Improved production of various polyunsaturated fatty acids through filamentous fungus Mortierella alpina breeding

Characterization of potassium-solubilizing fungi, Mortierella spp., isolated from a poplar plantation rhizosphere soil

Potassium-solubilizing microorganisms are capable of secreting acidic chemicals that dissolve and release potassium from soil minerals, thus facilitating potassium uptake by plants. In this study, three potassium-dissolving filamentous fungi were isolated from the rhizosphere soil of a poplar plantation in Jiangsu Province, China. Phylogenetic analyses based on ITS, 18 S, and 28 S showed that these three isolates were most similar to Mortierella. These strains also possessed spherical or ellipsoidal spores, produced sporangia at the hyphal tip, and formed petal-like colonies on PDA media resembling those of Mortierella species. These findings, along with further phenotypic observations, suggest that these isolates were Mortierella species. In addition, the potassium-dissolution experiment showed that strain 2K4 had a relatively high potassium-solubilizing capacity among these isolated fungi. By investigating the influences of different nutrient conditions (carbon source, nitrogen source, and inorganic salt) and initial pH values on the potassium-dissolving ability, the optimal potassium-solubilization conditions of the isolate were determined. When potassium feldspar powder was used as an insoluble potassium source, isolate 2K4 exhibited a significantly better polysaccharide aggregation ability on the formed mycelium-potassium feldspar complex. The composition and content of organic acids secreted by strain 2K4 were further detected, and the potassium-dissolution mechanism of the Mortierella species and its growth promotion effect were discussed, using maize as an example.

The physiological and pathological properties of Mead acid, an endogenous multifunctional n-9 polyunsaturated fatty acid

Mead acid (MA, 5,8,11-eicosatrienoic acid) is an n-9 polyunsaturated fatty acid (PUFA) and a marker of essential fatty acid deficiency, but nonetheless generally draws little attention. MA is distributed in various normal tissues and can be converted to several specific lipid mediators by lipoxygenase and cyclooxygenase. Recent pathological and epidemiological studies on MA raise the possibility of its effects on inflammation, cancer, dermatitis and cystic fibrosis, suggesting it is an endogenous multifunctional PUFA. This review summarizes the biosynthesis, presence, metabolism and physiological roles of MA and its relation to various diseases, as well as the significance of MA in PUFA metabolism.

Flocculation of oleaginous green algae with Mortierella alpina fungi

Microalgae are promising sources of valuable bioproducts such as biofuels, food, and nutraceuticals. However, harvesting microalgae is challenging due to their small size and low biomass concentrations. To address this challenge, bio-flocculation of starchless mutants of Chlamydomonas reinhardtii (sta6/sta7) was investigated with Mortierella alpina, an oleaginous fungus with high concentrations of arachidonic acid (ARA). Triacylglycerides (TAG) reached 85 % of total lipids in sta6 and sta7 through a nitrogen regime. Scanning electron microscopy determined cell-wall attachment and extra polymeric substances (EPS) to be responsible for flocculation. An algal-fungal biomass ratio around 1:1 (three membranes) was optimal for bio-flocculation (80-85 % flocculation efficiency in 24 h). Nitrogen-deprived sta6/sta7 were flocculated with strains of M. alpina (NVP17b, NVP47, and NVP153) with aggregates exhibiting fatty acid profiles similar to C. reinhardtii, with ARA (3-10 % of total fatty acids). This study showcases M. alpina as a strong bio-flocculation candidate for microalgae and advances a mechanistic understanding of algal-fungal interaction.

Pioneering Metabolomic Studies on Diaporthe eres Species Complex from Fruit Trees in the South-Eastern Poland

Fungi from the genus Diaporthe have been reported as plant pathogens, endophytes, and saprophytes on a wide range of host plants worldwide. Their precise identification is problematic since many Diaporthe species can colonize a single host plant, whereas the same Diaporthe species can inhabit many hosts. Recently, Diaporthe has been proven to be a rich source of bioactive secondary metabolites. In our initial study, 40 Diaporthe isolates were analyzed for their metabolite production. A total of 153 compounds were identified based on their spectroscopic properties-Ultraviolet-visible and mass spectrometry. From these, 43 fungal metabolites were recognized as potential chemotaxonomic markers, mostly belonging to the drimane sesquiterpenoid-phthalide hybrid class. This group included mainly phytotoxic compounds such as cyclopaldic acid, altiloxin A, B, and their derivatives. To the best of our knowledge, this is the first report on the metabolomic studies on Diaporthe eres species complex from fruit trees in the South-Eastern Poland. The results from our study may provide the basis for the future research on the isolation of identified metabolites and on their bioactive potential for agricultural applications as biopesticides or biofertilizers.

Metabolic disorder and intestinal microflora dysbiosis in chronic inflammatory demyelinating polyradiculoneuropathy

OBJECTIVE

Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is a rare acquired immune-mediated neuropathy. Although microbial infection is potentially a contributing factor, a causative link between CIDP and microbial infection remains unclear. There is also no definitive biomarker for CIDP diagnostics and therapies. The present study aimed to characterize the serum metabolic profile and gut microbiome structure in CIDP.

METHODS

Targeted metabolomics profiling of serum, using liquid chromatography-mass spectrometry, and metagenomics sequencing of stool samples from a cohort of CIDP and non-CIDP subjects were performed to evaluate serum metabolic profiles and gut microbiome structure in CIDP subjects relative to healthy controls.

