Abstract:Streptococcus pneumoniae (pneumococcus) causes multiple infectious diseases. The pneumococcal competence system facilitates genetic transformation, spreads antibiotic resistance, and contributes to virulence. DNA-processing protein A (DprA) regulates the exit of pneumococcus from the competent state. Previously, we have shown that DprA is important in both bacteremia and pneumonia infections. Here, we examined the mechanisms of virulence attenuation in a ΔdprA mutant. Compared to the parental wild-type D39, th… Show more
“…We used the serotype 2 strain D39 to construct the reporter strain AD2501 harboring a firefly luciferase transcriptionally fused to the ssbB gene (D39-ssbB-luc; Fig. 1A) (29). The ssbB gene encodes a single-stranded DNAbinding protein and is uniquely induced during competence induction and directly protects internalized single-stranded DNA (30).…”
Section: Resultsmentioning
confidence: 99%
“…For example, we found that D39 was not able to enter the competent state spontaneously when cultured in the nutrient-rich THY medium most widely used to cultivate pneumococci ( Fig. 1) (29). The competence-permissible CϩY medium, which contains defined amino acids, bovine serum albumin (BSA), and other nutrients, was formulated based on early findings that BSA or bodily fluids, including peritoneal washings and blood, provided better conditions for competence induction (6)(7)(8).…”
Section: Discussionmentioning
confidence: 99%
“…Under in vitro conditions, it has been reported that DprA is highly expressed and stable (34), rendering competent pneumococcal cells refractory to subsequent induction by CSP (35). Deletion of the dprA gene causes elevated and prolonged expression of "late" competence genes (16,17,29,34). Because of the prolonged and persistent competent state during pneumonia-derived sepsis, we examined whether the expression of DprA was compromised in vivo.…”
Section: Figmentioning
confidence: 99%
“…We predicted that such high levels of CSP should be able to stimulate a noncompetent recipient reporter strain. We generated a ssbB-luc reporter strain in the ΔdprA genetic background (ΔdprA-ssbB-luc, AD2506), which has heightened sensitivity and response to competence induction due to its inability to shut off the competent state (29). The pneumococcal cells that secreted these CSPs were removed from the blood samples by filtration to eliminate possible competence transfer by cell-cell direct contact mechanism.…”
The competence regulon of pneumococcus regulates both genetic transformation and virulence. However, competence induction during host infection has not been examined. By using the serotype 2 strain D39, we transcriptionally fused the firefly luciferase (luc) to competence-specific genes and spatiotemporally monitored the competence development in a mouse model of pneumonia-derived sepsis. In contrast to the universally reported short transient burst of competent state in vitro, the naturally developed competent state was prolonged and persistent during pneumonia-derived sepsis. The competent state began at approximately 20 h postinfection (hpi) and facilitated systemic invasion and sepsis development and progressed in different manners. In some mice, acute pneumonia quickly led to sepsis and death, accompanied by increasing intensity of the competence signal. In the remaining mice, pneumonia lasted longer, with the competence signal decreasing at first but increasing as the infection became septic. The concentration of pneumococcal inoculum (1 × 106 to 1 × 108 CFU/mouse) and postinfection lung bacterial burden did not appreciably impact the kinetics of competence induction. Exogenously provided competence stimulating peptide 1 (CSP1) failed to modulate the onset kinetics of competence development in vivo. The competence shutoff regulator DprA was highly expressed during pneumonia-derived sepsis but failed to turn off the competent state in mice. Competent D39 bacteria propagated the competence signal through cell-to-cell contact rather than the classically described quorum-sensing mechanism. Finally, clinical pneumococcal strains of different serotypes were also able to develop natural competence during pneumonia-derived sepsis.
