Application of an engineered chromatic acclimation sensor for red-light-regulated gene expression in cyanobacteria

Abstract

The development of a versatile tool for the gene regulation in cyanobacteria is critical for the future realization of cyanobacterial bioprocessing. The use of chemical inducers to regulate gene expression are not practical considering their cost and technical difficulty in removing them from culture. Therefore, we have focused on a cyanobacteria-derived chromatic acclimation sensor, the green-light sensing system, CcaS/CcaR two-component system, derived from Synechocystis sp. PCC6803 (PCC6803) as a toll for genetic regulation. However, the regulation of gene expression levels by CcaS is not strict. We have previously developed a miniaturized CcaS, CcaS#11, which is a truncated CcaS showing gene induction under red-light illumination and strict repression under green-light illumination in Escherichia coli. In this study, CcaS#11 was transformed in cyanobacteria to achieve red-light-regulated gene expression in cyanobacteria. The application was first attempted in PCC6803 after knocking out genomic CcaS/CcaR system to exclude interference. The results revealed gene expression was only induced under red-light illumination and strictly repressed under green-light illumination. The red-light-regulated gene expression was also applied for a marine cyanobacteria, Synechococcus sp. NKBG15041c (NKBG15041c). In NKBG15041c, gene expression was induced under red-light illumination and strictly repressed under green-light illumination with a 2-fold higher ON/OFF ratio compared with the original CcaS/CcaR two-component system. Therefore, the constructed red-light-regulated gene expression system using CcaS#11 has a great potential as a platform technology for the further development of light-regulated bioprocesses with strict control in cyanobacteria.