Multiple and Variable NHEJ-Like Genes Are Involved in Resistance to DNA Damage in Streptomyces ambofaciens

International audienceNon-homologous end-joining (NHEJ) is a double strand break (DSB) repair pathway which does not require any homologous template and can ligate two DNA ends together. The basic bacterial NHEJ machinery involves two partners: the Ku protein, a DNA end binding protein for DSB recognition and the multifunctional LigD protein composed a ligase, a nuclease and a polymerase domain, for end processing and ligation of the broken ends. In silico analyses performed in the 38 sequenced genomes of Streptomyces species revealed the existence of a large panel of NHEJ-like genes. Indeed, ku genes or ligD domain homologues are scattered throughout the genome in multiple copies and can be distinguished in two categories: the " core " NHEJ gene set constituted of conserved loci and the " variable " NHEJ gene set constituted of NHEJ-like genes present in only a part of the species. In Streptomyces ambofaciens ATCC23877, not only the deletion of " core " genes but also that of " variable " genes led to an increased sensitivity to DNA damage induced by electron beam irradiation. Multiple mutants of ku, ligase or polymerase encoding genes showed an aggravated phenotype compared to single mutants. Biochemical assays revealed the ability of Ku-like proteins to protect and to stimulate ligation of DNA ends. RT-qPCR and GFP fusion experiments suggested that ku-like genes show a growth phase dependent expression profile consistent with their involvement in DNA repair during spores formation and/or germination

Wavelength-scale stationary-wave integrated Fourier-transform spectrometry

Spectrometry is a general physical-analysis approach for investigating light-matter interactions. However, the complex designs of existing spectrometers render them resistant to simplification and miniaturization, both of which are vital for applications in micro- and nanotechnology and which are now undergoing intensive research. Stationary-wave integrated Fourier-transform spectrometry (SWIFTS)-an approach based on direct intensity detection of a standing wave resulting from either reflection (as in the principle of colour photography by Gabriel Lippmann) or counterpropagative interference phenomenon-is expected to be able to overcome this drawback. Here, we present a SWIFTS-based spectrometer relying on an original optical near-field detection method in which optical nanoprobes are used to sample directly the evanescent standing wave in the waveguide. Combined with integrated optics, we report a way of reducing the volume of the spectrometer to a few hundreds of cubic wavelengths. This is the first attempt, using SWIFTS, to produce a very small integrated one-dimensional spectrometer suitable for applications where microspectrometers are essential

Les puces et les maladies qu'elles transmettent à l'être humain

CHATENAY M.-PARIS 11-BU Pharma. (920192101) / SudocSudocFranceF

Genome plasticity is governed by double strand break DNA repair in Streptomyces

International audienceThe linear chromosome of the bacterium Streptomyces exhibits a remarkable genetic organization with grossly a central conserved region flanked by variable chromosomal arms. The terminal diversity co-locates with an intense DNA plasticity including the occurrence of large deletions associated to circularization and chromosomal arm exchange. These observations prompted us to assess the role of double strand break (DSB) repair in chromosome plasticity following. For that purpose, DSBs were induced along the chromosome using the meganuclease I-SceI. DSB repair in the central region of the chromosome was mutagenic at the healing site but kept intact the whole genome structure. In contrast, DSB repair in the chromosomal arms was mostly associated to the loss of the targeted chromosomal arm and extensive deletions beyond the cleavage sites. While homologous recombination occurring between copies of DNA sequences accounted for the most part of the chromosome rescue events, Non Homologous End Joining was involved in mutagenic repair as well as in huge genome rearrangements (i.e. circularization). Further, NHEJ repair was concomitant with the integration of genetic material at the healing site. We postulate that DSB repair drives genome plasticity and evolution in Streptomyces and that NHEJ may foster horizontal transfer in the environment

Compact spectrometer modelling based on wavelength stationary wave Fourier transform in integrated optics

