Role of the Putative Histidine Kinase BP1092 in Bordetella pertussis Virulence Regulation and Intracellular Survival

Bordetella pertussis persists inside host cells, and virulence factors are crucial for intracellular adaptation. The regulation of B. pertussis virulence factor transcription primarily occurs through the modulation of the two-component system (TCS) known as BvgAS. However, additional regulatory systems have emerged as potential contributors to virulence regulation. Here, we investigate the impact of BP1092, a putative TCS histidine kinase that shows increased levels after bacterial internalization by macrophages, on B. pertussis proteome adaptation under nonmodulating (Bvg+) and modulating (Bvg-) conditions. Using mass spectrometry, we compare B. pertussis wild-type (wt), a BP1092-deficient mutant (ΔBP1092), and a ΔBP1092 trans-complemented strain under both conditions. We find an altered abundance of 10 proteins, including five virulence factors. Specifically, under nonmodulating conditions, the mutant strain showed decreased levels of FhaB, FhaS, and Cya compared to the wt. Conversely, under modulating conditions, the mutant strain exhibited reduced levels of BvgA and BvgS compared to those of the wt. Functional assays further revealed that the deletion of BP1092 gene impaired B. pertussis ability to survive within human macrophage THP-1 cells. Taken together, our findings allow us to propose BP1092 as a novel player involved in the intricate regulation of B. pertussis virulence factors and thus in adaptation to the intracellular environment. The data have been deposited to the ProteomeXchange Consortium via the PRIDE partner repository with the data set identifier PXD041940.

MassSpecPreppy-An end-to-end solution for automated protein concentration determination and flexible sample digestion for proteomics applications

In proteomics, fast, efficient, and highly reproducible sample preparation is of utmost importance, particularly in view of fast scanning mass spectrometers enabling analyses of large sample series. To address this need, we have developed the web application MassSpecPreppy that operates on the open science OT-2 liquid handling robot from Opentrons. This platform can prepare up to 96 samples at once, performing tasks like BCA protein concentration determination, sample digestion with normalization, reduction/alkylation and peptide elution into vials or loading specified peptide amounts onto Evotips in an automated and flexible manner. The performance of the developed workflows using MassSpecPreppy was compared with standard manual sample preparation workflows. The BCA assay experiments revealed an average recovery of 101.3% (SD: ± 7.82%) for the MassSpecPreppy workflow, while the manual workflow had a recovery of 96.3% (SD: ± 9.73%). The species mix used in the evaluation experiments showed that 94.5% of protein groups for OT-2 digestion and 95% for manual digestion passed the significance thresholds with comparable peptide level coefficient of variations. These results demonstrate that MassSpecPreppy is a versatile and scalable platform for automated sample preparation, producing injection-ready samples for proteomics research.

NAD+ metabolism is a key modulator of bacterial respiratory epithelial infections

Lower respiratory tract infections caused by Streptococcus pneumoniae (Spn) are a leading cause of death globally. Here we investigate the bronchial epithelial cellular response to Spn infection on a transcriptomic, proteomic and metabolic level. We found the NAD+ salvage pathway to be dysregulated upon infection in a cell line model, primary human lung tissue and in vivo in rodents, leading to a reduced production of NAD+. Knockdown of NAD+ salvage enzymes (NAMPT, NMNAT1) increased bacterial replication. NAD+ treatment of Spn inhibited its growth while growth of other respiratory pathogens improved. Boosting NAD+ production increased NAD+ levels in immortalized and primary cells and decreased bacterial replication upon infection. NAD+ treatment of Spn dysregulated the bacterial metabolism and reduced intrabacterial ATP. Enhancing the bacterial ATP metabolism abolished the antibacterial effect of NAD+. Thus, we identified the NAD+ salvage pathway as an antibacterial pathway in Spn infections, predicting an antibacterial mechanism of NAD+.

