4. Conclusion
Squalene is a super lubricant with skin compatibility and
thermostability. Traditional source of squalene from shark-hunting or
oil plant extraction is cost-prohibitive and not sustainable. Microbial
fermentation is considered as a promising route to upgrade sugar
renewable feedstock to squalene. By reconstituting mevalonate pathway in
yeast, a few of studies have achieved considerable amount of squalene.
In this work, we reported the engineering of the oleaginous yeast,Y. lipolytica , as a potential host for squalene production. We
surveyed a number of HMG-CoA reductase and discovered that endogenous
HMG-CoA reductase led to the highest squalene improvement. With the
recycling of NADPH from the mannitol cycle, the engineered strain (with
MnDH2 overexpression) produced about 180.3 mg/l and 188.2 mg/L squalene
from glucose or acetate minimal media, respectively. We identified the
optimal NADPH and acetyl-CoA supply mode. Upon overexpression of
squalene synthase, HMG-CoA reductase, mannitol dehydrogenase or
ATP-citrate lyase, we further optimized the cultivation conditions. The
engineered strain fermented with C/N 40:1 media conditioned with PBS
buffer with supplementation of 1 mg/L cerulenin produced about 502.7
mg/L squalene in shake flaks. The metabolic byproduct citric acid and
mannitol level were also profiled, both byproducts were reincorporated
into cell metabolism at the late stage of fermentation. This work may
serve as a starting point to harness Y. lipolytica as an
oleaginous yeast factory for cost-efficient production of squalene or
terpene-based chemicals.