Oleaginous Fungus Research Articles

The role of phenylalanine hydroxylase in lipogenesis in the oleaginous fungus Mortierella alpina.

Phenylalanine hydroxylase (PAH) catalyses the irreversible hydroxylation of phenylalanine to tyrosine, which is the rate-limiting reaction in phenylalanine metabolism in animals. A variety of polyunsaturated fatty acids can be synthesized by the lipid-producing fungus Mortierella alpina, which has a wide range of industrial applications in the production of arachidonic acid. In this study, RNA interference (RNAi) with the gene PAH was used to explore the role of phenylalanine hydroxylation in lipid biosynthesis in M. alpina. Our results indicated that PAH knockdown decreased the PAH transcript level by approximately 55% and attenuated cellular fatty acid biosynthesis. Furthermore, the level of NADPH, which is a critical reducing agent and the limiting factor in lipogenesis, was decreased in response to PAH RNAi, in addition to the downregulated transcription of other genes involved in NADPH production. Our study indicates that PAH is part of an overall enzymatic and regulatory mechanism supplying NADPH required for lipogenesis in M. alpina.

Deletion of Plasma Membrane Malate Transporters Increased Lipid Accumulation in the Oleaginous Fungus Mucor circinelloides WJ11

Malate as an important intermediate metabolite, its subcellular location, and concentration have a significant impact on fungal lipid metabolism. Previous studies showed that the mitochondrial malate transporter plays an important role in lipid accumulation in Mucor circinelloides by manipulating intracellular malate concentration. However, the role of plasma membrane malate transporters in oleaginous fungi remains unexplored. Therefore, in this work, two plasma membrane malate transporters "2-oxoglutarate:malate antiporters" (named SoDIT-a and SoDIT-b) of M. circinelloides WJ11 were deleted, and the consequences in growth capacity, lipid accumulation, and metabolism were analyzed. The results showed that deletion of sodit-a or/and sodit-b reduced the extracellular malate, confirming that the products of both genes participate in malate transportation. In parallel, the lipid contents in mutants increased approximately 10-40% higher than that in the control strain, suggesting that the defect in plasma membrane malate transport results in an increase of malate available for lipid biosynthesis. Furthermore, transcriptional analysis showed that the expression levels of multiple key genes involved in the lipid biosynthesis were also increased in the knockout mutants. To the best of our knowledge, this is the first report that demonstrated the association between plasma membrane malate transporters and lipid accumulation in M. circinelloides.

Production of biodiesel from oleaginous fungal lipid using highly catalytic bimetallic gold-silver core-shell nanoparticle.

This study aims to synthesize, characterize and apply gold-silver core-shell nanoparticles (Au@Ag NPs), a nanocatalyst, to maximize biodiesel production from fungal isolate Fusarium solani (FS12) via a transesterification one-step reaction. The Au@Ag NPs structure was examined by UV-vis spectrophotometer, transmission electron microscopy, X-ray diffraction and Fourier transform infrared (FTIR). All devices were used to characterize Au@Ag NPs and confirmed successful synthesis of nanoparticles. Fungal lipid was quantitatively determined by sulfo-phospho-vanillin colorimetric method. Among 15 F. solani isolates obtained from rhizospheric soils of the date palm, F. solani (AF12) was chosen as the highly significant producer that accumulates above 20% lipid. The maximum biodiesel yield was 91.28±0.19%, obtained under the optimum reaction conditions of 3% Au@Ag NPs as nanocatalyst concentration, and 1:20 oil to methanol molar ratio at 70℃ for 30min. HPLC method was applied for monitoring in situ transesterification reaction. FTIR spectroscopy was used in qualitative analysis of biodiesel by verifying the presence of unique characteristic peaks of diagnostic significance. The quality of the biodiesel produced was confirmed by the high purity of fatty acid methyl esters analysis content up to >99%. These findings propose the applicability of F. solani (FS12) as a promising isolate to accumulate lipids and biodiesel production as a feedstock. The link between nanotechnology and fungi. Au@Ag NPs were synthesized at room temperature, which displayed high catalytic activity for in situ transesterification reaction. Catalytic activity appeared at low temperature, mole ratio and short reaction time. Oleaginous fungi are described as easily grown, have short life cycle, are cost-effective, and they utilized various sources of carbon up to waste and a simplified process to develop scale-up production as well, economic value, opposite the usage of vegetable oils which need for large agricultural areas.

