Development of a reversible regulatory system for gene expression in the cyanobacterium Synechocystis sp. PCC 6803 by quorum-sensing machinery from marine bacteria

Abstract

Histidine kinases are common sensory proteins used to detect environmental changes in bacteria. They respond to specific stimuli via a signal-input domain and alter gene expression through a cognate response regulator. The modulation/control of transcriptional regulation in cyanobacteria is important to reinforce the production of useful target compounds via photosynthesis without altering the growth profiles. For instance, heavy metal ions (Ni2+ and Cu2+), chemical inducers (IPTG), and a volatile compound (toluene) have been previously applied to regulate gene expression in cyanobacteria. However, most systems/regulators are only able to regulate gene expression once because it is impossible to eliminate them from the medium. To construct a reversible regulation system, a chimeric sensor, VanN_SphS, was developed by fusing the signal input domain of a quorum-sensing (QS) sensor, VanN, from Vibrio anguillarum, responding N-3-hydroxyhexanoyl-L-homoserine lactone (OHC6-HSL), with the kinase domain of SphS, a phosphate-deficiency sensor from the cyanobacterium Synechocystis sp. PCC 6803. After expression of the chimeric sensor in Synechocystis cells, responses to the various N-acyl-homoserine-lactones (AHLs) were evaluated by measuring the alkaline phosphatase (AP) activity, which is regulated by SphS. VanN_SphS responded only to OHC6-HSL and repressed AP activity. Then, the coexpression of the AHLs-degradation enzyme, Aii20J, a lactonase from Tenacibaculum sp. 20J, resumed the activity. This is the first report on the use of AHL-mediated transcriptional regulation in Synechocystis, which could be used in the future for the controlled production of useful compounds in the cyanobacterium.