The LiaFSR System Regulates the Cell Envelope Stress Response in Streptococcus mutans

Dental Research Institute, Faculty of Dentistry, University of Toronto, 124 Edward St., Toronto, Ontario M5G1G6, Canada.
Journal of bacteriology (Impact Factor: 2.81). 03/2009; 191(9):2973-84. DOI: 10.1128/JB.01563-08
Source: PubMed


Maintaining cell envelope integrity is critical for bacterial survival, including bacteria living in a complex and dynamic
environment such as the human oral cavity. Streptococcus mutans, a major etiological agent of dental caries, uses two-component signal transduction systems (TCSTSs) to monitor and respond
to various environmental stimuli. Previous studies have shown that the LiaSR TCSTS in S. mutans regulates virulence traits such as acid tolerance and biofilm formation. Although not examined in streptococci, homologs
of LiaSR are widely disseminated in Firmicutes and function as part of the cell envelope stress response network. We describe here liaSR and its upstream liaF gene in the cell envelope stress tolerance of S. mutans strain UA159. Transcriptional analysis established liaSR as part of the pentacistronic liaFSR-ppiB-pnpB operon. A survey of cell envelope antimicrobials revealed that mutants deficient in one or all of the liaFSR genes were susceptible to Lipid II cycle interfering antibiotics and to chemicals that perturbed the cell membrane integrity.
These compounds induced liaR transcription in a concentration-dependent manner. Notably, under bacitracin stress conditions, the LiaFSR signaling system
was shown to induce transcription of several genes involved in membrane protein synthesis, peptidoglycan biosynthesis, envelope
chaperone/proteases, and transcriptional regulators. In the absence of an inducer such as bacitracin, LiaF repressed LiaR-regulated
expression, whereas supplementing cultures with bacitracin resulted in derepression of liaSR. While LiaF appears to be an integral component of the LiaSR signaling cascade, taken collectively, we report a novel role
for LiaFSR in sensing cell envelope stress and preserving envelope integrity in S. mutans.

