Coordinated expression of metabolic pathway enzymes is crucial for efficient bioprocesses optimally exploiting cellular resources, avoiding pathway bottlenecks and the consequent accumulation of (toxic) intermediates. Fine-tuning of enzyme activities requires controlling gene expression and translation level by using regulatory parts, e.g., promoters and ribosomal binding sites, of defined strength. Synthetic Biologists have developed methods and tools to generate well-characterized libraries of these regulatory parts. However, the work done so far mainly focused on Escherichia coli and it is unknown how the characterized parts perform in other microorganisms.
Here, we created new libraries of synthetic promoters and characterized their performance in both Pseudomonas taiwanensis VLB120, a non-model organisms with high potential as microbial cell factory, and the industrial workhorse and model organism Escherichia coli, using msfGFP as a reporter. To avoid differences in promoter strength related to plasmid copy number variation or cell growth state, all promoter-msfGFP constructs were genetically integrated in single-copy and specific GFP expression (fluorescence per g CDW) monitored over complete batch experiments by online biomass and fluorescence measurements. Despite the relatedness of the two organisms and the conservativism of RNA polymerase and sigma70 promoter interaction, promoter variants exerted different strengths in the two strains.
These results are discussed in view of the aim of Synthetic Biology to generate re-usable and interchangeable standardized parts.