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Interspecies communication among commensal and pathogenic streptococci.

Cook LC, LaSarre B, Federle MJ - MBio (2013)

Bottom Line: Using isogenic mutant strains and transcriptional reporters, we confirmed that RovS/SHP1520 comprise a QS circuit in GBS.Environmental cues and interspecies signaling between members of the human flora likely play an important role in the transition to a disease state.Here we provide evidence of a bidirectional QS system between GAS, GBS, and Streptococcus dysgalactiae subsp. equisimilis, demonstrating the possibility of evolved communication systems between human pathogens.

View Article: PubMed Central - PubMed

Affiliation: Center for Pharmaceutical Biotechnology, Department of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, University of Illinois at Chicago, Chicago, Illinois, USA.

ABSTRACT

Unlabelled: Quorum sensing (QS) regulates diverse and coordinated behaviors in bacteria, including the production of virulence factors, biofilm formation, sporulation, and competence development. It is now established that some streptococci utilize Rgg-type proteins in concert with short hydrophobic peptides (SHPs) to mediate QS, and sequence analysis reveals that several streptococcal species contain highly homologous Rgg/SHP pairs. In group A streptococcus (GAS), two SHPs (SHP2 and SHP3 [SHP2/3]) were previously identified to be important in GAS biofilm formation. SHP2/3 are detected by two antagonistic regulators, Rgg2 and Rgg3, which control expression of the shp genes. In group B streptococcus (GBS), RovS is a known virulence gene regulator and ortholog of Rgg2, whereas no apparent Rgg3 homolog exists. Adjacent to rovS is a gene (shp1520) encoding a peptide nearly identical to SHP2. Using isogenic mutant strains and transcriptional reporters, we confirmed that RovS/SHP1520 comprise a QS circuit in GBS. More important, we performed experiments demonstrating that production and secretion of SHP1520 by GBS can modulate Rgg2/3-regulated gene expression in GAS in trans; likewise, SHP2/3 production by GAS can stimulate RovS-mediated gene regulation in GBS. An isolate of Streptococcus dysgalactiae subsp. equisimilis also produced a secreted factor capable of simulating the QS circuits of both GAS and GBS, and sequencing confirms the presence of an orthologous Rgg2/SHP2 pair in this species as well. To our knowledge, this is the first documented case of bidirectional signaling between streptococcal species in coculture and suggests a role for orthologous Rgg/SHP systems in interspecies communication between important human pathogens.

Importance: Pathogenic streptococci, such as group A (GAS) and group B (GBS) streptococcus, are able to persist in the human body without causing disease but become pathogenic under certain conditions that are not fully characterized. Environmental cues and interspecies signaling between members of the human flora likely play an important role in the transition to a disease state. Since quorum-sensing (QS) peptides have been consistently shown to regulate virulence factor production in pathogenic species, the ability of bacteria to signal via these peptides may prove to be an important link between the carrier and pathogenic states. Here we provide evidence of a bidirectional QS system between GAS, GBS, and Streptococcus dysgalactiae subsp. equisimilis, demonstrating the possibility of evolved communication systems between human pathogens.

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GBS responds to other bacterially derived SHPs. An SHP-deficient strain of GBS (BLC101) carrying a Pshp1520 reporter (pSar110) is highly induced in response to spent culture supernatants from GAS Δrgg3 (JCC131) and S. dysgalactiae subsp. equisimilis (GGS-LT1) strains but not in response to fresh medium or WT GAS (NZ131) supernatant. Data are shown as a function of relative light units (CPS/OD600) versus OD600. The graph is representative of at least 3 biological replicates.
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fig4: GBS responds to other bacterially derived SHPs. An SHP-deficient strain of GBS (BLC101) carrying a Pshp1520 reporter (pSar110) is highly induced in response to spent culture supernatants from GAS Δrgg3 (JCC131) and S. dysgalactiae subsp. equisimilis (GGS-LT1) strains but not in response to fresh medium or WT GAS (NZ131) supernatant. Data are shown as a function of relative light units (CPS/OD600) versus OD600. The graph is representative of at least 3 biological replicates.

Mentions: Based on the confirmed functions of RovS and SHP1520 in a QS circuit and the finding that GAS responds to SHP peptides produced by GBS and S. dysgalactiae subsp. equisimilis (Fig. 2A), we predicted that GBS would also respond to SHPs produced by other streptococcal species. To test this, we used the GBS shp1520GGG reporter strain carrying the Pshp1520 reporter plasmid [BLC101(pSar110)]. Since this strain cannot produce its own SHP pheromone but carries an intact copy of rovS, spent culture supernatants should be able to induce reporter expression if they contain a secreted SHP peptide recognizable by RovS. Consistent with the ability of SHP2-like peptides to cross-activate strains carrying an Rgg2 ortholog, spent supernatants from JCC131 (GAS Δrgg3 mutant in which shp expression is robust) and GGS-LT1 cultures were able to induce high-level reporter induction compared to results with fresh medium (Fig. 4). Surprisingly, spent supernatant from the negative-control strain NZ131 was able to slightly induce reporter expression compared to fresh medium (Fig. 4), albeit far below the levels induced by JCC131 or GGS-LT1. This slight induction may represent low-level expression of SHPs in WT GAS that was previously undetected (26) because of the single-copy nature of the GAS transcriptional reporters as opposed to the multicopy plasmid GBS reporter. Alternatively, the concentration of SHP that effectively activates RovS may be lower than that needed for Rgg2/3 activation. Further studies will be needed to investigate these possibilities.


