S15: Enhancing bioprocess productivity through dynamic control of gene expression

A central component of bioprocess development is the engineering of microbial strains to meet specific product yield, productivity and titer targets. Carbon balance indicates that the trade-off between growth and product formation is critical for bioprocess optimization and economics. While metabolic engineering approaches focus on increasing the yield of a desired product, they typically come at the expense of reduced growth rate and productivity.

Here, we describe a dynamic strategy that can be applied to engineered strains suffering from low growth rate as a result of the carbon redirection. This strategy involves the dynamic expression of target genes contributing to growth instead of their deletion. The optimal pattern of gene expression suggests that target genes must be expressed in the first phase of a batch to allow for maximum biomass formation. In the second phase, these genes are repressed to redirect carbon flux towards product formation.

Dynamic control of gene expression is applied using a genetic toggle switch plasmid. At this stage we are evaluating the dynamic method using an IPTG-inducible plasmid and the advantage over the static strategy is shown. The next step is to couple the genetic toggle switch with the quorum sensing mechanism to manipulate expression in inducer-free conditions. The dynamic method is valuable in cases of engineered strains with impaired growth rate and is expected to improve the productivity of fermentations. Also, the final design, including quorum sensing, provides a self-regulated and programmable process that eliminates the cost of inducer and leads to improved economics.