Mevalonate secretion is not mediated by a singular non-essential transporter in Saccharomyces cerevisiae

Isoprenoids are highly valued targets for microbial chemical production, allowing the creation of fragrances, biofuels, and pharmaceuticals from renewable carbon feedstocks. To increase isoprenoid production, previous efforts have manipulated pyruvate dehydrogenase (PDH) bypass pathway flux to increase cytosolic acetyl-coA; however, this results in mevalonate secretion and does not necessarily translate into higher isoprenoid production. Identification and disruption of the transporter mediating mevalonate secretion would allow us to determine whether increasing PDH bypass activity in the absence of secretion improves conversion of mevalonate into downstream isoprenoids. Attempted identification of the mevalonate transporter was accomplished using a pooled CRISPR library targeting all nonessential transporters and two different screening methods. Using a high throughput screen, based on growth of a mevalonate auxotrophic Escherichia coli strain, it was found that ZRT3 disruption largely abolished accumulation of extracellular mevalonate. However, disruption of ZRT3 was found to lower overall mevalonate pathway activity, rather than prevent secretion, indicating a previously unreported interaction between zinc availability and the mevalonate pathway. In a second screen, significant differences in PDR5/15 and QDR1/2 library representation were found between wild-type and mevalonate secreting Saccharomyces cerevisiae strains. However, no single deletion (or selected pair of double deletions) abolishes mevalonate secretion, indicating that this process appears to be mediated through multiple redundant transporters.