Production of squalene by lactose-fermenting yeast Kluyveromyces lactis with reduced squalene epoxidase activity.

UNLABELLED: Utilization of yeast as squalene source for commercial use is limited by relatively high production costs. The ability of Kluyveromyces lactis to grow on cheap lactose-containing diary industry wastes could improve the economy of the production process. We therefore tested the potential of this yeast for squalene production. Accumulation of squalene was induced by partial inhibition of squalene epoxidase by a specific inhibitor terbinafine. Kluyveromyces lactis cultivated on glucose and lactose media showed similar growth sensitivity to terbinafine as Saccharomyces cerevisiae. The effect of terbinafine on neutral lipid pattern was tested at concentrations with low, moderate and strong growth inhibition (2·5, 5 and 7·5 µg ml(-1) , respectively). Compared to S. cerevisiae, treatment with subinhibitory terbinafine doses had a weaker effect on steryl ester levels and total ergosterol levels in K. lactis. Quantification of squalene levels in terbinafine-treated K. lactis cells revealed high accumulation of squalene particularly in cells treated with 7·5 µg ml(-1) terbinafine in lactose medium. Terbinafine treatment stimulated the development of lipid droplets as lipid storage organelles and this effect was different in K. lactis grown on glucose or lactose media. Present report is the first attempt to utilize lactose-fermenting yeast K. lactis for production of a high-value lipid and it proves squalene epoxidase as a promising target for squalene overproduction in this yeast. SIGNIFICANCE AND IMPACT OF THE STUDY: Squalene is a natural substance with wide applications in food, cosmetic and pharmaceutic industries. The suitability of lactose-fermenting yeast Kluyveromyces lactis for the production of squalene was tested in the study. Partial inhibition of squalene epoxidase by specific inhibitor terbinafine resulted in high accumulation of squalene in K. lactis grown on glucose or lactose comparable to values found in terbinafine-treated Saccharomyces cerevisiae. Our results prove that K. lactis is a promising micro-organism for genetic manipulations aimed at the production of squalene on industrial waste like whey as the growth substrate.

[Lyme borreliosis--the great imitator]. / Lymská borelióza--velký imitátor.

Three different pathomorphological findings were presented in patients with seropositive borreliosis. Skin biopsy, cytology of joint synovial fluid and imprint cytology of bulbar conjunctiva were included. Skin vasculitis as well as pleocytosis of synovial fluid were found in accordance with literature, the inclusions in conjunctival imprint were unusual.