RESULTS

Metabolome data revealed that the bile acids profile was perturbed in CIDP with bile acids and arachidonic acid enriched significantly in CIDP versus non-CIDP controls. Metagenome data revealed that opportunistic pathogens, such as Klebsiella pneumonia and Megamonas funiformis, and genes involved in bacterial infection were notably more abundant in CIDP subjects, while gut microbes related to biotransformation of secondary bile acids were abnormal in CIDP versus non-CIDP subjects. Correlation analysis revealed that changes in secondary bile acids were associated with altered gut microbes, including Bacteroides ovatus, Bacteroides caccae, and Ruminococcus gnavus.

CONCLUSION

Bile acids and arachidonic acid metabolism were disturbed in CIDP subjects and might be affected by the dysbiosis of gut microbial flora. These findings suggest that the combination of bile acids and arachidonic acid could be used as a CIDP biomarker and that modulation of gut microbiota might impact the clinical course of CIDP.

Engineering and fermenter production of fungi GLA in Pichia pastoris GS115 using oil waste

γ-Linolenic acid (GLA) is an essential n-6 polyunsaturated fatty acid (PUFA) that has received considerable attention in human and animal feed. GLA is used in many nutritional and medicinal applications, such as the treatment of cancer, inflammatory disorders, and diabetes. Currently, plant seed is the primary dietary source of GLA that is not enough to utilize on an industrial scale. To generate a sustainable novel source of GLA, the gene of delta-6 desaturase, one of the essential enzymes in the GLA production pathway, was isolated from Mucor rouxii DSM1194 and expressed in P. pastoris GS115 by pPICZC vector. The recombinant yeast expressed the GLA up to 19.2% (72 mg/g) of total fatty acids. GLA production of recombinant yeast was studied in a fermenter by oil waste for 5 days, and results detected 6.3 g/l lipid, and 103 mg/g GLA was produced in 72 h. The present study may provide an opportunity to develop an alternative host for manufacturing GLA on an industrial scale.

Fungal and bacterial oxylipins are signals for intra- and inter-cellular communication within plant disease

Lipids are central at various stages of host-pathogen interactions in determining virulence and modulating plant defense. Free fatty acids may act as substrates for oxidizing enzymes [e.g., lipoxygenases (LOXs) and dioxygenases (DOXs)] that synthesize oxylipins. Fatty acids and oxylipins function as modulators of several pathways in cell-to-cell communication; their structural similarity among plant, fungal, and bacterial taxa suggests potential in cross-kingdom communication. We provide a prospect of the known role of fatty acids and oxylipins in fungi and bacteria during plant-pathogen interactions. In the pathogens, oxylipin-mediated signaling pathways are crucial both in development and host infection. Here, we report on case studies suggesting that oxylipins derived from oleic, linoleic, and linolenic acids are crucial in modulating the pathogenic lifestyle in the host plant. Intriguingly, overlapping (fungi-plant/bacteria-plant) results suggest that different inter-kingdom pathosystems use similar lipid signals to reshape the lifestyle of the contenders and occasionally determine the outcome of the challenge.

Immune Response and Fatty Acid Profile of Eggs from Laying Hens Fed Fermented Feed Rich in Polyunsaturated Fatty Acids

Western diets are dominated by the consumption of chemically modified foods, characterized by a deficiency of n-3 polyunsaturated fatty acids (PUFAs). Lack of n-3 PUFAs is also present in livestock feed, which negatively affects livestock health, including immune response, and results in a low content of n-3 PUFAs in animal products. The goal of this experiment was to study the effect of the addition of feed containing PUFAs produced by the fungus Mortierella alpina on immune parameters (IgA, MUC-2, IGF-2, phagocytoses and selected lymphocyte subsets) and the composition of the intestinal microbiota of hens and egg fatty acids profile. Hens were divided into groups (control, F10—supplemented with 10% of fermented feed, F15—supplemented with 15% of fermented feed). The relative expression of all genes was markedly upregulated, mainly in the F15 group. Likewise, in F15, a significant increase in both phagocytes engulfing capacity and the level of oxidative burst was observed. Neither CD T cell subpopulations nor the CD4/CD8 ratio were significantly affected. A significant increase in small intestinal enterobacteria was observed in the F15. The fatty acid profile of eggs in both experimental groups showed an increased proportion of n-3 PUFAs and decreased n-6/n-3 PUFAs ratio. The results of this work show that the addition of 15% omega-3 acids enriched fermented feed positively affected the immune response of laying hens and improved the fatty acid composition of eggs.

Habitat, Snow-Cover and Soil pH, Affect the Distribution and Diversity of Mortierellaceae Species and Their Associations to Bacteria

