Biomedical subjects

Tony Le Gall

Publications and source records attributed to Tony Le Gall.

3 recordsLinked to original sources

PubMed2006

Identification of forces shaping the commensal Escherichia coli genetic structure by comparing animal and human isolates.

To identify forces shaping the Escherichia coli intraspecies ecological structure, we have characterized in terms of phylogenetic group (A, B1, D and B2) belonging, presence/absence of extraintestinal virulence genes (pap, sfa, hly and aer) and intra-host phylotype diversity a collection of 1898 commensal isolates originating from 387 animals (birds and mammals) sampled in the 1980s and the 2000s. These data have been compared with 760 human commensal isolates, sampled from 152 healthy subjects in the 2000s, and analysed with the same approach. The prevalence of the E. coli phylogenetic groups in birds, non-human mammals and humans is clearly different with a predominance of D/B1, A/B1 and A/B2 strains respectively. A major force shaping the ecological structure is the environment with a strong effect of domestication and the year of sampling followed by the climate. Host characteristics, as the diet and body mass, also influence the ecological structure. Human microbiota are characterized by a higher prevalence of virulence genes and a lower intra-host diversity than the non-human mammal ones. This work identifies for the first time a group of strains specific to the animals, the B1 phylogenetic group strains exhibiting the hly gene. In conclusion, a complex network of factors seems to shape the ecological structure of commensal E. coli, with anthropogenic factors playing a major role and perturbing natural niche equilibrium.

Animals↗

PubMed2005

Analysis of virulence plasmid gene expression defines three classes of effectors in the type III secretion system of Shigella flexneri.

Proteins directly involved in entry and dissemination of Shigella flexneri into epithelial cells are encoded by a virulence plasmid of 200 kb. A 30-kb region (designated the entry region) of this plasmid encodes components of a type III secretion (TTS) apparatus, substrates of this apparatus and their dedicated chaperones. During growth of bacteria in broth, expression of these genes is induced at 37 degrees C and the TTS apparatus is assembled in the bacterial envelope but is not active. Secretion is activated upon contact of bacteria with host cells and is deregulated in an ipaB mutant. The plasmid encodes four transcriptional regulators, VirF, VirB, MxiE and Orf81. VirF controls transcription of virB, whose product is required for transcription of entry region genes. MxiE, with the chaperone IpgC acting as a co-activator, controls expression of several effectors that are induced under conditions of secretion. Genes under the control of Orf81 are not known. The aim of this study was to define further the repertoires of virulence plasmid genes that are under the control of (i) the growth temperature, (ii) each of the known virulence plasmid-encoded transcriptional regulators (VirF, VirB, MxiE and Orf81) and (iii) the activity of the TTS apparatus. Using a macroarray analysis, the expression profiles of 71 plasmid genes were compared in the wild-type strain grown at 37 and 30 degrees C and in virF, virB, mxiE, ipaB, ipaB mxiE and orf81 mutants grown at 37 degrees C. Many genes were found to be under the control of VirB and indirectly of VirF. No alteration of expression of any gene was detected in the orf81 mutant. Expression of 13 genes was increased in the secretion-deregulated ipaB mutant in an MxiE-dependent manner. On the basis of their expression profile, substrates of the TTS apparatus can be classified into three categories: (i) those that are controlled by VirB, (ii) those that are controlled by MxiE and (iii) those that are controlled by both VirB and MxiE. The differential regulation of expression of TTS effectors in response to the TTS apparatus activity suggests that different effectors might be required at different times following contact of bacteria with host cells.

Bacterial Proteins↗

PubMed2005

Selection-driven transcriptome polymorphism in Escherichia coli/Shigella species.

To explore the role of transcriptome polymorphism in adaptation of organisms to their environment, we evaluated this parameter for the Escherichia coli/Shigella bacterial species, which is composed of well-characterized phylogenetic groups that exhibit characteristic life styles ranging from commensalism to intracellular pathogenicity. Both the genomic content and the transcriptome of 10 strains representative of the major E. coli/Shigella phylogenetic groups were evaluated using macroarrays displaying the 4290 K12-MG1655 open reading frames (ORFs). Although Shigella and enteroinvasive E. coli (EIEC) are not monophyletic, phylogenetic analysis of the binary coded (presence/absence) gene content data showed that these organisms group together due to similar patterns of undetectable K12-MG1655 genes. The variation in transcript abundance was then analyzed using a core genome of 2880 genes present in all strains, after adjusting RNA hybridization signals for DNA hybridization signals. Nonrandom changes in gene expression during the evolution of the E. coli/Shigella species were evidenced. Phylogenetic analysis of transcriptome data again showed that Shigella and EIEC strains group together in terms of gene expression, and this convergence involved groups of genes displaying biologically coherent patterns of functional divergence. Unlike the other E. coli strains evaluated, Shigella and EIEC are intracellular pathogens, and therefore face similar selective pressures. Thus, within the E. coli/Shigella species, strains exhibiting a particular life style have converged toward a specific gene expression pattern in a subset of genes common to the species, revealing the role of selection in shaping transcriptome polymorphism.

Caco-2 Cells↗