[Seminar] Synthetic biology for bioalcohol production by Associate Prof. Taizo Hanai

Speaker: Associate Professor Taizo Hanai
Laboratory for Bioinformatics, Graduate School of Systems Life Science
Kyushu Univeristy

Date: 14 December, Monday
Time: 3pm - 4pm
Venue: C700 Lab 3, Level C

Title: Synthetic biology for bioalcohol production
Abstruct: Quorum sensing (QS) systems have been found in several microbial species as a sensor-regulator system detecting local cell population density in order to induce gene expression in response to threshold cell population for optimal adaptation to their environment. QS in Vibrio fischeri is well known as lux system which harbors the luminescence (lux) operon, and its induction scheme has been clarified. The lux system-mediated detection of cell density requires the interaction of a receptor-type transcription factor LuxR with a diffusible auto-inducer acylhomoserine lactone (AHL) produced by LuxI under the control of the lux promoter activated by the AHL-LuxR complex. When extracellular concentration of AHL reaches threshold associated with increasing cell population, the gene expression under lux promoter is induced. In synthetic biological studies, using LuxI, LuxR and the lux promoter, rewiring of the lux system has been performed in Escherichia coli to investigate dynamic characteristics of the lux network. The lux and other QS systems have also been applied as a cell-cell communication signal to construction of several synthetic genetic circuits, but there is no example of QS application to the microbial chemical production by using synthetic metabolic pathways. Moreover, in almost all synthetic or native QS systems, a threshold cell density (cell density at QS dependent induction of gene expression) is fixed at a constant value, although microbial fermentation requires different appropriate time and cell density for the optimal induction depending on fermentation process and target compounds.

In this study, we developed a synthetic lux system by a combination of a synthetic lux promoter and a positive feedback loop for the versatile use of QS in metabolic engineering. This system can be tuned its threshold cell density depending on the concentration of chemical inducer isopropyl β-D-1-thiogalactopyranoside (IPTG). Using a synthetic lux system as an induction signal, it is not only possible to exert an autonomous control over the initiation of target compound production, but also to trigger genetic circuit at a desired cell density. We have already developed a metabolic flux regulation system as a metabolic toggle switch (MTS), a synthetic genetic circuit. This flux regulation system improved the microbial chemical production through the excess flux redirection from the central metabolic pathway toward desired synthetic pathway, and it required an optimal induction to achieve its desired function. Integrating the lux system and the MTS, we demonstrated the autonomous redirection of metabolic flux from the TCA cycle toward isopropanol production at a desired E. coli density. As the result, our approach achieved a significant improvement in isopropanol fermentation.

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Soma, Y. et al., Metab. Eng 23, 175 (2014).
Soma, Y and Hanai, T., Metab. Eng. 30, 7 (2015).