Boosting productivity of heterotrophic microalgae by efficient control of the oxygen transfer coefficient using a microbubble sparger

Turning waste into treasure: A new direction for low-cost production of lipid chemicals from Thraustochytrids

Thraustochytrids are marine microorganisms known for their fast growth and ability to store lipids, making them useful for producing polyunsaturated fatty acids (PUFAs), biodiesel, squalene, and carotenoids. However, the high cost of production, mainly due to expensive fermentation components, limits their wider use. A significant challenge in this context is the need to balance production costs with the value of the end products. This review focuses on integrating the efficient utilization of waste with Thraustochytrids fermentation, including the economic substitution of carbon sources, nitrogen sources, and fermentation water. This approach aligns with the 3Rs principles (reduction, recycling, and reuse). Furthermore, it emphasizes the role of Thraustochytrids in converting waste into lipid chemicals and promoting sustainable circular production models. The aim of this review is to emphasize the value of Thraustochytrids in converting waste into treasure, providing precise cost reduction strategies for future commercial production.

Enhanced fatty acid storage combined with the multi-factor optimization of fermentation for high-level production of docosahexaenoic acid in Schizochytrium sp

Schizochytrium sp. hasreceived much attention for itsability to synthesize and accumulate high-level docosahexaenoic acid (DHA), which can reach nearly 40 % of total fatty acids. In this study, the titer of DHA in Schizochytrium sp. was successfully improved by enhancing DHA storage through overexpressing the diacylglycerol acyltransferase (ScDGAT2C) gene, as well as optimizing the supply of precursors and cofactors required for DHA synthesis by response surface methodology. Notably, malic acid, citric acid, and biotin showed synergistic and time-dependent effects on DHA accumulation. The maximum lipid and DHA titers of the engineered Schizochytrium sp. strain reached 84.28 ± 1.02 g/L and 42.23 ± 0.69 g/L, respectively, with the optimal concentration combination (1.62 g/L malic acid + 0.37 g/L citric acid + 8.28 mg/L biotin) were added 48 h after inoculation. This study provides an effective strategy for improving lipid and DHA production in Schizochytrium sp.

Microbubbles in Food Technology

Microbubbles are largely unused in the food industry yet have promising capabilities as environmentally friendly cleaning and supporting agents within products and production lines due to their unique physical behaviors. Their small diameters increase their dispersion throughout liquid materials, promote reactivity because of their high specific surface area, enhance dissolution of gases into the surrounding liquid phase, and promote the generation of reactive chemical species. This article reviews techniques to generate microbubbles, their modes of action to enhance cleaning and disinfection, their contributions to functional and mechanical properties of food materials, and their use in supporting the growth of living organisms in hydroponics or bioreactors. The utility and diverse applications of microbubbles, combined with their low intrinsic ingredient cost, strongly encourage their increased adoption within the food industry in coming years.

Recent advances on microalgae cultivation for simultaneous biomass production and removal of wastewater pollutants to achieve circular economy

Microalgae are known for containing high value compounds and its significant role in sequestering carbon dioxide. This review mainly focuses on the emerging microalgae cultivation technologies such as nanomaterials technology that can improve light distribution during microalgae cultivation, attached cultivation and co-cultivation approaches that can improve growth and proliferation of algal cells, biomass yield and lipid accumulation in microalgal. This review includes a comprehensive discussion on the use of microbubbles technology to enhance aerated bubble capacity in photobioreactor to improve microalgal growth. This is followed by discussion on the role of microalgae as phycoremediation agent in removal of contaminants from wastewater, leading to better water quality and high productivity of shellfish. The review also includes techno-economic assessment of microalgae biorefinery technology, which is useful for scaling up the microalgal biofuel production system or integrated microalgae-shellfish cultivation system to support circular economy.

