Design and implementation of synthetic
biological circuits highly
depends on well-characterized, robust promoters with predictable input–output
responses. While great progress has been made with heterotrophic model
organisms such as Escherichia coli, the available
variety of tunable promoter parts for phototrophic cyanobacteria is
still limited. Commonly used synthetic and semisynthetic promoters
show weak dynamic ranges or no regulation at all in cyanobacterial
models. Well-controlled alternatives such as native metal-responsive
promoters, however, pose the problems of inducer toxicity and lacking
orthogonality. Here, we present the comparative assessment of dose–response
functions of four different inducible promoter systems in the model
cyanobacterium Synechocystis sp. PCC 6803. Using
the novel bimodular reporter plasmid pSHDY, dose–response dynamics
of the re-established vanillate-inducible promoter PvanCC was compared to the previously described rhamnose-inducible P
rha
, the anhydrotetracycline-inducible PL03, and the Co2+-inducible P
coaT
. We estimate individual advantages and disadvantages regarding
dynamic range and strength of each promoter, also in comparison with
well-established constitutive systems. We observed a delicate balance
between transcription factor toxicity and sufficient expression to
obtain a dose-dependent response to the inducer. In summary, we expand
the current understanding and employability of inducible promoters
in cyanobacteria, facilitating the scalability and robustness of synthetic
regulatory network designs and of complex metabolic pathway engineering
strategies.
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