Lipid characterization of Mortierella alpina grown at different NaCl concentrations

Acyl-CoA:diacylglycerol acyltransferase: Properties, physiological roles, metabolic engineering and intentional control

Acyl-CoA:diacylglycerol acyltransferase (DGAT, EC 2.3.1.20) catalyzes the last reaction in the acyl-CoA-dependent biosynthesis of triacylglycerol (TAG). DGAT activity resides mainly in membrane-bound DGAT1 and DGAT2 in eukaryotes and bifunctional wax ester synthase-diacylglycerol acyltransferase (WSD) in bacteria, which are all membrane-bound proteins but exhibit no sequence homology to each other. Recent studies also identified other DGAT enzymes such as the soluble DGAT3 and diacylglycerol acetyltransferase (EaDAcT), as well as enzymes with DGAT activities including defective in cuticular ridges (DCR) and steryl and phytyl ester synthases (PESs). This review comprehensively discusses research advances on DGATs in prokaryotes and eukaryotes with a focus on their biochemical properties, physiological roles, and biotechnological and therapeutic applications. The review begins with a discussion of DGAT assay methods, followed by a systematic discussion of TAG biosynthesis and the properties and physiological role of DGATs. Thereafter, the review discusses the three-dimensional structure and insights into mechanism of action of human DGAT1, and the modeled DGAT1 from Brassica napus. The review then examines metabolic engineering strategies involving manipulation of DGAT, followed by a discussion of its therapeutic applications. DGAT in relation to improvement of livestock traits is also discussed along with DGATs in various other eukaryotic organisms.

Effect of Sea Salt and Taro Waste on Fungal Mortierella alpina Cultivation for Arachidonic Acid-Rich Lipid Production

Arachidonic acid (ARA), an important polyunsaturated fatty acid (PUFA), acts as a precursor for eicosanoid hormones, such as prostaglandins, leukotrienes and other biological substances in human and animal bodies. Mortierella alpina is considered to be a potential strain for ARA production. Using agricultural waste as a substrate for microbial fermentation could achieve biorefinery concepts, and sea water utilization of the cultivation process could help to conserve fresh water resources. The objectives of this study were to find a potential M. alpina strain for ARA production, to investigate the tolerance of salinity and to evaluate the feasibility of the taro waste hydrolysate for M. alpina cultivation. The result showed that M. alpina FU30797 had the highest lipid content (25.97%) and ARA ratio (34.60%) among three strains. Furthermore, there was no significant difference between 0 and 10 g/L of sea salt solution on the biomass concentration and lipid content of M. alpina FU30797. The acidic hydrolysate and enzymatic hydrolysate of taro peel waste (TPW) were both utilized as culture substrates by M. alpina FU30797; however, the substrate up-take rate and lipid content in the TPW enzymatic hydrolysate cultivation were 292.33 mg/L-h and 30.68%, respectively, which are higher than those in acidic hydrolysate cultivation, and the ARA ratio was 33.05% in the enzymatic hydrolysate cultivation. From fed-batch cultivation in the bioreactor, the lipid content and ARA ratio reached 36.97% and 46.04%, respectively. In summary, the results from this project could potentially provide useful information for developing the PUFA-ARA bioprocess by using M. alpina.

Efficient coproduction of gluconic acid and xylonic acid from lignocellulosic hydrolysate by Zn(II)-selective inhibition on whole-cell catalysis by Gluconobacter oxydans

With Zn(II)-selective inhibition on the whole-cell catalysis of Gluconobacter oxydans NL71, gluconic acid and xylonic acid were coproduced efficiently from the hydrolysate of corn stover. Further metabolism of gluconic acid to the by-product 2-ketogluconic acid was prevented by addition of 10g/L ZnCl₂. Remarkably, yields of 93.91% of gluconic acid and 93.36% of xylonic acid were obtained with the supplement of ZnCl₂ in the synthetic medium, without by-product production. After optimization of the concentrations of ZnCl₂ and inocula of the strain, maximum amounts of gluconic acid and xylonic acid were coproduced at titers of 63.01g/L and 33.81g/L, with an overall utilization of 100% of the sugars in the enzymatic hydrolysate of corn stover. The results showed execution of our objective to prove this novel bioconversion method for simultaneously producing gluconic acid and xylonic acid, which would benefit subsequent studies on the comprehensive utilization of lignocellulosic materials.