Screening for eukaryotic motifs in Legionella pneumophila reveals Smh1 as bacterial deacetylase of host histones

Legionella pneumophila (L.p.) is a bacterial pathogen which is a common causative agent of pneumonia. In humans, it infects alveolar macrophages and transfers hundreds of virulence factors that interfere with cellular signalling pathways and the transcriptomic landscape to sustain its own replication. By this interaction, it has acquired eukaryote-like protein motifs by gene transfer events that partake in the pathogenicity of Legionella. In a computational screening approach for eukaryotic motifs in the transcriptome of Legionella, we identified the L.p. strain Corby protein ABQ55614 as putative histone-deacetylase and named it "suppressing modifier of histones 1" (Smh1). During infection, Smh1 is translocated from the Legionella vacuole into the host cytosol. When expressed in human macrophage THP-1 cells, Smh1 was localized predominantly in the nucleus, leading to broad histone H3 and H4 deacetylation, blunted expression of a large number of genes (e.g. IL-1β and IL-8), and fostered intracellular bacterial replication. L.p. with a Smh1 knockdown grew normally in media but showed a slight growth defect inside the host cell. Furthermore, Smh1 showed a very potent histone deacetylation activity in vitro, e.g. at H3K14, that could be inhibited by targeted mutation of the putative catalytic center inferred by analogy with eukaryotic HDAC8, and with the deacetylase inhibitor trichostatin A. In summary, Smh1 displays functional homology with class I/II type HDACs. We identified Smh1 as a new Legionella virulence factor with a eukaryote-like histone-deacetylase activity that moderates host gene expression and might pave the way for further histone modifications.IMPORTANCELegionella pneumophila (L.p.) is a prominent bacterial pathogen, which is a common causative agent of pneumonia. In order to survive inside the host cell, the human macrophage, it profoundly interacts with host cell processes to advance its own replication. In this study, we identify a bacterial factor, Smh1, with yet unknown function as a host histone deacetylase. The activity of this factor in the host cell leads to attenuated gene expression and increased intracellular bacterial replication.

Bordetella pertussis outer membrane vesicles as virulence factor vehicles that influence bacterial interaction with macrophages

Gram-negative pathogenic bacteria constitutively shed outer membrane vesicles (OMVs) which play a significant role in the host-pathogen interaction, eventually determining the outcome of the infection. We previously found that Bordetella pertussis, the etiological agent of whooping cough, survives the innate interaction with human macrophages remaining alive inside these immune cells. Adenylate cyclase (CyaA), one of the main toxins of this pathogen, was found involved in the modulation of the macrophage defense response, eventually promoting bacterial survival within the cells. We here investigated whether B. pertussis OMVs, loaded with most of the bacterial toxins and CyaA among them, modulate the macrophage response to the bacterial infection. We observed that the pre-incubation of macrophages with OMVs led to a decreased macrophage defense response to the encounter with the bacteria, in a CyaA dependent way. Our results suggest that CyaA delivered by B. pertussis OMVs dampens macrophages protective function by decreasing phagocytosis and the bactericidal capability of these host cells. By increasing the chances of bacterial survival to the innate encounter with the macrophages, B. pertussis OMVs might play a relevant role in the course of infection, promoting bacterial persistence within the host and eventually, shaping the whole infection process.

Exploring metal availability in the natural niche of Streptococcus pneumoniae to discover potential vaccine antigens

Nasopharyngeal colonization by Streptococcus pneumoniae is a prerequisite for pneumococcal transmission and disease. Current vaccines protect only against disease and colonization caused by a limited number of serotypes, consequently allowing serotype replacement and transmission. Therefore, the development of a broadly protective vaccine against colonization, transmission and disease is desired but requires a better understanding of pneumococcal adaptation to its natural niche. Hence, we measured the levels of free and protein-bound transition metals in human nasal fluid, to determine the effect of metal concentrations on the growth and proteome of S. pneumoniae. Pneumococci cultured in medium containing metal levels comparable to nasal fluid showed a highly distinct proteomic profile compared to standard culture conditions, including the increased abundance of nine conserved, putative surface-exposed proteins. AliA, an oligopeptide binding protein, was identified as the strongest protective antigen, demonstrated by the significantly reduced bacterial load in a murine colonization and a lethal mouse pneumonia model, highlighting its potential as vaccine antigen.

Exploring Virulence Factors and Alternative Therapies against Staphylococcus aureus Pneumonia

Pneumonia is an acute pulmonary infection associated with high mortality and an immense financial burden on healthcare systems. Staphylococcus aureus is an opportunistic pathogen capable of inducing S. aureus pneumonia (SAP), with some lineages also showing multidrug resistance. Given the high level of antibiotic resistance, much research has been focused on targeting S. aureus virulence factors, including toxins and biofilm-associated proteins, in an attempt to develop effective SAP therapeutics. Despite several promising leads, many hurdles still remain for S. aureus vaccine research. Here, we review the state-of-the-art SAP therapeutics, highlight their pitfalls, and discuss alternative approaches of potential significance and future perspectives.