Improved glucose and xylose co-utilization by overexpression of xylose isomerase and/or xylulokinase genes in oleaginous fungus Mucor circinelloides.

Most of the oleaginous microorganisms cannot assimilate xylose in the presence of glucose, which is the major bottleneck in the bioconversion of lignocellulose to biodiesel. Our present study revealed that overexpression of xylose isomerase (XI) gene xylA or xylulokinase (XK) gene xks1 increased the xylose consumption by 25 to 37% and enhanced the lipid content by 8 to 28% during co-fermentation of glucose and xylose. In xylA overexpressing strain Mc-XI, the activity of XI was 1.8-fold higher and the mRNA level of xylA at 24 h and 48 h was 11- and 13-fold higher than that of the control, respectively. In xks1 overexpressing strain Mc-XK, the mRNA level of xks1 was 4- to 11-fold of that of the control strain and the highest XK activity of 950 nmol min-1 mg-1 at 72 h which was 2-fold higher than that of the control. Additionally, expression of a translational fusion of xylA and xks1 further enhanced the xylose utilization rate by 45%. Our results indicated that overexpression of xylA and/or xks1 is a promising strategy to improve the xylose and glucose co-utilization, alleviate the glucose repression, and produce lipid from lignocellulosic biomass in the oleaginous fungus M. circinelloides. KEY POINTS: • Overexpressing xylA or xks1 increased the xylose consumption and the lipid content. • The xylose isomerase activity and the xylA mRNA level were enhanced in strain Mc-XI. • Co-expression of xylA and xks1 further enhanced the xylose utilization rate by 45%.

Lipid production by Mortierella isabellina from pretreated corn cobs and effect of lignocellulose derived inhibitors on growth and lipid synthesis

High production costs of microbial lipids can be reduced by using available and cheap lignocellulosic biomass. The present study optimizes the cultivation conditions of oleaginous fungus Mortierella isabellina and lipid production in corn cobs hydrolysate regarding initial carbon to nitrogen ratio (C:N) in the growth medium, a pretreatment method and, inoculum type. Additionally, we studied the effect of the most abundant lignocellulose-derived inhibitors on lipid synthesis and fungus growth. Low C:N ratios from 5 to 25 mol mol−1 stimulated the fungus growth, while C:N ratios above 50 mol mol−1 gave rise to lipid accumulation. Corn cobs were subjected to dilute acid and alkali pretreatment, using 0.369 g of sulphuric acid and 0.16 g of sodium hydroxide per gram of lignocellulosic biomass, respectively. Growth media based on hydrolysate of alkaline pretreated corn cobs has proved suitable for growth and lipid production. Lipid yield and lipid concentration was 0.13 g g−1 and 8.40 g L−1, respectively. The most toxic inhibitors generated during pretreatment were phenolics, followed by furan aldehydes and aliphatic acids. Using vegetative mycelium instead of spores as inoculum helped cells to overcome the inhibition effect by 5-hydroxymethylfurfural and furan.

Isolation, characterization and fatty acid analysis of Gilbertella persicaria DSR1: A potential new source of high value single-cell oil

Oleaginous fungi accumulate a high amount of lipids in their dry biomass and have attracted more attention, due to their broad potential in biotechnological applications. The present study aimed to isolate and evaluate efficient oleaginous endophytic fungi from selected plants, followed by optimizing the potential strain's growth parameters. A total of 51 morphologically distinct fungal isolates were isolated and examined for their oleaginous character. From the preliminary screening and fermentation assay, 13 fungal isolates were identified based on their high lipid with biomass or polyunsaturated fatty acids in their fatty acid profile. During our screening process, the fungal isolate identified as Gilbertella persicaria DSR1 was found to have desirable features, such as the highest cell dry biomass (12.7 g L−1) and lipid content (34.5% of biomass) with 7% γ-linolenic acid (GLA) of total fatty acids. The least investigated isolated oleaginous strain DSR1 was subjected to optimization of various growth parameters for exploiting its full lipid accumulation potential. Under optimized conditions in the fermentor, the strain DSR1 produced 14 ± 0.3 g L−1 dry cell biomass with 42 ± 1.4% total lipid content. The major fatty acid composition of lipid confirmed by GC analysis was palmitic acid (14.7%), stearic acid (10.6%), oleic acid (37.4%), linoleic acid (20.6%), γ-linolenic acid (13.4%). This is the first report showing the oleaginous nature of G. persicaria and this isolate may be further exploited as a potential candidate for biodiesel and GLA production in larger-scale applications.