International audienc

Double strand break repair triggers genome plasticity in Streptomyces

International audienceDouble strand breaks (DSB) are the most detrimental damage that bacterial cells have to cope with. Two main DSB repair pathways, namely homologous recombination (HR) and non-homologous end joining (NHEJ) are in charge of DSB repair. HR relies on an intact copy of the damaged DNA molecule as a template. On the other hand, NHEJ, which is presumably present in only 20% to 25% of the bacteria, is considered as a mutagenic pathway. Hence, in the absence of template, NHEJ is an error-prone mechanism triggering nucleotide additions or deletions at DSB healing site. We recently identified a putative NHEJ repair mechanism in Streptomyces ambofaciens. Among the NHEJ-like genes, we distinguished a set of genes conserved across the Streptomyces species, and a set of variable genes likely inherited by horizontal transfer. Strikingly, both gene sets were involved in response to DNA damage treatments. Although the high plasticity of the Streptomyces linear chromosome was reported as soon as the first genetic studies, the relative contribution of HR and NHEJ to the stability and evolution of Streptomyces replicons remains unknown. Here we show that repair of chromosomal DSBs (induced by heterologous I-SceI expression) in the chromosome arms is accompanied by the formation of large deletions. In contrast, DSB healing in the conserved region of the chromosome is associated to mutagenic repair in the absence of chromosome rearrangement (probably counterselected). This mutagenic repair is resulting from NHEJ as shown by DSB repair surveys in mutants deficient for different putative NHEJ actors (Ku, ligases). Homologous recombination is shown to occur between duplicated genes (sigma factor encoding genes, transposases) distributed along the chromosome, leading to chromosomal arm replacement and intense DNA amplification. NHEJ repair occurs between sequences sharing or not microhomologies (up to six nucleotides) and induces chromosomal circularization and the formation of large deletions. Further, the involvement of NHEJ was concomitant with the integration of genetic material at the healing site. These data strongly support that DSB repair drives genome plasticity in Streptomyces, and that NHEJ may favor insertion of information from horizontal transfer. These recombination processes could confer a strong capacity to evolve in response to environmental adversity

Double strand break repair triggers genome plasticity in Streptomyces

International audienceDouble strand breaks (DSB) are the most detrimental damage that bacterial cells have to cope with. Two main DSB repair pathways, namely homologous recombination (HR) and non-homologous end joining (NHEJ) are in charge of DSB repair. HR relies on an intact copy of the damaged DNA molecule as a template. On the other hand, NHEJ, which is presumably present in only 20% to 25% of the bacteria, is considered as a mutagenic pathway. Hence, in the absence of template, NHEJ is an error-prone mechanism triggering nucleotide additions or deletions at DSB healing site. We recently identified a putative NHEJ repair mechanism in Streptomyces ambofaciens. Among the NHEJ-like genes, we distinguished a set of genes conserved across the Streptomyces species, and a set of variable genes likely inherited by horizontal transfer. Strikingly, both gene sets were involved in response to DNA damage treatments. Although the high plasticity of the Streptomyces linear chromosome was reported as soon as the first genetic studies, the relative contribution of HR and NHEJ to the stability and evolution of Streptomyces replicons remains unknown. Here we show that repair of chromosomal DSBs (induced by heterologous I-SceI expression) in the chromosome arms is accompanied by the formation of large deletions. In contrast, DSB healing in the conserved region of the chromosome is associated to mutagenic repair in the absence of chromosome rearrangement (probably counterselected). This mutagenic repair is resulting from NHEJ as shown by DSB repair surveys in mutants deficient for different putative NHEJ actors (Ku, ligases). Homologous recombination is shown to occur between duplicated genes (sigma factor encoding genes, transposases) distributed along the chromosome, leading to chromosomal arm replacement and intense DNA amplification. NHEJ repair occurs between sequences sharing or not microhomologies (up to six nucleotides) and induces chromosomal circularization and the formation of large deletions. Further, the involvement of NHEJ was concomitant with the integration of genetic material at the healing site. These data strongly support that DSB repair drives genome plasticity in Streptomyces, and that NHEJ may favor insertion of information from horizontal transfer. These recombination processes could confer a strong capacity to evolve in response to environmental adversity