Molecular insights into RmcA-mediated c-di-GMP consumption: Linking redox potential to biofilm morphogenesis in Pseudomonas aeruginosa

Tandem GGDEF-EAL Domain Proteins Pleiotropically Modulate c-di-GMP Metabolism Enrolled in Bacterial Cellulose Biosynthesis

Cyclic diguanosine monophosphate (c-di-GMP) is a crucial secondary messenger that regulates bacterial cellulose (BC) synthesis. It is synthesized by diguanylate cyclase (DGC) containing a Gly-Gly-Asp/Glu-Glu-Phe (GGDEF) domain and degraded by phosphodiesterase (PDE) with a Glu-Ala-Leu (EAL) domain. In this work, a systematic analysis of ten GGDEF-EAL tandem domain proteins from Komagataeibacter xylinus CGMCC 2955 assessed their c-di-GMP metabolic functions and effects on BC titer and structure. Of these, five proteins exhibited DGC activity, and five exhibited PDE activity in vitro. GE03 was identified as a bifunctional protein. Most mutant strains deficient in GGDEF-EAL protein showed changes in BC metabolism, motility, and c-di-GMP levels. The combined knockout of identified PDE proteins increased the BC titer by 48.1% compared to the wild type. Overall, our findings advance our understanding of c-di-GMP signaling and its role in BC synthesis, introducing novel concepts and effective strategies for enhancing industrial BC production.

ArgR regulates motility and virulence through positive control of flagellar genes and inhibition of diguanylate cyclase expression in Aeromonas veronii

Flagella are essential for biofilm formation, adhesion, virulence, and motility. In this study, the deletion of argR resulted in defects in flagellar synthesis and reduced motility, nevertheless, the underlying mechanism by which ArgR regulated bacterial motility remained unclear. ChIP-Seq and RNA-Seq analysis revealed that ArgR regulated the expression of flagellar genes, concluding two-component system flrBC and multitudinous flagellar structure genes. Specifically, ArgR bound to the ARG box in the flrBC promoter, positively regulating flrBC expression, which in turn promoted flagellar synthesis and enhanced motility. Additionally, in the absence of arginine, ArgR inhibited the expression of diguanylate cyclase, leading to reduced c-di-GMP levels, thereby alleviating its inhibitory effect on motility. Thus, ArgR coordinated two distinct pathways to regulate flagellar assembly and motility, ultimately affecting adhesion, virulence, and biofilm formation. In summary, this study elucidates the molecular mechanism by which ArgR regulates motility, highlighting its crucial role in bacterial virulence and offering new insights for the prevention and control of pathogenic bacteria.

Multidrug resistance in Pseudomonas aeruginosa: genetic control mechanisms and therapeutic advances

Pseudomonas aeruginosa is a significant opportunistic pathogen, and its complex mechanisms of antibiotic resistance pose a challenge to modern medicine. This literature review explores the advancements made from 1979 to 2024 in understanding the regulatory networks of antibiotic resistance genes in Pseudomonas aeruginosa, with a particular focus on the molecular underpinnings of these resistance mechanisms. The review highlights four main pathways involved in drug resistance: reducing outer membrane permeability, enhancing active efflux systems, producing antibiotic-inactivating enzymes, and forming biofilms. These pathways are intricately regulated by a combination of genetic regulation, transcriptional regulators, two-component signal transduction, DNA methylation, and small RNA molecules. Through an in-depth analysis and synthesis of existing literature, we identify key regulatory elements mexT, ampR, and argR as potential targets for novel antimicrobial strategies. A profound understanding of the core control nodes of drug resistance offers a new perspective for therapeutic intervention, suggesting that modulating these elements could potentially reverse resistance and restore bacterial susceptibility to antibiotics. The review looks forward to future research directions, proposing the use of gene editing and systems biology to further understand resistance mechanisms and to develop effective antimicrobial strategies against Pseudomonas aeruginosa. This review is expected to provide innovative solutions to the problem of drug resistance in infectious diseases.

Cyclic di-GMP incorporates the transcriptional factor FleQ03 in Pseudomonas syringae MB03 to elicit biofilm-dependent resistance in response to Caenorhabditis elegans predation

Bacteria usually form biofilms as a defense mechanism against predation by bacterivorous nematodes. In this context, the second messenger c-di-GMP from the wild-type Pseudomonas syringae MB03 actuates the transcriptional factor FleQ03 to elicit biofilm-dependent nematicidal activity against Caenorhabditis elegans N2. P. syringae MB03 cells exhibited nematicidal activity and c-di-GMP content in P. syringae MB03 cells was increased after feeding to nematodes. Expression of a diguanylate cyclase (DGC) gene in P. syringae MB03 resulted in an increased c-di-GMP content, biofilm yield and nematicidal activity, whereas converse effects were obtained when expressing a phosphodiesterase (PDE) gene. Molecular docking and isothermal titration calorimetry assays verified the affinity activity between c-di-GMP and the FleQ03 protein. The disruption of the fleQ03 gene in P. syringae MB03, while increasing c-di-GMP content, significantly diminished both biofilm formation and nematicidal activity. Interestingly, P. syringae MB03 formed a full-body biofilm around the worms against predation, probably extending from the tail to the head, whereas it was not observed in the fleQ03 gene disrupted cells. Thus, we hypothesized that c-di-GMP incorporated FleQ03 to reinforce bacterial biofilm and biofilm-dependent pathogenicity in response to C. elegans predation, providing insights into a possible means of resisting bacterivorous nematodes by bacteria in natural ecosystems.

BrfA functions as a bacterial enhancer-binding protein to regulate functional amyloid Fap-dependent biofilm formation in Pseudomonas fluorescens by sensing cyclic diguanosine monophosphate

The functional amyloid of Pseudomonas (Fap) is essential for the formation of macrocolony biofilms, pellicles, and solid surface-associated (SSA) biofilms of Pseudomonas fluorescens PF07, an isolate from refrigerated marine fish. However, limited information on the expression regulation of fap genes is available. Herein, we found that a novel bacterial enhancer-binding protein (bEBP), BrfA, regulated Fap-dependent biofilm formation by directly sensing cyclic diguanosine monophosphate (c-di-GMP). Our in vivo data showed that the REC domain deletion of BrfA promoted fap gene expression and biofilm formation, and c-di-GMP positively regulated the transcription of fapA in a BrfA-dependent manner. In in vitro experiments, we found that the ATPase activity of BrfA was inhibited by the REC domain and was activated by c-di-GMP. BrfA and the sigma factor RpoN bound to the upstream region of fapA, and the binding ability of BrfA was not affected by either deletion of the REC domain or c-di-GMP. BrfA specifically bound to the three enhancer sites upstream of the fapA promoter, which contain the consensus sequence CA-(N4)-TGA(A/T)ACACC. In vivo experiments using a lacZ fusion reporter indicated that all three BrfA enhancer sites were essential for the activation of fapA transcription. Overall, these findings reveal that BrfA is a new type of c-di-GMP-responsive transcription factor that directly controls the transcription of Fap biosynthesis genes in P. fluorescens. Fap functional amyloids and BrfA-type transcription factors are widespread in Pseudomonas species. The novel insights into the c-di-GMP- and BrfA-dependent expression regulation of fap provided by this work will contribute to the development of antibiofilm strategies.

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.