Gas and light: triggers of c-di-GMP-mediated regulation

Gene expression reprogramming of Pseudomonas alloputida in response to arginine through the transcriptional regulator ArgR

Different bacteria change their life styles in response to specific amino acids. In Pseudomonas putida (now alloputida) KT2440, arginine acts both as an environmental and a metabolic indicator that modulates the turnover of the intracellular second messenger c-di-GMP, and expression of biofilm-related genes. The transcriptional regulator ArgR, belonging to the AraC/XylS family, is key for the physiological reprogramming in response to arginine, as it controls transport and metabolism of the amino acid. To further expand our knowledge on the roles of ArgR, a global transcriptomic analysis of KT2440 and a null argR mutant growing in the presence of arginine was carried out. Results indicate that this transcriptional regulator influences a variety of cellular functions beyond arginine metabolism and transport, thus widening its regulatory role. ArgR acts as positive or negative modulator of the expression of several metabolic routes and transport systems, respiratory chain and stress response elements, as well as biofilm-related functions. The partial overlap between the ArgR regulon and those corresponding to the global regulators RoxR and ANR is also discussed.

A c-di-GMP signaling module controls responses to iron in Pseudomonas aeruginosa

Cyclic dimeric guanosine monophosphate (c-di-GMP) serves as a bacterial second messenger that modulates various processes including biofilm formation, motility, and host-microbe symbiosis. Numerous studies have conducted comprehensive analysis of c-di-GMP. However, the mechanisms by which certain environmental signals such as iron control intracellular c-di-GMP levels are unclear. Here, we show that iron regulates c-di-GMP levels in Pseudomonas aeruginosa by modulating the interaction between an iron-sensing protein, IsmP, and a diguanylate cyclase, ImcA. Binding of iron to the CHASE4 domain of IsmP inhibits the IsmP-ImcA interaction, which leads to increased c-di-GMP synthesis by ImcA, thus promoting biofilm formation and reducing bacterial motility. Structural characterization of the apo-CHASE4 domain and its binding to iron allows us to pinpoint residues defining its specificity. In addition, the cryo-electron microscopy structure of ImcA in complex with a c-di-GMP analog (GMPCPP) suggests a unique conformation in which the compound binds to the catalytic pockets and to the membrane-proximal side located at the cytoplasm. Thus, our results indicate that a CHASE4 domain directly senses iron and modulates the crosstalk between c-di-GMP metabolic enzymes.

A growing battlefield in the war against biofilm-induced antimicrobial resistance: insights from reviews on antibiotic resistance

Biofilms are a common survival strategy employed by bacteria in healthcare settings, which enhances their resistance to antimicrobial and biocidal agents making infections difficult to treat. Mechanisms of biofilm-induced antimicrobial resistance involve reduced penetration of antimicrobial agents, increased expression of efflux pumps, altered microbial physiology, and genetic changes in the bacterial population. Factors contributing to the formation of biofilms include nutrient availability, temperature, pH, surface properties, and microbial interactions. Biofilm-associated infections can have serious consequences for patient outcomes, and standard antimicrobial therapies are often ineffective against biofilm-associated bacteria, making diagnosis and treatment challenging. Novel strategies, including antibiotics combination therapies (such as daptomycin and vancomycin, colistin and azithromycin), biofilm-targeted agents (such as small molecules (LP3134, LP3145, LP4010, LP1062) target c-di-GMP), and immunomodulatory therapies (such as the anti-PcrV IgY antibodies which target Type IIIsecretion system), are being developed to combat biofilm-induced antimicrobial resistance. A multifaceted approach to diagnosis, treatment, and prevention is necessary to address this emerging problem in healthcare settings.