Physiological impact of transposable elements encoding DDE transposases in the environmental adaptation of Streptococcus agalactiae

International audienceWe have referenced and described Streptococcus agalactiae transposable elements encoding DDE transposases. These elements belonged to nine families of insertion sequences (ISs) and to a family of conjugative transposons (TnGBSs). An overview of the physiological impact of the insertion of all these elements is provided. DDE-transposable elements affect S. agalactiae in a number of aspects of its capability to adapt to various environments and modulate the expression of several virulence genes, the scpB-lmB genomic region and the genes involved in capsule expression and haemolysin transport being the targets of several different mobile elements. The referenced mobile elements modify S. agalactiae behaviour by transferring new gene(s) to its genome, by modifying the expression of neighbouring genes at the integration site or by promoting genomic rearrangements. Transposition of some of these elements occurs in vivo, suggesting that by dynamically regulating some adaptation and/or virulence genes, they improve the ability of S. agalactiae to reach different niches within its host and ensure the 'success' of the infectious process

Regulation of competence for natural transformation in streptococci.

Natural DNA transformation is a lateral gene transfer mechanism during which bacteria take up naked DNA from their environment and stably integrate it in their genome. The proteins required for this process are conserved between species and are produced during a specific physiological state known as competence. Although natural transformation drives genome plasticity and adaptability, it is also likely to cause deleterious effects in the chromosome of the recipient bacteria and negatively impact cell growth. The competence window is thus generally tightly regulated in response to species-specific environmental conditions and limited to a proportion of the cell population. In streptococci species, the entry into competence is dictated by the amount of the competence sigma factor σ(X), the master regulator of natural transformation in those species. The Streptococcus genus includes 7 phylogenetic groups that have evolved different regulatory circuits to govern natural transformation. Here, we review the current knowledge on transcriptional and post-transcriptional mechanisms that control the activity of σ(X) at the whole population and the single-cell level, with an emphasis on growth conditions that modulate their activation. Recent findings regarding competence regulation by the ComCDE and ComRS cell-cell signalling pathways and the Clp proteolytic system are specifically highlighted

Intensive targeting of regulatory competence genes by transposable elements in streptococci.

Competence for natural transformation is a widespread developmental process of streptococci. By allowing the uptake and recombination of exogenous naked DNA into the genome, natural transformation, as transposable elements, plays a key role in the plasticity of bacterial genomes. We previously analysed the insertion sites of IS1548, an insertion sequence present in Streptococcus agalactiae and S. pyogenes, and showed that some targeted loci are involved in competence induction. In this work, we investigated on a large scale if loci coding for early competence factors (ComX and the two pheromone-dependent signalling systems ComCDE and ComRS) of streptococci are especially targeted by transposable elements. The transposable elements inserted in regions surrounding these genes and housekeeping genes used for Multilocus Sequence Typing (MLST) were systematically searched for. We found numerous insertion events in the close vicinity of early competence genes, but only very few into the MLST loci. The incidence of transposable elements, mainly insertion sequences, is particularly high in the intergenic regions surrounding comX alleles in numerous species belonging to most streptococcal groups. The identification of scarce disruptive insertions inside early competence genes indicates that the maintenance of competence is essential for streptococci. The specific association of transposable elements with intergenic regions bordering the main regulatory genes of competence may impact on the induction of transformability and so, on the genome plasticity and adaptive evolution of streptococci. This widespread phenomenon brings new perspectives on our understanding of competence regulation and its role in the bacterial life cycle

ICEEc2, a New Integrative and Conjugative Element Belonging to the pKLC102/PAGI-2 Family, Identified in Escherichia coli Strain BEN374▿ †

