# | Rank | Similarity | Title + Abs. | Year | PMID |
|---|---|---|---|---|---|
| 0 | 1 | 2 | 3 | 4 | 5 |
| 705 | 0 | 1.0000 | First structure of the polymyxin resistance proteins. PmrA/PmrB and PhoP/PhoQ are a pair of two-component systems (TCSs) that allow the Gram-negative bacteria to survive the cationic antimicrobial peptide polymyxin B. The two TCSs are linked by the polymyxin resistance protein, PmrD. The PhoP-activated PmrD protects the phosphorylated response regulator PmrA from dephosphorylation, and promotes the transcription of PmrA-activated genes responsible for polymyxin resistance. PmrD is the first protein identified to mediate the connectivity between two TCSs by protecting the phosphorylated response regulator of the downstream TCS. PmrD shows no homology to proteins with known structures. We present here the solution structure of PmrD from Escherichia coli, the first three-dimensional structure of the PmrD family. Our study provides the structural basis of the novel interacting mechanism of bacterial two-component signal-transduction systems. | 2007 | 17686460 |
| 706 | 1 | 0.9997 | Effect of PhoP-PhoQ activation by broad repertoire of antimicrobial peptides on bacterial resistance. Pathogenic bacteria can resist their microenvironment by changing the expression of virulence genes. In Salmonella typhimurium, some of these genes are controlled by the two-component system PhoP-PhoQ. Studies have shown that activation of the system by cationic antimicrobial peptides (AMPs) results, among other changes, in outer membrane remodeling. However, it is not fully clear what characteristics of AMPs are required to activate the PhoP-PhoQ system and whether activation can induce resistance to the various AMPs. For that purpose, we investigated the ability of a broad repertoire of AMPs to traverse the inner membrane, to activate the PhoP-PhoQ system, and to induce bacterial resistance. The AMPs differ in length, composition, and net positive charge, and the tested bacteria include two wild-type (WT) Salmonella strains and their corresponding PhoP-PhoQ knock-out mutants. A lacZ-reporting system was adapted to follow PhoP-PhoQ activation. The data revealed that: (i) a good correlation exists among the extent of the positive charge, hydrophobicity, and amphipathicity of an AMP and its potency to activate PhoP-PhoQ; (ii) a +1 charged peptide containing histidines was highly potent, suggesting the existence of an additional mechanism independent of the peptide charge; (iii) the WT bacteria are more resistant to AMPs that are potent activators of PhoP-PhoQ; (iv) only a subset of AMPs, independent of their potency to activate the system, is more toxic to the mutated bacteria compared with the WT strains; and (v) short term exposure of WT bacteria to these AMPs does not enhance resistance. Overall, this study advances our understanding of the molecular mechanism by which AMPs activate PhoP-PhoQ and induce bacterial resistance. It also reveals that some AMPs can overcome such a resistance mechanism. | 2012 | 22158870 |
| 631 | 2 | 0.9996 | Effects of Regulatory Network Organization and Environment on PmrD Connector Activity and Polymyxin Resistance in Klebsiella pneumoniae and Escherichia coli. Polymyxins are a class of cyclic peptides with antimicrobial activity against Gram-negative bacteria. In Enterobacteriaceae, the PhoQ/PhoP and PmrB/PmrA two-component systems regulate many genes that confer resistance to both polymyxins and host antimicrobial peptides. The activities of these two-component systems are modulated by additional proteins that are conserved across Enterobacteriaceae, such as MgrB, a negative regulator of PhoQ, and PmrD, a "connector" protein that activates PmrB/PmrA in response to PhoQ/PhoP stimulation. Despite the conservation of many protein components of the PhoQ/PhoP-PmrD-PmrB/PmrA network, the specific molecular interactions and regulatory mechanisms vary across different genera. Here, we explore the role of PmrD in modulating this signaling network in Klebsiella pneumoniae and Escherichia coli We show that in K. pneumoniae, PmrD is not required for polymyxin resistance arising from mutation of mgrB-the most common cause of spontaneous polymyxin resistance in this bacterium-suggesting that direct activation of polymyxin resistance genes by PhoQ/PhoP plays a critical role in this resistance pathway. However, for conditions of low pH or intermediate iron concentrations, both of which stimulate PmrB/PmrA, we find that PmrD does contribute to resistance. We further show that in E. coli, PmrD functions as a connector between PhoQ/PhoP and PmrB/PmrA, in contrast with previous reports. In this case, activity also depends on PmrB/PmrA stimulation, or on very high activation of PhoQ/PhoP. Our results indicate that the importance of the PmrD connector in modulating the polymyxin resistance network depends on both the network organization and on the environmental conditions associated with PmrB stimulation. | 2021 | 33361295 |
