Genetically encoded biosensor for the evolution of licorice triterpenoid production in yeast
The synthesis of natural products using microbial cell factories is anticipated to be an environmentally conscious and sustainable production method. A considerable number of natural products synthesized by cell factories by insufficient conversion efficiency, necessitating the development of efficient methods to enhance the yield. However, a significant proportion of natural products cannot be detected in situ or with high throughput, hindering the efficiency of engineering construction. The development of biosensors for natural products not only improves the efficiency of product detection, but also enables the dynamic regulation of product synthesis. Here, we used differential transcriptomics to identify a gene, PDR5, in Saccharomyces cerevisiae that responds to glycyrrhizinic acid (GA), a licorice triterpenoid. This gene exhibits a more specific response to GA than other intermediates in the GA biosynthesis pathway. Modification of the PDR5 promoter sequence can modulate the dynamic range of its response to GA. Using the biosensor encoded by the PDR5 promoter, we designed a genetic circuit for coupling GA production to cell growth, which was used for laboratory evolution to obtain high-yielding strains. This system resulted in a 46.8% increase in GA production and greatly improved the genotype stability of the strain production. Differential expression of the xx gene in the evolved strain proved to be the key to the increased GA production. The concept of developing natural product biosensors and strain evolution in this study offers insights into the potential for enhancing the efficiency of microbial cell factories.