Screening and intensity analysis of promoters in Starmerella bombicola

Abstract:

[Background] Starmerella bombicola, as an unconventional yeast strain, has attracted wide attention owing to its ability to produce sophorolipids biosurfactant. However, its expression system is not well defined, which limits the development of metabolic engineering. [Objective] A panel of endogenous promoters were cloned and characterized from S. bombicola. [Methods] In this study, through the comparative analysis of the whole genome of S. bombicola and 9 target genes, combined with the promoter prediction website, a series of promoter candidate sequences were screened and obtained, and SbGFP (codon-optimized yeast enhanced green fluorescent protein for S. bombicola), as the reporter gene, was integrated and expressed in S. bombicola. The promoter strength was identified by analyzing the intensity of green fluorescent protein and its transcriptional levels. [Results] When glucose and colleseed oil were respectively used as the sole carbon source, the promoters P_TEF1 and P_GPD showed higher transcription levels under both conditions. The promoters P_CYP52M1, P_UGTA1, P_UGTB1, and P_MOB had weak transcriptional activity when colleseed oil was used as the sole carbon source, but no transcriptional activity was detected when cultured with glucose. It was speculated that they were colleseed oil-inducible promoters. Transcriptional level of SbGFP was further analyzed by real-time fluorescence quantitative PCR (RT-qPCR), the result was consistent with the expression level of SbGFP.[Conclusion] A panel of different promoters were screened and characterized, which would further enrich its expression elements and lay a theoretical foundation for the metabolic engineering for S. bombicola.