Interaction of Staphylococcus aureus and Host Cells upon Infection of Bronchial Epithelium during Different Stages of Regeneration

The primary barrier that protects our lungs against infection by pathogens is a tightly sealed layer of epithelial cells. When the integrity of this barrier is disrupted as a consequence of chronic pulmonary diseases or viral insults, bacterial pathogens will gain access to underlying tissues. A major pathogen that can take advantage of such conditions is Staphylococcus aureus, thereby causing severe pneumonia. In this study, we investigated how S. aureus responds to different conditions of the human epithelium, especially nonpolarization and fibrogenesis during regeneration using an in vitro infection model. The infective process was monitored by quantification of the epithelial cell and bacterial populations, fluorescence microscopy, and mass spectrometry. The results uncover differences in bacterial internalization and population dynamics that correlate with the outcome of infection. Protein profiling reveals that, irrespective of the polarization state of the epithelial cells, the invading bacteria mount similar responses to adapt to the intracellular milieu. Remarkably, a bacterial adaptation that was associated with the regeneration state of the epithelial cells concerned the early upregulation of proteins controlled by the redox-responsive regulator Rex when bacteria were confronted with a polarized cell layer. This is indicative of the modulation of the bacterial cytoplasmic redox state to maintain homeostasis early during infection even before internalization. Our present observations provide a deeper insight into how S. aureus can take advantage of a breached epithelial barrier and show that infected epithelial cells have limited ability to respond adequately to staphylococcal insults.

Shotgun proteomic analysis of Bordetella parapertussis provides insights into the physiological response to iron starvation and potential new virulence determinants absent in Bordetella pertussis

Bordetella parapertussis is one of the pathogens that cause whooping cough. Even though its incidence has been rising in the last decades, this species remained poorly investigated. This study reports the first extensive proteome analysis of this bacterium. In an attempt to gain some insight into the infective phenotype, we evaluated the response of B. parapertussis to iron starvation, a critical stress the bacteria face during infection. Among other relevant findings, we observed that the adaptation to this condition involves significant changes in the abundance of two important virulence factors of this pathogen, namely, adenylate cyclase and the O-antigen. We further used the proteomic data to search for B. parapertussis proteins that are absent or classified as pseudogenes in the genome of Bordetella pertussis to unravel differences between both whooping cough causative agents. Among them, we identified proteins involved in stress resistance and virulence determinants that might help to explain the differences in the pathogenesis of these species and the lack of cross-protection of current acellular vaccines. Altogether, these results contribute to a better understanding of B. parapertussis biology and pathogenesis. SIGNIFICANCE: Whooping cough is a reemerging disease caused by both Bordetella pertussis and Bordetella parapertussis. Current vaccines fail to induce protection against B parapertussis and the incidence of this species has been rising over the years. The proteomic analysis of this study provided relevant insights into potential virulence determinants of this poorly-studied pathogen. It further identified proteins produced by B. parapertussis not present in B. pertussis, which might help to explain both the differences on their respective infectious process and the current vaccine failure. Altogether, the results of this study contribute to the better understanding of B. parapertussis pathogenesis and the eventual design of improved preventive strategies against whooping cough.

Metabolic Cross-talk Between Human Bronchial Epithelial Cells and Internalized Staphylococcus aureus as a Driver for Infection

Staphylococcus aureus is infamous for causing recurrent infections of the human respiratory tract. This is a consequence of its ability to adapt to different niches, including the intracellular milieu of lung epithelial cells. To understand the dynamic interplay between epithelial cells and the intracellular pathogen, we dissected their interactions over 4 days by mass spectrometry. Additionally, we investigated the dynamics of infection through live cell imaging, immunofluorescence and electron microscopy. The results highlight a major role of often overlooked temporal changes in the bacterial and host metabolism, triggered by fierce competition over limited resources. Remarkably, replicating bacteria reside predominantly within membrane-enclosed compartments and induce apoptosis of the host within ∼24 h post infection. Surviving infected host cells carry a subpopulation of non-replicating bacteria in the cytoplasm that persists. Altogether, we conclude that, besides the production of virulence factors by bacteria, it is the way in which intracellular resources are used, and how host and intracellular bacteria subsequently adapt to each other that determines the ultimate outcome of the infectious process.

