Identification and characterization of Δ12 and Δ12/Δ15 bifunctional fatty acid desaturases in the oleaginous yeast Lipomyces starkeyi

Linoleic acid enrichment of cheese by okara flour and Geotrichum candidum overexpressing Δ12 fatty acid desaturase

BACKGROUND

Mold-ripened cheeses have low levels of unsaturated fatty acids (UFAs). Geotrichum candidum is an adjunct culture for the development of Geotrichum-ripened cheese but has a low ability to produce high levels of UFAs. Δ12 fatty acid desaturase (FADS12) is a pivotal enzyme that converts oleic acid (OA) to linoleic acid (LA) and plays a vital role in UFA biosynthesis. By investigating FADS12 catalytic activity from various species with OA substrates, we found that FADS12 from Mucor circinelloides (McFADS12) had the highest catalytic activity for OA.

RESULTS

In the current study, a plasmid harboring McFADS12 was constructed and overexpressed in G. candidum. Our results showed that LA production increased to 31.1 ± 1.4% in engineered G. candidum - three times higher than that in wild-type G. candidum. To enhance LA production, an exogenous substrate (OA) was supplemented, and the yield of LA was increased to 154 ± 6 mg L^-1 in engineered G. candidum. Engineered G. candidum was used as an adjunct culture for Geotrichum-ripened cheese production. The LA level reached 74.3 ± 5.4 g kg^-1 cheese, whereas the level of saturated fatty acids (SFAs) decreased by 9.9 ± 0.5%. In addition, the soybean byproduct (okara) was introduced into the engineered G. candidum growth and the level of LA increased to 126 ± 4 g kg^-1 cheese and the percentage of UFAs:SFAs increased from 0.8:1 to 1.3:1.

CONCLUSION

This study offers a suitable technology for converting SFAs to UFAs in Geotrichum-ripened cheeses and provides a novel trend for converting soybean waste into a value-added product. © 2022 Society of Chemical Industry.

Exploring Yeast Diversity to Produce Lipid-Based Biofuels from Agro-Forestry and Industrial Organic Residues

Exploration of yeast diversity for the sustainable production of biofuels, in particular biodiesel, is gaining momentum in recent years. However, sustainable, and economically viable bioprocesses require yeast strains exhibiting: (i) high tolerance to multiple bioprocess-related stresses, including the various chemical inhibitors present in hydrolysates from lignocellulosic biomass and residues; (ii) the ability to efficiently consume all the major carbon sources present; (iii) the capacity to produce lipids with adequate composition in high yields. More than 160 non-conventional (non-Saccharomyces) yeast species are described as oleaginous, but only a smaller group are relatively well characterised, including Lipomyces starkeyi, Yarrowia lipolytica, Rhodotorula toruloides, Rhodotorula glutinis, Cutaneotrichosporonoleaginosus and Cutaneotrichosporon cutaneum. This article provides an overview of lipid production by oleaginous yeasts focusing on yeast diversity, metabolism, and other microbiological issues related to the toxicity and tolerance to multiple challenging stresses limiting bioprocess performance. This is essential knowledge to better understand and guide the rational improvement of yeast performance either by genetic manipulation or by exploring yeast physiology and optimal process conditions. Examples gathered from the literature showing the potential of different oleaginous yeasts/process conditions to produce oils for biodiesel from agro-forestry and industrial organic residues are provided.

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

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

Oleaginous Yeasts as Cell Factories for the Sustainable Production of Microbial Lipids by the Valorization of Agri-Food Wastes

The agri-food industry annually produces huge amounts of crops residues and wastes, the suitable management of these products is important to increase the sustainability of agro-industrial production by optimizing the entire value chain. This is also in line with the driving principles of the circular economy, according to which residues can become feedstocks for novel processes. Oleaginous yeasts represent a versatile tool to produce biobased chemicals and intermediates. They are flexible microbial factories able to grow on different side-stream carbon sources such as those deriving from agri-food wastes, and this characteristic makes them excellent candidates for integrated biorefinery processes through the production of microbial lipids, known as single cell oils (SCOs), for different applications. This review aims to present an extensive overview of research progress on the production and use of oleaginous yeasts and present discussions on the current bottlenecks and perspectives of their exploitation in different sectors, such as foods, biofuels and fine chemicals.

Identification and characterization of Pseudozyma antarctica Δ12 fatty acid desaturase and its utilization for the production of polyunsaturated fatty acids

Fatty acid desaturases, especially Δ12 fatty acid desaturases, are key enzymes for the production of unsaturated fatty acids in oleaginous yeasts. In this study, we identified and characterized a gene encoding Δ12 fatty acid desaturase of Pseudozyma antarctica named PaFAD2. Almost all oleic acid (C18:1) was converted to linoleic acid by the heterologous expression of the PaFAD2 gene in Saccharomyces cerevisiae and Lipomyces starkeyi oleaginous yeast. Notably, PaFad2 converted not only oleic acid to linoleic acid, but also palmitoleic acid (C16:1) to 9,12-hexadecadienoic acid (C16:2). These results indicated that the PaFAD2 gene was very useful for the production of polyunsaturated fatty acids in yeast, including oleaginous yeast.

Identification and characterization of two fatty acid elongases in Lipomyces starkeyi

The oleaginous yeast Lipomyces starkeyi is a potential cost-effective source for the production of microbial lipids. Fatty acid elongases have vital roles in the syntheses of long-chain fatty acids. In this study, two genes encoding fatty acid elongases of L. starkeyi, LsELO1, and LsELO2 were identified and characterized. Heterologous expression of these genes in Saccharomyces cerevisiae revealed that LsElo1 is involved in the production of saturated long-chain fatty acids with 24 carbon atoms (C24:0) and that LsElo2 is involved in the conversion of C16 fatty acids to C18 fatty acids. In addition, both LsElo1 and LsElo2 were able to elongate polyunsaturated fatty acids. LsElo1 elongated linoleic acid (C18:2) to eicosadienoic acid (C20:2), and LsElo2 elongated α-linolenic acid (C18:3) to eicosatrienoic acid (C20:3). Overexpression of LsElo2 in L. starkeyi caused a reduction in C16 fatty acids, such as palmitic and palmitoleic acids, and an accumulation of C18 fatty acids such as oleic and linoleic acids. Our findings have the potential to contribute to the remodeling of fatty acid composition and the production of polyunsaturated long-chain fatty acids in oleaginous yeasts.

Overexpression of delta-12 desaturase in the yeast Schwanniomyces occidentalis enhances the production of linoleic acid

The oleaginous yeast Schwanniomyces occidentalis was previously isolated because of its excellent suitability to convert lignocellulosic hydrolysates into triacyl glycerides: it is able to use a broad range of sugars and is able to tolerate high concentrations of lignocellulosic hydrolysate inhibitors. Compared to other oleaginous yeasts S. occidentalis however produces a low content of unsaturated fatty acids. We show here that the linoleic acid content can be significantly improved by (over)expression Δ12-desaturases derived from S. occidentalis and Fusarium moniliforme. Expression was stable for the homologous expression but decreased during heterologous expression. Both homologous and heterologous expression of mCherry-Δ12-desaturase led to a 4-fold increase in linoleic acid from 0.02 g/g biomass to 0.08 g/g biomass resulting in the production of 2.23 g/L and 2.05 g/L of linoleic acid.