Enhanced lipid production by addition of malic acid in fermentation of recombinant Mucor circinelloides Mc-MT-2

In our previous work, we reported a novel approach for increasing lipid production in an oleaginous fungus Mucor circinelloides by overexpression of mitochondrial malate transporter protein. This transporter plays a vital role in fatty acid biosynthesis during malate and citrate transport systems in oleaginous fungi. In this study, the controlling metabolic supplementation strategy was used to improve the lipid production by overexpression of malate transporter protein in M. circinelloides strain coded as Mc-MT-2. The effects of different metabolic intermediates on lipid production in batch fermentation by Mc-MT-2 were investigated. The optimal lipid production was obtained at 0.8% malic acid after 24 h of fermentation. Furthermore, in fed-batch bioreactors containing glucose as a carbon source supplemented with malic acid, the highest cell growth, and lipid production were achieved. The resulting strain showed the fungal dry biomass of 16 g/L, a lipid content of 32%, lipid yield of 5.12 g/L in a controlled bench-top bioreactor, with 1.60-, 1.60- and 2.56-fold improvement, respectively, compared with the batch control without supplementation of malic acid. Our findings revealed that the addition of malic acid during fermentation might play an important role in lipid accumulation in the recombinant M. circinelloides Mc-MT-2. This study provides valuable insights for enhanced microbial lipid production through metabolic supplementation strategy in large scale and industrial applications.

Transcriptome Analysis of Oleaginous Fungus Mucor circinelloides WJ11 in Response to Exogenous Soybean Oil as Carbon Source

Mucor circinelloides is an oleaginous fungus that utilizes a wide variety of carbon substrates for its growth. The different sources of carbon strongly influence the total lipid content of the fungus. These different carbon substrates are assimilated and dissimilated through different metabolic pathways before entering into the TAG synthesis pathway. In the present study, we attempted to explore the mechanism of ex-novo lipid biosynthesis in M. circinelloides WJ11 in response to exogenous plant oil as a carbon source through transcriptomic analysis. The lipid content of WJ11 grown in a media containing mixed soybean oil with glucose as a carbon source was up to 43.8%, an increase of 13.9% as compared to glucose alone as the carbon source. RNA-Seq analysis was performed to investigate global gene expression patterns in the oil-treated WJ11. Based on RNA-seq analysis, among the 4646 differentially expressed genes (DEGs), 2379 were up-regulated and 2267 down-regulated. The expression of acetyl-CoA synthetase, 6-phosphofructokinase, alcohol dehydrogenase (NADP+), fructose-bisphosphate aldolase, and pyruvate kinase was down-regulated while genes related to triglyceride synthesis were up-regulated. The majority of genes and pathways related to lipid biosynthesis were up-regulated indicating a diversion of metabolic pathways towards lipid biosynthesis. The data generated advance the genomic resources and provide insights into the mechanisms of ex-novo lipid accumulation in fungi that use exogenous oil as a carbon source.

Influence of the Different Carbon and Nitrogen Sources on the Production of Biodiesel by Oleaginous Fungi Aspergillus terreus, Aspergillus fumigatus

