Production Strategies and Applications of Microbial Single Cell Oils

Biotechnological Innovations Unleashing the Potential of Olive Mill Wastewater in Added-Value Bioproducts

Byproducts and wastes from the food processing industry represent an important group of wastes generated annually in large quantities. It is important to note that the amount of this waste will increase with industrialization, and effective solutions must be found urgently. Many wastes that cause environmental pollution are evaluated by their low-tech conversion into products with little economic value, such as animal feed and fertilizer. Therefore, the evaluation of food processing waste using effective recycling techniques has become an interesting subject with increasing population, ongoing biotechnological studies, and advances in technology. The conversion of food waste into biotechnological products via fermentation is a sustainable, environmentally friendly, and economical method in line with the principles of green chemistry. This approach promotes the reuse of food waste by supporting the principles of a circular economy and offers sustainable alternatives to fossil fuels and synthetic chemicals. This contributes to reducing the carbon footprint, preserving soil and water quality, and providing economic sustainability through the production of high-value products. In this study, the properties of olive mill wastewater, an important and valuable waste in the olive oil industry, its environmental aspects, and its use in biotechnological applications that integrate green chemistry are evaluated.

Mushroom oils: A review of their production, composition, and potential applications

This review delves into the world of mushroom oils, highlighting their production, composition, and versatile applications. Despite mushrooms' overall low lipid content, their fatty acid composition, rich in essential fatty acids like linoleic acid and oleic acid, proves nutritionally significant. Variations in fatty acid profiles across mushroom species and the prevalence of unsaturated fats contribute to their cardiovascular health benefits. The exploration extends to mushroom essential oils, revealing diverse volatile compounds through extraction methods like hydrodistillation and solvent-assisted flavor evaporation (SAFE). The identification of 1-octen-3-ol as a key contributor to the distinct "mushroom flavor" adds a nuanced perspective. The focus broadens to applications, encompassing culinary and industrial uses with techniques like cold pressing and supercritical fluid extraction (SFE). Mushroom oils, with their unique nutritional and flavor profiles, enhance gastronomic experiences. Non-food applications in cosmetics and biofuels underscore the oils' versatility. The nutritional composition, enriched with essential fatty acids, bioactive compositions, and trace elements, is explored for potential health benefits. Bioactive compounds such as phenolic compounds and terpenes contribute to antioxidant and anti-inflammatory properties, positioning mushroom oils as nutritional powerhouses. In short, this concise review synthesizes the intricate world of mushroom oils, emphasizing their nutritional significance, extraction methodologies, and potential health benefits. The comprehensive overview underscores mushroom oils as a promising area for further exploration and utilization. The characteristics of mushroom biomass oil for the use in various industries are influenced by the mushroom species, chemical composition, biochemical synthesis of mushroom, and downstream processes including extraction, purification and characterization. Therefore, further research and exploration need to be done to achieve a circular bioeconomy with the integration of SDGs, waste reduction, and economic stimulation, to fully utilize the benefits of mushroom, a valuable gift of nature.

Innovation in precision fermentation for food ingredients

A transformation in our food production system is being enabled by the convergence of advances in genome-based technologies and traditional fermentation. Science at the intersection of synthetic biology, fermentation, downstream processing for product recovery, and food science is needed to support technology development for the production of fermentation-derived food ingredients. The business and markets for fermentation-derived ingredients, including policy and regulations are discussed. A patent landscape of fermentation for the production of alternative proteins, lipids and carbohydrates for the food industry is provided. The science relating to strain engineering, fermentation, downstream processing, and food ingredient functionality that underpins developments in precision fermentation for the production of proteins, fats and oligosaccharides is examined. The production of sustainably-produced precision fermentation-derived ingredients and their introduction into the market require a transdisciplinary approach with multistakeholder engagement. Successful innovation in fermentation-derived ingredients will help feed the world more sustainably.

The role of areA in lipid accumulation in high lipid-producing fungus Mucor circinelloides WJ11

In the oleaginous fungus Mucor circinelloides, lipid accumulation is regulated by nitrogen metabolism, which is regulated by the areA gene, a member of the GATA zinc finger transporter family and a major regulator for nitrogen metabolism. However, the role of areA in lipid accumulation in this fungus has not been reported. In order to explore the regulatory effect of areA gene on nitrogen metabolism and lipid accumulation in M. circinelloides, we constructed areA gene knockout and overexpression strains. Then, the recombinant strains were cultured and their biochemical indexes were measured. Simultaneously, transcriptomic studies on the recombinant strains were conducted to infer the regulatory mechanism of areA. The results showed that the areA knockout strain accumulated more lipid, which is 42 % higher than the control. While the areA overexpressing strain obtained the higher biomass accumulation (23 g/L) and used up the nitrogen source in the medium earlier than the control strain and knockout strain. Transcriptome data analysis showed that nr and nit-6 genes related to nitrogen metabolism were up-regulated. And the expression levels of key genes acc and aclY were higher in the areA knockout strain than others, which was positively correlated with the increased lipid accumulation. In addition, in knockout strains, protein catabolism tended to provide substrates for the lipid production, and the expression levels of the related genes were also higher than others. These results indicated that the areA gene not only controls the transcription level of genes related to nitrogen metabolism but also affects lipid accumulation.

Unlocking the potential of one-carbon gases (CO2, CO) for concomitant bioproduction of β-carotene and lipids

This study investigates the use of a Yarrowia lipolytica strain for the bioconversion of syngas-derived acetic acid into β-carotene and lipids. A two-stage process was employed, starting with the acetogenic fermentation of syngas by Clostridium aceticum, metabolising CO, CO2, H2, to produce acetic acid, which is then utilized by Y. lipolytica for simultaneous lipid and β-carotene synthesis. The research demonstrates that acetic acid concentration plays a pivotal role in modulating lipid profiles and enhancing β-carotene production, with increased acetic acid consumption leading to higher yields of these compounds. This approach showcases the potential of using one-carbon gases as substrates in bioprocesses for generating valuable bioproducts, providing a sustainable and cost-effective alternative to more conventional feedstocks and substrates, such as sugars.

Screening for the production of polyunsaturated fatty acids and cerebrosides in fungi

AIMS

To investigate fatty acid, including polyunsaturated fatty acids (PUFA), and cerebroside production of a large diversity of fungi from the Ascomycota, Basidiomycota, and Mucoromycota phyla.

METHODS AND RESULTS

Seventy-nine fungal strains were grown in Kavadia medium using a microcultivation system, i.e. Duetz microtiter plates. Following cultivation, fatty acid and cerebroside contents were analyzed by gas chromatography-flame ionization detection (GC-FID) and high performance thin-layer chromatography (HPTLC), respectively. Mucoromycota fungi appeared as the most promising candidates for omega-6 PUFA production. The best omega-6 producer, including γ-linolenic acid (GLA, 18:3n-6), was Mucor fragilis UBOCC-A109196 with a concentration of 647 mg L-1 total omega-6 PUFA (representing 35% of total fatty acids) and 225 mg L-1 GLA (representing 12% of total fatty acids). Arachidonic acid concentration (20:4n-6) was the highest in Mortierella alpina UBOCC-A-112046, reaching 255 mg L-1 and 18.56% of total fatty acids. Interestingly, several fungal strains were shown to produce omega-7 monounsaturated fatty acids. Indeed, Torulaspora delbrueckii strains accumulated palmitoleic acid (16:1n-7) up to 20% of total fatty acids, reaching 114 mg L-1 in T. delbrueckii UBOCC-A-214128, while C. elegans UBOCC-A-102008 produced mainly paullinic acid (20:1n-7) with concentrations up to 100 mg L-1. Concerning cerebroside production, HPTLC appeared as a relevant approach for their detection and quantification. Promising candidates belonging to the Mucoromycota phylum were found, especially in the Absidia genus with A. spinosa UBOCC-A-101332 as the best producer (12.7 mg L-1).

