MucA-Mediated Coordination of Type III Secretion and Alginate Synthesis in Pseudomonas aeruginosa

Abstract

The type III secretion system (T3SS) of Pseudomonas aeruginosa is an important virulence factor. The T3SS of P. aeruginosa can be induced by a low calcium signal or upon direct contact with the host cells. The exact pathway of signal sensing and T3SS activation is not clear. By screening a transposon insertion mutant library of the PAK strain, mutation in the mucA gene was found to cause repression of T3SS expression under both type III-inducing and -noninducing conditions. Mutation in the mucA gene is known to cause alginate overproduction, resulting in a mucoid phenotype. Alginate production responds to various environmental stresses and plays a protective role for P. aeruginosa. Comparison of global gene expression of mucA mutant and wild-type PAK under T3SS-inducing conditions confirmed the down regulation of T3SS genes and up regulation of genes involved in alginate biosynthesis. Further analysis indicated that the repression of T3SS in the mucA mutant was AlgU and AlgR dependent, as double mutants mucA/algU and mucA/algR showed normal type III expression. An algR::Gm mutant showed a higher level of type III expression, while overexpression of the algR gene inhibited type III gene expression; thus, it seems that the AlgR-regulated product inhibits the expression of the T3SS genes. It is likely that P. aeruginosa has evolved tight regulatory networks to turn off the energy-expensive T3SS when striving for survival under environmental stresses.

A novel human antimicrobial factor targets Pseudomonas aeruginosa through its type III secretion system

“…Because the T3SS is highly conserved and since it is primarily found in pathogenic bacteria, T3SS would be an ideal target for innate immunity. This notion is supported by the findings that P. aeruginosa lung isolates obtained from chronically infected cystic fibrosis patients are predominantly T3SS mutants (Wu et al, 2004;Li et al, 2005;Yahr & Wolfgang, 2006), indicating that T3SS may also be selected against in the lung environment as well. Moreover, Franchi et al (2012) recently reported that intestinal phagocytes produce massive amounts of pro-inflammatory cytokines only in response to pathogenic Salmonella, but not when they encounter commensal bacteria.…”

Global Regulatory Pathways and Cross-talk ControlPseudomonas aeruginosaEnvironmental Lifestyle and Virulence Phenotype

“…In a murine model of acute pneumonia a cyaB mutant is attenuated, indicating a role for cAMP in P. aeruginosa virulence . CyaA is a cytosolic cIass I AC, a class found primarily in enterobacteria, while CyaB is a member of the class III AC family ubiquitous among both eukaryotes and prokaryotes (Baker, 2004). CyaB consists of a N-terminal MASE2 (membrane associated sensor 2) domain and a C-terminal AC catalytic domain (Nikolskaya, 2003).…”

“…Both AlgU and AlgR are necessary for activation of the genes encoding the biosynthetic enzymes required for alginate production, resulting in the mucoid phenotype (Mohr, 1992;Martin, 1994). Loss-of-function mutations in mucA are also associated with reduced expression of many acute virulence factors, including: the T3SS, ETA, LasA protease, and Tfp ( Figure 1E) (Mohr, 1990;Wu, 2004;Jones, 2010). Recent work by our group demonstrated that mucA mutation blocks the production of invasive virulence factors by inhibiting the cAMP/Vfr signaling pathway at the level of vfr expression (Jones, 2010).…”

Pseudomonas aeruginosa Biofilm Formation in the CF Lung and Its Implications for Therapy

“…In fact, recent evidence has revealed an inverse regulation of biofilm formation and virulence attributes associated with acute infections (Goodman, Kulasekara et al 2004;Furukawa, Kuchma et al 2006;Harmsen, Yang et al 2010). For instance, expression of the AlgU alternative sigma factor leads to decreased expression of T3SS and increased production of the biofilm exopolysaccharide alginate (Wu, Badrane et al 2004;Diaz, King et al 2011). Similarly, the SadARS (also known as RocARS) three component regulatory system positively regulates biofilm maturation but inhibits the transcription of genes encoding components of the T3SS (Kuchma, Connolly et al 2005;Kulasekara, Ventre et al 2005).…”