Exploring environmental control of cyclic di-GMP signaling in Vibrio cholerae by using the ex vivo lysate cyclic di-GMP assay (TELCA).

Vibrio cholerae senses its environment, including the surrounding bacterial community, using both the second messenger cyclic di-GMP (c-di-GMP) and quorum sensing (QS) to regulate biofilm formation and other bacterial behaviors. Cyclic di-GMP is synthesized by diguanylate cyclase (DGC) enzymes and degraded by phosphodiesterase (PDE) enzymes. V. cholerae encodes a complex network of 61 enzymes predicted to mediate changes to the levels of c-di-GMP in response to extracellular signals, and the transcription of many of these enzymes is influenced by QS. Because of the complexity of the c-di-GMP signaling system in V. cholerae, it is difficult to determine if modulation of intracellular c-di-GMP in response to different stimuli is driven primarily by changes in c-di-GMP synthesis or hydrolysis. Here, we describe a novel method, named the ex vivo lysate c-di-GMP assay (TELCA), that systematically measures total DGC and PDE cellular activity. We show that V. cholerae grown in different environments exhibits significantly different intracellular levels of c-di-GMP, and we used TELCA to determine that these differences correspond to changes in both c-di-GMP synthesis and hydrolysis. Furthermore, we show that the increased concentration of c-di-GMP at low cell density is primarily due to increased DGC activity due to the DGC CdgA. Our findings highlight the idea that modulation of both total DGC and PDE activity alters the intracellular concentration of c-di-GMP, and we present a new method that is widely applicable to the systematic analysis of complex c-di-GMP signaling networks.