| 707 | 3 | 0.9996 | Reciprocal control between a bacterium's regulatory system and the modification status of its lipopolysaccharide. Gram-negative bacteria often modify their lipopolysaccharide (LPS), thereby increasing resistance to antimicrobial agents and avoidance of the host immune system. However, it is unclear how bacteria adjust the levels and activities of LPS-modifying enzymes in response to the modification status of their LPS. We now address this question by investigating the major regulator of LPS modifications in Salmonella enterica. We report that the PmrA/PmrB system controls expression of a membrane peptide that inhibits the activity of LpxT, an enzyme responsible for increasing the LPS negative charge. LpxT's inhibition and the PmrA-dependent incorporation of positively charged L-4-aminoarabinose into the LPS decrease Fe(3+) binding to the bacterial cell. Because Fe(3+) is an activating ligand for the sensor PmrB, transcription of PmrA-dependent LPS-modifying genes is reduced. This mechanism enables bacteria to sense their cell surface by its effect on the availability of an inducing signal for the system regulating cell-surface modifications. | 2012 | 22921935 |
| 703 | 4 | 0.9996 | Bacterial modification of LPS and resistance to antimicrobial peptides. Antimicrobial peptides (APs) are ubiquitous in nature and are thought to kill micro-organisms by affecting membrane integrity. These positively charged peptides interact with negative charges in the LPS of Gram-negative bacteria. A common mechanism of resistance to AP killing is LPS modification. These modifications include fatty acid additions, phosphoethanolamine (PEtN) addition to the core and lipid A regions, 4-amino-4-deoxy-L-arabinose (Ara4N) addition to the core and lipid A regions, acetylation of the O-antigen, and possibly hydroxylation of fatty acids. In Salmonella typhimurium, LPS modifications are induced within host tissues by the two-component regulatory systems PhoPQ and PmrAB. PmrAB activation results in AP resistance by Ara4N addition to lipid A through the activation of at least 8 genes, 7 of which are transcribed as an operon. Loss of this operon and, therefore, Ara4N LPS modification, affects S. typhimurium virulence when administered orally. Transposon mutagenesis of Proteus mirabilis also suggests that LPS modifications affect AP resistance and virulence phenotypes. Therefore, LPS modification in Gram-negative bacteria plays a significant role during infection in resistance to host antimicrobial factors, avoidance of immune system recognition, and maintenance of virulence phenotypes. | 2001 | 11521084 |
| 709 | 5 | 0.9996 | Structure of the Response Regulator NsrR from Streptococcus agalactiae, Which Is Involved in Lantibiotic Resistance. Lantibiotics are antimicrobial peptides produced by Gram-positive bacteria. Interestingly, several clinically relevant and human pathogenic strains are inherently resistant towards lantibiotics. The expression of the genes responsible for lantibiotic resistance is regulated by a specific two-component system consisting of a histidine kinase and a response regulator. Here, we focused on a response regulator involved in lantibiotic resistance, NsrR from Streptococcus agalactiae, and determined the crystal structures of its N-terminal receiver domain and C-terminal DNA-binding effector domain. The C-terminal domain exhibits a fold that classifies NsrR as a member of the OmpR/PhoB subfamily of regulators. Amino acids involved in phosphorylation, dimerization, and DNA-binding were identified and demonstrated to be conserved in lantibiotic resistance regulators. Finally, a model of the full-length NsrR in the active and inactive state provides insights into protein dimerization and DNA-binding. | 2016 | 26930060 |
