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Increasing NADPH Concentration in Cells
Since lipogenesis is an energy-consuming process, increasing NADPH concentration in cells can potentially increase lipid synthesis. Therefore, targeting NADPHgenerating pathways can be viewed as a potential boost to PUFA accumulation. Two
NADPH-generating enzymes of pentose phosphate pathway (PPP) and malic
enzyme were overexpressed in native PUFA producers Mortierella alpina, Mucor
circinelloides and Aurantiochytrium sp., and it was revealed that overexpression of
malic enzyme increased desaturation of fatty acids, while PPP enzymes had a more
significant effect on biosynthesis of fatty acids (Ji and Huang 2019).
Regulating the Activity of Desaturases and Elongases
Tailor-made PUFAs can be produced from a given microorganism by genetic reconstruction of the biosynthetic pathways involved in PUFA synthesis. The most common targets are desaturases and elongases. Mucor circinelloides, a filamentous
fungus, had been mainly studied for its GLA production. However, a study by Khan
et al. exploited the potential of Mucor circinelloides in the production of DGLA by
the introduction of foreign delta-6 elongase enzyme coding gene from Mortierella
alpine into it. Though the production was low (5.72%), the ease of purification of
DGLA from other PUFA in this strain makes it a promising candidate for further
exploration for commercial DGLA production (Khan et al. 2019). Overexpression
of delta-12 fatty acid desaturase in Rhodosporidium toruloides has shown a fivefold
increase in linoleic acid titre of these cells (Park et al. 2018).
Metabolite Regulation
Acetyl-CoA and citrate are important precursors of fatty acid synthesis. It has been
shown in Y. lipolytica that deletion of PDH1 gene can increase citrate accumulation
in cytoplasm irrespective of nitrogen-limiting conditions. Similarly, other active
metabolites involved in fatty acid synthesis can also be increased in these cells by
genetic manipulation (Bellou et al. 2016).
7.4 Large-Scale Cultivation of PUFA-Producing Fungi
The PUFA production from fungal can be realized by both submerged and solidstate fermentation. However, the metabolic fate of the substrate is primarily determined by the type of fermentation employed (Costa et al. 2018). Industrial
production of PUFAs is largely carried out in submerged mode due to the ease of
scale-up, recovery of biomass and high production yield with less fermentation
time (Mamani et al. 2019). However, the large amount of wastewater generated
and high energy requirement for the process have made the process costly and
unsustainable (Asadi et al. 2015). Aerobic fermentation of a solid substrate by
microorganisms in the absence/very low amount of free water to produce certain
value-added bioproducts is referred to as solid-state fermentation (Dulf et al.
2020). Solid-state fermentation (SSF) application in food is an age-old practice.
R. Gupta and S. Gaur
Increasing NADPH Concentration in Cells
Since lipogenesis is an energy-consuming process, increasing NADPH concentration in cells can potentially increase lipid synthesis. Therefore, targeting NADPHgenerating pathways can be viewed as a potential boost to PUFA accumulation. Two
NADPH-generating enzymes of pentose phosphate pathway (PPP) and malic
enzyme were overexpressed in native PUFA producers Mortierella alpina, Mucor
circinelloides and Aurantiochytrium sp., and it was revealed that overexpression of
malic enzyme increased desaturation of fatty acids, while PPP enzymes had a more
significant effect on biosynthesis of fatty acids (Ji and Huang 2019).
Regulating the Activity of Desaturases and Elongases
Tailor-made PUFAs can be produced from a given microorganism by genetic reconstruction of the biosynthetic pathways involved in PUFA synthesis. The most common targets are desaturases and elongases. Mucor circinelloides, a filamentous
fungus, had been mainly studied for its GLA production. However, a study by Khan
et al. exploited the potential of Mucor circinelloides in the production of DGLA by
the introduction of foreign delta-6 elongase enzyme coding gene from Mortierella
alpine into it. Though the production was low (5.72%), the ease of purification of
DGLA from other PUFA in this strain makes it a promising candidate for further
exploration for commercial DGLA production (Khan et al. 2019). Overexpression
of delta-12 fatty acid desaturase in Rhodosporidium toruloides has shown a fivefold
increase in linoleic acid titre of these cells (Park et al. 2018).
Metabolite Regulation
Acetyl-CoA and citrate are important precursors of fatty acid synthesis. It has been
shown in Y. lipolytica that deletion of PDH1 gene can increase citrate accumulation
in cytoplasm irrespective of nitrogen-limiting conditions. Similarly, other active
metabolites involved in fatty acid synthesis can also be increased in these cells by
genetic manipulation (Bellou et al. 2016).
7.4 Large-Scale Cultivation of PUFA-Producing Fungi
The PUFA production from fungal can be realized by both submerged and solidstate fermentation. However, the metabolic fate of the substrate is primarily determined by the type of fermentation employed (Costa et al. 2018). Industrial
production of PUFAs is largely carried out in submerged mode due to the ease of
scale-up, recovery of biomass and high production yield with less fermentation
time (Mamani et al. 2019). However, the large amount of wastewater generated
and high energy requirement for the process have made the process costly and
unsustainable (Asadi et al. 2015). Aerobic fermentation of a solid substrate by
microorganisms in the absence/very low amount of free water to produce certain
value-added bioproducts is referred to as solid-state fermentation (Dulf et al.
2020). Solid-state fermentation (SSF) application in food is an age-old practice.
R. Gupta and S. Gaur