LuxS impacts on LytA-dependent autolysis and on competence in Streptococcus pneumoniae

Abstract

The ubiquitous protein LuxS with S-ribosylhomocysteinase activity is involved in S-adenosyl methionine detoxification, C-1 unit recycling and the production of autoinducers that allow the cell to sense and respond to cell density. Independent reports describe the impact of LuxS deficiency on Streptococcus pneumoniae virulence in the mouse. In vitro, LuxS deficiency confers discrete phenotypes. A combined approach using genetic dissection and mixed-culture experiments allowed the involvement of LuxS in the developmental physiology of S. pneumoniae to be investigated. Functional LuxS was found to be related on the one hand to down-regulation of competence, and on the other hand to attenuation of autolysis in cultures entering stationary phase. The competence phenotype of luxS mutant bacteria was complemented by media conditioned by competence-defective ComAB0 bacteria, but not by BSA. The autolytic phenotype was complemented by BSA, but not by conditioned supernatants. It is suggested that the impact of LuxS on competence, but not on autolysis, involves cell-cell communication. The phenotype of luxS mutant strains reveals a hierarchy in the competence regulatory networks of S. pneumoniae. INTRODUCTIONLuxS, the S-ribosylhomocysteinase involved in furanosyl borate diester, autoinducer 2 (AI-2) production from Sribosylhomocysteine, is ubiquitous in prokaryotes (Sun et al., 2004). Since its discovery (Bassler et al., 1997) and chemical characterization (Chen et al., 2002), the role of AI-2 in the regulation of light production, biofilm formation and virulence in response to high cell density (quorum sensing) has been elucidated in several Gram-negative bacteria, including Vibrio species (Surette et al., 1999;Miller et al., 2002;Hammer & Bassler, 2003;Henke & Bassler, 2004;Vendeville et al., 2005). In some species, furanone uptake and processing involving the lsrACDBFGE operon has been described Xavier & Bassler, 2005). Bioluminescence activation in Vibrio harveyi by conditioned media represents the test for AI-2 production by a given species and supports the paradigm of AI-2-mediated interspecies cell-cell communication culminating in genetic regulation Xavier & Bassler, 2003). Recent studies give credence to the involvement of LuxS in host-bacterial communication (Maroui & Sela, 2003;Sperandino et al., 2003). However, in Neisseria meningitis, AI-2 production is not related to the regulation of specific genes in vitro (Schauder et al., 2005;Dove et al., 2003). In Streptococcus pneumoniae, the impact of LuxS loss-offunction mutations on experimental virulence and genetic expression has been reported; however, results concerning production of AI-2, active in the 'vibrio test', by pneumococci, are divergent (Joyce et al. 2004;Stroeher et al., 2003). In order to get further insight into the function of LuxS in these Gram-positive bacteria, we have investigated its role in vitro on the developmental phenotypes classically observed: competence for genetic transformation during exponential growth, and autolysis when the cult...

Heterologous Expression of sahH Reveals That Biofilm Formation Is Autoinducer-2-independent in Streptococcus sanguinis but Is Associated with an Intact Activated Methionine Cycle

“…This has been demonstrated for S. mutans and is consistent with the findings of the present study (47). An influence on expression of late competence genes was also found in LuxS mutants of S. pneumonia (22,62); however, in those studies the direct influence of AI-2 was not investigated.…”

“…A LuxS mutant was reduced in virulence with a defect in the ability to spread from initial colonization sites and to persist in nasopharyngeal tissue (20,21). A down-regulation of natural competence and a severe defect in biofilm formation was also noted (22,23).…”

The atlA Operon of Streptococcus mutans : Role in Autolysin Maturation and Cell Surface Biogenesis

“…The atlA gene is also not under control of AI-2-mediated quorum sensing, because no obvious differences were observed in the expression of atlA in the wild-type and a luxS mutant (data not shown). This finding contrasts with a recent study in S. pneumoniae demonstrating that LuxS is involved in the control of LytA-dependent autolysis, as well as in cell-cell communication culminating in repression of competence (63).…”

The StkP/PhpP Signaling Couple inStreptococcus pneumoniae: Cellular Organization and Physiological Characterization

“…We postulate that StkP activity might allow the entry of "periplasmic signals" into the competence regulatory network, culminating in a competence trigger. In addition to the ComDE TCS, ComAB, the CSP-autoregulated signaling network, TCSs CiaRH and MicAB (11,15,26,41), the global regulator RegR (8), and the putative AI2 autoinducer system (38) have been shown to modulate competence expression in S. pneumoniae, implying that integration of different signals determines the pattern of competence development in growing cultures. Taking into account that PhpP is essential in the wild-type stkP genetic background, indicating strong control on StkP activity (Table 3), the StkP-PhpP signaling couple also represents an important actor determining the kinetics of competence development during bacterial growth in Streptococcus pneumoniae.…”