CONCLUSIONS

The present study highlighted PUFA and cerebroside production in a large diversity of fungi and the fact that members of the Mucoromycota phylum are good producers of PUFA as well as cerebrosides.

The balance of n-6 and n-3 fatty acids in canine, feline, and equine nutrition: exploring sources and the significance of alpha-linolenic acid

Both n-6 and n-3 fatty acids (FA) have numerous significant physiological roles for mammals. The interplay between these families of FA is of interest in companion animal nutrition due to the influence of the n-6:n-3 FA ratio on the modulation of the inflammatory response in disease management and treatment. As both human and animal diets have shifted to greater consumption of vegetable oils rich in n-6 FA, the supplementation of n-3 FA to canine, feline, and equine diets has been advocated for. Although fish oils are commonly added to supply the long-chain n-3 FA eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), a heavy reliance on this ingredient by the human, pet food, and equine supplement industries is not environmentally sustainable. Instead, sustainable sourcing of plant-based oils rich in n-3 α-linolenic acid (ALA), such as flaxseed and camelina oils, emerges as a viable option to support an optimal n-6:n-3 FA ratio. Moreover, ALA may offer health benefits that extend beyond its role as a precursor for endogenous EPA and DHA production. The following review underlines the metabolism and recommendations of n-6 and n-3 FA for dogs, cats, and horses and the ratio between them in promoting optimal health and inflammation management. Additionally, insights into both marine and plant-based n-3 FA sources will be discussed, along with the commercial practicality of using plant oils rich in ALA for the provision of n-3 FA to companion animals.

Sequential bioconversion of C1-gases (CO, CO2, syngas) into lipids, through the carboxylic acid platform, with Clostridium aceticum and Rhodosporidium toruloides

Syngas (CO, CO2, H2) was effectively bioconverted into lipids in a two-stage process. In the first stage, C1-gases were bioconverted into acetic acid by the acetogenic species Clostridium aceticum through the Wood-Ljungdahl metabolic pathway in a stirred tank bioreactor, reaching a maximum acetic acid concentration of 11.5 g/L, with a production rate of 0.05 g/L·h. Throughout this experiment, samples were extracted at different periods, i.e., different concentrations, to be used in the second stage, aiming at the production of lipids from acetic acid. The yeast Rhodosporidium toruloides, inoculated in the acetogenic medium, was able to efficiently accumulate lipids from acetic acid generated in the first stage. The best results, in terms of lipid content, dry biomass, biomass yield (Y(X/S)) and lipid yield (Y(L/S)) were 39.5% g/g dry cell weight, 3 g/L, 0.35 and 0.107, respectively. In terms of abundance, the lipid profile followed the order: C18:1 > C16:0 > C18:2 > C18:0 > Others. Experiments were also performed to determine the toxicity exerted by high concentrations of acetic acid on R. toruloides, resulting in inhibition at initial acid concentrations around 18 g/L leading to a higher lag phase and being lethal to the yeast at initial acetic acid concentrations around 22 g/L and above. This research paves the way for a novel method of growing oleaginous yeasts to produce sustainable biofuels from syngas or C1-pollutant gases.

Production of Single-Cell Oil from a Local Isolate Bacillus subtilis Using Palm Fronds

This study, conducted at the Department of Biology, University of Anbar, Iraq, focuses on addressing the escalating issue of contamination and aims to acquire microbial oils to alleviate the global shortage in plant and animal oil production, utilizing environmental waste as a carbon source to reduce global pollution and select efficient local bacterial isolates of Bacillus subtilis for the production of single-cell oil (SCO) using local soil and environmental waste as a carbon source. Four isolates were selected as the best in producing single-cell oil, with the isolate with code C4 standing out as it recorded the highest production. It is worth noting that all these isolates belong to the bacteria type Bacillus subtilis. Palm fronds were found to be the most suitable environmental residue for SCO production compared to other waste materials (wheat straw and wheat bran). Submerged cultures were used to improve SCO production, with optimal conditions determined as pH 7, a temperature of 30°C, carbon source concentration of 3 g/100 ml, inoculum volume of 3 ml/100 ml, inoculum density of 20 × 107 cells, and an incubation period of 72 hours. The Soxhlet extraction method was used to obtain the oil, which was found to contain high percentages of unsaturated fatty acids, particularly linoleic acid (46.030%) and palmitoleic acid (16.579%). The oil was highly soluble in chloroform and ethanol but insoluble in water. The saponification test indicated the potential for soap production from the oil. This comprehensive research addresses the need for locally sourced and sustainable SCO production, offering insights into the selection of efficient bacterial isolates, the optimization of cultivation conditions, and the valuable properties of the resulting SCO. The significance of this study lies in the production of single-cell oil from soil-isolated Bacillus subtilis bacteria for use in food applications.

From straw to salmon: a technical design and energy balance for production of yeast oil for fish feed from wheat straw

BACKGROUND

Aquaculture is a major user of plant-derived feed ingredients, such as vegetable oil. Production of vegetable oil and protein is generally more energy-intensive than production of the marine ingredients they replace, so increasing inclusion of vegetable ingredients increases the energy demand of the feed. Microbial oils, such as yeast oil made by fermentation of lignocellulosic hydrolysate, have been proposed as a complement to plant oils, but energy assessments of microbial oil production are needed. This study presents a mass and energy balance for a biorefinery producing yeast oil through conversion of wheat straw hydrolysate, with co-production of biomethane and power.

RESULTS

The results showed that 1 tonne of yeast oil (37 GJ) would require 9.2 tonnes of straw, 14.7 GJ in fossil primary energy demand, 14.6 GJ of process electricity and 13.3 GJ of process heat, while 21.5 GJ of biomethane (430 kg) and 6 GJ of excess power would be generated simultaneously. By applying economic allocation, the fossil primary energy demand was estimated to 11.9 GJ per tonne oil.

CONCLUSIONS

Fossil primary energy demand for yeast oil in the four scenarios studied was estimated to be 10-38% lower than for the commonly used rapeseed oil and process energy demand could be met by parallel combustion of lignin residues. Therefore, feed oil can be produced from existing non-food biomass without causing agricultural expansion.

Optimization of Rhodococcus erythropolis JCM3201T Nutrient Media to Improve Biomass, Lipid, and Carotenoid Yield Using Response Surface Methodology

The oleaginous bacterium Rhodococcus erythropolis JCM3201T offers various unique enzyme capabilities, and it is a potential producer of industrially relevant compounds, such as triacylglycerol and carotenoids. To develop this strain into an efficient production platform, the characterization of the strain's nutritional requirement is necessary. In this work, we investigate its substrate adaptability. Therefore, the strain was cultivated using nine nitrogen and eight carbon sources at a carbon (16 g L-1) and nitrogen (0.16 g L-1) weight ratio of 100:1. The highest biomass accumulation (3.1 ± 0.14 g L-1) was achieved using glucose and ammonium acetate. The highest lipid yield (156.7 ± 23.0 mg g-1DCW) was achieved using glucose and yeast extract after 192 h. In order to enhance the dependent variables: biomass, lipid and carotenoid accumulation after 192 h, for the first time, a central composite design was employed to determine optimal nitrogen and carbon concentrations. Nine different concentrations were tested. The center point was tested in five biological replicates, while all other concentrations were tested in duplicates. While the highest biomass (8.00 ± 0.27 g L-1) was reached at C:N of 18.87 (11 g L-1 carbon, 0.583 g L-1 nitrogen), the highest lipid yield (100.5 ± 4.3 mg g-1DCW) was determined using a medium with 11 g L-1 of carbon and only 0.017 g L-1 of nitrogen. The highest carotenoid yield (0.021 ± 0.001 Abs454nm mg-1DCW) was achieved at a C:N of 12 (6 g L-1 carbon, 0.5 g L-1 nitrogen). The presented results provide new insights into the physiology of R. erythropolis under variable nutritional states, enabling the selection of an optimized media composition for the production of valuable oleochemicals or pigments, such as rare odd-chain fatty acids and monocyclic carotenoids.