Mortierellaceae species are among the most frequent and globally distributed soil fungi. However, the factors shaping their diversity and distribution remain obscure. Several species have been reported to be associated to bacteria, but the kind and frequency of such associations were not addressed up to now. We hypothesized that such associations could be important for Mortierellaceae ecology. Therefore, our aim was to understand the driving factors responsible for the Mortierellaceae diversity, community composition and bacterial associations in alpine and subalpine habitats. For answering our question, we collected both snow-free and snow-covered soil at sampling sites from different habitats: bare alpine soil in a glacier forefield, alpine dwarf-willow habitats, and high-altitude Pinus cembra forests. The isolations were carried out by direct cultivation without any antibiotics to the isolation media. Altogether, we obtained 389 Mortierellaceae isolates representing 29 operational taxonomic units (OTUs). Many OTUs could be placed to the genera Mortierella sensu stricto, Dissophora, Entomortierella, Gamsiella, Linnemannia, and Podila, but others could not unambiguously be assigned to a genus. Our results demonstrate that both, the distribution as well as the diversity of the Mortierellaceae species, were significantly influenced by habitat, soil pH, and snow-cover. We noticed that >30% of our isolates were associated to a non-contaminant bacterium. The bacteria associated to our Mortierellaceae isolates belonged to seven different genera. Pseudomonas was the most frequently detected genus associated to the isolated Mortierellaceae species and it was found to be species-specific. Mortierellaceae–bacteria pairs, including those with Pseudomonas, were influenced by location, habitat, and snow-cover. The majority of the fungus–bacterium associations were potentially epihyphal, but we also detected potential endohyphal bacterial species belonging to Mycoavidus, Burkholderiaceae, and Paraburkholderia. Taken together, the non-random associations we detected suggest that fungus–bacterium associations are ecologically meaningful – an interesting path that needs to be investigated further.

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.

Characterization of ω3 fatty acid desaturases from oomycetes and their application toward eicosapentaenoic acid production in Mortierella alpina

ω3 Polyunsaturated fatty acids are currently obtained mainly from fisheries; thus, sustainable alternative sources such as oleaginous microorganisms are required. Here, we describe the isolation, characterization, and application of 3 novel ω3 desaturases with ω3 polyunsaturated fatty acid-producing activity at ordinary temperatures (28 °C). First, we selected Pythium sulcatum and Plectospira myriandra after screening for oomycetes with high eicosapentaenoic acid/arachidonic acid ratios and isolated the genes psulω3 and pmd17, respectively, which encode ω3 desaturases. Subsequent characterization showed that PSULω3 exhibited ω3 desaturase activity on both C18 and C20 ω6 polyunsaturated fatty acids while PMD17 exhibited ω3 desaturase activity exclusively on C20 ω6 polyunsaturated fatty acids. Expression of psulω3 and pmd17 in the arachidonic acid-producer Mortierella alpina resulted in transformants that produced eicosapentaenoic acid/total fatty acid values of 38% and 40%, respectively, at ordinary temperatures. These ω3 desaturases should facilitate the construction of sustainable ω3 polyunsaturated fatty acid sources.

Enhancement of lipid productivity from a promising oleaginous fungus

Oleaginous fungi have recently gained increasing attention among different microorganisms due to their ability for lipid production for the preparation of biofuel. In the present study, a locally isolated fungus E45, identified genetically as Aspergillus sp. strain EM2018, was found to produce 25.2% of the total lipids content of its dry cell weight (DCW). Optimization of culture conditions was performed and lipid accumula­tion increased by about 2.4 fold (from 25.2% to 60.1% of DCW) when the fungus was grown for seven days in the potato dextrose (50 g/L) liquid medium at pH 5.0, incubation temperature at 30 ºC and inoculum size of 2 × 106 spore/mL. Supplementation of the medium with yeast extract and NaNO3 at a concentration of 0.05% as organic and inorganic nitrogen sources, respectively, increased lipid production (53.3% lipid/dry biomass). Gas chromatography analysis of fungal lipids revealed the presence of saturated (mainly palmitic acid C16:0 (33%) and lignoceric acid C24:0 (15%)) and unsaturated fatty acids in different proportions (mainly linoleic acid C18:2 (24.4%), oleica cid C18:1 (14%) and arachidonic C20:4 (7.4%). These findings suggest this new oleaginous fungus as a promising feedstock for various industrial applications and for the preparation of biodiesel.

The Role of Glyceraldehyde-3-Phosphate Dehydrogenases in NADPH Supply in the Oleaginous Filamentous Fungus Mortierella alpina

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a highly conserved enzyme within the glycolytic pathway. GAPDH catalyzes the transformation of glyceraldehyde 3-phosphate to glycerate-1, 3-biphosphate, a process accompanied by the production of NADH. Its role in the NADPH production system of the oleaginous filamentous fungus Mortierella alpina was explored. Two copies of genes encoding GAPDH were characterized, then endogenously overexpressed and silenced through Agrobacterium tumefaciens-mediated transformation methods. The results showed that the lipid content of the overexpression strain, MA-GAPDH1, increased by around 13%. RNA interference of GAPDH1 and GAPDH2 (MA-RGAPDH1 and MA-RGAPDH2) greatly reduced the biomass of the fungus. The lipid content of MA-RGAPDH2 was found to be about 23% higher than that of the control. Both of the lipid-increasing transformants showed a higher NADPH/NADP ratio. Analysis of metabolite and enzyme expression levels revealed that the increased lipid content of MA-GAPDH1 was due to enhanced flux of glyceraldehyde-3-phosphate to glycerate-1, 3-biphosphate. MA-RGAPDH2 was found to strengthen the metabolic flux of dihydroxyacetone phosphate to glycerol-3-phosphate. Thus, GAPDH1 contributes to NADPH supply and lipid accumulation in M. alpina, and has a distinct role from GAPDH2.