Comparative transcriptomic and lipidomic analyses indicate that cold stress enhanced the production of the long C18–C22 polyunsaturated fatty acids in Aurantiochytrium sp

Aurantiochytrium sp. belonging to Thraustochytrids are known for their capacity to produce long-chain polyunsaturated fatty acids (PUFAs). However, effects of cold stress accompanied with staged-temperature control on the fatty acid metabolism in Aurantiochytrium sp. were rarely studied. In this study, cold stress (15°C, 5°C) was applied for Aurantiochytrium sp., with the physiological responses (morphology, growth, fatty acid profiling) and gene expression related FA synthesis, lipid metabolism, and regulatory processes was observed. Results showed that there is a significant change for the lipid types under 5°C (251 species) and 15°C (97 species) treatment. The 5°C treatment was benefit for the C18–C22 PUFAs with the yield of docosahexaenoic acid (DHA) increased to 1.25 times. After incubation at 15°C, the accumulation of eicosadienoic acid (EA) (20:2) was increased to 2.00-fold. Based on transcriptomic and qPCR analysis, an increase in genes involved in fatty acid synthase (FAS) and polyketide synthase (PKS) pathways was observed under low-temperature treatment. With upregulation of 3-ketoacyl-CoA synthase (2.44-fold), ketoreductase (2.50-fold), and dTDP-glucose 4,6-Dehydratase (rfbB) (2.31-fold) involved in PKS pathway, the accumulation of DHA was enhanced under 5°C. While, FAS and fatty elongase 3 (ELO) involved in the FAS pathway were upregulated (1.55-fold and 2.45-fold, respectively) to accumulate PUFAs at 15°C. Additionally, glycerol-3-phosphate acyltransferase (GPAT), lysophospholipid acyltransferase (LPAT), phosphatidic acid phosphatase (PAP), phosphatidylserine synthase (PSS), and phosphatidylserine decarboxylase (PSD) involved in glycerophospholipid biosynthesis were upregulated at 5°C increasing the accumulation of phosphatidic acid (PA), phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), and phosphatidylinositol (PI). However, glycolysis and the TCA cycle were inhibited under 5°C. This study provides a contribution to the application of two-staged temperature control in the Aurantiochytrium sp. fermentation for producing cold stress-enhancing PUFAs, in order to better understand the function of the key genes for future genetic engineering.

A Two-Stage Adaptive Laboratory Evolution Strategy to Enhance Docosahexaenoic Acid Synthesis in Oleaginous Thraustochytrid

Thraustochytrid is a promising algal oil resource with the potential to meet the demand for docosahexaenoic acid (DHA). However, oils with high DHA content produced by genetic modified thraustochytrids are not accepted by the food and pharmaceutical industries in many countries. Therefore, in order to obtain non-transgenic strains with high DHA content, a two-stage adaptive laboratory evolution (ALE) strategy was applied to the thraustochytrid Aurantiochytrium sp. Heavy-ion irradiation technique was first used before the ALE to increase the genetic diversity of strains, and then two-step ALE: low temperature based ALE and ACCase inhibitor quizalofop-p-ethyl based ALE were employed in enhancing the DHA production. Using this strategy, the end-point strain E-81 with a DHA content 51% higher than that of the parental strain was obtained. The performance of E-81 strain was further analyzed by component analysis and quantitative real-time PCR. The results showed that the enhanced in lipid content was due to the up-regulated expression of key enzymes in lipid accumulation, while the increase in DHA content was due to the increased transcriptional levels of polyunsaturated fatty acid synthase. This study demonstrated a non-genetic approach to enhance lipid and DHA content in non-model industrial oleaginous strains.

Production of polyunsaturated fatty acids by Schizochytrium (Aurantiochytrium) spp

Diverse health benefits are associated with dietary consumption of omega-3 long-chain polyunsaturated fatty acids (ω-3 LC-PUFA), particularly docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Traditionally, these fatty acids have been obtained from fish oil, but limited supply, variably quality, and an inability to sustainably increase production for a rapidly growing market, are driving the quest for alternative sources. DHA derived from certain marine protists (heterotrophic thraustochytrids) already has an established history of commercial production for high-value dietary use, but is too expensive for use in aquaculture feeds, a much larger potential market for ω-3 LC-PUFA. Sustainable expansion of aquaculture is prevented by its current dependence on wild-caught fish oil as the source of ω-3 LC-PUFA nutrients required in the diet of aquacultured animals. Although several thraustochytrids have been shown to produce DHA and EPA, there is a particular interest in Schizochytrium spp. (now Aurantiochytrium spp.), as some of the better producers. The need for larger scale production has resulted in development of many strategies for improving productivity and production economics of ω-3 PUFA in Schizochytrium spp. Developments in fermentation technology and metabolic engineering for enhancing LC-PUFA production in Schizochytrium spp. are reviewed.