Oleaginous yeasts for biochemicals, biofuels and food from lignocellulose-hydrolysate and crude glycerol

Microbial lipids produced from lignocellulose and crude glycerol (CG) can serve as sustainable alternatives to vegetable oils, whose production is, in many cases, accompanied by monocultures, land use changes or rain forest clearings. Our projects aim to understand the physiology of microbial lipid production by oleaginous yeasts, optimise the production and establish novel applications of microbial lipid compounds. We have established methods for fermentation and intracellular lipid quantification. Following the kinetics of lipid accumulation in different strains, we found high variability in lipid formation even between very closely related oleaginous yeast strains on both, wheat straw hydrolysate and CG. For example, on complete wheat straw hydrolysate, we saw that one Rhodotorula glutinis strain, when starting assimilating D-xylosealso assimilated the accumulated lipids, while a Rhodotorula babjevae strain could accumulate lipids on D-xylose. Two strains (Rhodotorula toruloides CBS 14 and R. glutinis CBS 3044) were found to be the best out of 27 tested to accumulate lipids on CG. Interestingly, the presence of hemicellulose hydrolysate stimulated glycerol assimilation in both strains. Apart from microbial oil, R. toruloides also produces carotenoids. The first attempts of extraction using the classical acetone-based method showed that β-carotene is the major carotenoid. However, there are indications that there are also substantial amounts of torulene and torularhodin, which have a very high potential as antioxidants.

Current advances in alteration of fatty acid profile in Rhodotorula toruloides: a mini-review

Microbial lipids are considered promising and environmentally friendly substitutes for fossil fuels and plant-derived oils. They alleviate the depletion of limited petroleum storage and the decrement of arable lands resulting from the greenhouse effect. Microbial lipids derived from oleaginous yeasts provide fatty acid profiles similar to plant-derived oils, which are considered as sustainable and alternative feedstocks for use in the biofuel, cosmetics, and food industries. Rhodotorula toruloides is an intriguing oleaginous yeast strain that can accumulate more than 70% of its dry biomass as lipid content. It can utilize a wide range of substrates, including low-cost sugars and industrial waste. It is also robust against various industrial inhibitors. However, precise control of the fatty acid profile of the lipids produced by R. toruloides is essential for broadening its biotechnological applications. This mini-review describes recent progress in identifying fatty synthesis pathways and consolidated strategies used for specific fatty acid-rich lipid production via metabolic engineering, strain domestication. In addition, this mini-review summarized the effects of culture conditions on fatty acid profiles in R. toruloides. The perspectives and constraints of harnessing R. toruloides for tailored lipid production are also discussed in this mini-review.

OMICS and Other Advanced Technologies in Mycological Applications

Fungi play many roles in different ecosystems. The precise identification of fungi is important in different aspects. Historically, they were identified based on morphological characteristics, but technological advancements such as polymerase chain reaction (PCR) and DNA sequencing now enable more accurate identification and taxonomy, and higher-level classifications. However, some species, referred to as "dark taxa", lack distinct physical features that makes their identification challenging. High-throughput sequencing and metagenomics of environmental samples provide a solution to identifying new lineages of fungi. This paper discusses different approaches to taxonomy, including PCR amplification and sequencing of rDNA, multi-loci phylogenetic analyses, and the importance of various omics (large-scale molecular) techniques for understanding fungal applications. The use of proteomics, transcriptomics, metatranscriptomics, metabolomics, and interactomics provides a comprehensive understanding of fungi. These advanced technologies are critical for expanding the knowledge of the Kingdom of Fungi, including its impact on food safety and security, edible mushrooms foodomics, fungal secondary metabolites, mycotoxin-producing fungi, and biomedical and therapeutic applications, including antifungal drugs and drug resistance, and fungal omics data for novel drug development. The paper also highlights the importance of exploring fungi from extreme environments and understudied areas to identify novel lineages in the fungal dark taxa.

Microbial Lipid Based Biorefinery Concepts: A Review of Status and Prospects

The use of lignocellulosic biomass as a raw material for the production of lipids has gained increasing attention, especially in recent years when the use of food in the production of biofuels has become a current technology. Thus, the competition for raw materials for both uses has brought the need to create technological alternatives to reduce this competition that could generate a reduction in the volume of food offered and a consequent commercial increase in the value of food. Furthermore, the use of microbial oils has been studied in many industrial branches, from the generation of renewable energy to the obtainment of several value-added products in the pharmaceutical and food industries. Thus, this review provides an overview of the feasibility and challenges observed in the production of microbial lipids through the use of lignocellulosic biomass in a biorefinery. Topics covered include biorefining technology, the microbial oil market, oily microorganisms, mechanisms involved in lipid-producing microbial metabolism, strain development, processes, lignocellulosic lipids, technical drawbacks, and lipid recovery.

Marine Natural Products as Innovative Cosmetic Ingredients

Over the course of the last 20 years, numerous studies have identified the benefits of an array of marine natural ingredients for cosmetic purposes, as they present unique characteristics not found in terrestrial organisms. Consequently, several marine-based ingredients and bioactive compounds are under development, used or considered for skin care and cosmetics. Despite the multitude of cosmetics based on marine sources, only a small proportion of their full potential has been exploited. Many cosmetic industries have turned their attention to the sea to obtain innovative marine-derived compounds for cosmetics, but further research is needed to determine and elucidate the benefits. This review gathers information on the main biological targets for cosmetic ingredients, different classes of marine natural products of interest for cosmetic applications, and the organisms from which such products can be sourced. Although organisms from different phyla present different and varied bioactivities, the algae phylum seems to be the most promising for cosmetic applications, presenting compounds of many classes. In fact, some of these compounds present higher bioactivities than their commercialized counterparts, demonstrating the potential presented by marine-derived compounds for cosmetic applications (i.e., Mycosporine-like amino acids and terpenoids’ antioxidant activity). This review also summarizes the major challenges and opportunities faced by marine-derived cosmetic ingredients to successfully reach the market. As a future perspective, we consider that fruitful cooperation among academics and cosmetic industries could lead to a more sustainable market through responsible sourcing of ingredients, implementing ecological manufacturing processes, and experimenting with inventive recycling and reuse programs.

Biofuel production from Euglena: Current status and techno-economic perspectives

Sustainable aviation fuels (SAFs) can contribute reduce greenhouse gas emissions compared to conventional fuel. With the increasing SAFs demand, various generations of resources have been shifted from the 1st generation (oil crops), the 2nd generation (agricultural waste), to the 3rd generation (microalgae). Microalgae are the most suitable feedstock for jet biofuel production than other resources because of their productivity and capability to capture carbon dioxide. However, microalgae-based biofuel has a limitation of high freezing point. Recently, a jet biofuel derived from Euglena wax ester has been paying attention due to its low freezing point. Challenges still remain to enhance production yields in both upstream and downstream processes. Studies on downstream processes as well as techno-economic analysis on biofuel production using Euglena are highly limited to date. Economic aspects for the biofuel production will be ensured via valorization of industrial byproducts such as food wastes.

