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.
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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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    • "Multiple TCS are predicted by whole genome analysis in GBS, but only a few such as CsrR/S (CovR/S) (Lamy et al., 2004; Jiang et al., 2005, 2008, 2012; Rajagopal et al., 2006; Lembo et al., 2010; Cumley et al., 2012; Park et al., 2012) and RgfA/C (Spellerberg et al., 2002; Al Safadi et al., 2011) have been studied in detail to date. Here we report the identification of a TCS in GBS that is a homologue of the LiaSR TCS of Bacillus subtilis, the LiaRS TCS in Streptococcus pneumoniae and Streptococcus mutans and the VraSK TCS of S. aureus, all of which are involved in the species-specific response to cell wall-active antibiotics and antimicrobial peptides (Gardete et al., 2006; Jordan et al., 2007; Kuroda et al., 2003; Mascher et al., 2004; Eldholm et al., 2010; Suntharalingam et al., 2009). We demonstrate here that the LiaR response regulator is involved in GBS response to cell wall-active antimicrobial agents, including antibiotics and antimicrobial peptides, and may regulate the response to these agents by expression of genes involved in cell wall synthesis as well as genes involved in cell membrane modifications and pili formation in GBS. "
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    ABSTRACT: Group B Streptococcus (GBS) remains the leading cause of early-onset sepsis among term infants. Evasion of innate immune defenses is critical to neonatal GBS disease pathogenesis. Effectors of innate immunity, as well as numerous antibiotics, frequently target the peptidoglycan layer of the Gram-positive bacterial cell wall. The intramembrane-sensing histidine kinase (IM-HK) class of two-component regulatory systems has been identified as important to the Gram-positive response to cell wall stress. We have characterized the GBS homolog of LiaR, the response regulator component of the Lia system, to determine its role in GBS pathogenesis. LiaR is expressed as part of a three-gene operon (liaFSR) with a promoter located upstream of liaF. An LiaR deletion mutant is more susceptible to cell wall active antibiotics (vancomycin and bacitracin) as well as antimicrobial peptides (colistin, polymixin B and nisin) compared to isogenic wild-type GBS. LiaR mutant GBS are significantly attenuated in mouse models of both GBS sepsis and pneumonia. Transcriptional profiling with DNA microarray and northern blot demonstrates that LiaR regulates expression of genes involved in microbial defense against host antimicrobial systems including genes functioning in cell wall synthesis, pili formation and cell membrane modification. We conclude that the LiaFSR system, the first member of the IM-HK regulatory systems to be studied in GBS, is involved in sensing perturbations in the integrity of the cell wall and activates a transcriptional response that is important to the pathogenesis of GBS infection.
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