Effective bioconversion of 1,3-propanediol from biodiesel-derived crude glycerol using organic acid resistance-enhanced Lactobacillus reuteri JH83

Organic acids produced during the fermentation of lactic acid bacteria inhibit cellular growth and the production of 1,3-propanediol (1,3-PDO). Lactobacillus reuteri JH83, which has an increase of 18.6% in organic acid resistance, was obtained through electron beam irradiation mutagenesis irrelevant to the problem of genetically modified organisms. The maximum bioconversion of 1,3-PDO in fed-batch fermentation using pure glycerol by L. reuteri JH83 was 93.2 g/L at 72 h, and the productivity was 1.29 g/L·h, which achieved an increase by 34.6%, compared to that of the wild-type strain. In addition, the result of fed-batch fermentation for the production of 1,3-PDO using crude glycerol was not significantly different from that of pure glycerol. Additionally, transcriptome analysis confirmed changes in the expression levels of sucrose phosphorylase, which is a major facilitator superfamily transporter, and muramyl ligase family proteins, which protect lactic acid bacteria from various stressors, such as organic acids.

Effectiveness of various bioreactors for thraustochytrid culture and production (Aurantiochytruim limacinum BUCHAXM 122)

This study aimed to develop bioreactors for cultivation of thraustochytrid, Aurantiochytrium limacinum BUCHAXM 122, that are low in cost and simple to operate. Obtaining maximum biomass and fatty acid production was a prerequisite. Three bioreactor designs were used: stirred tank bioreactor (STB), bubble bioreactor (BB) and internal loop airlift bioreactor (ILAB). The bioreactors were evaluated for their influence on oxygen mass transfer coefficient (k_La), using various spargers, mixing speed, and aeration rates. Biomass and DHA production from STB, BB, ILAB were then compared with an incubator shaker, using batch culture experiments. Results showed that a bundle of eight super-fine pore air stones was the best type of aeration sparger for all three bioreactors. Optimal culture conditions in STB were 600 rpm agitation speed and 2 vvm aeration rate, while 2 vvm and 1.5 vvm aeration provided highest biomass productivity in BB and ILAB, respectively. Antifoam agent was needed for all reactor types in order to reduce excessive foaming. Results indicated that with optimized conditions, these bioreactors are capable of thraustochytrid cultivation with a similar efficiency as cultivation using a rotary shaker. STB had the highest k_La and provided the highest biomass of 43.05 ± 0.35 g/L at 48 h. BB was simple in design, had low operating costs and was easy to build, but yielded the lowest biomass (27.50 ± 1.56 g/L). ILAB, on the other hand, had lower k_La than STB, but provided highest fatty acid productivity, of 35.36 ± 2.51% TFA.

Implementation of kLa-Based Strategy for Scaling Up Porphyridium purpureum (Red Marine Microalga) to Produce High-Value Phycoerythrin, Fatty Acids, and Proteins

Porphyridium purpureum is a well-known Rhodophyta that recently has attracted enormous attention because of its capacity to produce many high-value metabolites such as the pigment phycoerythrin and several high-value fatty acids. Phycoerythrin is a fluorescent red protein-pigment commercially relevant with antioxidant, antimicrobial activity, and fluorescent properties. The volumetric mass transfer coefficient (k_La) was kept constant within the different scaling-up stages in the present study. This scaling-up strategy was sought to maintain phycoerythrin production and other high-value metabolites by Porphyridium purpureum, using hanging-bag photobioreactors. The k_La was monitored to ensure the appropriate mixing and CO₂ diffusion in the entire culture during the scaling process (16, 80, and 400 L). Then, biomass concentration, proteins, fatty acids, carbohydrates, and phycoerythrin were determined in each step of the scaling-up process. The k_La at 16 L reached a level of 0.0052 s^-1, while at 80 L, a value of 0.0024 s^-1 was achieved. This work result indicated that at 400 L, 1.22 g L^-1 of biomass was obtained, and total carbohydrates (117.24 mg L^-1), proteins (240.63 mg L^-1), and lipids (17.75% DW) were accumulated. Regarding fatty acids production, 46.03% palmitic, 8.03% linoleic, 22.67% arachidonic, and 2.55% eicosapentaenoic acid were identified, principally. The phycoerythrin production was 20.88 mg L^-1 with a purity of 2.75, making it viable for food-related applications. The results of these experiments provide insight into the high-scale production of phycoerythrin via the cultivation of P. purpureum in an inexpensive and straightforward culture system.