Biofuels and Nanocatalysts: Python Boosting Visualization of Similarities

Among the most relevant themes of modernity, using renewable resources to produce biofuels attracts several countries' attention, constituting a vital part of the global geopolitical chessboard since humanity's energy needs will grow faster and faster. Fortunately, advances in personal computing associated with free and open-source software production facilitate this work of prospecting and understanding complex scenarios. Thus, for the development of this work, the keywords "biofuel" and "nanocatalyst" were delivered to the Scopus database, which returned 1071 scientific articles. The titles and abstracts of these papers were saved in Research Information Systems (RIS) format and submitted to automatic analysis via the Visualization of Similarities Method implemented in VOSviewer 1.6.18 software. Then, the data extracted from the VOSviewer were processed by software written in Python, which allowed the use of the network data generated by the Visualization of Similarities Method. Thus, it was possible to establish the relationships for the pair between the nodes of all clusters classified by Link Strength Between Items or Terms (LSBI) or by year. Indeed, other associations should arouse particular interest in the readers. However, here, the option was for a numerical criterion. However, all data are freely available, and stakeholders can infer other specific connections directly. Therefore, this innovative approach allowed inferring that the most recent pairs of terms associate the need to produce biofuels from microorganisms' oils besides cerium oxide nanoparticles to improve the performance of fuel mixtures by reducing the emission of hydrocarbons (HC) and oxides of nitrogen (NOx).

Promising Sources of Plant-Derived Polyunsaturated Fatty Acids: A Narrative Review

(1) Background: Polyunsaturated fatty acids (PUFAs) are known for their ability to protect against numerous metabolic disorders. The consumption of oily fish is the main source of PUFAs in human nutrition and is commonly used for supplement production. However, seafood is an overexploited source that cannot be guaranteed to cover the global demands. Furthermore, it is not consumed by everyone for ecological, economic, ethical, geographical and taste reasons. The growing demand for natural dietary sources of PUFAs suggests that current nutritional sources are insufficient to meet global needs, and less and less will be. Therefore, it is crucial to find sustainable sources that are acceptable to all, meeting the world population's needs. (2) Scope: This review aims to evaluate the recent evidence about alternative plant sources of essential fatty acids, focusing on long-chain omega-3 (n-3) PUFAs. (3) Method: A structured search was performed on the PubMed search engine to select available human data from interventional studies using omega-3 fatty acids of non-animal origin. (4) Results: Several promising sources have emerged from the literature, such as algae, microorganisms, plants rich in stearidonic acid and GM plants. However, the costs, acceptance and adequate formulation deserve further investigation.

Structure of fungal communities in sequencing batch reactors operated at different salinities for the selection of triacylglyceride-producers from a fish-canning lipid-rich waste stream

Oleaginous fungi natively accumulate large amounts of triacylglycerides (TAG), widely used as precursors for sustainable biodiesel production. However, little attention has been paid to the diversity and roles of fungal mixed microbial cultures (MMCs) in sequencing batch reactors (SBR). In this study, a lipid-rich stream produced in the fish-canning industry was used as a substrate in two laboratory-scale SBRs operated under the feast/famine (F/F) regime to enrich microorganisms with high TAG-storage ability, under two different concentrations of NaCl (SBR-N: 0.5g/L; SBR-S: 10g/L). The size of the fungal community in the enriched activated sludge (EAS) was analyzed using 18S rRNA-based qPCR, and the fungal community structure was determined by Illumina sequencing. The different selective pressures (feeding strategy and control of pH) implemented in the enrichment SBRs throughout operation increased the abundance of total fungi. In general, there was an enrichment of genera previously identified as TAG-accumulating fungi (Apiotrichum, Candida, Cutaneotrichosporon, Geotrichum, Haglerozyma, Metarhizium, Mortierella, Saccharomycopsis, and Yarrowia) in both SBRs. However, the observed increase of their relative abundances throughout operation was not significantly linked to a higher TAG accumulation.

Towards the Physiological Understanding of Yarrowia lipolytica Growth and Lipase Production Using Waste Cooking Oils

The yeast Yarrowia lipolytica is an industrially relevant microorganism, which is able to convert low-value wastes into different high-value, bio-based products, such as enzymes, lipids, and other important metabolites. Waste cooking oil (WCO) represents one of the main streams generated in the food supply chain, especially from the domestic sector. The need to avoid its incorrect disposal makes this waste a resource for developing bioprocesses in the perspective of a circular bioeconomy. To this end, the strain Y. lipolytica W29 was used as a platform for the simultaneous production of intracellular lipids and extracellular lipases. Three different minimal media conditions with different pH controls were utilized in a small-scale (50 mL final volume) screening strategy, and the best condition was tested for an up-scaling procedure in higher volumes (800 mL) by selecting the best-performing possibility. The tested media were constituted by YNB media with high nitrogen restriction (1 g L−1 (NH4)2SO4) and different carbon sources (3% w v−1 glucose and 10% v v−1 WCO) with different levels of pH controls. Lipase production and SCO content were analyzed. A direct correlation was found between decreasing FFA availability in the media and increasing SCO levels and lipase activity. The simultaneous production of extracellular lipase (1.164 ± 0.025 U mL−1) and intracellular single-cell oil accumulation by Y. lipolytica W29 growing on WCO demonstrates the potential and the industrial relevance of this biorefinery model.

Identification, Quantification and Kinetic Study of Carotenoids and Lipids in Rhodotorula toruloides CBS 14 Cultivated on Wheat Straw Hydrolysate

Production of carotenoids and lipids by Rhodotorula toruloides CBS 14 cultivated on wheat straw hydrolysate was investigated. An ultra-high-performance liquid chromatography (UHPLC) method for carotenoid quantification was developed and validated. Saponification effects on individual carotenoid quantification were identified, and lipid and carotenoid kinetics during cultivation were determined. The carotenoids β-carotene, γ-carotene, torularhodin, and torulene were identified; β-carotene was the major carotenoid, reaching a maximum of 1.48 mg/100 g dry weight. Recoveries of the carotenoids were between 66 and 76%, except torulene and torularhodin, which had lower recoveries due to saponification effects. Total carotenoid content in saponified and unsaponified yeast extract, respectively, determined by UHPLC or photometer, respectively, was 1.99 mg/100 g and 4.02 mg β-EQ/100 g dry weight. Growth kinetics showed a positive correlation between carotenoid content and lipid accumulation. β-carotene was the major carotenoid at all time points. At the end of the cultivation, triacylglycerols (TAGs) were the major lipid class, with 58.1 ± 3.32% of total lipids. There was also a high proportion of free fatty acids, reaching from 20.5 to 41.8% of total lipids. Oleic acid (C18:1) was the major fatty acid. The lipid yield at the end of the cultivation was 0.13 g/g of sugar consumed.

The Role of Methyl-(Z)-11-tetradecenoate Acid from the Bacterial Membrane Lipid Composition in Escherichia coli Antibiotic Resistance

Background

The bacterial membrane plays a critical role in the survival of bacteria and the effectiveness of antimicrobial peptides in protecting the host. The lipid constituents of the bacterial membrane are not evenly distributed, and they could be affected by clustering anionic lipids with cationic peptides with multiple positive charges. That could be harmful to bacteria because it prevents lipids from interacting with other molecular components of the cell membrane, disrupts existing natural domains, or creates phase boundary defects between the clustered lipids and the bulk of the membrane. This preliminary quantitative study is aimed at assembling a correlation between antibiotic resistance and bacterial lipid composition in E. coli, based on the function and arrangement of the bilipid coating of the bacterial cell, intimately associated with the path of antimicrobials through membranes.