| 632 | 6 | 0.9995 | The Role of the Two-Component System PhoP/PhoQ in Intrinsic Resistance of Yersinia enterocolitica to Polymyxin. Polymyxin is the "last resort" of antibiotics. The self-induced resistance to polymyxin in Gram-negative bacteria could be mediated by lipopolysaccharide (LPS) modification, which is regulated by the two-component system, PhoP/PhoQ. Yersinia enterocolitica is a common foodborne pathogen. However, PhoP/PhoQ has not been thoroughly studied in Y. enterocolitica. In this study, the functions of PhoP/PhoQ in Y. enterocolitica intrinsic resistance were investigated. The resistance of Y. enterocolitica was found to decrease with the deletion of PhoP/PhoQ. Further, PhoP/PhoQ was found to play an important role in maintaining membrane permeability, intercellular metabolism, and reducing membrane depolarization. Based on subsequent studies, the binding ability of polymyxin to Y. enterocolitica was decreased by the modification of LPS with structures, such as L-Ara4N and palmitate. Analysis of the gene transcription levels revealed that the LPS modification genes, pagP and arn operon, were downregulated with the deletion of PhoP/PhoQ in Y. enterocolitica during exposure to polymyxin. In addition, pmrA, pmrB, and eptA were downregulated in the mutants compared with the wild-type strain. Such findings demonstrate that PhoP/PhoQ contributes to the intrinsic resistance of Y. enterocolitica toward polymyxins. LPS modification with L-Ara4N or palmitate is mainly responsible for the resistance of Y. enterocolitica to polymyxins. The transcription of genes related to LPS modification and PmrA/PmrB can be both affected by PhoP/PhoQ in Y. enterocolitica. This study adds to current knowledge regarding the role of PhoP/PhoQ in intrinsic resistance of Y. enterocolitica to polymyxin. | 2022 | 35222323 |
| 704 | 7 | 0.9995 | Aminoarabinose is essential for lipopolysaccharide export and intrinsic antimicrobial peptide resistance in Burkholderia cenocepacia(†). One common mechanism of resistance against antimicrobial peptides in Gram-negative bacteria is the addition of 4-amino-4-deoxy-L-arabinose (L-Ara4N) to the lipopolysaccharide (LPS) molecule. Burkholderia cenocepacia exhibits extraordinary intrinsic resistance to antimicrobial peptides and other antibiotics. We have previously discovered that unlike other bacteria, B. cenocepacia requires L-Ara4N for viability. Here, we describe the isolation of B. cenocepacia suppressor mutants that remain viable despite the deletion of genes required for L-Ara4N synthesis and transfer to the LPS. The absence of L-Ara4N is the only structural difference in the LPS of the mutants compared with that of the parental strain. The mutants also become highly sensitive to polymyxin B and melittin, two different classes of antimicrobial peptides. The suppressor phenotype resulted from a single amino acid replacement (aspartic acid to histidine) at position 31 of LptG, a protein component of the multi-protein pathway responsible for the export of the LPS molecule from the inner to the outer membrane. We propose that L-Ara4N modification of LPS provides a molecular signature required for LPS export and proper assembly at the outer membrane of B. cenocepacia, and is the most critical determinant for the intrinsic resistance of this bacterium to antimicrobial peptides. | 2012 | 22742453 |
| 8308 | 8 | 0.9994 | PhoPQ Regulates Quinolone and Cephalosporin Resistance Formation in Salmonella Enteritidis at the Transcriptional Level. The two-component system (TCS) PhoPQ has been demonstrated to be crucial for the formation of resistance to quinolones and cephalosporins in Salmonella Enteritidis (S. Enteritidis). However, the mechanism underlying PhoPQ-mediated antibiotic resistance formation remains poorly understood. Here, it was shown that PhoP transcriptionally regulated an assortment of genes associated with envelope homeostasis, the osmotic stress response, and the redox balance to confer resistance to quinolones and cephalosporins in S. Enteritidis. Specifically, cells lacking the PhoP regulator, under nalidixic acid and ceftazidime stress, bore a severely compromised membrane on the aspects of integrity, fluidity, and permeability, with deficiency to withstand osmolarity stress, an increased accumulation of intracellular reactive oxygen species, and dysregulated redox homeostasis, which are unfavorable for bacterial survival. The phosphorylated PhoP elicited transcriptional alterations of resistance-associated genes, including the outer membrane porin ompF and the aconitate hydratase acnA, by directly binding to their promoters, leading to a limited influx of antibiotics and a well-maintained intracellular metabolism. Importantly, it was demonstrated that the cavity of the PhoQ sensor domain bound to and sensed quinolones/cephalosporins via the crucial surrounding residues, as their mutations abrogated the binding and PhoQ autophosphorylation. This recognition mode promoted signal transduction that activated PhoP, thereby modulating the transcription of downstream genes to accommodate cells to antibiotic stress. These