Monique Ladiré

Ruminococcin A, a New Lantibiotic Produced by a Ruminococcus gnavus Strain Isolated from Human Feces

ABSTRACT When cultivated in the presence of trypsin, the Ruminococcus gnavus E1 strain, isolated from a human fecal sample, was able to produce an antibacterial substance that accumulated in the supernatant. This substance, called ruminococcin A, was purified to homogeneity by reverse-phase chromatography. It was shown to be a 2,675-Da bacteriocin harboring a lanthionine structure. The utilization of Edman degradation and tandem mass spectrometry techniques, followed by DNA sequencing of part of the structural gene, allowed the identification of 21 amino acid residues. Similarity to other bacteriocins present in sequence libraries strongly suggested that ruminococcin A belonged to class IIA of the lantibiotics. The purified ruminococcin A was active against various pathogenic clostridia and bacteria phylogenetically related to R. gnavus. This is the first report on the characterization of a bacteriocin produced by a strictly anaerobic bacterium from human fecal microbiota.

Trypsin Mediates Growth Phase-Dependent Transcriptional Regulation of Genes Involved in Biosynthesis of Ruminococcin A, a Lantibiotic Produced by a Ruminococcus gnavus Strain from a Human Intestinal Microbiota

Ruminococcin A (RumA) is a trypsin-dependent lantibiotic produced by Ruminococcus gnavus E1, a gram-positive strict anaerobic strain isolated from a human intestinal microbiota. A 12.8-kb region from R. gnavus E1 chromosome, containing the biosynthetic gene cluster of RumA, has been cloned and sequenced. It consisted of 13 open reading frames, organized in three operons with predicted functions in lantibiotic biosynthesis, signal transduction regulation, and immunity. One unusual feature of the locus is the presence of three almost identical structural genes, all of them encoding the RumA precursor. In order to determine the role of trypsin in RumA production, the transcription of the rum genes has been investigated under inducing and noninducing conditions. Trypsin activity is needed for the growth phase-dependent transcriptional activation of RumA operons. Our results suggest that bacteriocin production by R. gnavus E1 is controlled through a complex signaling mechanism involving the proteolytic processing of a putative extracellular inducer-peptide by trypsin, a specific environmental cue of the digestive ecosystem.

Characterization of ISRgn1, a Novel Insertion Sequence of the IS3 Family Isolated from a Bacteriocin-Negative Mutant of Ruminococcus gnavus E1

ABSTRACT ISRgn1, an insertion sequence of the IS3 family, has been identified in the genome of a bacteriocin-negative mutant of Ruminococcus gnavus E1. The copy number of ISRgn1 in R. gnavus E1, as well as its distribution among phylogenetically E1-related strains, has been determined. Results obtained suggest that ISRgn1 is not indigenous to the R. gnavus phylogenetic group but that it can transpose in this bacterium.

Évolution de la flore microbienne caecale après isolement chirurgical du gros intestin chez le porc

Summary An ileo-rectal anastomosis was created in growing pigs. The caecum and colon were left in place and their contents slowly emptied through a cannula located in the distal colon; accordingly, no food arrived in this caeco-colic compartment. Animals were slaughtered 14 to 54 days after the surgical operation. Using a quantitative differential analysis technique, the large intestine microflora were studied upon operation and at slaughter. It was observed that the number of strictly anaerobic bacteria did not vary or only slightly increased according to cell population counts. The most marked variations involved disappearance of the Lactobacillus population in all animals and disappearance of some morphological types of bacteria found in the dominant flora at the beginning of the experiment.

Genetic diversity of b -glucuronidase activity among 14 strains of the dominant human gut anaerobe Ruminococcus gnavus

Bacterial b-glucuronidase activity in the gut increases the enterohepatic circulation of toxic compounds and plays a major role in the etiology of colon cancer. Previously, we had found that the gus gene, which codes for b-glucuronidase in a dominant anaerobic species of the gut microbiota, Ruminococcus gnavus strain E1, is transcribed as part of an operon that includes three ORFs that code for b-glucoside permeases of the phosphotransferase systems. This genetic organization had never been described. We have now compared b-glucuronidase activity and the genetic environment of the gus gene in 14 strains of Ruminococcus gnavus.We found that five out of the seven glucuronidase-positive R. gnavus strains possessed another glucuronidase gene different from the gusA operon of R. gnavus E1. This dominant commensal intestinal species appears to have a high degree of genetic diversity in the genes that control b-glucuronidase activity.

Implantation d'un mutant de Escherichia coli exigeant en acide diaminopimélique dans le tube digestif de souris gnotoxéniques

Summary A DAP − auxotroph mutant of Escherichia coli DP 50 requiring DAP and thymidine for growth was used as the receptor strain in genetic engineering. It failed to be implanted in axenic mice. However, when an inoculum containing more than 10 7 bacteria/ml was used, the DAP + reverse mutant devoid of requirement for DAP became implanted. When axenic mice were previously associated with Clostridium difficile containing DAP in the cell wall, the strain DAP − became implanted even when the inoculum was too small to permit implantation in axenic mice. Conversely, C. butyricum and C. perenne , whose cell walls also contain DAP, did not allow the establishment of a DAP − mutant. In animals associated with complex human flora without enterobacteria, neither of the 2 DAP − and DAP + mutants became implanted.