Regulation of competence for natural transformation in streptococci

Fontaine, Laetitia; Wahl, Astrid Klopstad; Fléchard, Maud; Mignolet, Johann; Hols, Pascal

doi:10.1016/j.meegid.2014.09.010

Cited by 106 publications

(178 citation statements)

References 205 publications

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“…Other bacterial species possess sophisticated mechanisms for switching off the competence genes and limiting the duration of the competent state, such as the DprA and Clp mechanisms (1,2). At least some of these mechanisms have been described in S. mutans (37).…”

Section: Discussionmentioning

confidence: 99%

“…Competence occurs in many bacterial species but was first described in the streptococci, where its regulation has been the subject of intensive study (1,2). In the oral pathogen Streptococcus mutans, competence is important not only because it contributes to genetic diversity but also because its regulation is closely intertwined with the manifestation of virulence-related behaviors, including bacteriocin production, biofilm formation, tolerance of low pH, and carbohydrate catabolism (3)(4)(5)(6)(7).…”

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confidence: 99%

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Sharply Tuned pH Response of Genetic Competence Regulation in Streptococcus mutans: a Microfluidic Study of the Environmental Sensitivity of comX

Son

Ghoreishi

Ahn

et al. 2015

Appl Environ Microbiol

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Genetic competence in Streptococcus mutans is a transient state that is regulated in response to multiple environmental inputs. These include extracellular pH and the concentrations of two secreted peptides, designated CSP (competence-stimulating peptide) and XIP (comX-inducing peptide). The role of environmental cues in regulating competence can be difficult to disentangle from the effects of the organism's physiological state and its chemical modification of its environment. We used microfluidics to control the extracellular environment and study the activation of the key competence gene comX. We find that the comX promoter (P comX ) responds to XIP or CSP only when the extracellular pH lies within a narrow window, about 1 pH unit wide, near pH 7. Within this pH range, CSP elicits a strong P comX response from a subpopulation of cells, whereas outside this range the proportion of cells expressing comX declines sharply. Likewise, P comX is most sensitive to XIP only within a narrow pH window. While previous work suggested that comX may become refractory to CSP or XIP stimulus as cells exit early exponential phase, our microfluidic data show that extracellular pH dominates in determining sensitivity to XIP and CSP. The data are most consistent with an effect of pH on the ComR/ComS system, which has direct control over transcription of comX in S. mutans. Genetic competence is a transient physiological state during which a bacterial cell is able to internalize DNA from its environment. Competence occurs in many bacterial species but was first described in the streptococci, where its regulation has been the subject of intensive study (1, 2). In the oral pathogen Streptococcus mutans, competence is important not only because it contributes to genetic diversity but also because its regulation is closely intertwined with the manifestation of virulence-related behaviors, including bacteriocin production, biofilm formation, tolerance of low pH, and carbohydrate catabolism (3-7). S. mutans regulates competence in part through two secreted quorum-sensing peptides, designated competence-stimulating peptide (CSP) and comX-inducing peptide (XIP). Interestingly, the activity of these peptides depends on environmental parameters, including pH, carbohydrate, and media (8-11). Through mechanisms that are not well understood, the competence regulon integrates the peptide signals with environmental and internal parameters (12, 13) to trigger a transient state of competence during early exponential growth phase.The interaction of the extracellular environment with competence and related virulence behaviors is important in the context of oral biofilms. Heterogeneous local environments of pH and oxygen/redox, carbohydrate, and secreted-peptide concentrations in a biofilm could potentially lead to spatial variations in virulence gene expression in S. mutans (14-17). pH is particularly important because the fermentation of carbohydrates by S. mutans generates acids that can rapidly modify the pH of the environment. The pH in a biofilm ...