findings have revealed how bacteria employ a specific TCS to sense antibiotics and combat them, suggesting PhoPQ as a potential drug target with which to surmount S. Enteritidis. IMPORTANCE The prevalence of quinolone and cephalosporin-resistant S. Enteritidis is of increasing clinical concern. Thus, it is imperative to identify novel therapeutic targets with which to treat S. Enteritidis-associated infections. The PhoPQ two-component system is conserved across a variety of Gram-negative pathogens, by which bacteria adapt to a range of environmental stimuli. Our earlier work has demonstrated the importance of PhoPQ in the resistance formation in S. Enteritidis to quinolones and cephalosporins. In the current work, we identified a global profile of genes that are regulated by PhoP under antibiotic stresses, with a focus on how PhoP regulated downstream genes, either positively or negatively. Additionally, we established that PhoQ sensed quinolones and cephalosporins in a manner of directly binding to them. These identified genes and pathways that are mediated by PhoPQ represent promising targets for the development of a drug potentiator with which to neutralize antibiotic resistance in S. Enteritidis. | 2023 | 37184399 |
| 771 | 9 | 0.9994 | The multiple antibiotic resistance operon of enteric bacteria controls DNA repair and outer membrane integrity. The multiple antibiotic resistance (mar) operon of Escherichia coli is a paradigm for chromosomally encoded antibiotic resistance in enteric bacteria. The locus is recognised for its ability to modulate efflux pump and porin expression via two encoded transcription factors, MarR and MarA. Here we map binding of these regulators across the E. coli genome and identify an extensive mar regulon. Most notably, MarA activates expression of genes required for DNA repair and lipid trafficking. Consequently, the mar locus reduces quinolone-induced DNA damage and the ability of tetracyclines to traverse the outer membrane. These previously unrecognised mar pathways reside within a core regulon, shared by most enteric bacteria. Hence, we provide a framework for understanding multidrug resistance, mediated by analogous systems, across the Enterobacteriaceae. Transcription factors MarR and MarA confer multidrug resistance in enteric bacteria by modulating efflux pump and porin expression. Here, Sharma et al. show that MarA also upregulates genes required for lipid trafficking and DNA repair, thus reducing antibiotic entry and quinolone-induced DNA damage. | 2017 | 29133912 |
| 8310 | 10 | 0.9994 | Dynamic heterogeneity in an E. coli stress response regulon mediates gene activation and antimicrobial peptide tolerance. The bacterial stress response is an intricately regulated system that plays a critical role in cellular resistance to drug treatment. The complexity of this response is further complicated by cell-to-cell heterogeneity in the expression of bacterial stress response genes. These genes are often organized into networks comprising one or more transcriptional regulators that control expression of a suite of downstream genes. While the expression heterogeneity of many of these upstream regulators has been characterized, the way in which this variability affects the larger downstream stress response remains hard to predict, prompting two key questions. First, how does heterogeneity and expression noise in stress response regulators propagate to the diverse downstream genes in their regulons. Second, when expression levels vary, how do multiple downstream genes act together to protect cells from stress. To address these questions, we focus on the transcription factor PhoP, a critical virulence regulator which coordinates pathogenicity in several gram-negative species. We use optogenetic stimulation to precisely control PhoP expression levels and examine how variations in PhoP affect the downstream activation of genes in the PhoP regulon. We find that these downstream genes exhibit differences both in mean expression level and sensitivity to increasing levels of PhoP. These response functions can also vary between individual cells, increasing heterogeneity in the population. We tie these variations to cell survival when bacteria are exposed to a clinically-relevant antimicrobial peptide, showing that high expression of the PhoP-regulon gene pmrD provides a protective effect against Polymyxin B. Overall, we demonstrate that even subtle heterogeneity in expression of a stress response regulator can have clear consequences for enabling bacteria to survive stress. | 2024 | 39677761 |
