Optogenetic module for dichromatic control of c-di-GMP signaling

Abstract

Many aspects of bacterial physiology and behavior, including motility, surface attachment, and the cell cycle, are controlled by cyclic di-GMP (c-di-GMP)- dependent signaling pathways on the scale of seconds to minutes. Interrogation of such processes in real time requires tools for introducing rapid and reversible changes in intracellular c-di-GMP levels. Inducing the expression of genes encoding c-di-GMP-synthetic (diguanylate cyclases) and -degrading (c-di-GMP phosphodiesterase) enzymes by chemicals may not provide adequate temporal control. In contrast, light-controlled diguanylate cyclases and phosphodiesterases can be quickly activated and inactivated. A red/near-infrared-light-regulated diguanylate cyclase, BphS, was engineered previously, yet a complementary light-activated c-di-GMP phosphodiesterase has been lacking. In search of such a phosphodiesterase, we investigated two homologous proteins from Allochromatium vinosum and Magnetococcus marinus, designated BldP, which contain C-terminal EAL-BLUF modules, where EAL is a c-di-GMP phosphodiesterase domain and BLUF is a blue light sensory domain. Characterization of the BldP proteins in Escherichia coli and in vitro showed that they possess light-activated c-di-GMP phosphodiesterase activities. Interestingly, light activation in both enzymes was dependent on oxygen levels. The truncated EAL-BLUF fragment from A. vinosum BldP lacked phosphodiesterase activity, whereas a similar fragment from M. marinus BldP, designated EB1, possessed such activity that was highly ( > 30-fold) upregulated by light. Following light withdrawal, EB1 reverted to the inactive ground state with a half-life of ~6 min. Therefore, the bluelight- activated phosphodiesterase EB1 can be used in combination with the red/nearinfrared- light-regulated diguanylate cyclase BphS for the bidirectional regulation of c-di-GMP-dependent processes in E. coli as well as other bacterial and nonbacterial cells.