Regulation of dispersion in response to environmental cues and its contribution to pathogenicity in Pseudomonas aeruginosa.

摘要

The human pathogen Pseudomonas aeruginosa is well known of its capability to cause both acute and chronic infections. The difference in virulence is attributed to the mode of growth: bacteria growing planktonically cause acute infections, while bacteria growing in matrix-enclosed aggregates known as biofilms are associated with chronic, persistent infections. These two growth states furthermore differ in the level of the second messenger 3', 5'-cyclic diguanylic acid (c-di-GMP), with high levels of this molecule correlated with biofilms and low levels associated with the planktonic growth state. C-di-GMP is modulated by enzymes called diguanylate cyclases (DGCs) and phosphodiesterases (PDEs). Recent findings suggested dispersion to coincide with a reduction in c-di-GMP levels. Dispersion in P. aeruginosa occurs in response to a variety of environmental cues including nutrients and nitric oxide (NO). Here, we demonstrate that nutrient-induced dispersion involved the action of the membrane-bound diguanylate cyclase CrdA. CrdA was found to interact with BdlA, RbdA and DipA that were previously described to be required for induced dispersion. While CrdA contributed to dispersion in response to a variety of environmental cues, the membrane-bound PDE NbdA was found to specifically contribute to NO-induced dispersion. NbdA also harbors a MHYT domain predicted to sense diatomic signals. In addition to elucidating the dispersion response by P. aeruginosa, this study furthermore focused on the contribution of dispersion to virulence. We demonstrate that, while having left a biofilm, dispersed cells are distinct from planktonic cells with respect to gene expression, release of matrix-degrading enzymes, and pathogenicity. We found that mutant impaired in induced dispersion, are impaired in mounting acute infections in the plant host Arabidopsis thaliana. In contrast, mutants inactivated in genes involved in the modulation of c-di-GMP level but capable of dispersion, were as virulent as wild type. In summary, our findings demonstrated for the first time a requirement of a diguanylate cyclase and a membrane-bound, NO-sensing phosphodiesterase for dispersion. Last but not least, our data suggested a role of dispersion in P. aeruginosa pathogenicity.