Interspecies communication among commensal and pathogenic streptococci.

Cook LC, LaSarre B, Federle MJ - MBio (2013)

GBS responds to other bacterially derived SHPs. An SHP-deficient strain of GBS (BLC101) carrying a Pshp1520 reporter (pSar110) is highly induced in response to spent culture supernatants from GAS Δrgg3 (JCC131) and S. dysgalactiae subsp. equisimilis (GGS-LT1) strains but not in response to fresh medium or WT GAS (NZ131) supernatant. Data are shown as a function of relative light units (CPS/OD600) versus OD600. The graph is representative of at least 3 biological replicates.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3735184&req=5

fig4: GBS responds to other bacterially derived SHPs. An SHP-deficient strain of GBS (BLC101) carrying a Pshp1520 reporter (pSar110) is highly induced in response to spent culture supernatants from GAS Δrgg3 (JCC131) and S. dysgalactiae subsp. equisimilis (GGS-LT1) strains but not in response to fresh medium or WT GAS (NZ131) supernatant. Data are shown as a function of relative light units (CPS/OD600) versus OD600. The graph is representative of at least 3 biological replicates.
Mentions: Based on the confirmed functions of RovS and SHP1520 in a QS circuit and the finding that GAS responds to SHP peptides produced by GBS and S. dysgalactiae subsp. equisimilis (Fig. 2A), we predicted that GBS would also respond to SHPs produced by other streptococcal species. To test this, we used the GBS shp1520GGG reporter strain carrying the Pshp1520 reporter plasmid [BLC101(pSar110)]. Since this strain cannot produce its own SHP pheromone but carries an intact copy of rovS, spent culture supernatants should be able to induce reporter expression if they contain a secreted SHP peptide recognizable by RovS. Consistent with the ability of SHP2-like peptides to cross-activate strains carrying an Rgg2 ortholog, spent supernatants from JCC131 (GAS Δrgg3 mutant in which shp expression is robust) and GGS-LT1 cultures were able to induce high-level reporter induction compared to results with fresh medium (Fig. 4). Surprisingly, spent supernatant from the negative-control strain NZ131 was able to slightly induce reporter expression compared to fresh medium (Fig. 4), albeit far below the levels induced by JCC131 or GGS-LT1. This slight induction may represent low-level expression of SHPs in WT GAS that was previously undetected (26) because of the single-copy nature of the GAS transcriptional reporters as opposed to the multicopy plasmid GBS reporter. Alternatively, the concentration of SHP that effectively activates RovS may be lower than that needed for Rgg2/3 activation. Further studies will be needed to investigate these possibilities.

Bottom Line: Using isogenic mutant strains and transcriptional reporters, we confirmed that RovS/SHP1520 comprise a QS circuit in GBS.Environmental cues and interspecies signaling between members of the human flora likely play an important role in the transition to a disease state.Here we provide evidence of a bidirectional QS system between GAS, GBS, and Streptococcus dysgalactiae subsp. equisimilis, demonstrating the possibility of evolved communication systems between human pathogens.

View Article: PubMed Central - PubMed

Affiliation: Center for Pharmaceutical Biotechnology, Department of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, University of Illinois at Chicago, Chicago, Illinois, USA.

ABSTRACT

Unlabelled: Quorum sensing (QS) regulates diverse and coordinated behaviors in bacteria, including the production of virulence factors, biofilm formation, sporulation, and competence development. It is now established that some streptococci utilize Rgg-type proteins in concert with short hydrophobic peptides (SHPs) to mediate QS, and sequence analysis reveals that several streptococcal species contain highly homologous Rgg/SHP pairs. In group A streptococcus (GAS), two SHPs (SHP2 and SHP3 [SHP2/3]) were previously identified to be important in GAS biofilm formation. SHP2/3 are detected by two antagonistic regulators, Rgg2 and Rgg3, which control expression of the shp genes. In group B streptococcus (GBS), RovS is a known virulence gene regulator and ortholog of Rgg2, whereas no apparent Rgg3 homolog exists. Adjacent to rovS is a gene (shp1520) encoding a peptide nearly identical to SHP2. Using isogenic mutant strains and transcriptional reporters, we confirmed that RovS/SHP1520 comprise a QS circuit in GBS. More important, we performed experiments demonstrating that production and secretion of SHP1520 by GBS can modulate Rgg2/3-regulated gene expression in GAS in trans; likewise, SHP2/3 production by GAS can stimulate RovS-mediated gene regulation in GBS. An isolate of Streptococcus dysgalactiae subsp. equisimilis also produced a secreted factor capable of simulating the QS circuits of both GAS and GBS, and sequencing confirms the presence of an orthologous Rgg2/SHP2 pair in this species as well. To our knowledge, this is the first documented case of bidirectional signaling between streptococcal species in coculture and suggests a role for orthologous Rgg/SHP systems in interspecies communication between important human pathogens.

Importance: Pathogenic streptococci, such as group A (GAS) and group B (GBS) streptococcus, are able to persist in the human body without causing disease but become pathogenic under certain conditions that are not fully characterized. Environmental cues and interspecies signaling between members of the human flora likely play an important role in the transition to a disease state. Since quorum-sensing (QS) peptides have been consistently shown to regulate virulence factor production in pathogenic species, the ability of bacteria to signal via these peptides may prove to be an important link between the carrier and pathogenic states. Here we provide evidence of a bidirectional QS system between GAS, GBS, and Streptococcus dysgalactiae subsp. equisimilis, demonstrating the possibility of evolved communication systems between human pathogens.

Show MeSH
Related in: MedlinePlus