Quorum sensing mechanism dependent violacein production by constructing a synthetic ecosystem

Violacein is a natural purple-blue indolocarbazole pigment which is produced in nature by some Gram Negative bacteria. This microbial natural pigment is produced by many different bacterial species, and among them Chromobacterium violaceum is so far the most thoroughly studied one. Alongside violacein's important biological activities, there has been increased interest shown for the use of this pigment in various industrial applications, such as cosmetics, medicine, food and textile. However, due to the lack of stability of pigment production, spontaneous biosynthesis in the non-producing strain variants, and overall poor production yields exhibited by natural wild type strain producers, serial production of violacein for industrial applications is difficult and as a result, although this pigment is very versatile, its' practical use is still very limited. In this study, in order to obtain stable and high production yield of violacein, the biosynthetic pathway which is responsible for pigment production was reconstructed in the Escherichia coli host cell. The aim of this study was to investigate the effect of synchronous population behavior on pigment biosynthesis efficiency of a heterologous biosynthetic operon by forming a synthetic ecosystem using synthetic biology and metabolic engineering principles, where as a result violacein pigment was produced. To control the coordinated population behavior of the synthetic ecosystem, the violacein biosynthetic pathway was put under the bacterial communication system Quorum Sensing mechanism. For violacein biosynthetic pathway to be controlled by Quorum Sensing mechanism, the synthetic ecosystem was planned to constitute of two separate modules: sender and recipient cell modules. Quorum Sensing gene responsible for the synthesis of the diffusible signal molecules was placed into the "sender" cell, and the genes which are responsible for the violacein production were placed under the Quorum Sensing promotor's (Plux) control into the "recipient" cell. For the heterologous production of violacein, the needed concentration of the signal is dependent on the concentration of the sender cell in the environment and furthermore, the recipient cell's violacein production is based on sender cell concentration, thus ensuring high production yield and stable production of the pigment. This violacein production-based synthetic ecosystem may help us detect the concentration of the signal molecules that are present in the environment. Keywords: Synthetic biology, metabolic engineering, violacein, Quorum Sensing, ecosystem.