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Available from: Dilani B Senadheera, Aug 14, 2014
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    • "During oxidative stress, the expression of the LytST system is enhanced in S. mutans; this system regulates potential oxidative stress genes, such as yghU (encoding an antioxidant enzyme), tpx (encoding thiol peroxidase), and recJ, a single-stranded DNA exonuclease that triggers the DNA repair system in response to oxidative stress (Ahn et al., 2012). In addition, S. mutans has been shown to respond to cell envelop stress via the LiaFSR system, which upregulates the expression of several genes, including those involved in membrane protein synthesis, envelope chaperone/proteases, peptidoglycan biosynthesis, and transcriptional regulators (Suntharalingam et al., 2009). "
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    ABSTRACT: Streptococci cause a variety of diseases, such as dental caries, pharyngitis, meningitis, pneumonia, bacteremia, endocarditis, erysipelas, and necrotizing fasciitis. The natural niche of this genus of bacteria ranges from the mouth and nasopharynx to the skin, indicating that the bacteria will inevitably be subjected to environmental changes during invasion into the host, where it is exposed to the host immune system. Thus, the Streptococcus−host interaction determines whether bacteria are cleared by the host’s defenses or whether they survive after invasion to cause serious disease. If this interaction were to be deciphered, it could aid in the development of novel preventive and therapeutic agents. Streptococcus species possess many virulent factors, such as peroxidases and heat-shock proteins (HSPs), which play key roles in protecting the bacteria from hostile host environments. This review will discuss insights into the mechanism(s) by which streptococci adapt to host environments. Additionally, we will address how streptococcal infections trigger host stress responses; however, the mechanism by which bacterial components modulate host stress responses remains largely unknown.
    The Journal of Microbiology 10/2015; DOI:10.1007/s12275-015-5432-6 · 1.44 Impact Factor
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    • "Several mechanisms have been reported to be involved in bacitracin resistance in S. mutans, including the biosynthesis of cell wall rhamnose-glucose polysaccharides (Yamashita et al., 1998, 1999), altered expression of diacylglycerol kinase (DagK) in diacylglycerol phosphorylation (Lis & Kuramitsu , 2003) and induction of a bacitracin-specific efflux ATP-binding cassette (ABC) transporter (Tsuda et al., 2002). Recently, the BceABRS four-component system and the LiaFSR three-component system have also been found to play important roles in sensing and response to bacitracin and stress damage in S. mutans (Ouyang et al., 2010; Suntharalingam et al., 2009). To better understand the molecular mechanisms by which S. mutans copes with bacitracin or other related antibiotics, we constructed a mutant library by transposon mutagenesis followed by screening and identification of transposon insertion mutants defective in bacitracin resistance. "
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    ABSTRACT: Streptococcus mutans in dental biofilms often faces life-threatening threats such as killing by antimicrobial molecules from competing species or from the host. The ability of S. mutans to cope with such threats is crucial for its survival and persistence in dental biofilms. By screening a transposon mutant library, we identified 11 transposon insertion mutants that are sensitive to bacitracin. Two of these mutants, XTn-01 and XTn-03, had an independent insertion in the same locus, SMU.244, which encodes a homologue of undecaprenyl pyrophosphate phosphatase or UppP. In this study, we describe genetic and phenotypic characterizations of SMU.244 in antibiotic resistance. The results reveal that deletion of SMU.244 results in a mutant (XTΔ244) that is highly sensitive to bacitracin but confers more resistance to lactococcin G, a class IIb bacteriocin. Introduction of the intact SMU.244 into XTΔ244 in trans completely restores its resistance to bacitracin and the susceptibility to lactococcin G. The XTΔ244 is also defective in forming the wild type biofilm, although its growth is not significantly affected. Using recombinant protein technology, we demonstrate that SMU.244-encoded protein displays an enzyme activity of catalyzing dephosphorylation of the substrate. The lux transcriptional reporter assays show that S. mutans maintains a moderate level of expression of SMU.244 in the absence of bacitracin, but bacitracin at a sub-MIC can further induce its expression. We conclude that SMU.244 encodes an UppP protein that plays important roles in the cell wall biosynthesis and bacitracin resistance in S. mutans.
    Microbiology 07/2015; 161(9). DOI:10.1099/mic.0.000142 · 2.56 Impact Factor
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    • "Cell viability was assessed by counting colony forming units (CFUs). The minimum inhibitory concentration (MIC) test was performed according to the broth microdilution method using BHI broth as previously described 29 . Briefly, ∼105 CFU/ml of bacterial cells were added to a 96-well plate containing BHI medium supplemented with twofold serial dilutions of EGCg or CHX. "
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    ABSTRACT: Objective: To test the inhibitory growth activity of green tea catechin incorporated into dental resins compared to resins containing the broad-spectrum antimicrobial compound chlorhexidine against Streptococcus mutans in vitro. Material and Methods: The minimum inhibitory concentrations (MICs) of epigallocatechin-gallate (EGCg) and chlorhexidine (CHX) were determined according to the microdilution method. Resin discs (5 mm x 3 mm) were prepared from Bis-GMA/TEGDMA (R1) and Bis-GMA/CH3Bis-GMA (R2) comonomers (n=9) containing: a) no drug, b) EGCg, c) CHX. Two concentrations of each drug (0.5x MIC and 1x MIC) were incorporated into the resin discs. Samples were individually immersed in a bacterial culture and incubated for 24 h at 37º C under constant agitation. Cell viability was assessed by counting the number of colonies on replica agar plates. Statistical analysis was performed using one-way ANOVA, Tukey and Student t-tests (α=0.05). Results: Both resins containing EGCg and CHX showed a significant inhibition of bacterial growth at both concentrations tested (p<0.05). A significantly higher inhibition was observed in response to resins containing CHX at 0.5x MIC and 1x MIC, and EGCg at 1x MIC when compared to EGCg at 0.5x MIC. Also, EGCg at 0.5x MIC in R1 had a significantly higher growth inhibition than in R2. Conclusions: Both EGCg and CHX retained their antibacterial activity when incorporated into the resin matrix. EGCg at 1x MIC in R1 and R2 resins significantly reduced S. mutans survival at a level similar to CHX. The data generated from this study will provide advances in the field of bioactive dental materials with the potential of improving the lifespan of resin-based restorations.
    Journal of applied oral science: revista FOB 03/2013; 21(2). DOI:10.1590/1678-7757201302430 · 0.92 Impact Factor
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