In the present study, the growth and total lipid contents of two oleaginous fungal isolates Aspergillus terreus, Aspergillus fumigatus were compared in different nitrogen and organic carbon sources. Artificially the fungi were cultured on media consisting of various mono- or di- or polysaccharides and peptone or yeast extract as elementary sources for carbon and nitrogen, respectively. Media containing sucrose /yeast extract or glucose/ yeast extract were the most effective for lipid production from fungal, during two weeks incubation period, the highest biomass of dry weight was (19.6 , 18.8) g / L , (25.8 , 30.5) g /L and lipid yield (1, 0.97 )g/L, (0.65, 0.65) g/ L for two isolates Aspergillus terreus and Aspergillus fumigatus respectively then followed maltose/ yeast extract then starch / yeast extract .Analysis of fatty acid produced by two fungal isolates using Gas Chromatography showed the existence of a wide range of fatty acids, these fatty acids were together saturated and unsaturated. The results revealed that the unevenness in the fatty acids composition mainly depends on the type of carbon and nitrogen sources. The existence of saturated and mono saturated fatty acids in A.fumigatus, A. terreus prove that they are good candidate for biodiesel production. The analysis of fatty acid from the fungal growth showed the existence of a wide range of fatty acids Palmitic ,Oleic acids , stearic acid and linoleic acid together saturated and unsaturated. The results revealed that the unevenness in the fatty acid composition mainly depends on the type of carbon and nitrogen sources. The presence of saturated and mono saturated fatty acid in A.fumigatus , A. terreus prove that it is a good candidate for biodiesel production.

Significance of two intracellular triacylglycerol lipases of Aspergillus oryzae in lipid mobilization: A perspective in industrial implication for microbial lipid production.

Microbial lipid production of oleaginous strains involves in a complex cellular metabolism controlling lipid biosynthesis, accumulation and degradation. Particular storage lipid, triacylglycerol (TAG), contributes to dynamic traits of intracellular lipids and cell growth. To explore a basis of TAG degradation in the oleaginous strain of Aspergillus oryzae, the functional role of two intracellular triacylglycerol lipases, AoTgla and AoTglb, were investigated by targeted gene disruption using CRISPR/Cas9 system. Comparative lipid profiling of different cultivation stages between the control, single and double disruptant strains (ΔAotgla, ΔAotglb and ΔAotglaΔAotglb strains) showed that the inactivation of either AoTgla or AoTglb led to the increase of total lipid contents, particularly in the TAG fraction. Moreover, the prolonged lipid-accumulating stage of all disruptant strains was obtained as indicated by a reduction in specific rate of lipid turnover, in which a holding capacity in maximal lipid and TAG levels was achieved. The involvement of AoTgls in spore production of A. oryzae was also discovered. In addition to the significance in lipid physiology of the oleaginous fungi, this study provides an impact on industrial practice by overcoming the limitation in short lipid-accumulating stage of the fungal strain, which facilitate the cell harvesting step at the maximum lipid production yield.

Role of beta-isopropylmalate dehydrogenase in lipid biosynthesis of the oleaginous fungus Mortierella alpina

Branched-chain amino acids (BCAAs) play an important role in lipid metabolism by serving as signal molecules as well as a potential acetyl-CoA source. Our previous study found that in the oleaginous fungus Mucor circinelloides, beta-isopropylmalate dehydrogenase (IPMDH), an important enzyme participating in the key BCAA leucine biosynthesis, was differentially expressed during lipid accumulation phase and has a positive role on lipogenesis. To further analyze its effects on lipogenesis in another oleaginous fungus Mortierella alpina, the IPMDH-encoding gene MaLeuB was homologously expressed. It was found that the total fatty acid content in the recombinant strain was increased by 20.2% compared with the control strain, which correlated with a 4-fold increase in the MaLeuB transcriptional level. Intracellular metabolites analysis revealed significant changes in amino acid biosynthesis and metabolism, tricarboxylic acid cycle and butanoate metabolism; specifically, leucine and isoleucine levels were upregulated by 6.4-fold and 2.2-fold, respectively. Our genetic engineering approach and metabolomics study demonstrated that MaLeuB is involved in fatty acid metabolism in M. alpina by affecting BCAAs metabolism, and this newly discovered role of IPMDH provides a potential bypass route to increase lipogenesis in oleaginous fungi.

Role of the mitochondrial citrate-oxoglutarate carrier in lipid accumulation in the oleaginous fungus Mortierella alpina.

