammonium nitrogen optimizes growth and protein accumulation by serving as an energy-efficient precursor for biomolecule synthesis compared to nitrate. Additionally, sulfate supplies sulfur for amino acid synthesis, and ammonium sulfate further enhances protein production. Under high-protein conditions, lipids and pigments increase while paramylon decreases significantly, underscoring nitrogen's role in carbon allocation and energy metabolism. This study establishes a metabolic framework for nitrogen-sulfur coordinated regulation of protein synthesis in E. gracilis, paving the way for its industrial application as a next-generation protein resource.

Microalga Nannochloropsis gaditana as a Sustainable Source of Bioactive Peptides: A Proteomic and In Silico Approach

The impact of the world's growing population on food systems and the role of dietary patterns in the management of non-communicable diseases underscore the need to explore sustainable and dietary protein sources. Although microalgae have stood out as alternative sources of proteins and bioactive peptides, some species such as Nannochloropsis gaditana remain unexplored. This study aimed to characterize N. gaditana's proteome and evaluate its potential as a source of bioactive peptides by using an in silico approach. A total of 1955 proteins were identified and classified into functional groups of cellular components, molecular functions, and biological processes. In silico gastrointestinal digestion of identified proteins demonstrated that 202 hydrophobic and low-molecular-size peptides with potential bioactivity were released. Among them, 27 exhibited theorical antioxidant, antihypertensive, antidiabetic, anti-inflammatory, and/or antimicrobial activities. Seven of twenty-seven peptides showed ≥20% intestinal absorption, suggesting potential systemic effects, while the rest could act at local level. Molecular docking demonstrated strong affinities with key enzymes such as MPO, ACE, and DPPIV. Resistance to the digestion, capacity to be absorbed, and multifunctionality were demonstrated for peptide FIPGL. This study highlights N. gaditana's potential as a sustainable source of novel potential bioactive peptides with promising local and systemic biological effects.

Regulation Mechanism of Gibberellic Acid-3 for Astaxanthin Biosynthesis in Heterotrophic Growing Chromochloris zofingiensis

Chromochloris zofingiensis has been proven as a potential resource for large-scale astaxanthin production, but little information on phytohormones for its growth and astaxanthin accumulation could be obtained. This study explored the impact of gibberellic acid-3 (GA3) on growth and astaxanthin biosynthesis in heterotrophic C. zofingiensis. After 6 days of cultivation with GA3, biomass and astaxanthin yields in 7.5 L fermenters reached 268.5 g·L-1 and 0.34 g·L-1, respectively, which were 6% and 89% higher than those in the control. GA3 changed transcription levels of genes linked to carbon metabolism, lipid metabolism, astaxanthin production, and ABC transporters. Genes related to astaxanthin biosynthesis, such as phytoene synthase (PSY), phytoene desaturase (PDS), beta-carotenoid hydroxylase (CHYb), and beta-carotenoid ketolase (BKT), were up-regulated under GA3 induction. The enhancement of carbon metabolism and lipid metabolism led to elevated consumption of substrates and generation of reducing power, thus facilitating astaxanthin biosynthesis. By using GA3 and arginine together, the astaxanthin yield increased to 0.39 g·L-1, which was 18% higher than that obtained under GA3 induction. It could be concluded that GA3 showed significant effects on astaxanthin biosynthesis. This research proposed novel feasible approaches to enhance astaxanthin production in heterotrophic C. zofingiensis.

Effects of different trophic conditions on total fatty acids, amino acids, pigment and gene expression profiles in Euglena gracilis

Euglena gracilis is a unique microalga that lacks a cell wall and is able to grow under different trophic culture conditions. In this study, cell growth, biomass production, and changes in the ultrastructure of E. gracilis cells cultivated photoautotrophically, mixotrophically, and under sequential-heterotrophy-photoinduction (SHP) were assessed. Mixotrophy induced the highest cell growth and biomass productivity (6.27 ± 0.59 mg/L/d) in E. gracilis, while the highest content of fatty acids, 2.69 ± 0.04% of dry cell weight (DCW) and amino acids, 38.16 ± 0.08% of DCW was obtained under SHP condition. E. gracilis also accumulated significantly higher saturated fatty acids and lower unsaturated fatty acids when cultivated under SHP condition. Transcriptomic analysis showed that the expression of photosynthetic genes (PsbA, PsbC, F-type ATPase alpha and beta) was lower, carbohydrate and protein synthetic genes (glnA, alg14 and fba) were expressed higher in SHP-culture cells when compared to other groups. Different trophic conditions also induced changes in the cell ultrastructure, where paramylon and starch granules were more abundant in SHP-cultured cells. The findings generated in this study illustrated that aerobic SHP cultivation of E. gracilis possesses great potential in human and animal feed applications.

Microalgae as future food: Rich nutrients, safety, production costs and environmental effects

The improvement of food security and nutrition has attracted wide attention, and microalgae as the most promising food source are being further explored. This paper comprehensively introduces basic and functional nutrients rich in microalgae by elaborated tables incorporating a wide variety of studies and summarizes factors influencing their accumulation effects. Subsequently, multiple comparisons of nutrients were conducted, indicating that microalgae have a high protein content. Moreover, controllable production costs and environmental friendliness prompt microalgae into the list that contains more promising and reliable future food. However, microalgae and -based foods approved and sold are limited strictly, showing that safety is a key factor affecting dietary consideration. Notably, sensory profiles and ingredient clarity play an important role in improving the acceptance of microalgae-based foods. Finally, based on the bottleneck in the microalgae food industry, suggestions for its future development were discussed.

Metabolic responses of Euglena gracilis under photoheterotrophic and heterotrophic conditions

The protist Euglena gracilis has various trophic modes including heterotrophy and photoheterotrophy. To investigate how cultivation mode influences metabolic regulation, the chemical composition of cellular metabolites of Euglena gracilis grown under heterotrophic and photoheterotrophic conditions was monitored from the early exponential phase to the mid-stationary phase using two different techniques, i.e, nuclear magnetic resonance (NMR) spectroscopy and high-resolution mass spectrometry (HRMS). The combined metabolomics approach allowed an in-depth understanding of the mechanism of photoheterotrophic and heterotrophic growth for biomolecule production. Heterotrophic conditions promoted the production of polar amino and oxygenated compounds such as proteins and polyphenol compounds, especially at the end of the exponential phase while photoheterotrophic cells enhanced the production of organoheterocyclic compounds, carbohydrates, and alkaloids.

Microalgae Proteins as Sustainable Ingredients in Novel Foods: Recent Developments and Challenges

Microalgae are receiving increased attention in the food sector as a sustainable ingredient due to their high protein content and nutritional value. They contain up to 70% proteins with the presence of all 20 essential amino acids, thus fulfilling human dietary requirements. Microalgae are considered sustainable and environmentally friendly compared to traditional protein sources as they require less land and a reduced amount of water for cultivation. Although microalgae's potential in nutritional quality and functional properties is well documented, no reviews have considered an in-depth analysis of the pros and cons of their addition to foods. The present work discusses recent findings on microalgae with respect to their protein content and nutritional quality, placing a special focus on formulated food products containing microalgae proteins. Several challenges are encountered in the production, processing, and commercialization of foods containing microalgae proteins. Solutions presented in recent studies highlight the future research and directions necessary to provide solutions for consumer acceptability of microalgae proteins and derived products.