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Sharply Tuned pH Response of Genetic Competence Regulation in Streptococcus mutans: a Microfluidic Study of the Environmental Sensitivity of comX

Son

Ghoreishi

Ahn

et al. 2015

Appl Environ Microbiol

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“…Given that no genuine orthologues for competence signaling proteins (i.e., ComDE and ComR streptococci) have been found yet in L. lactis, we decided to target the well-known Clp machinery involved in the negative control of competence induction in both bacilli and streptococci (12,13). Interestingly, our results suggest that the MecA-ClpCP machinery might be involved in the degradation of ComX as reported in B. subtilis, S. thermophilus, and S. mutans (13), thereby contributing to the posttranslational control of competence development in L. lactis.…”

Section: Figmentioning

confidence: 99%

Natural DNA Transformation Is Functional in Lactococcus lactis subsp. cremoris KW2

David

Radziejwoski

Toussaint

et al. 2017

Appl Environ Microbiol

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Lactococcus lactis is one of the most commonly used lactic acid bacteria in the dairy industry. Activation of competence for natural DNA transformation in this species would greatly improve the selection of novel strains with desired genetic traits. Here, we investigated the activation of natural transformation in L. lactis subsp. cremoris KW2, a strain of plant origin whose genome encodes the master competence regulator ComX and the complete set of proteins usually required for natural transformation. In the absence of knowledge about competence regulation in this species, we constitutively overproduced ComX in a reporter strain of late competence phase activation and showed, by transcriptomic analyses, a ComX-dependent induction of all key competence genes. We further demonstrated that natural DNA transformation is functional in this strain and requires the competence DNA uptake machinery. Since constitutive ComX overproduction is unstable, we alternatively expressed comX under the control of an endogenous xylose-inducible promoter. This regulated system was used to successfully inactivate the adaptor protein MecA and subunits of the Clp proteolytic complex, which were previously shown to be involved in ComX degradation in streptococci. In the presence of a small amount of ComX, the deletion of mecA, clpC, or clpP genes markedly increased the activation of the late competence phase and transformability. Altogether, our results report the functionality of natural DNA transformation in L. lactis and pave the way for the identification of signaling mechanisms that trigger the competence state in this species.IMPORTANCE Lactococcus lactis is a lactic acid bacterium of major importance, which is used as a starter species for milk fermentation, a host for heterologous protein production, and a delivery platform for therapeutic molecules. Here, we report the functionality of natural transformation in L. lactis subsp. cremoris KW2 by the overproduction of the master competence regulator ComX. The developed procedure enables a flexible approach to modify the chromosome with single point mutation, sequence insertion, or sequence replacement. These results represent an important step for the genetic engineering of L. lactis that will facilitate the design of strains optimized for industrial applications. This will also help to discover natural regulatory mechanisms controlling competence in the genus Lactococcus.

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“…Natural genetic transformation is widespread in oral streptococci, including the mutans, the salivarius, the mitis, and the anginosus groups [1,2,3]. The mechanisms depend on streptococci entering competence, a physiological state triggered by pheromones, and characterized by the induction in expression of several gene clusters, including those essential for DNA uptake and recombination.…”

Section: Introductionmentioning

confidence: 99%

Natural Transformation of Oral Streptococci by Use of Synthetic Pheromones

Salvadori

Junges

Khan

et al. 2016

Methods in Molecular Biology

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The discovery that Streptococcus pneumoniae uses a competence-stimulating peptide (CSP) to induce competence for natural transformation, and that other species of the mitis and the anginosus streptococcal groups use a similar system, has expanded the tools to explore gene function and regulatory pathways in streptococci. Two other classes of pheromones have been discovered since then, comprising the bacteriocin-inducing peptide class found in Streptococcus mutans (also named CSP, although different from the former) and the SigX-inducing peptides (XIP), in the mutans, salivarius, bovis, and pyogenes groups of streptococci. The three classes of peptide pheromones can be ordered from peptide synthesis services at affordable prices, and used in transformation assays to obtain competent cultures consistently at levels usually higher than those achieved during spontaneous competence. In this chapter, we present protocols for natural transformation of oral streptococci that are based on the use of synthetic pheromones, with examples of conditions optimized for transformation of S. mutans and Streptococcus mitis.

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Regulation of competence for natural transformation in streptococci

Cited by 106 publications

References 205 publications

Sharply Tuned pH Response of Genetic Competence Regulation in Streptococcus mutans: a Microfluidic Study of the Environmental Sensitivity of comX

Sharply Tuned pH Response of Genetic Competence Regulation in Streptococcus mutans: a Microfluidic Study of the Environmental Sensitivity of comX

Natural DNA Transformation Is Functional in Lactococcus lactis subsp. cremoris KW2

Natural Transformation of Oral Streptococci by Use of Synthetic Pheromones

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