A Bordetella pertussis MgtC homolog plays a role in the intracellular survival

Bordetella pertussis, the causative agent of whooping cough, has the capability to survive inside the host cells. This process requires efficient adaptation of the pathogen to the intracellular environment and the associated stress. Among the proteins produced by the intracellular B. pertussis we identified a protein (BP0414) that shares homology with MgtC, a protein which was previously shown to be involved in the intracellular survival of other pathogens. To explore if BP0414 plays a role in B. pertussis intracellular survival a mutant strain defective in the production of this protein was constructed. Using standard in vitro growth conditions we found that BP0414 is required for B. pertussis growth under low magnesium availability or low pH, two environmental conditions that this pathogen might face within the host cell. Intracellular survival studies showed that MgtC is indeed involved in B. pertussis viability inside the macrophages. The use of bafilomycin A1, which inhibits phagosome acidification, abolished the survival defect of the mgtC deficient mutant strain suggesting that in intracellular B. pertussis the role of MgtC protein is mainly related to the bacterial adaptation to the acidic conditions found inside the of phagosomes. Overall, this work provides an insight into the importance of MgtC in B. pertussis pathogenesis and its contribution to bacterial survival within immune cells.

AureoWiki ̵ The repository of the Staphylococcus aureus research and annotation community

In light of continuously accumulating data and knowledge on major human pathogens, comprehensive and up-to-date sources of easily accessible information are urgently required. The AureoWiki database (http://aureowiki.med.uni-greifswald.de) provides detailed information on the genes and proteins of clinically and experimentally relevant S. aureus strains, currently covering NCTC 8325, COL, Newman, USA300_FPR3757, and N315. By implementing a pan-genome approach, AureoWiki facilitates the transfer of knowledge gained in studies with different S. aureus strains, thus supporting functional annotation and better understanding of this organism. All data related to a given gene or gene product is compiled on a strain-specific gene page. The gene pages contain sequence-based information complemented by data on, for example, protein function and localization, transcriptional regulation, and gene expression. The information provided is connected via links to other databases and published literature. Importantly, orthologous genes of the individual strains, which are linked by a pan-genome gene identifier and a unified gene name, are presented side by side using strain-specific tabs. The respective pan-genome gene page contains an orthologue table for 32 S. aureus strains, a multiple-strain genome viewer, a protein sequence alignment as well as other comparative information. The data collected in AureoWiki is also accessible through various download options in order to support bioinformatics applications. In addition, based on two large-scale gene expression data sets, AureoWiki provides graphical representations of condition-dependent mRNA levels and protein profiles under various laboratory and infection-related conditions.

Proteome data from a host-pathogen interaction study with Staphylococcus aureus and human lung epithelial cells

To simultaneously obtain proteome data of host and pathogen from an internalization experiment, human alveolar epithelial A549 cells were infected with Staphylococcus aureus HG001 which carried a plasmid (pMV158GFP) encoding a continuously expressed green fluorescent protein (GFP). Samples were taken hourly between 1.5 h and 6.5 h post infection. By fluorescence activated cell sorting GFP-expressing bacteria could be enriched from host cell debris, but also infected host cells could be separated from those which did not carry bacteria after contact (exposed). Additionally, proteome data of A549 cells which were not exposed to S. aureus but underwent the same sample processing steps are provided as a control. Time-resolved changes in bacterial protein abundance were quantified in a label-free approach. Proteome adaptations of host cells were monitored by comparative analysis to a stable isotope labeled cell culture (SILAC) standard. Proteins were extracted from the cells, digested proteolytically, measured by nanoLC-MS/MS, and subsequently identified by database search and then quantified. The data presented here are related to a previously published research article describing the interplay of S. aureus HG001 and human epithelial cells (Surmann et al., 2015 [1]). They have been deposited to the ProteomeXchange platform with the identifiers PRIDE: http://www.ebi.ac.uk/pride/archive/projects/PXD002384 for the S. aureus HG001 proteome dataset and PRIDE: http://www.ebi.ac.uk/pride/archive/projects/PXD002388 for the A549 proteome dataset.