| 8210 | 11 | 0.9994 | Bacterial sensing of antimicrobial peptides. Antimicrobial peptides (AMPs) form a crucial part of human innate host defense, especially in neutrophil phagosomes and on epithelial surfaces. Bacteria have a variety of efficient resistance mechanisms to human AMPs, such as efflux pumps, secreted proteases, and alterations of the bacterial cell surface that are aimed to minimize attraction of the typically cationic AMPs. In addition, bacteria have specific sensors that activate AMP resistance mechanisms when AMPs are present. The prototypical Gram-negative PhoP/PhoQ and the Gram-positive Aps AMP-sensing systems were first described and investigated in Salmonella typhimurium and Staphylococcus epidermidis, respectively. Both include a classical bacterial two-component sensor/regulator system, but show many structural, mechanistic, and functional differences. The PhoP/PhoQ regulon controls a variety of genes not necessarily limited to AMP resistance mechanisms, but apparently aimed to combat innate host defense on a broad scale. In contrast, the staphylococcal Aps system predominantly upregulates AMP resistance mechanisms, namely the D-alanylation of teichoic acids, inclusion of lysyl-phosphati-dylglycerol in the cytoplasmic membrane, and expression of the putative VraFG AMP efflux pump. Notably, both systems are crucial for virulence and represent possible targets for antimicrobial therapy. | 2009 | 19494583 |
| 702 | 12 | 0.9994 | Cutting edge: the toll pathway is required for resistance to gram-positive bacterial infections in Drosophila. In Drosophila, the response against various microorganisms involves different recognition and signaling pathways, as well as distinct antimicrobial effectors. On the one hand, the immune deficiency pathway regulates the expression of antimicrobial peptides that are active against Gram-negative bacteria. On the other hand, the Toll pathway is involved in the defense against filamentous fungi and controls the expression of antifungal peptide genes. The gene coding for the only known peptide with high activity against Gram-positive bacteria, Defensin, is regulated by both pathways. So far, survival experiments to Gram-positive bacteria have been performed with Micrococcus luteus and have failed to reveal the involvement of one or the other pathway in host defense against such infections. In this study, we report that the Toll pathway, but not that of immune deficiency, is required for resistance to other Gram-positive bacteria and that this response does not involve Defensin. | 2002 | 11823479 |
| 761 | 13 | 0.9994 | Copper-responsive gene regulation in bacteria. Copper is an essential cofactor of various enzymes, but free copper is highly toxic to living cells. To maintain cellular metabolism at different ambient copper concentrations, bacteria have evolved specific copper homeostasis systems that mostly act as defence mechanisms. As well as under free-living conditions, copper defence is critical for virulence in pathogenic bacteria. Most bacteria synthesize P-type copper export ATPases as principal defence determinants when copper concentrations exceed favourable levels. In addition, many bacteria utilize resistance-nodulation-cell division (RND)-type efflux systems and multicopper oxidases to cope with excess copper. This review summarizes our current knowledge on copper-sensing transcriptional regulators, which we assign to nine different classes. Widespread one-component regulators are CueR, CopY and CsoR, which were initially identified in Escherichia coli, Enterococcus hirae and Mycobacterium tuberculosis, respectively. CueR activates homeostasis gene expression at elevated copper concentrations, while CopY and CsoR repress their target genes under copper-limiting conditions. Besides these one-component systems, which sense the cytoplasmic copper status, many Gram-negative bacteria utilize two-component systems, which sense periplasmic copper concentrations. In addition to these well-studied transcriptional factors, copper control mechanisms acting at the post-transcriptional and the post-translational levels will be discussed. | 2012 | 22918892 |
| 731 | 14 | 0.9994 | Regulation of lipid A modifications by Salmonella typhimurium virulence genes phoP-phoQ. Bacterial pathogenesis requires proteins that sense host microenvironments and respond by regulating virulence gene transcription. For Salmonellae, one such regulatory system is PhoP-PhoQ, which regulates genes required for intracellular survival and resistance to cationic peptides. Analysis by mass spectrometry revealed that Salmonella typhimurium PhoP-PhoQ regulated structural modifications of lipid A, the host signaling portion of lipopolysaccharide (LPS), by the addition of aminoarabinose and 2-hydroxymyristate. Structurally modified lipid A altered LPS-mediated expression of the adhesion molecule E-selectin by endothelial cells and tumor necrosis factor-alpha expression by adherent monocytes. Thus, altered responses to environmentally induced lipid A structural modifications may represent a mechanism for bacteria to gain advantage within host tissues. | 1997 | 9092473 |
