Specialized and shared functions of diguanylate cyclases and phosphodiesterases in Streptomyces development.

Levels of the second messenger bis-3-5-cyclic di-guanosinemonophosphate (c-di-GMP) determine when Streptomyces initiate sporulation to survive under adverse conditions. c-di-GMP signals are integrated into the genetic differentiation network by the regulator BldD and the sigma factor WhiG. However, functions of the development-specific c-di-GMP diguanylate cyclases (DGCs) CdgB and CdgC, and the phosphodiesterases (PDEs) RmdA and RmdB, are poorly understood. Here, we provide biochemical evidence that the GGDEF-EAL domain protein RmdB from S. venezuelae is a monofunctional PDE that hydrolyzes c-di-GMP to 5-pGpG. Despite having an equivalent GGDEF-EAL domain arrangement, RmdA cleaves c-di-GMP to GMP and exhibits residual DGC activity. We show that an intact EAL motif is crucial for the in vivo function of both enzymes since strains expressing protein variants with an AAA motif instead of EAL are delayed in development, similar to null mutants. Global transcriptome analysis of ∆cdgB, ∆cdgC, ∆rmdA and ∆rmdB strains revealed that the c-di-GMP specified by these enzymes has a global regulatory role, with about 20 % of all S. venezuelae genes being differentially expressed in the cdgC mutant. Our data suggest that the major c-di-GMP-controlled targets determining the timing and mode of sporulation are genes involved cell division and the production of the hydrophobic sheath that covers Streptomyces aerial hyphae and spores. Altogether, this study provides a global view of the c-di-GMP-dependent genes that contribute to the hyphae-to-spores transition and sheds light on the shared and specific functions of the key enzymes involved in c-di-GMP metabolism in S. venezuelae.