Intelligent microbial cell factory with genetic pH shooting (GPS) for cell self-responsive base/acid regulation

Wenxin Bai,Xiaopeng Gao,Chenyi Li,Chun Li,Mengchao He,Jiadong Zhong,Jinlin Li,Ke Xu,Xiao Peng,Ying Wang

doi:10.1186/s12934-020-01457-3

Abstract

BackgroundIn industrial fermentation, pH fluctuation resulted from microbial metabolism influences the strain performance and the final production. The common way to control pH is adding acid or alkali after probe detection, which is not a fine-tuned method and often leads to increased costs and complex downstream processing. Here, we constructed an intelligent pH-sensing and controlling genetic circuits called “Genetic pH Shooting (GPS)” to realize microbial self-regulation of pH.ResultsIn order to achieve the self-regulation of pH, GPS circuits consisting of pH-sensing promoters and acid-/alkali-producing genes were designed and constructed. Designed pH-sensing promoters in the GPS can respond to high or low pHs and generate acidic or alkaline substances, achieving endogenously self-responsive pH adjustments. Base shooting circuit (BSC) and acid shooting circuit (ASC) were constructed and enabled better cell growth under alkaline or acidic conditions, respectively. Furthermore, the genetic circuits including GPS, BSC and ASC were applied to lycopene production with a higher yield without an artificial pH regulation compared with the control under pH values ranging from 5.0 to 9.0. In scale-up fermentations, the lycopene titer in the engineered strain harboring GPS was increased by 137.3% and ammonia usage decreased by 35.6%.ConclusionsThe pH self-regulation achieved through the GPS circuits is helpful to construct intelligent microbial cell factories and reduce the production costs, which would be much useful in industrial applications.

Highlights

In industrial fermentation, pH fluctuation resulted from microbial metabolism influences the strain performance and the final production
To achieve the self-regulation of pH during the cell fermentation process, a Genetic pH Shooting (GPS) circuit was designed in this study, including pH-sensing promoters that could respond to pH signals and produce acidic or alkaline substances to neutralize extra H+ or OH− in cells (Fig. 1)
In order to broaden the applications of pH self-regulation in diverse situations, single pH shooting circuits, acid shooting circuit (ASC) and base shooting circuit (BSC), were constructed to meet different requirements

Summary

Introduction

PH fluctuation resulted from microbial metabolism influences the strain performance and the final production. The common way to control pH is adding acid or alkali after probe detection, which is not a fine-tuned method and often leads to increased costs and complex downstream processing. We constructed an intelligent pH-sensing and controlling genetic circuits called “Genetic pH Shooting (GPS)” to realize microbial self-regulation of pH. PH control in the fermentation process is a widespread concern as its fluctuation results in numerous problems. A suitable environmental pH is essential for high fermentation productivity, and the optimization of pH in the fermentation process is critical. Problems concerning pH fluctuations in fermentation are complex. PH changes are nonlinearity along with the high sensitivity around neutral pH, leading to big challenges. To maintain a proper pH in fermentation processes, the most common method

Methods

Results

Discussion

Conclusion