Abstract
Inducible expression systems can be applied to control the expression of proteins or biochemical pathways in cell factories. However, several of the established systems require the addition of expensive inducers, making them unfeasible for large‐scale production. Here, we establish a genome integrated trp‐T7 expression system where tryptophan can be used to control the induction of a gene or a metabolic pathway. We show that the initiation of gene expression from low‐ and high‐copy vectors can be tuned by varying the initial concentration of tryptophan or yeast extract, and that expression is tightly regulated and homogenous when compared with the commonly used lac‐T7 system. Finally, we apply the trp‐T7 expression system for the production of l‐serine, where we reach titers of 26 g/L in fed‐batch fermentation.
Highlights
There are several inducible promoters and expression systems available for use in Escherichia coli (Terpe, 2006)
We show that the initiation of gene expression from low‐ and high‐copy vectors can be tuned by varying the initial concentration of tryptophan or yeast extract, and that expression is tightly regulated and homogenous when compared with the commonly used lac‐T7 system
We showed that induction of gene expression could be tuned by the initial tryptophan concentration for low‐ and high‐copy vectors, and that expression strength was dependent on the use of the native or leaderless promoter constructs
Summary
There are several inducible promoters and expression systems available for use in Escherichia coli (Terpe, 2006). Several attempts have been made to find affordable and easy‐to‐ apply (auto)inducible expression systems with low levels of basal expression and high, tunable levels of gene expression Such systems do for example include those based on sensing of temperature, cell signaling, or depletion/addition of a compound that is naturally occurring in the cultivation medium. For cell signaling‐based induction, the native bacterial quorum‐sensing system has been applied to establish autoinducible production by coupling gene expression to the concentration of secreted quorum signaling molecules (Gupta, Reizman, Reisch, & Prather, 2017; Kim et al, 2017) This type of system has been shown to work when coupled to the T7 polymerase for further amplification of protein output (Zargar, Quan, & Bentley, 2016). We showed that the trp‐T7 expression system can be used for biochemical production by applying it for batch and fed‐batch fermentation of L‐serine
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