Paradoxical enhancement of chemoreceptor detection sensitivity by a sensory adaptation enzyme

Antagonistic response regulators spatially regulate receptor methylation in the Pseudomonas aeruginosa Pil-Chp surface sensing system

Most bacterial chemosensory systems encode enzymes that are predicted to methylate and demethylate their chemoreceptors to control signaling activity. Here, we show that a predicted methyltransferase (PilK) and methylesterase (ChpB) methylate and demethylate, respectively, the chemoreceptor PilJ in the Pseudomonas aeruginosa (P. aeruginosa) Pil-Chp surface sensing system. PilJ methylation modulates the amplitude of cAMP production and the frequency of twitching motility reversals, outputs of Pil-Chp signaling. Dynamic imaging of fluorescent fusion proteins in individual twitching cells reveals that PilK and ChpB localize to opposite poles, with PilK at the lagging pole and ChpB at the leading pole. These enzymes switch poles upon bacterial reversals, a process dependent on the Pil-Chp response regulators PilG and PilH. Our results suggest that the PilJ population at each pole exists in dynamic and opposite methylation states that may reset the PilJ signaling activity at each pole during P. aeruginosa surface sensing, a key feature of adaptation.

Rational Engineering of a Dynamic, Enzyme-Driven DNA Walker for Intracellular Dual-Enzyme Activity Sequentially Monitoring and Imaging

Monitoring enzyme activity is crucial in both scientific research and clinical applications. However, abnormalities in a single enzyme's activity can indicate multiple diseases, limiting the specificity of single enzyme activity monitoring in clinical diagnosis. We developed a dynamic DNA walker that can be sequentially activated by two enzymes, enabling the monitoring and imaging of both enzyme activities within cells. Initially, the DNA walker contains a site for apurinic/apyrimidinic endonuclease 1 (APE1). Upon APE1 activation, the DNA walker forms specific structures recognized and cleaved by Flap endonuclease 1 (FEN1). The temporal disparity between the activities of APE1 and FEN1 allows for the sequential monitoring and imaging of both enzymes, reducing the likelihood of false-positive results. To enhance local concentration and decrease reaction time, the DNA walk sequence was attached to the surface of gold nanoparticles (AuNPs). The fruition of this endeavor will facilitate the investigation and advancement of multiple enzyme activity monitoring and imaging methods and technologies, while simultaneously broadening the domains of application for DNA nanotechnology.

Spatial control of sensory adaptation modulates mechanosensing in Pseudomonas aeruginosa

Sensory signaling pathways use adaptation to dynamically respond to changes in their environment. Here, we report the mechanism of sensory adaptation in the Pil-Chp mechanosensory system, which the important human pathogen Pseudomonas aeruginosa uses to sense mechanical stimuli during surface exploration. Using biochemistry, genetics, and cell biology, we discovered that the enzymes responsible for adaptation, a methyltransferase and a methylesterase, are segregated to opposing cell poles as P. aeruginosa explore surfaces. By coordinating the localization of both enzymes, we found that the Pil-Chp response regulators influence local receptor methylation, the molecular basis of bacterial sensory adaptation. We propose a model in which adaptation during mechanosensing spatially resets local receptor methylation, and thus Pil-Chp signaling, to modulate the pathway outputs, which are involved in P. aeruginosa virulence. Despite decades of bacterial sensory adaptation studies, our work has uncovered an unrecognized mechanism that bacteria use to achieve adaptation to sensory stimuli.

Mutations in surface-sensing receptor WspA lock the Wsp signal transduction system into a constitutively active state

Pseudomonas aeruginosa rugose small-colony variants (RSCVs) are frequently isolated from chronic infections, yet, they are rarely reported in environmental isolates. Here, during the comparative genomic analysis of two P. aeruginosa strains isolated from crude oil, we discovered a spontaneous in-frame deletion, wspA_Δ280-307 , which led to hyper-biofilm and RSCV phenotypes. WspA is a homologue of methyl-accepting chemotaxis proteins (MCPs) that senses surfaces to regulate biofilm formation by stimulating cyclic-di-guanosine monophosphate (c-di-GMP) synthesis through the Wsp system. However, the methylation sites of WspA have never been identified. In this study, we identified E280 and E294 of WspA as methylation sites. The wspA_Δ280-307 mutation enabled the Wsp system to lock into a constitutively active state that is independent of regulation by methylation. The result is an enhanced production of c-di-GMP. Sequence alignment revealed three conserved repeat sequences within the amino acid residues 280-313 (aa280-313) region of WspA homologues, suggesting that a spontaneous deletion within this DNA encoding region was likely a result of intragenic recombination and that similar mutations might occur in several related bacterial genera. Our results provide a plausible explanation for the selection of RSCVs and a mechanism to confer a competitive advantage for P. aeruginosa in a crude-oil environment.

Stimulus sensing and signal processing in bacterial chemotaxis

Motile bacteria use chemotaxis to migrate towards environments that are favorable for growth and survival. The signaling pathway that mediates this behavior is largely conserved among prokaryotes, with Escherichia coli chemotaxis system being one of the simplest and the best studied. At the core of this pathway are the arrays of clustered chemoreceptors that detect, amplify and integrate various stimuli. Recent work provided deeper understanding of spatial organization and signal processing by these clusters and uncovered the variety of sensory mechanisms used to detect environmental stimuli. Moreover, studies of bacteria with different lifestyles have led to new insights into the diversity and evolutionary conservation of the chemotaxis pathway, as well as the physiological relevance of chemotactic behavior in different environments.