Alternative fluorescent labeling strategies for characterizing gram-positive pathogenic bacteria: Flow cytometry supported counting, sorting, and proteome analysis of Staphylococcus aureus retrieved from infected host cells

Staphylococcus aureus is a Gram-positive opportunistic pathogen that is able to cause a broad range of infectious diseases in humans. Furthermore, S. aureus is able to survive inside nonprofessional phagocytic host cell which serve as a niche for the pathogen to hide from the immune system and antibiotics therapies. Modern OMICs technologies provide valuable tools to investigate host-pathogen interactions upon internalization. However, these experiments are often hampered by limited capabilities to retrieve bacteria from such an experimental setting. Thus, the aim of this study was to develop a labeling strategy allowing fast detection and quantitation of S. aureus in cell lysates or infected cell lines by flow cytometry for subsequent proteome analyses. Therefore, S. aureus cells were labeled with the DNA stain SYTO^® 9, or Vancomycin BODIPY^® FL (VMB), a glycopeptide antibiotic binding to most Gram-positive bacteria which was conjugated to a fluorescent dye. Staining of S. aureus HG001 with SYTO 9 allowed counting of bacteria from pure cultures but not in cell lysates from infection experiments. In contrast, with VMB it was feasible to stain bacteria from pure cultures as well as from samples of infection experiments. VMB can also be applied for histocytochemistry analysis of formaldehyde fixed cell layers grown on coverslips. Proteome analyses of S. aureus labeled with VMB revealed that the labeling procedure provoked only minor changes on proteome level and allowed cell sorting and analysis of S. aureus from infection settings with sensitivity similar to continuous gfp expression. Furthermore, VMB labeling allowed precise counting of internalized bacteria and can be employed for downstream analyses, e.g., proteomics, of strains not easily amendable to genetic manipulation such as clinical isolates. © 2016 International Society for Advancement of Cytometry.

Molecular and proteome analyses highlight the importance of the Cpx envelope stress system for acid stress and cell wall stability in Escherichia coli

Two‐component systems (TCS) play a pivotal role for bacteria in stress regulation and adaptation. However, it is not well understood how these systems are modulated to meet bacterial demands. Especially, for those TCS using an accessory protein to integrate additional signals, no data concerning the role of the accessory proteins within the coordination of the response is available. The Cpx envelope stress two‐component system, composed of the sensor kinase CpxA and the response regulator CpxR, is orchestrated by the periplasmic protein CpxP which detects misfolded envelope proteins and inhibits the Cpx system in unstressed cells. Using selected reaction monitoring, we observed that the amount of CpxA and CpxR, as well as their stoichiometry, are only marginally affected, but that a 10‐fold excess of CpxP over CpxA is needed to switch off the Cpx system. Moreover, the relative quantification of the proteome identified not only acid stress response as a new indirect target of the Cpx system, but also suggests a general function of the Cpx system for cell wall stability.

A peptide resource for the analysis of Staphylococcus aureus in host-pathogen interaction studies

Staphylococcus aureus is an opportunistic human pathogen, which can cause life-threatening disease. Proteome analyses of the bacterium can provide new insights into its pathophysiology and important facets of metabolic adaptation and, thus, aid the recognition of targets for intervention. However, the value of such proteome studies increases with their comprehensiveness. We present an MS-driven, proteome-wide characterization of the strain S. aureus HG001. Combining 144 high precision proteomic data sets, we identified 19 109 peptides from 2088 distinct S. aureus HG001 proteins, which account for 72% of the predicted ORFs. Peptides were further characterized concerning pI, GRAVY, and detectability scores in order to understand the low peptide coverage of 8.7% (19 109 out of 220 245 theoretical peptides). The high quality peptide-centric spectra have been organized into a comprehensive peptide fragmentation library (SpectraST) and used for identification of S. aureus-typic peptides in highly complex host-pathogen interaction experiments, which significantly improved the number of identified S. aureus proteins compared to a MASCOT search. This effort now allows the elucidation of crucial pathophysiological questions in S. aureus-specific host-pathogen interaction studies through comprehensive proteome analysis. The S. aureus-specific spectra resource developed here also represents an important spectral repository for SRM or for data-independent acquisition MS approaches. All MS data have been deposited in the ProteomeXchange with identifier PXD000702 (http://proteomecentral.proteomexchange.org/dataset/PXD000702).