Methods

Fifteen multiresistant E. coli samples are collected from swine with enterocolitis tested for resistance levels using the disc diffusimetric method (Kirby-Bauer disc diffusion). Pathogen identification completed using the API 20E multitest system revealed the E. coli presence in 11 samples. In these samples, bacterial membrane detection of fatty acid methyl esters (FAME) operating a 240 MS Ion Trap (Varian) GC/MS (Agilent Technologies, Santa Clara, CA, USA) was performed, using the MIDI Sherlock recognition software model.

Results

Interpreting the descriptive statistical method, the correlation matrix, and regression curves and after ANOVA analysis, we ascertained that the studied E. coli population statistically confirmed different degrees of resistance in most of the samples analyzed in this test.

Conclusions

In one case, the methyl-(Z)-11-tetradecenoate acid was observed to have a relationship with the susceptibility evaluation by using the disc diffusimetric method, which has revealed the lowest rate of antimicrobial resistance, so it has importance in further resistance evaluation studies.

Health Benefits, Food Applications, and Sustainability of MI-Croalgae-Derived N-3 Pufa

Today’s consumers are increasingly aware of the beneficial effects of n-3 PUFA in preventing, delaying, and intervening various diseases, such as coronary artery disease, hypertension, diabetes, inflammatory and autoimmune disorders, neurodegenerative diseases, depression, and many other ailments. The role of n-3 PUFA on aging and cognitive function is also one of the hot topics in basic research, product development, and clinical applications. For decades, n-3 PUFA, especially EPA and DHA, have been supplied by fish oil and seafood. With the continuous increase of global population, awareness about the health benefits of n-3 PUFA, and socioeconomic improvement worldwide, the supply chain is facing increasing challenges of insufficient production. In this regard, microalgae have been well considered as promising sources of n-3 PUFA oil to mitigate the supply shortages. The use of microalgae to produce n-3 PUFA-rich oils has been explored for over two decades and some species have already been used commercially to produce n-3 PUFA, in particular EPA- and/or DHA-rich oils. In addition to n-3 PUFA, microalgae biomass contains many other high value biomolecules, which can be used in food, dietary supplement, pharmaceutical ingredient, and feedstock. The present review covers the health benefits of n-3 PUFA, EPA, and DHA, with particular attention given to the various approaches attempted in the nutritional interventions using EPA and DHA alone or combined with other nutrients and bioactive compounds towards improved health conditions in people with mild cognitive impairment and Alzheimer’s disease. It also covers the applications of microalgae n-3 PUFA in food and dietary supplement sectors and the economic and environmental sustainability of using microalgae as a platform for n-3 PUFA-rich oil production.

In-situ transesterification of single-cell oil for biodiesel production: a review

In recent years, biodiesel synthesis and production demands have increased because of its high degradability, cleaner emissions, non-toxicity, and an alternative to petroleum diesel. In this context, Single Cell Oil (SCO) has been identified as an alternative feedstock, having the advantage of accumulating high intracellular lipid. SCO/microbial lipids are potential alternatives for sustainable biodiesel production. The traditional technique for biodiesel production from the oils obtained from microbes generally requires two steps: lipid extraction and transesterification. In-situ transesterification is an innovative and renewable process for biodiesel production. It rules out the need to isolate and refine the feedstock lipid, as it directly uses biomass in a single step, i.e., the pretreated biomass will be subjected to in-situ transesterification in the presence of catalysts. Hence, the production cost can be reduced by eliminating the lipid extraction procedure. The current review focuses on the basic features and advantages of in-situ transesterification of SCO for biodiesel production with the aid of short-chain alcohols along with different acid, base, and enzyme catalysts. In addition, a comparative study was carried out to highlight the merits of in-situ transesterification over conventional transesterification.

Evaluation of Lignocellulosic Wastewater Valorization with the Oleaginous Yeasts R. kratochvilovae EXF7516 and C. oleaginosum ATCC 20509

During the conversion of lignocellulose, phenolic wastewaters are generated. Therefore, researchers have investigated wastewater valorization processes in which these pollutants are converted to chemicals, i.e., lipids. However, wastewaters are lean feedstocks, so these valorization processes in research typically require the addition of large quantities of sugars and sterilization, which increase costs. This paper investigates a repeated batch fermentation strategy with Rhodotorula kratochvilovae EXF7516 and Cutaneotrichosporon oleaginosum ATCC 20509, without these requirements. The pollutant removal and its conversion to microbial oil were evaluated. Because of the presence of non-monomeric substrates, the ligninolytic enzyme activity was also investigated. The repeated batch fermentation strategy was successful, as more lipids accumulated every cycle, up to a total of 5.4 g/L (23% cell dry weight). In addition, the yeasts consumed up to 87% of monomeric substrates, i.e., sugars, aromatics, and organics acids, and up to 23% of non-monomeric substrates, i.e., partially degraded xylan, lignin, cellulose. Interestingly, lipid production was only observed during the harvest phase of each cycle, as the cells experienced stress, possibly due to oxygen limitation. This work presents the first results on the feasibility of valorizing non-sterilized lignocellulosic wastewater with R. kratochvilovae and C. oleaginosum using a cost-effective repeated batch strategy.

Microbial pathways for advanced biofuel production

Decarbonisation of the transport sector is essential to mitigate anthropogenic climate change. Microbial metabolisms are already integral to the production of renewable, sustainable fuels and, building on that foundation, are being re-engineered to generate the advanced biofuels that will maintain mobility of people and goods during the energy transition. This review surveys the range of natural and engineered microbial systems for advanced biofuels production and summarises some of the techno-economic challenges associated with their implementation at industrial scales.

Microbes: A Hidden Treasure of Polyunsaturated Fatty Acids

Microbes have gained a lot of attention for their potential in producing polyunsaturated fatty acids (PUFAs). PUFAs are gaining scientific interest due to their important health-promoting effects on higher organisms including humans. The current sources of PUFAs (animal and plant) have associated limitations that have led to increased interest in microbial PUFAs as most reliable alternative source. The focus is on increasing the product value of existing oleaginous microbes or discovering new microbes by implementing new biotechnological strategies in order to compete with other sources. The multidisciplinary approaches, including metabolic engineering, high-throughput screening, tapping new microbial sources, genome-mining as well as co-culturing and elicitation for the production of PUFAs, have been considered and discussed in this review. The usage of agro-industrial wastes as alternative low-cost substrates in fermentation for high-value single-cell oil production has also been discussed. Multidisciplinary approaches combined with new technologies may help to uncover new microbial PUFA sources that may have nutraceutical and biotechnological importance.

