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

Abstract

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.

Metabolic Engineering of Mortierella alpina for Enhanced Arachidonic Acid Production through the NADPH-Supplying Strategy

“…Fermentors were held at 28°C and stirred at 500 rpm with an aeration rate of 0.5 vol/vol/min (vvm), and pH was maintained at 6.0. Samples were harvested prior to (sample A, Ϫ12 h; sample B, Ϫ2 h; sample E, Ϫ30 min) and after (sample K, ϩ1 h; sample L, ϩ12 h; sample M, ϩ48 h) nitrogen exhaustion as previously described (1).…”

“…ADPH is a critical factor for many biological processes in oleaginous microbes (1,2). However, the function of the various sources of NADPH in fatty acid synthesis is still not fully understood.…”

“…Some evidence, however, indicated that ME is only one of several NADPH sources (4,5). We and others have recently demonstrated that the pentose phosphate pathway (PPP), specifically the glucose-6-phosphate dehydrogenase (G6PD; EC 1.1.1.49) and the 6-phosphogluconate dehydrogenase (PGD; EC 1.1.1.44) genes, plays a major role during microbial fatty acid synthesis (1,2,6). Isocitrate dehydrogenase (IDH; EC 1.1.1.42) is another potential NADPH source and was proven to play a key role in fatty acid metabolism in adipocytes (7).…”

“…An expression system using the uracil auxotroph strain CCFM 501 was recently established and reliably applied for gene manipulation (1,5,8,12, 13). In this study, the M. alpina genes encoding G6PD, PGD, and IDH were overexpressed in the same organism, and their effects on fatty acid synthesis were evaluated and compared with the effect of ME (5, 8).…”

Genetic Variations in the Bovine Fatty Acid Desaturase 6 (FADS6) Are Associated with Fatty Acid Composition in Hanwoo Cattle

“…Functional study of bovine FADS6 has not been reported, but they were found to be highly similar to human FADS6. The FADS6 gene in humans is homologous to FADS2 (Stroud et al, 2009;Chen et al, 2015). FADS2 synthesizes Delta-6-desaturase (D6D) that catalyzes the first step in the synthesis of highly unsaturated fatty acid (HUFA) or LC-PUFA (Long chain-Poly unsaturated fatty acid (Stroud et al, 2009;Zheng et al, 2004).…”