A proteomic perspective of the interplay of Staphylococcus aureus and human alveolar epithelial cells during infection

Infectious diseases caused by pathogens such as Staphylococcus aureus are still a major threat for human health. Proteome analyses allow detailed monitoring of the molecular interplay between pathogen and host upon internalization. However, the investigation of the responses of both partners is complicated by the large excess of host cell proteins compared to bacterial proteins as well as by the fact that only a fraction of host cells are infected. In the present study we infected human alveolar epithelial A549 cells with S. aureus HG001 pMV158GFP and separated intact bacteria from host cell debris or infected from non-infected A549 cells by cell sorting to enable detailed proteome analysis. During the first 6.5h in the intracellular milieu S. aureus displayed reduced growth rate, induction of the stringent response, adaptation to microaerobic conditions as well as cell wall stress. Interestingly, both truly infected host cells and those not infected but exposed to secreted S. aureus proteins and host cell factors showed differences in the proteome pattern compared to A549 cells which had never been in contact with S. aureus. However, adaptation reactions were more pronounced in infected compared to non-infected A549 bystander cells.

Comparative proteome analysis reveals conserved and specific adaptation patterns of Staphylococcus aureus after internalization by different types of human non-professional phagocytic host cells

Staphylococcus aureus is a human pathogen that can cause a wide range of diseases. Although formerly regarded as extracellular pathogen, it has been shown that S. aureus can also be internalized by host cells and persist within these cells. In the present study, we comparatively analyzed survival and physiological adaptation of S. aureus HG001 after internalization by two human lung epithelial cell lines (S9 and A549), and human embryonic kidney cells (HEK 293). Combining enrichment of bacteria from host-pathogen assays by cell sorting and quantitation of the pathogen's proteome by mass spectrometry we characterized S. aureus adaptation during the initial phase between 2.5 h and 6.5 h post-infection. Starting with about 2 × 10⁶ bacteria, roughly 1450 S. aureus proteins, including virulence factors and metabolic enzymes were identified by spectral comparison and classical database searches. Most of the bacterial adaptation reactions, such as decreased levels of ribosomal proteins and metabolic enzymes or increased amounts of proteins involved in arginine and lysine biosynthesis, enzymes coding for terminal oxidases and stress responsive proteins or activation of the sigma factor SigB were observed after internalization into any of the three cell lines studied. However, differences were noted in central carbon metabolism including regulation of fermentation and threonine degradation. Since these differences coincided with different intracellular growth behavior, complementary profiling of the metabolome of the different non-infected host cell types was performed. This revealed similar levels of intracellular glucose but host cell specific differences in the amounts of amino acids such as glycine, threonine or glutamate. With this comparative study we provide an impression of the common and specific features of the adaptation of S. aureus HG001 to specific host cell environments as a starting point for follow-up studies with different strain isolates and regulatory mutants.

Absolute quantification of the Kdp subunits of Escherichia coli by multiple reaction monitoring

The sensor kinase/response regulator system KdpD/KdpE of Escherichia coli regulates the expression of the kdpFABC operon, encoding the high-affinity KdpFABC potassium (K(+) )-transport complex. Additionally, it has been suggested that the kdpDE operon itself is subjected to autoregulation by its gene products KdpD and KdpE. However, since kdpFABC and kdpDE expression has mainly been studied on the transcriptional level, accurate information on absolute amounts and the stoichiometric subunit composition of KdpFABC and KdpD/KdpE under K(+) -limiting and K(+) -nonlimiting growth conditions are lacking. In this study, we used highly sensitive mass spectrometric methods to quantify the amount of subunits of the Kdp(F)ABC complex and KdpD/KdpE. Data-dependent shotgun MS was used to assess protein coverage and accessible peptides. Absolute amounts of Kdp(F)ABC and KdpD/KdpE were quantified by targeted MRM analysis in the presence of corresponding heavy labeled standard peptides. Baseline synthesis of Kdp(F)ABC and KdpD/KdpE was found to be in the attomolar range under K(+) -nonlimiting conditions. Under K(+) -limitation, synthesis of Kdp(F)ABC (KdpA:KdpB:KdpC ratio of 1:1:1) was amplified more than 100-fold, whereas only a tenfold amplification of KdpD/KdpE (KdpD:KdpE ratio of 1:4) was observed. The results obtained provide a solid basis for follow-up studies on the dynamic regulation of the Kdp system.