Isabelle Guillouard

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Streptococcus thermophilus is one of the most widely used lactic acid bacteria in the dairy industry, in particular in yoghurt manufacture, where it is associated with Lactobacillus delbrueckii subsp. bulgaricus. This bacterial association, known as a proto-cooperation, is poorly documented at the molecular and regulatory levels. We thus investigate the(More)
The way in which the genes involved in cysteine biosynthesis are regulated is poorly characterized in Bacillus subtilis. We showed that CysL (formerly YwfK), a LysR-type transcriptional regulator, activates the transcription of the cysJI operon, which encodes sulfite reductase. We demonstrated that a cysL mutant and a cysJI mutant have similar phenotypes.(More)
Streptococcus thermophilus is a thermophilic lactic acid bacterium widely used as starter in the manufacture of dairy products in particular in yoghurt manufacture in combination with Lactobacillus delbrueckii ssp. bulgaricus. However, in spite of its massive use, the physiological state of S. thermophilus in milk has hardly been investigated. We(More)
Clostridium perfringens phospholipase C (PLC), also called alpha-toxin, is the major virulence factor in the pathogenesis of gas gangrene. The toxic activities of genetically engineered alpha-toxin variants harboring single amino-acid substitutions in three loops of its C-terminal domain were studied. The substitutions were made in aspartic acid residues(More)
The YtlI regulator of Bacillus subtilis activates the transcription of the ytmI operon encoding an l-cystine ABC transporter, a riboflavin kinase, and proteins of unknown function. The expression of the ytlI gene and the ytmI operon was high with methionine and reduced with sulfate. Using deletions and site-directed mutagenesis, a cis-acting DNA sequence(More)
The NH2-terminal domain of the alpha-toxin of Clostridium perfringens is highly homologous to the complete phospholipase C from Bacillus cereus (PC-PLC), for which a high-resolution crystal structure is available. This structural information was used as the basis of a site-directed mutagenesis strategy in which critical amino acid residues of alpha-toxin(More)
The lethal, cytolytic alpha-toxin (phospholipase C) of Clostridium perfringens consists of two distinct modules: the larger N-terminal domain catalyses phospholipid hydrolysis, and its activity is potentiated by a smaller C-terminal domain. Calcium ions are essential for the binding of alpha-toxin to lipid films. Sixteen alpha-toxin variants with single(More)
A Chinese hamster cell line with a mutation in the UDP-glucose pyrophosphorylase (UDPG:PP) gene leading to UDP-glucose deficiency as well as a revertant cell were previously isolated. We now show that the mutant cell is 10(5) times more sensitive to the cytotoxic effect of Clostridium perfringens phospholipase C (PLC) than the revertant cell. To clarify(More)
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