Specific importance of low level dietary supplementation of Lypomyces starkeyi CB1807 yeast strain in red sea bream (Pagrus major)

Most probiotic yeast supplement in fish exhibit beneficial effect at ≤1% of the dietary proportion. This study aimed at evaluating the specific effects of Lypomyces starkeyi CB1807 yeast strain supplemented at ≤1% of dietary proportion on the performance of juvenile red sea bream (Pagrus major, 1.9 ± 0.04 g). Five diets were supplemented with yeast at graded levels of 0% (Control diet ‘CD1’), 0.05% (D2), 0.1% (D3), 0.5% (D4), and 1.0% (D5). After 45-days of feeding trial, significant (P<0.05) improvement was detected on final body weight (FBW) and body weight gain (BWG) in fish fed D3 and D5 compared to control. Low values of total cholesterol (T-Cho) and aspartate aminotransferase (AST) were recorded in fish groups fed on D2, D4, and D5, respectively. Fish fed on D3, D4 and D5 diets showed high (P<0.05) values of serum, mucus and liver lysozyme compared to control. Fish fed on D5 showed high values of Total immunoglobulin (Ig) compared to control. Fish fed on D2 showed strong correlation with biological antioxidant activity (BAP), superoxide dismutase (SOD) and catalase activity (CAT). The biological antioxidant potential (BAP) activity in fish fed on D2 was significantly higher compared to control (P<0.05). The reactive oxygen metabolites (d-ROM) were significantly lower in fish fed on D2 and D3 compared to CD1 (P<0.05). Peroxidase activity was improved significantly (P<0.05) in fish fed on D3, D4 and D5 compared to control. The tolerance ability (LT50) of fish fed on D5 against low salinity stress were significantly higher compared to control (P<0.05). It was concluded that dietary benefits of spent L. starkeyi yeast at ≤1% showed considerable improvement in antioxidant capacity in red sea bream, P. major.

Mucor circinelloides: a model organism for oleaginous fungi and its potential applications in bioactive lipid production

Microbial oils have gained massive attention because of their significant role in industrial applications. Currently plants and animals are the chief sources of medically and nutritionally important fatty acids. However, the ever-increasing global demand for polyunsaturated fatty acids (PUFAs) cannot be met by the existing sources. Therefore microbes, especially fungi, represent an important alternative source of microbial oils being investigated. Mucor circinelloides—an oleaginous filamentous fungus, came to the forefront because of its high efficiency in synthesizing and accumulating lipids, like γ-linolenic acid (GLA) in high quantity. Recently, mycelium of M. circinelloides has acquired substantial attraction towards it as it has been suggested as a convenient raw material source for the generation of biodiesel via lipid transformation. Although M. circinelloides accumulates lipids naturally, metabolic engineering is found to be important for substantial increase in their yields. Both modifications of existing pathways and re-formation of biosynthetic pathways in M. circinelloides have shown the potential to improve lipid levels. In this review, recent advances in various important metabolic aspects of M. circinelloides have been discussed. Furthermore, the potential applications of M. circinelloides in the fields of antioxidants, nutraceuticals, bioremediation, ethanol production, and carotenoids like beta carotene and astaxanthin having significant nutritional value are also deliberated.

Expression Profile of Selected Genes Involved in Storage Lipid Synthesis in a Model Oleaginous Yeast Species Yarrowia lipolytica

Yarrowia lipolytica yeast is a model species of the group of oleaginous microorganisms capable of intracellular lipids accumulation in an amount exceeding 20% of the dry mass. Single cell oil biosynthesis can follow one of two biochemical pathways—de novo accumulation of cellular lipids in medium containing non-lipid carbon sources (including saccharides, glycerol) and ex novo microbial oil synthesis which involves fatty acids uptake from the environment. The mRNA expression of selected genes of de novo and ex novo lipid synthesis pathways was analyzed and correlated with the phenotypically observed features. It was proved that the accumulation yield of storage lipids via ex novo pathway was to some extent dependent on the limitation of the nitrogen source in the medium. It was also proposed that the synthesis of intracellular lipids in lipid-rich medium proceeded mainly via ex novo pathway, although the activity of genes encoding the enzymes of the de novo pathway were not completely inhibited at the stage of transcription by fatty acids present in the medium (e.g., ATP-citrate lyase). Molecular markers of two biosynthesis routes has been outlined and a hypothetical connection point between de novo and ex novo route were indicated.

Insights on sustainable approaches for production and applications of value added products

The increasing demand for the development of sustainable strategies to utilize and process agro-industrial residues paves new paths for exploring innovative approaches in this area. Biotechnology based microbial transformations provide efficient, low cost and sustainable approaches for the production of value added products. The use of organic rich residues opens new avenues for the production of enzymes, pigments, biofuels, bioactive compounds, biopolymers etc. with vast industrial and therapeutic applications. Innovative technologies like strain improvement, enzyme immobilization, genome editing, morphological engineering, ultrasound/supercritical fluid/pulse electric field extraction, etc. can be employed. These will be helpful in achieving significant improvement in qualitative and quantitative parameters of the finished products. The global trend for the valorisation of biowaste has boosted the commercialization of these products which has transformed the markets by providing new investment opportunities. The upstream processing of raw materials using microbes poses a limitation in terms of product development and recovery which can be overcome by modifying the bioreactor design, physiological parameters or employing alternate technologies which will be discussed in this review. The other problems related to the processes include product stability, industrial applicability and cost competitiveness which needs to be addressed. This review comprehensively discusses the recent progress, avenues and challenges in the approaches aimed at valorisation of agro-industrial wastes along with possible opportunities in the bioeconomy.

Enhancing microbial lipids yield for biodiesel production by oleaginous yeast Lipomyces starkeyi fermentation: A review

The enhanced production of microbial lipids suitable for manufacturing biodiesel from oleaginous yeast Lipomyces starkeyi is critically reviewed. Recent advances in several aspects involving the biosynthetic pathways of lipids, current conversion efficiencies using various carbon sources, intensification strategies for improving lipid yield and productivity in L. starkeyi fermentation, and lipid extraction approaches are analyzed from about 100 papers for the past decade. Key findings on strategies are summarized, including (1) optimization of parameters, (2) cascading two-stage systems, (3) metabolic engineering strategies, (4) mutagenesis followed by selection, and (5) co-cultivation of yeast and algae. The current technical limitations are analyzed. Research suggestions like examination of more gene targets via metabolic engineering are proposed. This is the first comprehensive review on the latest technical advances in strategies from the perspective of process and metabolic engineering to further increase the lipid yield and productivity from L. starkeyi fermentation.

Comparison of Ex-Situ and In-Situ Transesterification for the Production of Microbial Biodiesel

Microbial biodiesel is converted from microbial lipids via transesterification process. Most microbial biodiesel studies are focusing on the use of microalgal lipids as feedstock. Apart from using microalgae for lipid biosynthesis, lipids can also be extracted from other oleaginous microorganisms like fungi and yeast. However, there are gaps in the studies of lipid production from filamentous fungi, especially in-situ transesterification process. The aim of this project is to compare in-situ with the ex-situ transesterification of fungal biomass from Aspergillus oryzae. In ex-situ transesterification, two methods of lipid extraction, the Soxhlet extraction and the Bligh and Dyer extraction, were performed. For in-situ transesterification, two methods using different catalysts were investigated. Base-catalyzed in-situ transesterification of fungal biomass resulted on the highest Fatty Acid Methyl Esters (FAME) yield. The base-catalyzed in-situ transesterification was further optimized via Central Composite Design (CCD) of Response Surface Methodology (RSM). The parameters investigated were the catalyst loading, methanol to biomass ratio and reaction time. The optimization showed that the highest FAME yield was at 25.1% (w/w) with 10 minutes reaction time, 5% catalyst and 360:1 of the ratio of the methanol to biomass. Based on Analysis of Variance (ANOVA), the model was found to be significant according to the value of “Prob >F” of 0.0028. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Transcriptome analysis of Rhizopus oryzae seed pellet formation using triethanolamine

Rhizopus oryzae (R. oryzae) can effectively produce organic acids, and its pellet formation in seed cultures has been shown to significantly enhance subsequent fermentation processes. Despite advances in strain development, simple and effective methods for inducing pellet morphology and a basic understanding of the mechanisms controlling this process could facilitate substantial increases in efficiency and product output. Here, we report that 1.5% triethanolamine (TEOA) in seed culture medium can activate the growth of R. oryzae spores in compact and uniform pellets which is optimal for fermentation conditions. Analysis of fermentation kinetics showed that the production of fumaric and L-malic acid increases 293% and 177%, respectively. Transcriptomic analysis revealed that exposure of R. oryzae to 1.5% TEOA during the seed culture activated the phosphatidylinositol and mitogen-activated protein kinase signaling pathways. Theses pathways subsequently stimulated the downstream carbohydrate-active synthases and hydrolases that required for cell wall component synthesis and reconstruction. Our results thus provide insight into the regulatory pathways controlling pellet morphology germane to the viability of seed cultures, and provide valuable reference data for subsequent optimization of organic acid fermentation by R. oryzae.