The transport of citrate from the mitochondria to the cytoplasm is essential during lipid accumulation. This study aimed to explore the role of mitochondrial citrate-oxoglutarate carrier in lipid accumulation in the oleaginous fungus Mortierella alpina. Homologous MaYHM (the gene encoding the mitochondrial citrate-oxoglutarate carrier) was overexpressed in M. alpina. The fatty acid content of MaYHM-overexpressing recombinant strains was increased by up to 30% compared with the control. Moreover, the intracellular α-ketoglutarate level in recombinant strains was increased by 2.2 fold, together with a 23-35% decrease in NAD+-isocitrate dehydrogenase activity compared with the control. The overexpression of MaYHM altered the metabolic flux in the glutamate dehydrogenase shunt and 4-aminobutyric acid shunt during metabolic reprogramming, supplying more carbon to synthesize fatty acids. Overexpression of MaYHM resulted in more efflux of citrate from mitochondria to the cytoplasm and enhanced lipid accumulation. These findings provide new perspectives for the improvement of industrial lipid production in M. alpina.

Potential Assessment of Oleaginous Fungi for Sustainable Biodiesel Production: Screening, Identification and Lipid Production Optimization

The present work, aiming to exploit oleaginous fungi for biodiesel production. Ten fungal strains were isolated from two petroleum polluted soil samples and screened for their abilities to accumulate lipid. Lipid rich three species viz, Aspergillus terreus, Aspergillus niger and Aspergillus flavus were found to be the highest lipid producers. Potential isolates were identified at the species level by morphological (macroscopic and microscopic) examination and molecularly confirmed by using 18S rRNA gene sequencing. Improvement of lipid accumulation was performed by optimization of various parameters of culture conditions. The results reported clearly that the suitable medium for high lipid production (38.33%) by Aspergillus terreus as the most potent lipid producer, was composed of 50 g/L sucrose, 0.5 g/L ammonium nitrate with initial pH 6.0, after seven days of incubation in a static condition. The three promising lipid isolates have been selected for fatty acids analysis by gas chromatograph (GC) after transesterification. Fatty acid methyl esters (FAME) profile indicated the presence of higher saturated fatty acid fractions compared to polyunsaturated fatty acids. The total concentration of fatty acids was 107.98, 38.29, and 37.48 mg/100g of lipid accumulated by A. terreus, A. niger and A. flavus, respectively. Gas chromatographic analysis of A. terreus lipid indicated that oleic acid (C18:1, 18.51%) was the most abundant fatty acid, followed by stearic acid (C18:0, 15.91%) and Myristic acid (C14:0, 14.64%), respectively. Therefore, fatty acid profile of A. terreus has confirmed its potentiality as feedstock for producing lipid for biodiesel manufacturing.

Enzymatic production of isopropyl and 2-ethylhexyl esters using γ-linolenic acid rich fungal oil produced from spent sulphite liquor

The enzymatic production of isopropyl and 2-ethylhexyl esters was investigated using fungal oil produced via fermentation of nanofiltrated spent sulphite liquor (SSL). Screening of five oleaginous fungi showed that Cunninghmamella echinulata could accumulate lipids with 12 % (w/w) γ-linolenic acid content in shake flask cultures. Ester formation by the commercial lipase Novozym 435 was favored when transesterifications of fungal oil with isopropyl and 2-ethylhexyl alcohols were performed at 60 °C, 1:3 microbial oil to alcohol molar ratio and 10 % biocatalyst concentration. Transesterifications of individual neutral lipids (NL), glycolipids and sphingolipids (GL + SL) and phospholipids (PL), with isopropanol and 2-ethyl-hexanol showed that the presence of GL + SL and PL in fungal oil hindered ester production. Transesterification of the NL fraction alone with isopropanol and 2-ethylhexanol led to the highest conversion yield of 80.2 % and 73.8 %, respectively. Conversion yields to isopropyl and 2-ethylhexyl esters reached up to 90 % and 80 % (w/w), respectively, when hydrolyzed fungal oil was used. The biocatalyst showed good stability in 5 repeated enzymatic reactions. The physicochemical properties and the ICP-MS analysis of esters demonstrated their potential utilization in cosmetic formulations. This study showed a perspective of valorizing SSL towards the production of value-added fatty acid esters for chemical, cosmetic and pharmaceutical applications.

