Driven by environmental cues, bacterial transition from the planktonic state to the sessile state, in which biofilms are formed, is mediated by a control system within the bacterial cell that is not quite understood yet. It is known that switching between these phenotypes is closely related to intracellular levels of a small signaling molecule (c-di-GMP) - when these levels are high, they usually promote biofilm formation. In this condition, which is predominant in chronic infections, bacterial resistance to antibiotics is elevated and constitutes an obstacle to conventional treatments. Intracellular levels of c-di-GMP are regulated by opposite reactions involving diguanylate cyclase enzymes from the GGDEF family (synthesis) and phosphodiesterase enzymes from the EAL family and from the HD-GYP family (degradation). Once present, c-di-GMP interacts with effector molecules that can alter the cellular phenotype by diverse mechanisms. Many c-di-GMP receptors have already been identificated - proteins that contain a PilZ domain and proteins that contain degenerate EAL or GGDEF domains are some examples. Pioneer studies that have been recently published have demonstrated that direct protein-protein interaction between members of the c-di-GMP signaling network play a important role in regulating these kind of pathways. Therefore, the present study proposes a global investigation of the network of interactions between proteins containing GGDEF, EAL, HD-GYP e PilZ in the organisms Pseudomonas aeruginosa (forty nine proteins) and Xanthomonas axonopodis pv. citri (thirty nine proteins), using the bacterial two-hybrid system. Identified interactions will be further characterized by biophysical and biochemical methods. It is expected that this analysis can provide more information about the molecular mechanisms involved in c-di-GMP signaling.
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