Development of Competence for Genetic Transformation of Streptococcus mutans in a Chemically Defined Medium

Abstract

c Streptococcus mutans develops competence for genetic transformation in response to regulatory circuits that sense at least two peptide pheromones. One peptide, known as CSP, is sensed by a two-component signal transduction system through a membrane receptor, ComD. The other, derived from the primary translation product ComS, is thought to be sensed by an intracellular receptor, ComR, after uptake by oligopeptide permease. To allow study of this process in a medium that does not itself contain peptides, development of competence was examined in the chemically defined medium (CDM) described by van de Rijn and Kessler (Infect. Immun. 27:444, 1980). We confirmed a previous report that in this medium comS mutants of strain UA159 respond to a synthetic peptide comprising the seven C-terminal residues of ComS (ComS 11-17 ) by increasing expression of the alternative sigma factor SigX, which in turn allows expression of competence effector genes. This response provided the basis for a bioassay for the ComS pheromone in the 100 to 1,000 nM range. It was further observed that comS ؉ (but not comS mutant) cultures developed a high level of competence in the late log and transition phases of growth in this CDM without the introduction of any synthetic stimulatory peptide. This endogenous competence development was accompanied by extracellular release of one or more signals that complemented a comS mutation at levels equivalent to 1 M synthetic ComS 11-17 .

Cross-feeding and interkingdom communication in dual-species biofilms of Streptococcus mutans and Candida albicans

“…Interestingly, the cultivation medium controls which of those two circuits is activated: XIP is only active in a peptidefree medium; it has been suggested that peptides might block the Opp transporter required for import of the active XIP heptamer . Conversely, CSP works only in a peptide-rich medium-here it has been suggested that the membrane-bound HtrA enzyme, which can degrade CSP, must be saturated by peptides to reduce CSP degradation (Desai et al, 2012;Federle and Morrison, 2012). In addition, it has been shown for S. thermophilus that the ComR response regulator is tolerant to small changes in the sequence of XIP and can even be activated by hydrolysis products of casein, that is, octapeptides present in the medium (Fontaine et al, 2013).…”

Plausible Drug Targets in the Streptococcus mutans Quorum Sensing Pathways to Combat Dental Biofilms and Associated Risks

“…The comS encodes the XIP precursor is processed to mature and internalize the cells through the transporter, Opp/Ami. The mature signal in-turn interacts with the comR and activate the gene comX to express the factor, r x [36,37]. Recent data has shown a drastic reduction of XIP levels in the comX (r x ) deficient S. mutans strains, as it evidence the positive feed-back role of ComX in ComRS/XIP expression where its binding sites were localized either within or upstream of ComRS [38].…”

“…Syvitski et al [29] reported that the C-terminal truncated CSP peptides could competitively affect the QS activity and the structural motif in the C-terminal domain restores the activation of the QS signal transduction pathway [34,35]. Further the mutational studies (Point deletion) revealed the loss of function of CSP in promoting genetic competence without affecting the binding of peptide to the receptor [34][35][36][37].…”

“…The peptides were designed to have a targeted domain (8-aminoacid region of the CSP) fused with an antimicrobial peptide domain to show a robust species SigX (ComX) comR DNA transport, uptake and Recombination [12,36] ComAB nlmAB (comAB) Mutacin IV (bacteriocins), Maturation and export of CSP outside the cell [16,49] ComD comC/comD/comE (TCSTS) Class II bacteriocins and HK receptor for CSP signal [14,22] immA and immB (VicRK) comC Self-immunity proteins for protection from bacteriocins, acid tolerance [55] Lux S luxS Interspecies communication [39,40] Indian…”

Proteolytic Regulation of Competence Development in the Genus Streptococcus: Implications in Competence, Stress Response and Antibacterial Therapy

“…This missing link has been recently filled by the discovery of a type II ComRS signaling system that proximally induces transcription of comX in Streptococcus mutans in response to signal peptide XIP [5,6]. When Streptococcus mutans is grown in CDM, competence activation through the ComRS system is superior, nearly involving the entire population [5,16]. However, XIP appears to be inactive when Streptococcus mutans is grown in a complex medium [5,[16][17][18].…”