Regulation of Ethanol Assimilation for Efficient Accumulation of Squalene in Saccharomyces cerevisiae.

Squalene is a triterpene that can be obtained from fish and plant oils. It is important in cosmetics and vaccines and is a precursor for many high-value terpenes and steroids. In order to increase squalene accumulation, the mevalonate pathway was systematically enhanced. Accumulation of squalene tended to increase when ethanol was added as a carbon source during fermentation, but a high concentration of ethanol affected both the strain growth and accumulation of products. By overexpressing the key trehalose synthesis gene TPS1 and the heat shock protein gene HSP104, the content of trehalose by Saccharomyces cerevisiae (S. cerevisiae) was enhanced, and stress caused by ethanol was relieved. The OD600 value of the modified S. cerevisiae strain was increased by 80.2%, its ethanol tolerance was increased to 30 g/L, and it retained excellent activity with 50 g/L ethanol. After optimizing the fermentation conditions, the squalene titer in a 5 L bioreactor reached 27.3 g/L and the squalene content was 650 mg/g dry cell weight, the highest squalene production parameters reported to date for a microorganism.

Characterization of highly gelatinous patatin storage protein from Pichia pastoris.

Patatin is a useful plant protein with excellent gelation properties that could be used as a gelling agent in the food industry. However, the commercial production of patatin is limited because the traditional extraction methods are inefficient and time consuming. Production of patatin with gelation properties by microorganisms is a promising alternative route. In this study, 1424.5 mg/L patatin storage protein with great gelation properties could be obtained in a 5-L bioreactor after optimization of the signal peptide, the promoter, and the fed-batch process when a Pichia pastoris GS115, but not Escherichia coli, expression system was used. Compared with commercial potato-extracted patatins, P. pastoris-derived patatins showed better gelation properties, such as a lower gel-forming concentration and gelation temperature. In addition, the gel strength of P. pastoris-derived patatins was comparable with that of potato-extracted patatins. These results suggested that P. pastoris-derived patatins have the potential to replace current potato-derived ones, which are now widely used in plant-based meat products.

Efficient bioconversion of epimedin C to icariin by a glycosidase from Aspergillus nidulans.

Herba Epimedii is a traditional Chinese herbal medicine that contains a mixture of bioactive flavonoid glycosides. Among them, icariin has the most outstanding bioactive functions, while epimedin C exhibits substantial toxicity. A recombinant α-L-rhamnosidase (synAnRhaE) from Aspergillus nidulans was expressed in Escherichia coli to promote the efficient bioconversion of epimedin C to icariin. A hydrolase activity of 574.5 U L-1 was acquired via optimized fed-batch fermentation in a 5-L bioreactor. The enzyme proved to be stable in an acidulous pH range below 55 °C with an optimal pH of 4.5 and optimal temperature of 55 °C. Epimedin C (1 g L-1) was 100% converted to icariin within 90 min using recombinant cells. The resting cells proved to be selective for epimedin C and 2″-O-rhamnosylicariside II in crude extracts of the epimedium plant. This work provides an original and efficient biocatalyst system that can be applied in industrialized production of icariin.