The Beneficial Root-Colonizing Fungus Mortierella hyalina Promotes the Aerial Growth of Arabidopsis and Activates Calcium-Dependent Responses That Restrict Alternaria brassicae-Induced Disease Development in Roots

The endophytic fungus Mortierella hyalina colonizes the roots of Arabidopsis thaliana and stimulates growth and biomass production of the aerial parts but not of roots. An exudate fraction from the fungus induces rapid and transient cytoplasmic Ca²⁺elevation in the roots. The Ca²⁺ response does not require the well-characterized (co)receptors BAK1, CERK1, and FLS2 for pathogen-associated molecular patterns, and the Ca²⁺ channels GLR-2.4, GLR-2.5, and GLR-3.3 or the vacuolar TWO PORE CHANNEL1, which might be involved in cytoplasmic Ca²⁺ elevation. We isolated an ethyl-methane-sulfonate-induced Arabidopsis mutant that is impaired in this Ca²⁺ response. The roots of the mutant are impaired in M. hyalina-mediated suppression of immune responses after Alternaria brassicae infection, i.e., jasmonate accumulation, generation of reactive oxygen species, as well as the activation of jasmonate-related defense genes. Furthermore, they are more colonized by M. hyalina than wild-type roots. We propose that the mutant gene product is involved in a Ca²⁺-dependent signaling pathway activated by M. hyalina to suppress immune responses in Arabidopsis roots.

Microbial Lipid Alternatives to Plant Lipids

Lipids are in high demand in food production, nutritional supplements, detergents, lubricants, and biofuels. Different oil seeds produced from plants are conventionally extracted to yield lipids. With increasing population and reduced availability of cultivable land, conventional methods of producing lipids alone will not satisfy increasing demand. Lipids produced using different microbial sources are considered as sustainable alternative to plant derived lipids. Various microorganisms belonging to the genera of algae, bacteria, yeast, fungi, or marine-derived microorganisms such as thraustochytrids possess the ability to accumulate lipids in their cells. A variety of microbial production technologies are being used to cultivate these organisms under specific conditions using agricultural residues as carbon source to be cost competitive with plant derived lipids. Microbial oils, also known as single cell oils, have many advantages when compared with plant derived lipids, such as shorter life cycle, less labor required, season and climate independence, no use of arable land and ease of scale-up. In this chapter we compare the lipids derived from plants and different microorganisms. We also highlight various analytical techniques that are being used to characterize the lipids produced in oleaginous organisms and their applications in various processes.

Enhancing oil production and harvest by combining the marine alga Nannochloropsis oceanica and the oleaginous fungus Mortierella elongata

BACKGROUND

Although microalgal biofuels have potential advantages over conventional fossil fuels, high production costs limit their application in the market. We developed bio-flocculation and incubation methods for the marine alga, Nannochloropsis oceanica CCMP1779, and the oleaginous fungus, Mortierella elongata AG77, resulting in increased oil productivity.

RESULTS

By growing separately and then combining the cells, the M. elongata mycelium could efficiently capture N. oceanica due to an intricate cellular interaction between the two species leading to bio-flocculation. Use of a high-salt culture medium induced accumulation of triacylglycerol (TAG) and enhanced the contents of polyunsaturated fatty acids (PUFAs) including arachidonic acid and docosahexaenoic acid in M. elongata. To increase TAG productivity in the alga, we developed an effective, reduced nitrogen-supply regime based on ammonium in environmental photobioreactors. Under optimized conditions, N. oceanica produced high levels of TAG that could be indirectly monitored by following chlorophyll content. Combining N. oceanica and M. elongata to initiate bio-flocculation yielded high levels of TAG and total fatty acids, with ~ 15 and 22% of total dry weight (DW), respectively, as well as high levels of PUFAs. Genetic engineering of N. oceanica for higher TAG content in nutrient-replete medium was accomplished by overexpressing DGTT5, a gene encoding the type II acyl-CoA:diacylglycerol acyltransferase 5. Combined with bio-flocculation, this approach led to increased production of TAG under nutrient-replete conditions (~ 10% of DW) compared to the wild type (~ 6% of DW).

CONCLUSIONS

The combined use of M. elongata and N. oceanica with available genomes and genetic engineering tools for both species opens up new avenues to improve biofuel productivity and allows for the engineering of polyunsaturated fatty acids.

Metabolic engineering of oleaginous fungus Mortierella alpina for high production of oleic and linoleic acids

The aim of this work was to study the molecular breeding of oleaginous filamentous Mortierella alpina for high production of linoleic (LA) or oleic acid (OA). Heterologous expression of the Δ12-desaturase (DS) gene derived from Coprinopsis cinerea in the Δ6DS activity-defective mutant of M. alpina increased the LA production rate as to total fatty acid to 5 times that in the wild strain. By suppressing the endogenous Δ6I gene expression by RNAi in the Δ12DS activity-defective mutant of M. alpina, the OA accumulation rate as to total fatty acid reached 68.0%. The production of LA and OA in these transformants reached 1.44 and 2.76g/L, respectively, on the 5th day. The Δ6I transcriptional levels of the RNAi-treated strains were suppressed to 1/10th that in the parent strain. The amount of Δ6II RNA in the Δ6I RNAi-treated strain increased to 8 times that in the wild strain.

