Promoter engineering enables precise metabolic regulation towards efficientβ-elemene production in Ogataea polymorpha

Precisely controlling gene expression is beneficial for optimizing biosynthetic pathways for improving the production.However,promoters in nonconventional yeasts such as Ogataea polymorpha are always limited,which results in incompatible gene modulation.Here,we expanded the promoter library in O.polymorpha based on transcriptional data,among which 13 constitutive promoters had the strengths ranging from 0–55%of PGAP,the commonly used strong constitutive promoter,and 2 were growth phase-dependent promoters.Subsequently,2 hybrid growth phase-dependent promoters were constructed and characterized,which had 2-fold higher activities.Finally,promoter engineering was applied to precisely regulate cellular metabolism for efficient production ofβ-elemene.The glyceraldehyde-3-phosphate dehydrogenase gene GAP was downregulated to drive more flux into pentose phosphate pathway(PPP)and then to enhance the supply of acetyl-CoA by using phosphoketolase-phosphotransacetylase(PK-PTA)pathway.Coupled with the phase-dependent expression of synthase module(ERG20∼LsLTC2 fusion),the highest titer of 5.24 g/L with a yield of 0.037 g/(g glucose)was achieved in strain YY150U under fed-batch fermentation in shake flasks.This work characterized and engineered a series of promoters,that can be used to fine-tune genes for constructing efficient yeast cell factories.

Screening and engineering of high-activity promoter elements through transcriptomics and red fluorescent protein visualization in Rhodobacter sphaeroides

The versatile photosyntheticα-proteobacterium Rhodobacter sphaeroides,has recently been extensively engineered as a novel microbial cell factory(MCF)to produce pharmaceuticals,nutraceuticals,commodity chemicals and even hydrogen.However,there are no well-characterized high-activity promoters to modulate gene transcription during the engineering of R.sphaeroides.In this study,several native promoters from R.sphaeroides JDW-710(JDW-710),an industrial strain producing high levels of co-enzyme Q10(Q10)were selected on the basis of transcriptomic analysis.These candidate promoters were then characterized by using gusA as a reporter gene.Two native promoters,Prsp_7571 and Prsp_6124,showed 620%and 800%higher activity,respectively,than the tac promoter,which has previously been used for gene overexpression in R.sphaeroides.In addition,a Prsp_7571-derived synthetic promoter library with strengths ranging from 54%to 3200%of that of the tac promoter,was created on the basis of visualization of red fluorescent protein(RFP)expression in R.sphaeroides.Finally,as a demonstration,the synthetic pathway of Q10 was modulated by the selected promoter T334*in JDW-710;the Q10 yield in shake-flasks increased 28%and the production reached 226 mg/L.These well-characterized promoters should be highly useful in current synthetic biology platforms for refactoring the biosynthetic pathway in R.sphaeroides-derived MCFs.