The second messenger cyclic di-GMP (c-di-GMP) controls the transition between different lifestyles in bacterial pathogens. Here, we report the identification of DgcP (diguanylate cyclase conserved in Pseudomonads), whose activity in the olive tree pathogen Pseudomonas savastanoi pv. savastanoi is dependent on the integrity of its GGDEF domain. Furthermore, deletion of the dgcP gene revealed that DgcP negatively regulates motility and positively controls biofilm formation in both the olive tree pathogen P. savastanoi pv. savastanoi and the human opportunistic pathogen Pseudomonas aeruginosa. Overexpression of the dgcP gene in P. aeruginosa¿PAK led to increased exopolysaccharide production and upregulation of the type VI secretion system; in turn, it repressed the type III secretion system, which is a hallmark of chronic infections and persistence for P. aeruginosa. Deletion of the dgcP gene in P. savastanoi pv. savastanoi NCPPB 3335 and P. aeruginosa¿PAK reduced their virulence in olive plants and in a mouse acute lung injury model respectively. Our results show that diguanylate cyclase DgcP is a conserved Pseudomonas protein with a role in virulence, and confirm the existence of common c-di-GMP signalling pathways that are capable of regulating plant and human Pseudomonas spp. infections.

This study was supported by the Spanish Plan Nacional I+D+i Grants AGL2011-30343-CO2-01 and BIO2011-23032, by the Programa de Incentivos, Consejería de Innovación, Ciencia y Empresas of the Andalusian Government (P10-CVI-05800), and by FEDER funds. Research in AF’s laboratory is supported by BBSRC GrantBB/L007959/1. IMA was supported by a FPU fellowship (Ministerio de Ciencia e Innovación/ Ministerio de Economía y Competitividad, Spain) and by an EMBO short-term fellowship during her stay at AF’slaboratory. JAM was supported by a grant from the Fundação para a Ciencia e a Tecnologia (Portugal).

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