Stable Carbon Isotope Composition of the Lipids in Natural Ophiocordyceps sinensis from Major Habitats in China and Its Substitutes

Ophiocordyceps sinensis is one rare medicinal fungus produced in the Qinghai-Tibetan Plateau. Its quality and price varies hugely with different habitat, and its numerous substitutes have sprung up in functional food markets. This paper aims to discriminate the geographic origin of wild O. sinensis and its substitutes via element analyzer-isotope ratio mass spectrometry and gas chromatography-isotope ratio mass spectrometry. The δ13C values of major fatty acids in the lipids of O. sinensis are characterized unanimously by the variation relation C18:0 < C18:2 ≈ C16:0 < C18:1, while their fluctuation intervals are notably different between those of neutral and polar lipids. The comparative analysis of the δ13C ratios of major fatty acids in lipids of O. sinensis suggests that the δ13C patterns may be sensitive potential indicators to discriminate its geographical origin. The δ13C values of individual major fatty acids of lipids from the cultivated stromata of Cordyceps militaris (SCM), the fermented mycelia of Hirsurella sinensis (FMH) and Paecilomyces epiali (FMP) range from -31.2‰ to -29.7‰, -16.9‰ to -14.3‰, and -26.5‰ to -23.9‰, respectively. Their δ13C pattern of individual major fatty acids may be used as a potential indicator to discriminate the products of natural O. sinensis and its substitutes.

Effects of aeration on metabolic profiles of Mortierella alpina during the production of arachidonic acid

To investigate the metabolic regulation against oxygen supply, comparative metabolomics was performed to explore the metabolic responses of Mortierella alpina in the process of arachidonic acid (ARA) production. More than 110 metabolites involved in Embden–Meyerhof–Parnas pathway, pentose phosphate pathway, tricarboxylic acid cycle, inositol phosphate metabolism, fatty acid biosynthesis, and amino acid metabolism were identified by gas chromatography–mass spectrometry. Samples at different aeration rates were clearly distinguished by principal components analysis and partial least squares analysis, indicating that oxygen supply had a profound effect on the metabolism of M. alpina. Eleven major metabolites were identified as potential biomarkers to be primarily responsible for the difference of metabolism. Further study of metabolic changes with the relevant pathways demonstrated that the levels of several intermediate metabolites in relation to central carbon metabolism changed remarkably via both processes and citrate and malate was supposed to play vital roles in polyunsaturated acid (PUFA) synthesis. Increase of myo-inositol and sorbitol were probably for osmo-regulation and redox balance, while enhanced phosphoric acid and pyroglutamic acid were supposed to have function in the activation of signal transduction pathway for stress resistance. The present study provides a novel insight into the metabolic responses of M. alpina to aeration rates and the metabolic characteristics during the ARA fermentation.

Microbial oil - A plausible alternate resource for food and fuel application

Microbes have recourse to low-priced substrates like agricultural wastes and industrial efflux. A pragmatic approach towards an emerging field- the exploitation of microbial oils for biodiesel production, pharmaceutical and cosmetic applications, food additives, biopolymer production will be of immense remunerative significance in the near future. Due to high free fatty acid, nutritive content and simpler solvent extraction processes of microbial oils with plant oil, microbial oils can back plant oils in food applications. The purpose of this review is to evaluate the opulence of lipid production in native and standard micro-organisms and also to emphasize the vast array of applications including food and fuel by obtaining maximum yield.

Influence of Supplementation of Vegetable Oil Blends on Omega-3 Fatty Acid Production in Mortierella alpina CFR-GV15

Objectives of this study were designed for improved production of mycelial omega-3 fatty acids with particular reference to EPA and DHA from the oleaginous fungus Mortierella alpina CFR-GV15 under submerged low temperatures fermentation supplemented with linseed oil and garden cress oil as an additional energy source. The fungus was grown at 20°C temperature for four days initially followed by 12°C temperature for next five days. The basal medium contained starch, yeast extract, and a blend of linseed oil (LSO) and garden cress oil (GCO) in the ratio 1 : 1. Results of the study revealed that, after nine days of total incubation period, the enhancement of biomass was up to 16.7 g/L dry weight with a total lipid content of 55.4% (v/w). Enrichment of omega-3 fatty acids indicated a significant increase in fatty acid bioconversion (ALA 32.2 ± 0.42%, EPA 7.9 ± 0.1%, and DHA 4.09 ± 0.2%) by 2.5-fold. The two-stage temperature cultivation alters the fatty acid profile due to activation of the desaturase enzyme in the cellular levels due to which arachidonic acid (AA) content reduced significantly. It can be concluded that Mortierella alpina CFR-GV15 is a fungal culture suitable for commercial production of PUFAs with enriched EPA and DHA.

Differential expression of desaturase genes and changes in fatty acid composition of Mortierella sp. AGED in response to environmental factors

BACKGROUND

Some oleaginous fungi can produce large amounts of polyunsaturated fatty acids (PUFAs) which serve many physiological functions. Numerous desaturases are critical for the synthesis of PUFAs. This study aimed to investigate the regulation of lipid production and desaturase gene expression in Mortierella sp. AGED in response to different environmental factors, and the relationships between lipid production and desaturase gene expression.

RESULTS

The fatty acid composition and mRNA levels of desaturase genes were significantly changed under low temperatures. With the exception of Δ5-desaturase, the transcript levels of all desaturase genes increased at a temperature of 20 °C. Changes in content of lipid and PUFAs responding to low temperature were consistent with desaturase gene expression. Time course studies on gene expression showed that mRNA levels of four desaturase genes increased rapidly after transferring the cells to low temperature. Ethanol (1.5% v/v) increased the transcript levels of Δ9-, Δ6- and Δ5-desaturase genes significantly and of Δ12-desaturase gene slightly. Different metal ions such as Ca²⁺ , Zn²⁺ and Fe³⁺ could stimulate PUFA synthesis and up-regulate desaturase gene transcription, while Cu²⁺ inhibited desaturase gene expression and lipid accumulation.