Cutaneotrichosporon oleaginosus: A Versatile Whole-Cell Biocatalyst for the Production of Single-Cell Oil from Agro-Industrial Wastes

Cutaneotrichosporon oleaginosus is an oleaginous yeast with several favourable qualities: It is fast growing, accumulates high amounts of lipids and has a very broad substrate spectrum. Its resistance to hydrolysis by-products makes it a promising biocatalyst for custom tailored microbial oils. C. oleaginosus can accumulate up to 60 wt.% of its biomass as lipids. This species is able to grow by using several compounds as a substrate, such as acetic acid, biodiesel-derived glycerol, N-acetylglucosamine, lignocellulosic hydrolysates, wastepaper and other agro-industrial wastes. This review is focused on state-of-the-art innovative and sustainable biorefinery schemes involving this promising yeast and second- and third-generation biomasses. Moreover, this review offers a comprehensive and updated summary of process strategies, biomass pretreatments and fermentation conditions for enhancing lipid production by C. oleaginosus as a whole-cell biocatalyst. Finally, an overview of the main industrial applications of single-cell oil is reported together with future perspectives.

Waste-to-nutrition: a review of current and emerging conversion pathways

Residual biomass is acknowledged as a key sustainable feedstock for the transition towards circular and low fossil carbon economies to supply whether energy, chemical, material and food products or services. The latter is receiving increasing attention, in particular in the perspective of decoupling nutrition from arable land demand. In order to provide a comprehensive overview of the technical possibilities to convert residual biomasses into edible ingredients, we reviewed over 950 scientific and industrial records documenting existing and emerging waste-to-nutrition pathways, involving over 150 different feedstocks here grouped under 10 umbrella categories: (i) wood-related residual biomass, (ii) primary crop residues, (iii) manure, (iv) food waste, (v) sludge and wastewater, (vi) green residual biomass, (vii) slaughterhouse by-products, (viii) agrifood co-products, (ix) C₁ gases and (x) others. The review includes a detailed description of these pathways, as well as the processes they involve. As a result, we proposed four generic building blocks to systematize waste-to-nutrition conversion sequence patterns, namely enhancement, cracking, extraction and bioconversion. We further introduce a multidimensional representation of the biomasses suitability as potential as nutritional sources according to (i) their content in anti-nutritional compounds, (ii) their degree of structural complexity and (iii) their concentration of macro- and micronutrients. Finally, we suggest that the different pathways can be grouped into eight large families of approaches: (i) insect biorefinery, (ii) green biorefinery, (iii) lignocellulosic biorefinery, (iv) non-soluble protein recovery, (v) gas-intermediate biorefinery, (vi) liquid substrate alternative, (vii) solid-substrate fermentation and (viii) more-out-of-slaughterhouse by-products. The proposed framework aims to support future research in waste recovery and valorization within food systems, along with stimulating reflections on the improvement of resources' cascading use.

High value-added products derived from crude glycerol via microbial fermentation using Yarrowia clade yeast

BACKGROUND

Contemporary biotechnology focuses on many problems related to the functioning of developed societies. Many of these problems are related to health, especially with the rapidly rising numbers of people suffering from civilization diseases, such as obesity or diabetes. One factor contributing to the development of these diseases is the high consumption of sucrose. A very promising substitute for this sugar has emerged: the polyhydroxy alcohols, characterized by low caloric value and sufficient sweetness to replace table sugar in food production.

RESULTS

In the current study, yeast belonging to the Yarrowia clade were tested for erythritol, mannitol and arabitol production using crude glycerol from the biodiesel and soap industries as carbon sources. Out of the 13 tested species, Yarrowia divulgata and Candida oslonensis turned out to be particularly efficient polyol producers. Both species produced large amounts of these compounds from both soap-derived glycerol (59.8-62.7 g dm-3) and biodiesel-derived glycerol (76.8-79.5 g dm-3). However, it is equally important that the protein and lipid content of the biomass (around 30% protein and 12% lipid) obtained after the processes is high enough to use this yeast in the production of animal feed.

CONCLUSIONS

The use of waste glycerol for the production of polyols as well as utilization of the biomass obtained after the process for the production of feed are part of the development of modern waste-free technologies.

Rhodococcus as Biofactories for Microbial Oil Production

Bacteria belonging to the Rhodococcus genus are frequent components of microbial communities in diverse natural environments. Some rhodococcal species exhibit the outstanding ability to produce significant amounts of triacylglycerols (TAG) (>20% of cellular dry weight) in the presence of an excess of the carbon source and limitation of the nitrogen source. For this reason, they can be considered as oleaginous microorganisms. As occurs as well in eukaryotic single-cell oil (SCO) producers, these bacteria possess specific physiological properties and molecular mechanisms that differentiate them from other microorganisms unable to synthesize TAG. In this review, we summarized several of the well-characterized molecular mechanisms that enable oleaginous rhodococci to produce significant amounts of SCO. Furthermore, we highlighted the ability of these microorganisms to degrade a wide range of carbon sources coupled to lipogenesis. The qualitative and quantitative oil production by rhodococci from diverse industrial wastes has also been included. Finally, we summarized the genetic and metabolic approaches applied to oleaginous rhodococci to improve SCO production. This review provides a comprehensive and integrating vision on the potential of oleaginous rhodococci to be considered as microbial biofactories for microbial oil production.

A Brief Journey into the History of and Future Sources and Uses of Fatty Acids

Fats and lipids have always had a primary role in the history of humankind, from ancient civilisations to the modern and contemporary time, going from domestic and cosmetic uses, to the first medical applications and later to the large-scale industrial uses for food, pharmaceutical, cosmetics, and biofuel production. Sources and uses of those have changed during time following the development of chemical sciences and industrial technological advances. Plants, fish, and animal fats have represented the primary source of lipids and fats for century. Nowadays, the use of fatty acid sources has taken a turn: industries are mainly interested in polyunsaturated fatty acids (PUFAs), which have beneficial properties in human health; and also, for high-value fatty acids product for innovative and green production of biofuel and feedstocks. Thus, the constant increase in demand of fatty acids, the fact that marine and vegetable sources are not adequate to meet the high level of fatty acids required worldwide and climate change, have determined the necessity of the search for renewable and sustainable sources for fatty acids. Biotechnological advances and bioengineering have started looking at the genetic modification of algae, bacteria, yeasts, seeds, and plants to develop cell factory able to produce high value fatty acid products in a renewable and sustainable manner. This innovative approach applied to FA industry is a peculiar example of how biotechnology can serve as a powerful mean to drive the production of high value fatty acid derivatives on the concept of circular bioeconomy, based on the reutilisation of organic resources for alternative and sustainable productive patterns that are environmentally friendly.