“…We used the serotype 2 strain D39 to construct the reporter strain AD2501 harboring a firefly luciferase transcriptionally fused to the ssbB gene (D39-ssbB-luc; Fig. 1A) (29). The ssbB gene encodes a single-stranded DNAbinding protein and is uniquely induced during competence induction and directly protects internalized single-stranded DNA (30).…”
Section: Resultsmentioning
confidence: 99%
“…For example, we found that D39 was not able to enter the competent state spontaneously when cultured in the nutrient-rich THY medium most widely used to cultivate pneumococci ( Fig. 1) (29). The competence-permissible CϩY medium, which contains defined amino acids, bovine serum albumin (BSA), and other nutrients, was formulated based on early findings that BSA or bodily fluids, including peritoneal washings and blood, provided better conditions for competence induction (6)(7)(8).…”
Section: Discussionmentioning
confidence: 99%
“…Under in vitro conditions, it has been reported that DprA is highly expressed and stable (34), rendering competent pneumococcal cells refractory to subsequent induction by CSP (35). Deletion of the dprA gene causes elevated and prolonged expression of "late" competence genes (16,17,29,34). Because of the prolonged and persistent competent state during pneumonia-derived sepsis, we examined whether the expression of DprA was compromised in vivo.…”
Section: Figmentioning
confidence: 99%
“…We predicted that such high levels of CSP should be able to stimulate a noncompetent recipient reporter strain. We generated a ssbB-luc reporter strain in the ΔdprA genetic background (ΔdprA-ssbB-luc, AD2506), which has heightened sensitivity and response to competence induction due to its inability to shut off the competent state (29). The pneumococcal cells that secreted these CSPs were removed from the blood samples by filtration to eliminate possible competence transfer by cell-cell direct contact mechanism.…”
The competence regulon of pneumococcus regulates both genetic transformation and virulence. However, competence induction during host infection has not been examined. By using the serotype 2 strain D39, we transcriptionally fused the firefly luciferase (luc) to competence-specific genes and spatiotemporally monitored the competence development in a mouse model of pneumonia-derived sepsis. In contrast to the universally reported short transient burst of competent state in vitro, the naturally developed competent state was prolonged and persistent during pneumonia-derived sepsis. The competent state began at approximately 20 h postinfection (hpi) and facilitated systemic invasion and sepsis development and progressed in different manners. In some mice, acute pneumonia quickly led to sepsis and death, accompanied by increasing intensity of the competence signal. In the remaining mice, pneumonia lasted longer, with the competence signal decreasing at first but increasing as the infection became septic. The concentration of pneumococcal inoculum (1 × 106 to 1 × 108 CFU/mouse) and postinfection lung bacterial burden did not appreciably impact the kinetics of competence induction. Exogenously provided competence stimulating peptide 1 (CSP1) failed to modulate the onset kinetics of competence development in vivo. The competence shutoff regulator DprA was highly expressed during pneumonia-derived sepsis but failed to turn off the competent state in mice. Competent D39 bacteria propagated the competence signal through cell-to-cell contact rather than the classically described quorum-sensing mechanism. Finally, clinical pneumococcal strains of different serotypes were also able to develop natural competence during pneumonia-derived sepsis.
“…sobrinus is one of the few species of oral streptococci that lack a natural competence pathway. Competence is central to pathogenicity in streptococci, and competence pathways are connected to metabolism [4], virulence [5,6], quorum sensing [7], and antibiotic tolerance [8]. The natural competence of streptococci has been known for over 75 years [9].…”
Streptococcus sobrinus is one of two species of bacteria that cause dental caries (tooth decay) in humans. Our knowledge of S. sobrinus is limited despite the organism's important role in oral health. It is widely believed that S. sobrinus lacks the natural competence pathways that are used by other streptococci to regulate growth, virulence, and quorum sensing. The lack of natural competence has also prevented genetic manipulation of S. sobrinus, limiting our knowledge of its pathogenicity.We discovered a functional ComRS competence system in S. sobrinus. The ComRS pathway in S. sobrinus has a unique structure, including two copies of the transcriptional regulator ComR and a peptide pheromone (XIP) that lacks aromatic amino acids. We show that synthetic XIP allows transformation of S. sobrinus with plasmid or linear DNA, and we leverage this newfound genetic tractability to confirm that only one of the ComR homologs is required for induced competence.Although S. sobrinus is typically placed among the mutans group streptococci, the S. sobrinus ComRS system is structurally and functionally similar to the competence pathways in the salivarius group. Like S. salivarius, the ComRS gene cluster in S. sobrinus includes a peptide cleavage/export gene, and the ComRS system appears coupled to a bacteriocin response system. These findings raise questions about the true phylogenetic placement of S. sobrinus.Finally, we identified two strains of S. sobrinus appear to be "cheaters" by either not responding to or not producing XIP. While the mechanisms of cheating could be independent, we show how a recombination event in the non-responsive strain would restore function of the ComRS pathway but delete the gene encoding XIP. Thus the S. sobrinus ComRS pathway provides a lens into the evolution of ecological cheaters.
Antibiotic resistance is acquired in response to antibiotic therapy by activating SOS-depended mutagenesis and horizontal gene transfer pathways. Compounds able to inhibit SOS response are extremely important to develop new combinatorial strategies aimed to block mutagenesis. The regulators of homologous recombination involved in the processes of DNA repair should be considered as potential targets for blocking. This review highlights the current knowledge of the protein targets for the evolution of antibiotic resistance and the inhibitory effects of some new compounds on this pathway.
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