The diversity of the Escherichia coli species is in part due to the large number of mobile genetic elements that are exchanged between strains. We report here the identification of a new integrative and conjugative element (ICE) of the pKLC102/PAGI-2 family located downstream of the tRNA gene pheU in the E. coli strain BEN374. Indeed, this new region, which we called ICEEc2, can be transferred by conjugation from strain BEN374 to the E. coli strain C600. We were also able to transfer this region into a Salmonella enterica serovar Typhimurium strain and into a Yersinia pseudotuberculosis strain. This transfer was then followed by the integration of ICEEc2 into the host chromosome downstream of a phe tRNA gene. Our data indicated that this transfer involved a set of three genes encoding DNA mobility enzymes and a type IV pilus encoded by genes present on ICEEc2. Given the wide distribution of members of this family, these mobile genetic elements are likely to play an important role in the diversification of bacteria

Reduced membrane fluidity of a SigX deficient strain results in altered carbon catabolic repression response in Pseudomonas aeruginosa

International audienceThe extracytoplasmic sigma factor SigX is a master regulator of bacterial adaptation that is involved in fatty acids biosynthesis and membrane homeostasis in P. aeruginosa. The growth of a sigX mutant was strongly affected in LB broth, but not in M9-glucose minimal medium. Through comparative transcriptomics and proteomics conducted in LB medium, we show that the absence of SigX results in strong dysregulation of genes, the products of which are mainly involved in transport, carbon and energy metabolisms. The CbrA/B two components system was strongly activated in a sigX mutant, leading to a higher production of crcZ and a reduced activity of the major translational repressors Hfq and Crc compared to the wildtype strain. Remarkably, growth as well as genes, the expression of which was dysregulated in the mutant strain, were restored when the C189-structurally related detergent Polysorbate 80 was supplemented to LB medium. Anisotropy data further showed that the sigX mutant displayed a less fluid membrane than the WT strain, a phenotype that was restored by adding Polysorbate 80. Altogether, our data show that the altered membrane of the sigX mutant strain was probably the leading cause of the strong metabolic alterations and the reduced carbon catabolic repression response (CCR) encountered by this mutant strain. Thus, by controlling membrane homeostasis, SigX behaves as a master regulator of the nutritional response, in addition to its involvement in P. aeruginosa adaptation, virulence and biofilm formation

Reduced membrane fluidity of a SigX deficient strain results in altered carbon catabolic repression response in Pseudomonas aeruginosa

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WISArD : Weak Interaction Studies with 32^{32}Ar Decay

International audienceThe WISArD experiment is probing the possible existence of exotic currents in the electroweak sector using nuclear $\beta$ decay, to improve the constraints on beyond Standard Model physics. The setup of the experiment underwent a full upgrade between 2018 and 2021 in preparation of a second run of data taking at ISOLDE, CERN, scheduled for October 2021. The detector stage was completely renewed to improve statistics and minimize the main systematic effects identified in a proof-of-principle run in 2018. With this upgrade, the objective is to reach the per-mil level of uncertainty on the angular correlation coefficent $a$ and on the Fierz interference term $b$, in a pure Fermi transition. In this case, both parameters are directly sensitive to the possible contribution of exotic scalar currents

The absence of SigX results in impaired carbon metabolism and membrane fluidity in Pseudomonas aeruginosa

Abstract In Pseudomonas aeruginosa, SigX is an extra-cytoplasmic function σ factor that belongs to the cell wall stress response network. In previous studies, we made the puzzling observation that sigX mutant growth was severely affected in rich lysogeny broth (LB) but not in minimal medium. Here, through comparative transcriptomic and proteomic analysis, we show that the absence of SigX results in dysregulation of genes, whose products are mainly involved in transport, carbon and energy metabolisms. Production of most of these genes is controlled by carbon catabolite repression (CCR), a key regulatory system than ensures preferential carbon source uptake and utilization, substrate prioritization and metabolism. The strong CCR response elicited in LB was lowered in a sigX mutant, suggesting altered nutrient uptake. Since the absence of SigX affects membrane composition and fluidity, we suspected membrane changes to cause such phenotype. The detergent polysorbate 80 (PS80) can moderately destabilize the envelope resulting in non-specific increased nutrient intake. Remarkably, growth, membrane fluidity and expression of dysregulated genes in the sigX mutant strain were restored in LB supplemented with PS80. Altogether, these data suggest that SigX is indirectly involved in CCR regulation, possibly via its effects on membrane integrity and fluidity