Isolation of fast-growing thraustochytrids and seasonal variation on the fatty acid composition of thraustochytrids from mangrove regions of Navi Mumbai, India

This study was aimed to isolate fast-growing thraustochytrids and the influence of seasonal variation in fatty acid composition from the mangrove habitat. The thraustochytrids were isolated from fallen yellowish or green mangrove leaves, in four seasons, including winter, summer, rainy, and post rainy season in one year. The thraustochytrids were analyzed for biomass production, total lipid content, and fatty acid profile. The thraustochytrid isolates showed biomass yield and total lipid content in the range of 14.12 ± 0.69 to 22.98 ± 0.53 g/L and 34.98-58.86% per dry cell weight, respectively. The isolates showed two dominant fatty acids, palmitic acid (PA) as saturated fatty acid (SFA) and docosahexaenoic acid (DHA) as long-chain polyunsaturated fatty acids (LC-PUFA) in total fatty acid (TFA) content. The significant differences (P < 0.05) were observed for seasonal variations in SFA and DHA content in summer isolates and winter isolates. The maximum DHA content with 47.12% of TFA, recorded in winter (January) isolates and summer (April) isolates with SFA 68.82% of TFA. The results from this study were verified the hypothesis that the presence of high DHA producing thraustochytrids in lower temperature season in the same habitat. These findings have also emphasized the role of the environmental temperature conditions and the importance of thraustochytrid fatty acid composition as a dietary biomarker. Also, it revealed the ecological significance of thraustochytrid in DHA enrichment in the food web of the marine ecosystem. These findings could be useful while isolating thraustochytrids according to seasons for industrial application for omega 3 fatty acids and biodiesel production.

Microbial lipid biosynthesis from lignocellulosic biomass pyrolysis products

Lipids are a biorefinery platform to prepare fuel, food and health products. They are traditionally obtained from plants, but those of microbial origin allow for a better use of land and C resources, among other benefits. Several (thermo)chemical and biochemical strategies are used for the conversion of C contained in lignocellulosic biomass into lipids. In particular, pyrolysis can process virtually any biomass and is easy to scale up. Products offer cost-effective, renewable C in the form of readily fermentable molecules and other upgradable intermediates. Although the production of microbial lipids has been studied for 30 years, their incorporation into biorefineries was only described a few years ago. As pyrolysis becomes a profitable technology to depolymerize lignocellulosic biomass into assimilable C, the number of investigations on it raises significantly. This article describes the challenges and opportunities resulting from the combination of lignocellulosic biomass pyrolysis and lipid biosynthesis with oleaginous microorganisms. First, this work presents the basics of the individual processes, and then it shows state-of-the-art processes for the preparation of microbial lipids from biomass pyrolysis products. Advanced knowledge on separation techniques, structure analysis, and fermentability is detailed for each biomass pyrolysis fraction. Finally, the microbial fatty acid platform comprising biofuel, human food and animal feed products, and others, is presented. Literature shows that the microbial lipid production from anhydrosugars, like levoglucosan, and short-chain organic acids, like acetic acid, is straightforward. Indeed, processes achieving nearly theoretical yields form the latter have been described. Some authors have shown that lipid biosynthesis from different lignin sources is biochemically feasible. However, it still imposes major challenges regarding strain performance. No report on the fermentation of pyrolytic lignin is yet available. Research on the microbial uptake of pyrolytic humins remains vacant. Microorganisms that make use of methane show promising results at the proof-of-concept level. Overall, despite some issues need to be tackled, it is now possible to conceive new versatile biorefinery models by combining lignocellulosic biomass pyrolysis products and robust oleaginous microbial cell factories.

Recent advances in biotechnological production of polyunsaturated fatty acids by Yarrowia lipolytica

Owing to the important physiological functions, polyunsaturated fatty acids (PUFAs) play a vital role in protecting human health, such as preventing cancer, cardiovascular disease, and diabetes. Specifically, Yarrowia lipolytica has been identified as the most popular non-conventional oleaginous yeast, which can accumulate the abundant intracellular lipids, indicating that has great potential as an industrial host for production of PUFAs. Notably, some novel engineering strategies have been applied to endow and improve the abilities of Y. lipolytica to synthesize PUFAs, including construction and optimization of PUFAs biosynthetic pathways, improvement of preucrsors acetyl-coA and NADPH supply, inhibition of competing pathways, knockout of β-oxidation pathways, regulation of oxidative stress defense pathways, and regulation of genes involved in upstream lipid metabolism. Besides, some bypass approaches, such as strain mating, evolutionary engineering, and computational model based on omics, also have been proposed to improve the performance of engineering strains. Generally, in this review, we summarized the recent advances in engineering strategies and bypass approaches for improving PUFAs production by Y. lipolytica. In addition, we further summarized the latest efforts of CRISPR/Cas genome editing technology in Y. lipolytica, which is aimed to provide its potential applications in PUFAs production.

Advances in production of high-value lipids by oleaginous yeasts

The global market for high-value fatty acids production, mainly omega-3/6, hydroxy fatty-acids, waxes and their derivatives, has seen strong development in the last decade. The reason for this growth was the increasing utilization of these lipids as significant ingredients for cosmetics, food and the oleochemical industries. The large demand for these compounds resulted in a greater scientific interest in research focused on alternative sources of oil production - among which microorganisms attracted the most attention. Microbial oil production offers the possibility to engineer the pathways and store lipids enriched with the desired fatty acids. Moreover, costly chemical steps are avoided and direct commercial use of these fatty acids is available. Among all microorganisms, the oleaginous yeasts have become the most promising hosts for lipid production - their efficient lipogenesis, ability to use various (often highly affordable) carbon sources, feasible large-scale cultivations and wide range of available genetic engineering tools turns them into powerful micro-factories. This review is an in-depth description of the recent developments in the engineering of the lipid biosynthetic pathway with oleaginous yeasts. The different classes of valuable lipid compounds with their derivatives are described and their importance for human health and industry is presented. The emphasis is also placed on the optimization of culture conditions in order to improve the yield and titer of these valuable compounds. Furthermore, the important economic aspects of the current microbial oil production are discussed.

Genome Sequence Analysis of the Oleaginous Yeast, Rhodotorula diobovata, and Comparison of the Carotenogenic and Oleaginous Pathway Genes and Gene Products with Other Oleaginous Yeasts

Rhodotorula diobovata is an oleaginous and carotenogenic yeast, useful for diverse biotechnological applications. To understand the molecular basis of its potential applications, the genome was sequenced using the Illumina MiSeq and Ion Torrent platforms, assembled by AbySS, and annotated using the JGI annotation pipeline. The genome size, 21.1 MB, was similar to that of the biotechnological “workhorse”, R. toruloides. Comparative analyses of the R. diobovata genome sequence with those of other Rhodotorula species, Yarrowia lipolytica, Phaffia rhodozyma, Lipomyces starkeyi, and Sporidiobolus salmonicolor, were conducted, with emphasis on the carotenoid and neutral lipid biosynthesis pathways. Amino acid sequence alignments of key enzymes in the lipid biosynthesis pathway revealed why the activity of malic enzyme and ATP-citrate lyase may be ambiguous in Y. lipolytica and L. starkeyi. Phylogenetic analysis showed a close relationship between R. diobovata and R. graminis WP1. Dot-plot analysis of the coding sequences of the genes crtYB and ME1 corroborated sequence homologies between sequences from R. diobovata and R. graminis. There was, however, nonsequential alignment between crtYB CDS sequences from R. diobovata and those from X. dendrorhous. This research presents the first genome analysis of R. diobovata with a focus on its biotechnological potential as a lipid and carotenoid producer.