The oligopeptide ABC transporter OppA4 negatively regulates the virulence factor OspC production of the Lyme disease pathogen

The plasmid-encoded members of paralogous gene family 52 are dispensable to the enzootic cycle of Borrelia burgdorferi

Lyme disease, the leading vector-borne disease in the United States and Europe, develops after infection with Borrelia burgdorferi sensu lato bacteria. Transmission of the spirochete from the tick vector to a vertebrate host requires global changes in gene expression that are controlled, in part, by the Rrp2/RpoN/RpoS alternative sigma factor cascade. Transcriptional studies defining the B. burgdorferi RpoS regulon have suggested that RpoS activates the transcription of paralogous family 52 (PFam52) genes. In strain B31, PFam52 genes (bbi42, bbk53, and bbq03) encode a set of conserved hypothetical proteins with >89% amino acid identity that are predicted to be surface-localized. Extensive homology among members of paralogous families complicates studies of protein contributions to pathogenicity as the potential for functional redundancy will obfuscate findings. Using a sequential mutagenesis approach, we generated clones expressing a single PFam52 paralog, as well as a strain deficient in all three. The single paralog expressing strains were used to confirm BBI42, BBK53, and BBQ03 surface localization and RpoS regulation. Surprisingly, the PFam52-deficient strain was able to infect mice and complete the enzootic cycle similar to the wild-type parental strain. Indeed, the presence of numerous pseudogenes that contain frameshifts or internal stop codons among the PFam52 genes suggests that they may be subjected to gene loss in B. burgdorferi's reduced genome. Alternatively, the lack of phenotype might reflect the limitations of the experimental mouse infection model.

Secretome analysis and virulence assessment in Abiotrophia defectiva

Background

Abiotrophia defectiva, although infrequently occurring, is a notable cause of culture-negative infective endocarditis with limited research on its virulence. Associated with oral infections such as dental caries, exploring its secretome may provide insights into virulence mechanisms. Our study aimed to analyze and characterize the secretome of A. defectiva strain CCUG 27639.

Methods

Secretome of A. defectiva was prepared from broth cultures and subjected to mass spectrometry and proteomics for protein identification. Inflammatory potential of the secretome was assessed by ELISA.

Results

Eighty-four proteins were identified, with diverse subcellular localizations predicted by PSORTb. Notably, 20 were cytoplasmic, 12 cytoplasmic membrane, 5 extracellular, and 9 cell wall-anchored proteins. Bioinformatics tools revealed 54 proteins secreted via the 'Sec' pathway and 8 via a non-classical pathway. Moonlighting functions were found in 23 proteins, with over 20 exhibiting potential virulence properties, including peroxiredoxin and oligopeptide ABC transporter substrate-binding protein. Gene Ontology and KEGG analyses categorized protein sequences in various pathways. STRING analysis revealed functional protein association networks. Cytokine profiling demonstrated significant proinflammatory cytokine release (IL-8, IL-1β, and CCL5) from human PBMCs.

Conclusions

Our study provides a comprehensive understanding of A. defectiva's secretome, laying the foundation for insights into its pathogenicity.

Comparative proteomics and secretomics revealed virulence, and coresistance-related factors in non O1/O139 Vibrio cholerae recovered from 16 species of consumable aquatic animals

Vibrio cholerae can cause pandemic cholera in humans. The bacterium resides in aquatic environments worldwide. Identification of risk factors of V. cholerae in aquatic products is imperative for assuming food safety. In this study, we determined virulence-associated genes, cross-resistance between antibiotics and heavy metals, and genome fingerprinting profiles of non O1/O139 V. cholerae isolates (n = 20) recovered from 16 species of consumable aquatic animals. Secretomes and proteomes of V. cholerae with distinct genotypes and phenotypes were obtained by using two-dimensional gel electrophoresis (2D-GE) and/or liquid chromatography-tandem mass spectrometry (LC-MS/MS) techniques. Comparative secretomic analysis revealed 4 common and 45 differential extracellular proteins among 20 V. cholerae strains, including 13 virulence- and 8 resistance-associated proteins. A total of 21,972 intracellular proteins were identified, and comparative proteomic analysis revealed 215 common and 913 differential intracellular proteins, including 22 virulence- and 8 resistance-associated proteins. Additionally, different secretomes and proteomes were observed between V. cholerae isolates of fish and shellfish origins. A number of novel proteins with unknown function and strain-specific proteins were also discovered in the V. cholerae isolates. SIGNIFICANCE: V. cholerae can cause pandemic cholera in humans. The bacterium is distributed in aquatic environments worldwide. Identification of risk factors of V. cholerae in aquatic products is imperative for assuming food safety. Non-O1/O139 V. cholerae has been reported to cause sporadic cholera-like diarrhea and bacteremia diseases, which indicates virulence factors rather than the major cholera toxin (CT) exist. This study for the first time investigated proteomes and secretomes of non-O1/O139 V. cholerae originating from aquatic animals. This resulted in the identification of a number of virulence and coresistance-related factors, as well as novel proteins and strain-specific proteins in V. cholerae isolates recovered from 16 species of consumable aquatic animals. These results fill gaps for better understanding of pathogenesis and resistance of V. cholerae, and also support the increasing need for novel diagnosis and vaccine targets against the leading waterborne pathogen worldwide.