CONCLUSION

This study should enable us to understand the regulatory mechanism of desaturase gene expression and lipid synthesis. It is helpful to improve PUFA productivity in Mortierella sp. AGED. © 2016 Society of Chemical Industry.

Enhanced polyunsaturated fatty acids production in Mortierella alpina by SSF and the enrichment in chicken breasts

BACKGROUND

Distiller's dried grains with solubles (DDGS) and soybean meal were used as the substrates for the production of polyunsaturated fatty acids (PUFA) in solid-state fermentation (SSF) by Mortierella alpine. These fermented products were fed to laying hens. PUFA enrichment from chicken breasts was studied.

METHODS

The maximum productivity of PUFA was achieved under optimized process condition, including 1% w/w yeast extract as additive, an incubation period of 5 days at 12°C, 10% v/w inoculum level, 75% moisture content, and pH 6.0. The hens were then fed with ration containing soybean DDGS, rapeseed oil, soybean oil, and peanut oil. The control group was fed with basal ration.

RESULTS

Under the optimal condition, M. alpine produced total fatty acids (TFA) of 182.34 mg/g dry substrate. It has better mycelial growth when soybean meal was added to DDGS (SDDGS). PUFA in fermentation product increased with higher soybean meal content. The addition of 70% soybean meal to DDGS substrate yielded 175.16 mg of TFA, including 2.49 mg eicosapentaenoic acid (EPA) and 5.26 mg docosahexaenoic acid (DHA). The ratios of ω-6/ω-3 found in chicken breasts fat were all lower than that found in control by 36.98, 31.51, 18.15, and 12.63% for SDDGS, rapeseed oil, soybean oil, and peanut oil, respectively.

CONCLUSIONS

This study identified an optimized SSF process to maximize PUFA productivity by M. alpine as the strain. This PUFA-enriched feed increased the PUFA contents as well as the proportions of ω-6 and ω-3 in chicken breasts and liver.

Production Strategies and Applications of Microbial Single Cell Oils

Polyunsaturated fatty acids (PUFAs) of the ω-3 and ω-6 class (e.g., α-linolenic acid, linoleic acid) are essential for maintaining biofunctions in mammalians like humans. Due to the fact that humans cannot synthesize these essential fatty acids, they must be taken up from different food sources. Classical sources for these fatty acids are porcine liver and fish oil. However, microbial lipids or single cell oils, produced by oleaginous microorganisms such as algae, fungi and bacteria, are a promising source as well. These single cell oils can be used for many valuable chemicals with applications not only for nutrition but also for fuels and are therefore an ideal basis for a bio-based economy. A crucial point for the establishment of microbial lipids utilization is the cost-effective production and purification of fuels or products of higher value. The fermentative production can be realized by submerged (SmF) or solid state fermentation (SSF). The yield and the composition of the obtained microbial lipids depend on the type of fermentation and the particular conditions (e.g., medium, pH-value, temperature, aeration, nitrogen source). From an economical point of view, waste or by-product streams can be used as cheap and renewable carbon and nitrogen sources. In general, downstream processing costs are one of the major obstacles to be solved for full economic efficiency of microbial lipids. For the extraction of lipids from microbial biomass cell disruption is most important, because efficiency of cell disruption directly influences subsequent downstream operations and overall extraction efficiencies. A multitude of cell disruption and lipid extraction methods are available, conventional as well as newly emerging methods, which will be described and discussed in terms of large scale applicability, their potential in a modern biorefinery and their influence on product quality. Furthermore, an overview is given about applications of microbial lipids or derived fatty acids with emphasis on food applications.

Role of dihydrofolate reductase in tetrahydrobiopterin biosynthesis and lipid metabolism in the oleaginous fungus Mortierella alpina

Mortierella alpina is a well-known polyunsaturated fatty acid-producing oleaginous fungus. Analysis of the Mort. alpina genome suggests that there is a putative dihydrofolate reductase (DHFR) gene playing a role in the salvage pathway of tetrahydrobiopterin (BH4), which has never been explored in fungi before. DHFR is the sole source of tetrahydrofolate and plays a key role in maintaining BH4 levels. Transcriptome data analysis revealed that DHFR was up-regulated by nitrogen exhaustion, when Mort. alpina starts to accumulate lipids. Significant changes were found in the fatty acid profile in Mort. alpina grown on medium containing DHFR inhibitors compared to Mort. alpina grown on medium without inhibitors. To explore the role of DHFR in folate/BH4 metabolism and its relationship to lipid biosynthesis, we expressed heterologously the gene encoding DHFR from Mort. alpina in Escherichia coli and we purified the recombinant enzyme to homogeneity. The enzymatic activity was investigated by liquid chromatography and MS and VIS-UV spectroscopy. The kinetic parameters and the effects of temperature, pH, metal ions and inhibitors on the activity of DHFR were also investigated. The transcript level of cytosolic NADPH-producing gene involved in folate metabolism is down-regulated by DHFR inhibitors, which highlights the functional significance of DHFR in lipid biosynthesis. The relationship between DHFR and lipid metabolism is thus of major importance, and folate metabolism may be an alternative NADPH source in fatty acid synthesis. To our knowledge, this study is the first to report the comprehensive characterization of a BH4salvage pathway in a fungus.

