Regulation and metabolic engineering strategies for permeases of Saccharomyces cerevisiae

Expression level of SOR1 is a bottleneck for efficient sorbitol utilization by yeast Komagataella kurtzmanii

The yeast strain Komagataella kurtzmanii VKPM Y-727 shows a significant defect in sorbitol utilization compared to closely related yeast K. phaffii (including strains formerly identified as Pichia pastoris). Our aim was to investigate the factors that determine the phenotype of the wild-type strain and to obtain a K. kurtzmanii strain with an improved ability to utilize sorbitol. We sequenced and annotated the genome of K. kurtzmanii VKPM Y-727 and compared it with that of K. phaffii GS115. Five K. phaffii GS115 genes that might be involved in sorbitol metabolism were selected and transferred into K. kurtzmanii Y-727. The transfer of the modified SOR1 gene resulted in an increased growth rate of K. kurtzmanii in sorbitol, despite the fact that Y-727 already contains its own SOR1 gene without any apparent mutations. The enzymes encoded by the SOR1 genes were analyzed in vitro and found to have similar properties. Differences in promoter activity were assessed using lacZ as a reporter gene, and the PSDH727  (promoter of SOR1 (SDH727) from K. kurtzmanii Y-727) promoter was shown to be 1.5-2.0 times weaker than PSDH115  (promoter of SOR1 (SDH115) from K. phaffii GS115). Moreover, both promoters were less active in K. kurtzmanii than in K. phaffii when evaluated in cells grown in synthetic complete media with glucose or sorbitol. Thus, SOR1 gene expression was identified as a bottleneck in sorbitol metabolism in K. kurtzmanii. Also, the positive effect of additional modified SOR1 gene copies was observed in both yeasts, as K. kurtzmanii and K. phaffii could grow on synthetic complete media with sorbitol three times faster than the original K. phaffii GS115 strain.

Sensing, Uptake and Catabolism of L-Phenylalanine During 2-Phenylethanol Biosynthesis via the Ehrlich Pathway in Saccharomyces cerevisiae

2-Phenylethanol (2-PE) is an important flavouring ingredient with a persistent rose-like odour, and it has been widely utilized in food, perfume, beverages, and medicine. Due to the potential existence of toxic byproducts in 2-PE resulting from chemical synthesis, the demand for “natural” 2-PE through biotransformation is increasing. L-Phenylalanine (L-Phe) is used as the precursor for the biosynthesis of 2-PE through the Ehrlich pathway by Saccharomyces cerevisiae. The regulation of L-Phe metabolism in S. cerevisiae is complicated and elaborate. We reviewed current progress on the signal transduction pathways of L-Phe sensing, uptake of extracellular L-Phe and 2-PE synthesis from L-Phe through the Ehrlich pathway. Moreover, the anticipated bottlenecks and future research directions for S. cerevisiae biosynthesis of 2-PE are discussed.