| 696 | 15 | 0.9993 | Identification of a two-component regulatory system involved in antimicrobial peptide resistance in Streptococcus pneumoniae. Two-component regulatory systems (TCS) are among the most widespread mechanisms that bacteria use to sense and respond to environmental changes. In the human pathogen Streptococcus pneumoniae, a total of 13 TCS have been identified and many of them have been linked to pathogenicity. Notably, TCS01 strongly contributes to pneumococcal virulence in several infection models. However, it remains one of the least studied TCS in pneumococci and its functional role is still unclear. In this study, we demonstrate that TCS01 cooperates with a BceAB-type ABC transporter to sense and induce resistance to structurally-unrelated antimicrobial peptides of bacterial origin that all target undecaprenyl-pyrophosphate or lipid II, which are essential precursors of cell wall biosynthesis. Even though tcs01 and bceAB genes do not locate in the same gene cluster, disruption of either of them equally sensitized the bacterium to the same set of antimicrobial peptides. We show that the key function of TCS01 is to upregulate the expression of the transporter, while the latter appears the main actor in resistance. Electrophoretic mobility shift assays further demonstrated that the response regulator of TCS01 binds to the promoter region of the bceAB genes, implying a direct control of these genes. The BceAB transporter was overexpressed and purified from E. coli. After reconstitution in liposomes, it displayed substantial ATPase and GTPase activities that were stimulated by antimicrobial peptides to which it confers resistance to, revealing new functional features of a BceAB-type transporter. Altogether, this inducible defense mechanism likely contributes to the survival of the opportunistic microorganism in the human host, in which competition among commensal microorganisms is a key determinant for effective host colonization and invasive path. | 2022 | 35395062 |
| 766 | 16 | 0.9993 | The essential inner membrane protein YejM is a metalloenzyme. Recent recurrent outbreaks of Gram-negative bacteria show the critical need to target essential bacterial mechanisms to fight the increase of antibiotic resistance. Pathogenic Gram-negative bacteria have developed several strategies to protect themselves against the host immune response and antibiotics. One such strategy is to remodel the outer membrane where several genes are involved. yejM was discovered as an essential gene in E. coli and S. typhimurium that plays a critical role in their virulence by changing the outer membrane permeability. How the inner membrane protein YejM with its periplasmic domain changes membrane properties remains unknown. Despite overwhelming structural similarity between the periplasmic domains of two YejM homologues with hydrolases like arylsulfatases, no enzymatic activity has been previously reported for YejM. Our studies reveal an intact active site with bound metal ions in the structure of YejM periplasmic domain. Furthermore, we show that YejM has a phosphatase activity that is dependent on the presence of magnesium ions and is linked to its function of regulating outer membrane properties. Understanding the molecular mechanism by which YejM is involved in outer membrane remodeling will help to identify a new drug target in the fight against the increased antibiotic resistance. | 2020 | 33082366 |
| 762 | 17 | 0.9993 | MerR family transcription activators: similar designs, different specificities. Living organisms use metals for a variety of essential functions, and face the problems of how to acquire and regulate the intracellular levels of those metals they need, differentiate between essential and toxic metals, and remove from the cell or detoxify metals that are toxic. In bacteria, cytoplasmic metal ion responsive transcriptional regulators are important in regulating the expression of genes involved in metal ion homeostasis and efflux systems. The MerR family of transcriptional activators are metal sensing regulators that are found in different bacteria and have a common design, but have evolved to recognize and respond to different metals. In this issue of Molecular Microbiology, work by Checa and colleagues describes for the first time a gold-specific MerR family regulator named GolS from Salmonella enterica serovar Typhimurium that controls the production of an efflux pump and a metal chaperone protein that confer resistance to Au salts. | 2007 | 17302809 |