FTIR Spectroscopy for Evaluation and Monitoring of Lipid Extraction Efficiency for Oleaginous Fungi

To assess whether Fourier Transform Infrared (FTIR) spectroscopy could be used to evaluate and monitor lipid extraction processes, the extraction methods of Folch, Bligh and Lewis were used. Biomass of the oleaginous fungi Mucor circinelloides and Mortierella alpina were employed as lipid-rich material for the lipid extraction. The presence of lipids was determined by recording infrared spectra of all components in the lipid extraction procedure, such as the biomass before and after extraction, the water and extract phases. Infrared spectra revealed the incomplete extraction after all three extraction methods applied to M.circinelloides and it was shown that mechanical disruption using bead beating and HCl treatment were necessary to complete the extraction in this species. FTIR spectroscopy was used to identify components, such as polyphosphates, that may have negatively affected the extraction process and resulted in differences in extraction efficiency between M.circinelloides and M.alpina. Residual lipids could not be detected in the infrared spectra of M.alpina biomass after extraction using the Folch and Lewis methods, indicating their complete lipid extraction in this species. Bligh extraction underestimated the fatty acid content of both M.circinelloides and M.alpina biomass and an increase in the initial solvent-to-sample ratio (from 3:1 to 20:1) was needed to achieve complete extraction and a lipid-free IR spectrum. In accordance with previous studies, the gravimetric lipid yield was shown to overestimate the potential of the SCO producers and FAME quantification in GC-FID was found to be the best-suited method for lipid quantification. We conclude that FTIR spectroscopy can serve as a tool for evaluating the lipid extraction efficiency, in addition to identifying components that may affect lipid extraction processes.

Lipid Fraction and Intracellular Metabolite Analysis Reveal the Mechanism of Arachidonic Acid-Rich Oil Accumulation in the Aging Process of Mortierella alpina

The mechanism of arachidonic acid (ARA) content increase during aging of Mortierella alpina was elucidated. Lipid fraction analysis showed that ARA content increased from 46.9% to 66.4% in the triacylglycerol (TAG) molecule, and ARA residue occupation increased in the majority of TAG molecules during the aging process. For the first time, intracellular metabolite analysis was conducted to reveal the pathways closely associated with ARA biosynthesis during aging. The main reason for the increased ARA content was not only at the expense of other fatty acids degradation but also at the expense of further ARA biosynthesis during aging. Furthermore, translocation played a vital role in ARA redistribution among the glycerol moiety, and mycelium did not die immediately with key pathways activated to maintain a relatively stable intracellular environment. This study lays a foundation for further improvement of ARA content in the oil product obtained from M. alpina.

Characterization of Pythium Transcriptome and Gene Expression Analysis at Different Stages of Fermentation

Background

The Pythium splendens is a potentially useful organism for the synthesis of large amounts of eicosapentaenoic acid. Peak biomass and lipid accumulation do not occur at the same time and growth temperature has an effect on the fatty acid composition. Little is known about the pathway or the genes involved in growth, lipid synthesis or temperature resistance in P. splendens. Analysis of the transcriptome and expression profile data for P.splendensRBB-5 were used to extend genetic information for this strain and to contribute to a comprehensive understanding of the molecular mechanisms involved in specific biological processes.

Methodology/Principal Findings

This study used transcriptome assembly and gene expression analysis with short-read sequencing technology combined with a tag-based digital gene expression (DGE) system. Assembled sequences were annotated with gene descriptions, such as gene ontology (GO), clusters of orthologous group (COG) terms and KEGG orthology (KO) to generate 23,796 unigenes. In addition, we obtained a larger number of genes at different stages of fermentation (48, 100 and 148 h). The genes related to growth characteristics and lipid biosynthesis were analyzed in detail. Some genes associated with lipid and fatty acid biosynthesis were selected to confirm the digital gene expression (DGE) results by quantitative real-time PCR (qRT-PCR).

Conclusion/Significance

The transcriptome improves our genetic understanding of P.splendensRBB-5 greatly and makes a large number of gene sequences available for further study. Notably, the transcriptome and DGE profiling data of P.splendensRBB-5 provide a comprehensive insight into gene expression profiles at different stages of fermentation and lay the foundation for the study of optimizing lipid content and growth speed at the molecular level.

Fungal arachidonic acid-rich oil: research, development and industrialization

Fungal arachidonic acid (ARA)-rich oil is an important microbial oil that affects diverse physiological processes that impact normal health and chronic disease. In this article, the historic developments and technological achievements in fungal ARA-rich oil production in the past several years are reviewed. The biochemistry of ARA, ARA-rich oil synthesis and the accumulation mechanism are first introduced. Subsequently, the fermentation and downstream technologies are summarized. Furthermore, progress in the industrial production of ARA-rich oil is discussed. Finally, guidelines for future studies of fungal ARA-rich oil production are proposed in light of the current progress, challenges and trends in the field.