Figure 1

Regulation of cyanobacterial lytic system by green light. Schematic diagram of a novel system to prepare lytic cyanobacterial cells by physical signal, green-light illumination. The lysis system is composed of the CcaS/CcaR green-light regulated two-component system derived from Synechocystis, combined with T4 phage-derived lysis genes under the CcaS/CcaR-regulated cpcG2 promoter. CcaS is a sensor histidine kinase that activates its cognate response regulator, CcaR, under green light to induce the expression of the cpcG2 gene. Under red light, CcaS is in an ‘off-state’ and expression of the target gene is not activated (A). However under green light, CcaS is in an ‘on-state’, resulting in activation of CcaR by phosphorylation and a concomitant induction of the target gene expression (B). Holin forms a ‘tunnel’ in the plasma membrane, which provides endolysin access to the peptidoglycan and allows it to enzymatically break it down, leading to lysis. Antiholin, which is regulated by a weak constitutive promoter, blocks holin and prevents premature lysis due to low background levels of endolysin.