| 8272 | 18 | 0.9993 | Ceragenins and Antimicrobial Peptides Kill Bacteria through Distinct Mechanisms. Ceragenins are a family of synthetic amphipathic molecules designed to mimic the properties of naturally occurring cationic antimicrobial peptides (CAMPs). Although ceragenins have potent antimicrobial activity, whether their mode of action is similar to that of CAMPs has remained elusive. Here, we reported the results of a comparative study of the bacterial responses to two well-studied CAMPs, LL37 and colistin, and two ceragenins with related structures, CSA13 and CSA131. Using transcriptomic and proteomic analyses, we found that Escherichia coli responded similarly to both CAMPs and ceragenins by inducing a Cpx envelope stress response. However, whereas E. coli exposed to CAMPs increased expression of genes involved in colanic acid biosynthesis, bacteria exposed to ceragenins specifically modulated functions related to phosphate transport, indicating distinct mechanisms of action between these two classes of molecules. Although traditional genetic approaches failed to identify genes that confer high-level resistance to ceragenins, using a Clustered Regularly Interspaced Short Palindromic Repeats interference (CRISPRi) approach we identified E. coli essential genes that when knocked down modify sensitivity to these molecules. Comparison of the essential gene-antibiotic interactions for each of the CAMPs and ceragenins identified both overlapping and distinct dependencies for their antimicrobial activities. Overall, this study indicated that, while some bacterial responses to ceragenins overlap those induced by naturally occurring CAMPs, these synthetic molecules target the bacterial envelope using a distinctive mode of action. IMPORTANCE The development of novel antibiotics is essential because the current arsenal of antimicrobials will soon be ineffective due to the widespread occurrence of antibiotic resistance. The development of naturally occurring cationic antimicrobial peptides (CAMPs) for therapeutics to combat antibiotic resistance has been hampered by high production costs and protease sensitivity, among other factors. The ceragenins are a family of synthetic CAMP mimics that kill a broad spectrum of bacterial species but are less expensive to produce, resistant to proteolytic degradation, and seemingly resistant to the development of high-level resistance. Determining how ceragenins function may identify new essential biological pathways of bacteria that are less prone to the development of resistance and will further our understanding of the design principles for maximizing the effects of synthetic CAMPs. | 2022 | 35073755 |
| 6218 | 19 | 0.9993 | An allele of an ancestral transcription factor dependent on a horizontally acquired gene product. Changes in gene regulatory circuits often give rise to phenotypic differences among closely related organisms. In bacteria, these changes can result from alterations in the ancestral genome and/or be brought about by genes acquired by horizontal transfer. Here, we identify an allele of the ancestral transcription factor PmrA that requires the horizontally acquired pmrD gene product to promote gene expression. We determined that a single amino acid difference between the PmrA proteins from the human adapted Salmonella enterica serovar Paratyphi B and the broad host range S. enterica serovar Typhimurium rendered transcription of PmrA-activated genes dependent on the PmrD protein in the former but not the latter serovar. Bacteria harboring the serovar Typhimurium allele exhibited polymyxin B resistance under PmrA- or under PmrA- and PmrD-inducing conditions. By contrast, isogenic strains with the serovar Paratyphi B allele displayed PmrA-regulated polymyxin B resistance only when experiencing activating conditions for both PmrA and PmrD. We establish that the two PmrA orthologs display quantitative differences in several biochemical properties. Strains harboring the serovar Paratyphi B allele showed enhanced biofilm formation, a property that might promote serovar Paratyphi B's chronic infection of the gallbladder. Our findings illustrate how subtle differences in ancestral genes can impact the ability of horizontally acquired genes to confer new properties. | 2012 | 23300460 |