The Role of ATP-Binding Cassette Transporters in Bacterial Phytopathogenesis

Bacteria use selective membrane transporting strategies to support cell survival in different environments. Of the membrane transport systems, ATP-binding cassette (ABC) transporters, which utilize the energy of ATP hydrolysis to deliver substrate across the cytoplasmic membrane, are the largest and most diverse superfamily. These transporters import nutrients, export molecules, and are required for diverse cell functions, including cell division and morphology, gene regulation, surface motility, chemotaxis, and interspecies competition. Phytobacterial pathogens encode numerous ABC transporter homologs compared with related nonphytopathogens, with up to 160 transporters per genome, suggesting that plant pathogens must be able to import or respond to a greater number of molecules compared with saprophytes or animal pathogens. Despite their importance, ABC transporters have been little examined in plant pathogens. To understand bacterial phytopathogenesis and evolution, we need to understand the roles that ABC transporters play in plant-microbe interactions. In this review, we outline a multitude of roles that bacterial ABC transporters play, using both plant and animal pathogens as examples, to emphasize the importance of exploring these transporters in phytobacteriology.

The Role of a Dipeptide Transporter in the Virulence of Human Pathogen, Helicobacter pylori

Helicobacter pylori harbors a dipeptide (Dpp) transporter consisting of a substrate-binding protein (DppA), two permeases (DppB and C), and two ATPases (DppD and F). The Dpp transporter is responsible for the transportation of dipeptides and short peptides. We found that its expression is important for the growth of H. pylori. To understand the role of the Dpp transporter in the pathogenesis of H. pylori, the expression of virulence factors and H. pylori-induced IL-8 production were investigated in H. pylori wild-type and isogenic H. pylori Dpp transporter mutants. We found that expression of CagA was downregulated, while expression of type 4 secretion system (T4SS) components was upregulated in Dpp transporter mutants. The DppA mutant strain expressed higher levels of outer membrane proteins (OMPs), including BabA, HopZ, OipA, and SabA, and showed a higher adhesion level to gastric epithelial AGS cells compared with the H. pylori 26695 wild-type strain. After infection of AGS cells, H. pylori ΔdppA induced a higher level of NF-κB activation and IL-8 production compared with wild-type. These results suggested that in addition to supporting the growth of H. pylori, the Dpp transporter causes bacteria to alter the expression of virulence factors and reduces H. pylori-induced NF-κB activation and IL-8 production in gastric epithelial cells.

DksA-dependent regulation of RpoS contributes to Borrelia burgdorferi tick-borne transmission and mammalian infectivity

Throughout its enzootic cycle, the Lyme disease spirochete Borreliella (Borrelia) burgdorferi, senses and responds to changes in its environment using a small repertoire of transcription factors that coordinate the expression of genes required for infection of Ixodes ticks and various mammalian hosts. Among these transcription factors, the DnaK suppressor protein (DksA) plays a pivotal role in regulating gene expression in B. burgdorferi during periods of nutrient limitation and is required for mammalian infectivity. In many pathogenic bacteria, the gene regulatory activity of DksA, along with the alarmone guanosine penta- and tetra-phosphate ((p)ppGpp), coordinate the stringent response to various environmental stresses, including nutrient limitation. In this study, we sought to characterize the role of DksA in regulating the transcriptional activity of RNA polymerase and its role in the regulation of RpoS-dependent gene expression required for B. burgdorferi infectivity. Using in vitro transcription assays, we observed recombinant DksA inhibits RpoD-dependent transcription by B. burgdorferi RNA polymerase independent of ppGpp. Additionally, we determined the pH-inducible expression of RpoS-dependent genes relies on DksA, but this relationship is independent of (p)ppGpp produced by Rel_bbu. Subsequent transcriptomic and western blot assays indicate DksA regulates the expression of BBD18, a protein previously implicated in the post-transcriptional regulation of RpoS. Moreover, we observed DksA was required for infection of mice following intraperitoneal inoculation or for transmission of B. burgdorferi by Ixodes scapularis nymphs. Together, these data suggest DksA plays a central role in coordinating transcriptional responses in B. burgdorferi required for infectivity through DksA’s interactions with RNA polymerase and post-transcriptional control of RpoS.

Lyme disease, caused by the spirochete bacteria Borreliella (Borrelia) burgdorferi, is the most common vector-borne illness in North America. The ability of B. burgdorferi to establish infection is predicated by its ability to coordinate the expression of virulence factors in response to diverse environmental stimuli encountered within Ixodes ticks and mammalian hosts. Previous studies have shown an essential role for the alternative sigma factor RpoS in regulating the expression of genes required for the successful transmission of B. burgdorferi by Ixodes ticks and infection of mammalian hosts. The DnaK suppressor protein (DksA) is a global gene regulator in B. burgdorferi that contributes to the expression of RpoS-dependent genes. In this study, using in vitro transcription assays, we determined DksA exerts its gene regulatory function through direct interactions with the B. burgdorferi RNA polymerase and controls the expression of RpoS-dependent genes required for mammalian infection by post-transcriptionally regulating cellular levels of RpoS. Our results demonstrate the utility of in vitro transcription assays to determine how gene regulatory proteins like DksA control gene expression in B. burgdorferi and reveal a novel role for DksA in the infectious cycle of B. burgdorferi.