Vegetable Oil: Nutritional and Industrial Perspective

Oils of plant origin have been predominantly used for food-based applications. Plant oils not only represent a non-polluting renewable resource but also provide a wide diversity in fatty acids (FAs) composition with diverse applications. Besides being edible, they are now increasingly being used in industrial applications such as paints, lubricants, soaps, biofuels etc. In addition, plants can be engineered to produce fatty acids which are nutritionally beneficial to human health. Thus these oils have potential to 1) substitute ever increasing demand of non –renewable petroleum sources for industrial application and 2) also spare the marine life by providing an alternative source to nutritionally and medically important long chain polyunsaturated fatty acids or ‘Fish oil’. The biochemical pathways producing storage oils in plants have been extensively characterized, but the factors regulating fatty acid synthesis and controlling total oil content in oilseed crops are still poorly understood. Thus understanding of plant lipid metabolism is fundamental to its manipulation and increased production. This review on oils discusses fatty acids of nutritional and industrial importance, and approaches for achieving future designer vegetable oil for both edible and non-edible uses. The review will discuss the success and bottlenecks in efficient production of novel FAs in non-native plants using genetic engineering as a tool.

Production of GDP-l-fucose from exogenous fucose through the salvage pathway in Mortierella alpina

This study is the first to report a comprehensive characterization of GDP-l-fucose pyrophosphorylase (GFPP) in a fungus.

Directed optimization of a newly identified squalene synthase from Mortierella alpine based on sequence truncation and site-directed mutagenesis

Terpenoids, a class of isoprenoids usually isolated from plants, are always used as commercial flavor and anticancer drugs. As a key precursor for triterpenes and sterols, biosynthesis of squalene (SQ) can be catalyzed by squalene synthase (SQS) from two farnesyl diphosphate molecules. In this work, the key SQS gene involved in sterols synthesis by Mortierella alpine, an industrial strain often used to produce unsaturated fatty acid such as γ-linolenic acid and arachidonic acid, was identified and characterized. Bioinformatic analysis indicated that MaSQS contained 416 amino acid residues involved in four highly conserved regions. Phylogenetic analysis revealed the closest relationship of MaSQS with Ganoderma lucidum and Aspergillus, which also belonged to the member of the fungus. Subsequently, the recombinant protein was expressed in Escherichia coli BL21(DE3) and detected by SDS-PAGE. To improve the expression and solubility of protein, 17 or 27 amino acids in the C-terminal were deleted. In vitro activity investigation based on gas chromatography–mass spectrometry revealed that both the truncated enzymes could functionally catalyze the reaction from FPP to SQ and the enzymatic activity was optimal at 37 °C, pH 7.2. Moreover, based on the site-directed mutagenesis, the mutant enzyme mMaSQSΔC17 (E186K) displayed a 3.4-fold improvement in catalytic efficiency (k  cat/K  m) compared to the control. It was the first report of characterization and modification of SQS from M. alpine, which facilitated the investigation of isoprenoid biosynthesis in the fungus. The engineered mMaSQSΔC17 (E186K) can be a potential candidate of the terpenes and steroids synthesis employed for synthetic biology.

A Caleosin-Like Protein with Peroxygenase Activity Mediates Aspergillus flavus Development, Aflatoxin Accumulation, and Seed Infection

Caleosins are a small family of calcium-binding proteins endowed with peroxygenase activity in plants. Caleosin-like genes are present in fungi; however, their functions have not been reported yet. In this work, we identify a plant caleosin-like protein in Aspergillus flavus that is highly expressed during the early stages of spore germination. A recombinant purified 32-kDa caleosin-like protein supported peroxygenase activities, including co-oxidation reactions and reduction of polyunsaturated fatty acid hydroperoxides. Deletion of the caleosin gene prevented fungal development. Alternatively, silencing of the gene led to the increased accumulation of endogenous polyunsaturated fatty acid hydroperoxides and antioxidant activities but to a reduction of fungal growth and conidium formation. Two key genes of the aflatoxin biosynthesis pathway, aflR and aflD, were downregulated in the strains in which A. flavus PXG (AfPXG) was silenced, leading to reduced aflatoxin B1 production in vitro. Application of caleosin/peroxygenase-derived oxylipins restored the wild-type phenotype in the strains in which AfPXG was silenced. PXG-deficient A. flavus strains were severely compromised in their capacity to infect maize seeds and to produce aflatoxin. Our results uncover a new branch of the fungal oxylipin pathway and may lead to the development of novel targets for controlling fungal disease.

Identification of a critical determinant that enables efficient fatty acid synthesis in oleaginous fungi

Microorganisms are valuable resources for lipid production. What makes one microbe but not the other able to efficiently synthesize and accumulate lipids is poorly understood. In the present study, global gene expression prior to and after the onset of lipogenesis was determined by transcriptomics using the oleaginous fungus Mortierella alpina as a model system. A core of 23 lipogenesis associated genes was identified and their expression patterns shared a high similarity among oleaginous microbes Chlamydomonas reinhardtii, Mucor circinelloides and Rhizopus oryzae but was dissimilar to the non-oleaginous Aspergillus nidulans. Unexpectedly, Glucose-6-phosphate dehydrogenase (G6PD) and 6-phosphogluconate dehydrogenase (PGD) in the pentose phosphate pathway (PPP) were found to be the NADPH producers responding to lipogenesis in the oleaginous microbes. Their role in lipogenesis was confirmed by a knockdown experiment. Our results demonstrate, for the first time, that the PPP plays a significant role during fungal lipogenesis. Up-regulation of NADPH production by the PPP, especially G6PD, may be one of the critical determinants that enables efficiently fatty acid synthesis in oleaginous microbes.

