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Rewiring TCSs for host adaptation
Clinical isolates of Pseudomonas aeruginosa from patients with cystic fibrosis (CF) often have mutations that affect two-component systems (TCSs) that sense and respond to environmental stimuli. Cao et al. found that mutations in CF-adapted P. aeruginosa strains that affected the sensor histidine kinase BfmS promoted phenotypic changes associated with chronic infection by causing the loss of BfmS-mediated inhibition of its downstream effector, BfmR. Under these conditions, GtrS, a sensor histidine kinase from a different TCS, promoted BfmR activity in the presence of glucose, which is abundant in the CF lung. Thus, mutations that affect a TCS may contribute to host adaptation both directly by dysregulating a cognate TCS and indirectly by enabling aberrant cross-talk between noncognate TCSs.
Abstract
Genetic mutations are a primary driving force behind the adaptive evolution of bacterial pathogens. Multiple clinical isolates of Pseudomonas aeruginosa, an important human pathogen, have naturally evolved one or more missense mutations in bfmS, which encodes the sensor histidine kinase of the BfmRS two-component system (TCS). A mutant BfmS protein containing both the L181P and E376Q substitutions increased the phosphorylation and thus the transcriptional regulatory activity of its cognate downstream response regulator, BfmR. This reduced acute virulence and enhanced biofilm formation, both of which are phenotypic changes associated with a chronic infection state. The increased phosphorylation of BfmR was due, at least in part, to the cross-phosphorylation of BfmR by GtrS, a noncognate sensor kinase. Other spontaneous missense mutations in bfmS, such as A42E/G347D, T242R, and R393H, also caused a similar remodeling of the BfmRS TCS in P. aeruginosa. This study highlights the plasticity of TCSs mediated by spontaneous mutations and suggests that mutation-induced activation of BfmRS may contribute to host adaptation by P. aeruginosa during chronic infections.
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