The Effect of Soybean Oil on Lipid Metabolism in Mucor circinelloides WJ11 by Metabolomic Analysis

Oleaginous fungus Mucor circinelloides utilizes different carbon sources associated with sustainable production of lipids, using soybean oil as carbon source, the fungus accumulated more intracellular lipids. Nonetheless, the metabolic changes in M. circinelloides upon vegetable oil as main carbon source have not been yet reported. Therefore, this study was conducted to investigate the metabolomics of M. circinelloides WJ11 cultivated in mixed glucose and soybean oil as carbon source and to reveal its effects on lipid metabolism. M. circinelloides strain WJ11 was cultured under optimized conditions in a fermenter and the biomass samples were collected after 24 h for lipid metabolite investigation. The frozen biomass samples were subjected to various chromatographic analyses like liquid chromatography mass spectrometry analysis and high resolution-mass spectrometry for metabolite profiling. A total of 438 differential metabolites were identified, of which 48 were up-regulated and 33 were down-regulated. Among them, lyso-phosphatidic acid and monoglyceride were up-regulated whereas phosphatidylglycerol and lyso-phosphatidylglycerol were down-regulated in the experimental group (soybean oil and glucose as mixed carbon sources) compared with the control group (glucose as single carbon source). Significant changes in metabolite levels correlated to lipid synthesis were identified. This study showed that the addition of soybean oil to the medium favors the triacylglycerol synthesis in M. circinelloides. Our results can also be applied to the investigation of other microorganisms and would contribute to further genetic engineering for higher lipid accumulation in fungi.

High-yield oleaginous fungi and high-value microbial lipid resources from Mucoromycota

Mucoromycota are diverse in microbial oils, but oil-related studies have long been confined to a few particular genera and species. This study used the Sherlock Microbial Identification System to determine fatty acid compositions and consequently discover potential resources from 669 strains representing 133 species in 28 genera in 11 families from the core mucoromycotan orders Mortierellales, Mucorales, and Umbelopsidales. Results showed that 34% of strains, 50% of species, and 46% of genera were oleaginous. Eleven genera were proposed as oleaginous taxa for the first time. Among them, Backusella was highlighted in accumulating as high as 59.08 ± 2.24% of oils. Twenty-five and 50 strains were screened as potential high-yield fungi for oils and high-value fatty acids respectively. Pilaira produced the most C18:2, while Rhizopus and Thamnostylum produced the most C18:3. Only strains of Mortierella produced C20:4; Mo. amoeboidea CGMCC 3.15949 yielded 58.00% ± 1.15% of C20:4, which suggests it is an excellent source of C20:4. This study suggests for the first time that the bulk of Mucoromycota is rich in lipids. More genera and species were discovered herein as oil-producing resources. These findings serve as a foundation for further research on microbial oil production.

Consolidated Bioprocessing of Sugarcane Bagasse to Microbial Oil by Newly Isolated Oleaginous Fungus: Mortierella wolfii

The crucial need for alternative oil sources due to increasing energy demand has motivated research to find alternatives resources. In the current study, different fungal groups were isolated from diverse Egyptian localities for oil production screening as well as sugarcane bagasse management. A total of 499 fungal isolates were recovered from soil and dung samples; one isolate was identified as Mortierella wolfii AH12 using morphological and molecular techniques and was demonstrated to produce high lipid concentrations. Taguchi design was used to obtain higher lipid productivity. Accordingly, dry biomass, total lipids, and lipid percentage were 3.81 g l−1, 1.57 g l−1, and 41.2%, respectively, under the optimized culture conditions: 40 g glucose, 5 g peptone, pH 5 at 30 0°C for 10 days. Non-pretreated sugarcane bagasse was not only utilized as an alternative carbon source, but it was also an effective source of nutrients for mold sprouting and lipid biosynthesis using solid-state fermentation (SSF) technique. Promising fatty acid profile was deduced, where palmitic (PA) and oleic acid (OA) were predominant. Moreover, unsaturated fatty acids (USFAs) as linoleic acid (LA), Gamma linolenic acid (GLA), Dihomo gamma linolenic acid (DGLA), arachidonic acid (ARA) were present in low quantities according to GC–MS analysis. The study offers a promising result that serves in the management of agricultural waste, converting it into lipids with a promising profile which could be considered as a precursor for biodiesel.