Screening and molecular identification of overproducing γ-linolenic acid fungi and cloning the delta 6-desaturase gene

This research aims at isolating and identifying γ-linolenic acid (GLA)-producing fungi in the traditional Chinese salt-fermented soybean food, Douchi, from Yongchuan, People's Republic of China. In this study, Rhizopus oryzae DR3 was identified as a novel fungal species that produces large amounts of GLA. A full-length cDNA, designated as RoD6 D, with high homology to fungal △6 fatty acid desaturase genes was isolated from R. oryzae by using the rapid amplification of cDNA ends method. It had an open reading frame of 1,176 bp encoding a deduced polypeptide of 391 amino acids. Bioinformatics analysis characterized the putative RoD6 D protein as a typical membrane-bound desaturase, including three conserved histidine-rich motifs, a hydropathy profile, and a cytochrome b5 -like domain in the N-terminus. When the coding sequence was expressed in the Saccharomyces cerevisiae strain INVScl, the encoded product of RoD6 D exhibited △6 fatty acid desaturase activity that led to the accumulation of GLA. The results show that Douchi contains a large natural diverse composition, and some strains could be selected as starters for functional fermented foods. This study has also laid a foundation for developing functional Douchi products for further research.

Gene targeting in the oil-producing fungus Mortierella alpina 1S-4 and construction of a strain producing a valuable polyunsaturated fatty acid

To develop an efficient gene-targeting system in Mortierella alpina 1S-4, we identified the ku80 gene encoding the Ku80 protein, which is involved in the nonhomologous end-joining pathway in genomic double-strand break (DSB) repair, and constructed ku80 gene-disrupted strains via single-crossover homologous recombination. The Δku80 strain from M. alpina 1S-4 showed no negative effects on vegetative growth, formation of spores, and fatty acid productivity, and exhibited high sensitivity to methyl methanesulfonate, which causes DSBs. Dihomo-γ-linolenic acid (DGLA)-producing strains were constructed by disruption of the Δ5-desaturase gene, encoding a key enzyme of bioconversion of DGLA to ARA, using the Δku80 strain as a host strain. The significant improvement of gene-targeting efficiency was not observed by disruption of the ku80 gene, but the construction of DGLA-producing strain by disruption of the Δ5-desaturase gene was succeeded using the Δku80 strain as a host strain. This report describes the first study on the identification and disruption of the ku80 gene in zygomycetes and construction of a DGLA-producing transformant using a gene-targeting system in M. alpina 1S-4.

Enhanced arachidonic acid production from Mortierella alpina combining atmospheric and room temperature plasma (ARTP) and diethyl sulfate treatments

To obtain mutant strains with higher arachidonic acid (ARA) yields, the oleaginous fungus Mortierella alpina was mutated using atmospheric and room temperature plasma (ARTP) coupled with diethyl sulfate (DES). A visual compound filter operation was used in which a screening medium was supplemented with cerulenin, an inhibitor of fatty acid synthase (FAS), and triphenyltetrazolium chloride (TTC). The mutant strain D20 with an ARA production of 5.09 g/L, a 40.61% increase over the original strain (3.62 g/L), was isolated. The relative ARA content increased from 38.99% to 45.64% of total fatty acids. After optimizing fermentation conditions, the maximum ARA yield (6.82 g/L) for strain D20 was obtained in shake flasks. This work provides an appropriate strategy for obtaining high ARA-yield strains by conventional random mutation methods with an efficient screening assay.

Reconstruction and analysis of a genome-scale metabolic model of the oleaginous fungus Mortierella alpina

Background

Mortierella alpina is an oleaginous fungus used in the industrial scale production of arachidonic acid (ARA). In order to investigate the metabolic characteristics at a systems level and to explore potential strategies for enhanced lipid production, a genome-scale metabolic model of M. alpina was reconstructed.

Results

This model included 1106 genes, 1854 reactions and 1732 metabolites. On minimal growth medium, 86 genes were identified as essential, whereas 49 essential genes were identified on yeast extract medium. A series of sequential desaturase and elongase catalysed steps are involved in the synthesis of polyunsaturated fatty acids (PUFAs) from acetyl-CoA precursors, with concomitant NADPH consumption, and these steps were investigated in this study. Oxygen is known to affect the degree of unsaturation of PUFAs, and robustness analysis determined that an oxygen uptake rate of 2.0 mmol gDW⁻¹ h⁻¹ was optimal for ARA accumulation. The flux of 53 reactions involving NADPH was significantly altered at different ARA levels. Of these, malic enzyme (ME) was confirmed as a key component in ARA production and NADPH generation. When using minimization of metabolic adjustment, a knock-out of ME led to a 38.28% decrease in ARA production.

Conclusions

The simulation results confirmed the model as a useful tool for future research on the metabolism of PUFAs.

Electronic supplementary material

The online version of this article (doi:10.1186/s12918-014-0137-8) contains supplementary material, which is available to authorized users.