Host-specific functional compartmentalization within the oligopeptide transporter during the Borrelia burgdorferi enzootic cycle

Borrelia burgdorferi must acquire all of its amino acids (AAs) from its arthropod vector and vertebrate host. Previously, we determined that peptide uptake via the oligopeptide (Opp) ABC transporter is essential for spirochete viability in vitro and during infection. Our prior study also suggested that B. burgdorferi employs temporal regulation in concert with structural variation of oligopeptide-binding proteins (OppAs) to meet its AA requirements in each biological niche. Herein, we evaluated the contributions to the B. burgdorferi enzootic cycle of three of the spirochete's five OppAs (OppA1, OppA2, and OppA5). An oppA1 transposon (tn) mutant lysed in the hyperosmolar environment of the feeding tick, suggesting that OppA1 imports amino acids required for osmoprotection. The oppA2tn mutant displayed a profound defect in hematogenous dissemination in mice, yet persisted within skin while inducing only a minimal antibody response. These results, along with slightly decreased growth of the oppA2tn mutant within DMCs, suggest that OppA2 serves a minor nutritive role, while its dissemination defect points to an as yet uncharacterized signaling function. Previously, we identified a role for OppA5 in spirochete persistence within the mammalian host. We now show that the oppA5tn mutant displayed no defect during the tick phase of the cycle and could be tick-transmitted to naïve mice. Instead of working in tandem, however, OppA2 and OppA5 appear to function in a hierarchical manner; the ability of OppA5 to promote persistence relies upon the ability of OppA2 to facilitate dissemination. Structural homology models demonstrated variations within the binding pockets of OppA1, 2, and 5 indicative of different peptide repertoires. Rather than being redundant, B. burgdorferi's multiplicity of Opp binding proteins enables host-specific functional compartmentalization during the spirochete lifecycle.

Borrelia burgdorferi spatiotemporal regulation of transcriptional regulator bosR and decorin binding protein during murine infection

Lyme disease, caused by Borrelia burgdorferi, is an inflammatory multistage infection, consisting of localized, disseminated, and persistent disease stages, impacting several organ systems through poorly defined gene regulation mechanisms. The purpose of this study is to further characterize the spatiotemporal transcriptional regulation of B. burgdorferi during mammalian infection of borrelial oxidative stress regulator (bosR) and decorin binding protein (dbpBA) by utilizing bioluminescent B. burgdorferi reporter strains and in vivo imaging. Fluctuating borrelial load was also monitored and used for normalization to evaluate expression levels. bosR transcription is driven by two promoters, P_bb0648 and P_bosR, and we focused on the native promoter. bosR expression is low relative to the robustly expressed dbpBA throughout infection. In distal tissues, bosR was the highest in the heart during in the first week whereas dbpBA was readily detectable at all time points with each tissue displaying a distinct expression pattern. This data suggests bosR may have a role in heart colonization and the induction of dbpBA indicates a RpoS independent transcriptional regulation occurring in the mammalian cycle of pathogenesis. These finding demonstrate that B. burgdorferi engages unknown genetic mechanisms to uniquely respond to mammalian tissue environments and/or changing host response over time.

A comprehensive genomic and growth proteomic analysis of antitumor lipopeptide bacillomycin Lb biosynthesis in Bacillus amyloliquefaciens X030

Lipopeptides (such as iturin, fengycin, and surfactin) from Bacillus possess antibacterial, antifungal, and antiviral activities and have important application in agriculture and pharmaceuticals. Although unremitting efforts have been devoted to improve lipopeptide production by designing gene regulatory circuits or optimizing fermentation process, little attention has been paid to utilizing multi-omics for systematically mining core genes and proteins during the bacterial growth cycle. Here, lipopeptide bacillomycin Lb from new Bacillus amyloliquefaciens X030 was isolated and first found to have anticancer activity in various cancer cells (such as SMMC-7721 and MDA-MB-231). A comprehensive genomic and growth proteomic analysis of X030 revealed bacillomycin Lb biosynthetic gene cluster, key enzymes and potential regulatory proteins (PerR, PhoP, CcpA, and CsfB), and novel links between primary metabolism and bacillomycin Lb production in X030. The antitumor activity of the fermentation supernatant supplemented with amino acids (such as glutamic acid) and sucrose was significantly increased, verifying the role of key metabolic switches in the metabolic regulatory network. Quantitative real-time PCR analysis confirmed that 7 differential expressed genes exhibited a positive correlation between changes at transcriptional and translational levels. The study not only will stimulate the deeper and wider antitumor study of lipopeptides but also provide a comprehensive database, which promotes an in-depth analysis of pathways and networks for complex events in lipopeptide biosynthesis and regulation and gives great help in improving the yield of bacillomycin Lb (media optimization, genetic modification, or pathway engineering).