Metabolomics analysis reveals the role of oxygen control in the nitrogen limitation induced lipid accumulation in Mortierella alpina

Lipid hyperaccumulation in oleaginous microorganisms is generally induced by nitrogen limitation, while oxygen supply can influence biomass growth and cell metabolism. Although strategies based on nitrogen limitation or oxygen control have been extensively explored and applied in various oleaginous microorganisms, the role of oxygen supply in nitrogen limitation induced lipid hyperaccumulation still remains unclear. Here, we systematically surveyed the effects of oxygen supply on the oleaginous fungus M. alpina cultured in nitrogen limited conditions through integration of physiochemical parameters and metabolomics analysis. Our results indicated that a high oxygen supply promoted carbon/nitrogen consumption and was used for rapid biomass synthesis, while either high or low oxygen supply conditions were adverse to lipid and ARA accumulation. Different oxygen supply level significantly affected the balance between fermentation for lipid synthesis and respiration for energy generation. Under nitrogen limitation, a suitable oxygen supply promoted the recycling of preformed nitrogen and increased the redirection of carbon towards fatty acid synthesis through the hub centred around glutamic acid coupled to the intermediate metabolism of carbon in the TCA cycle, while a high oxygen supply favored the respiration process and enhanced the degradation of LC-PUFAs, rather than fermentation for fatty acid synthesis. This system-level insight reveals the underlying metabolic mechanism of oxygen control in nitrogen limitation induced lipid accumulation, and provides theoretical support for the integration of oxygen control with nutrient supply for efficient microbial oil production.

Sustainable lipid production from oleaginous fungus Syncephalastrum racemosum using synthetic and watermelon peel waste media

Production of bio-oils was assessed by using two types of media; watermelon peel waste (WPW) medium against synthetic medium as a comparative study. Accordingly, total of 25 fungi were isolated from soil and dung samples. Fortunately, the most promising fungal isolate was reported for the first time in Egypt. Taguchi design was applied to recognize the optimum growth conditions on synthetic medium. Consequently, the optimized synthetic medium could facilitate the accumulation of lipid at 4.4 g/L with lipid content of 28.2% by the strain, corresponding to 5.12 g/L and 29.4% of WPW medium, respectively. Conclusively, Syncephalastrum racemosum is a novel promising oleaginous fungus screened on WPW medium that showed an excellent substitute for a high cost synthetic medium for lipid production. Oil accumulated from a low-cost WPW medium found to have fatty acids with good possibilities to be used as precursors for biodiesel manufacture.

Rare fungus, Mortierella capitata, promotes crop growth by stimulating primary metabolisms related genes and reshaping rhizosphere bacterial community

Rhizosphere and endosphere microorganisms are recognized as an extended plant genome. Changes in rhizosphere and endosphere microbial community structure are closely linked to plant nutrition uptake, development and immunity. Mortierella is a saprophytic oleaginous fungus, with various agricultural benefits, which have triggered interest in recent years. Here, we conducted Mortierella capitata inoculation experiments in a climate chamber. M. capitata inoculation increased biomass, chlorophyll and gibberellic acid content in maize. The concentration of available soil phosphorus was also increased, while O2 concentration and soil density decreased. Further, the prokaryotic and eukaryotic microbial structure was evaluated by MiSeq sequencing. M. capitata inoculants increased rhizosphere bacterial diversity and significantly altered rhizosphere bacterial community composition. Yet, the influence of M. capitata on fungal community structure was not significant according to ANOSIM analysis. RNA-seq was used to ascertain differentially expressed genes (DEGs) in maize roots following M. capitata inoculation. Genes encoding chitinase, peroxidase, lipid transfer protein, sugars exported transporter, and various transcription factor proteins were significantly up-regulated. All the DEGs, soil and plant basic properties were used to construct a co-occurrence network for modularity analysis. The whole network was divided into five modules based on Louvain algorithm, including organic substances metabolism and hormone regulation, nucleobases metabolism, stimulus response, primary metabolism and an unknown module. The stimulus response module showed the closest correlation with biomass, soil oxygen, and M. capitata, while genes in the primary metabolism module were closely associated with plant gibberellic acid and available soil phosphorus. Our results highlight that the rare fungus M. capitata can promote crop growth directly by altering the root gene expression levels, and indirectly via interaction with indigenous rhizosphere bacteria.