Enhanced Squalene Production by Thraustochytrium sp. RT2316-16 by Polyphenols from Barley Bagasse

Squalene, a hydrocarbon with several industrial applications, is obtained from plants, animals, and microorganisms. Oleaginous thraustochytrids are also potential sources of squalene. In eukaryotes, squalene, an intermediary in the sterol/cholesterol pathway, accumulates when the activity of squalene epoxidase or an Alternative SQualene Epoxidase (AltSQE) is inhibited. The objective of this study was to evaluate the polyphenols extracted from barley bagasse for enhancement of the squalene content in Thraustochytrium sp. RT2316-16. In the media supplemented with terbinafine, an antifungal compound known as an inhibitor of squalene epoxidase, or the polyphenols from barley bagasse 72 h after inoculation, the squalene concentration was 308.7 ± 0.8 and 286.5 ± 0.1 mg L−1 after 168 h, respectively, whereas in the control medium, it was 85.6 ± 0.2 mg L−1. The final concentrations of the lipid-free biomass (4.5 ± 0.1 g L−1) and total lipids (2.5 ± 0.3 g L−1) were not affected by the polyphenols from barley bagasse; on the contrary, the concentration of total lipids in the terbinafine treatment was 30% lower than in the control. In RT2316-16, the gene coding for AltSQE, which is not found in all thraustochytrids, was upregulated under the control treatment, whereas its relative expression was not affected by terbinafine. The squalene accumulation in RT2316-16 in response to the treatment with polyphenols and the antifungal agent makes this strain a promising source of the triterpenoid.