Global Regulator MorA Affects Virulence-Associated Protease Secretion in Pseudomonas aeruginosa PAO1.

Ayshwarya Ravichandran,Tanujaa Suriyanarayanan,Sanjay Swarup,Chui Ching Wong,Malarmathy Ramachandran

doi:10.1371/journal.pone.0123805

Abstract

Bacterial invasion plays a critical role in the establishment of Pseudomonas aeruginosa infection and is aided by two major virulence factors – surface appendages and secreted proteases. The second messenger cyclic diguanylate (c-di-GMP) is known to affect bacterial attachment to surfaces, biofilm formation and related virulence phenomena. Here we report that MorA, a global regulator with GGDEF and EAL domains that was previously reported to affect virulence factors, negatively regulates protease secretion via the type II secretion system (T2SS) in P. aeruginosa PAO1. Infection assays with mutant strains carrying gene deletion and domain mutants show that host cell invasion is dependent on the active domain function of MorA. Further investigations suggest that the MorA-mediated c-di-GMP signaling affects protease secretion largely at a post-translational level. We thus report c-di-GMP second messenger system as a novel regulator of T2SS function in P. aeruginosa. Given that T2SS is a central and constitutive pump, and the secreted proteases are involved in interactions with the microbial surroundings, our data broadens the significance of c-di-GMP signaling in P. aeruginosa pathogenesis and ecological fitness.

Highlights

Pseudomonas aeruginosa is a highly versatile opportunistic pathogen for humans and is a major cause of nosocomial infections in immunocompromised patients such as those suffering from cystic fibrosis, pneumonia and skin-burn
We have investigated the effect of MorA on protein secretion in planktonic P. aeruginosa PAO1 cultures and show evidence suggesting that MorA negatively controls T2SS-mediated protease secretion, which in turn impacts infection efficiency of P. aeruginosa
Based on our previous findings from gene expression profiling of MorA mutant [57] and other reports showing evidence that c-di-GMP regulating proteins control bacterial secretion systems [45, 46, 52,53,54,55], we tested the effect of MorA on the P. aeruginosa secretome

Summary

Introduction

Pseudomonas aeruginosa is a highly versatile opportunistic pathogen for humans and is a major cause of nosocomial infections in immunocompromised patients such as those suffering from cystic fibrosis, pneumonia and skin-burn. While tissue penetration requires cleavage of extracellular matrix proteins and tight junctions, cellular invasion happens mostly through receptor-mediated response by the host [7]. Pathogenic bacteria accomplish these by releasing an arsenal of diffusible factors into the surrounding environment and delivering effector proteins directly into the host cytosol, through virulence-associated secretion systems on the surface. Given the flexible lifestyles and adaptability of P. aeruginosa, it is not surprising that it possesses five out of the six secretion machineries described to date in Gram-negative pathogens [8] Their copy numbers and functional organization vary depending on the strain and its environment. It is a good model to study secretion processes and their control mechanisms

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Results

Conclusion