Synthesis of two new lipid mediators from docosahexaenoic acid by combinatorial catalysis involving enzymatic and chemical reaction

Omega-3 polyunsaturated fatty acids (PUFAs) have been known to have beneficial effects in the prevention of various diseases. Recently, it was identified that the bioactivities of omega-3 are related to lipid mediators, called pro-resolving lipid mediators (SPMs), converted from PUFAs, so they have attracted much attention as potential pharmaceutical targets. Here, we aimed to build an efficient production system composed of enzymatic and chemical catalysis that converts docosahexaenoic acid (DHA) into lipid mediators. The cyanobacterial lipoxygenase, named Osc-LOX, was identified and characterized, and the binding poses of enzyme and substrates were predicted by ligand docking simulation. DHA was converted into three lipid mediators, a 17S-hydroxy-DHA, a 7S,17S-dihydroxy-DHA (RvD5), and a 7S,15R-dihydroxy-16S,17S-epoxy-DPA (new type), by an enzymatic reaction and deoxygenation. Also, two lipid mediators, 7S,15R,16S,17S-tetrahydroxy-DPA (new type) and 7S,16R,17S-trihydroxy-DHA (RvD2), were generated from 7S,15R-dihydroxy-16S,17S-epoxy-DPA by a chemical reaction. Our study suggests that discovering new enzymes that have not been functionally characterized would be a powerful strategy for producing various lipid mediators. Also, this combination catalysis approach including biological and chemical reactions could be an effective production system for the manufacturing lipid mediators.

Optimizing Eicosapentaenoic Acid Production by Grafting a Heterologous Polyketide Synthase Pathway in the Thraustochytrid Aurantiochytrium

Eicosapentaenoic acid (EPA) is an essential nutritional supplement for human health. The most prominent dietary source of EPA is fish oil, which is unsustainable because of the decline in fishery resources and serious environmental pollution. Alternatively, a heterologous polyketide synthase pathway for EPA biosynthesis was assembled in Thraustochytrid Aurantiochytrium. A 2A peptide-based facile assembly platform that can achieve multigene expression as a polycistron was first established. The platform was then applied to express the EPA biosynthetic gene cluster from Shewanella japonica in Aurantiochytrium. In the shake flask fermentation, the lipid and PUFA yields of the mutant were increased by 26.9 and 36.0%, respectively, and led to about 5-fold increase of the EPA yield. The final EPA titer reached 2.7 g/L in fed-batch fermentation. This study provides a novel metabolic engineering strategy to regulate the EPA ratio in microalgal oil for human nutritional supplementation.

Enhancement of 1,3-propanediol production from industrial by-product by Lactobacillus reuteri CH53

Background

1,3-propanediol (1,3-PDO) is the most widely studied value-added product that can be produced by feeding glycerol to bacteria, including Lactobacillus sp. However, previous research reported that L. reuteri only produced small amounts and had low productivity of 1,3-PDO. It is urgent to develop procedures that improve the production and productivity of 1,3-PDO.

Results

We identified a novel L. reuteri CH53 isolate that efficiently converted glycerol into 1,3-PDO, and performed batch co-fermentation with glycerol and glucose to evaluate its production of 1,3-PDO and other products. We optimized the fermentation conditions and nitrogen sources to increase the productivity. Fed-batch fermentation using corn steep liquor (CSL) as a replacement for beef extract led to 1,3-PDO production (68.32 ± 0.84 g/L) and productivity (1.27 ± 0.02 g/L/h) at optimized conditions (unaerated and 100 rpm). When CSL was used as an alternative nitrogen source, the activity of the vitamin B12-dependent glycerol dehydratase (dhaB) and 1,3-propanediol oxidoreductase (dhaT) increased. Also, the productivity and yield of 1,3-PDO increased as well. These results showed the highest productivity in Lactobacillus species. In addition, hurdle to 1,3-PDO production in this strain were identified via analysis of the half-maximal inhibitory concentration for growth (IC50) of numerous substrates and metabolites.

Conclusions

We used CSL as a low-cost nitrogen source to replace beef extract for 1,3-PDO production in L. reuteri CH53. These cells efficiently utilized crude glycerol and CSL to produce 1,3-PDO. This strain has great promise for the production of 1,3-PDO because it is generally recognized as safe (GRAS) and non-pathogenic. Also, this strain has high productivity and high conversion yield.