Gérard Michel

The secretion apparatus of Pseudomonas aeruginosa: identification of a fifth pseudopilin, XcpX (GspK family)

The xcp gene products in Pseudomonas aeruginosa are required for the secretion of proteins across the outer membrane. Four of the Xcp proteins, XcpT, U, V and W, present sequence homology to the subunits of type IV pili at their N‐termini, and they were therefore designated pseudopilins. In this study, we characterized the xcpX gene product, a bitopic cytoplasmic membrane protein. Remarkably, amino acid sequence comparisons also suggested that the XcpX protein resembles the pilins and pseudopilins at the N‐terminus. We show that XcpX could be processed by the prepilin peptidase, PilD/XcpA, and that the highly conserved glycine residue preceding the hydrophobic segment could not be mutated without loss of the XcpX function. We, therefore, classified XcpX (GspK) as the fifth pseudopilin of the system.

Mutual stabilization of the XcpZ and XcpY components of the secretory apparatus in Pseudomonas aeruginosa

Protein secretion in gram-negative bacteria is often dependent on the general secretory pathway (GSP). In Pseudomonas aeruginosa, this system requires at least 12 Xcp (Gsp) proteins, which are proposed to constitute a multiprotein complex localized in the bacterial envelope. Hitherto, little was known about the mutual interactions between Xcp proteins. In this study, mutants affected in the xcpZ gene encoding a bitopic inner-membrane protein were analysed to investigate the role of this protein in the architecture of the secretory machinery. The absence of XcpZ resulted in a decreased amount of XcpY. Reciprocally, XcpZ was not detectable in a xcpY mutant, demonstrating a mutual stabilization of these two proteins. These results strongly suggest that XcpZ and XcpY interact within the functional secretory apparatus.

Lymph Node Biopsy Specimens and Diagnosis of Cat-scratch Disease

Histologic analysis of lymph node biopsy specimens may verify diagnosis of this disease.

Use of Amplification and Sequencing of the 16S rRNA Gene to Diagnose Mycoplasma pneumoniae Osteomyelitis in a Patient with Hypogammaglobulinemia

A splenectomized patient with hypogammaglobulinemia who was hospitalized because of a high-grade fever subsequently developed osteomyelitis. Although pus cultures were repeatedly sterile, polymerase chain reaction (PCR) analysis with use of 16S rRNA gene primers with a broad specificity detected bacterial DNA in pus samples. Subsequent nucleotide base determination of the amplified DNA demonstrated that the detected DNA was derived from Mycoplasma pneumoniae. The results were confirmed by a PCR assay with use of M. pneumoniae-specific primers. Our findings confirm the usefulness of 16S rRNA gene amplification and analysis in the rapid and specific diagnosis of infectious osteomyelitis and reaffirm the role of such methods in detecting fastidious or uncultivable pathogens.

Identification of XcpP domains that confer functionality and specificity to the Pseudomonas aeruginosa type II secretion apparatus

Gram‐negative bacteria have evolved several types of secretion mechanisms to release proteins into the extracellular medium. One such mechanism, the type II secretory system, is a widely conserved two‐step process. The first step is the translocation of signal peptide‐bearing exoproteins across the inner membrane. The second step, the translocation across the outer membrane, involves the type II secretory apparatus or secreton. The secretons are made up of 12–15 proteins (Gsp) depending on the organism. Even though the systems are conserved, hetero‐logous secretion is mostly species restricted. Moreover, components of the secreton are not systematically exchangeable, especially with distantly related microorganisms. In closely related species, two components, the GspC and GspD (secretin) family members, confer specificity for substrate recognition and/or secreton assembly. We used Pseudomonas aeruginosa as a model organism to determine which domains of XcpP (GspC member) are involved in specificity. By constructing hybrids between XcpP and OutC, the Erwinia chrysanthemi homologue, we identified a region of 35 residues that was not exchangeable. We showed that this region might influence the stability of the XcpYZ secreton subcomplex. Remarkably, XcpP and OutC have domains, coiled‐coil and PDZ, respectively, which exhibit the same function but that are structurally different. Those two domains are exchangeable and we provided evidence that they are involved in the formation of homomultimeric complexes of XcpP.

Marseillevirus Adenitis in an 11-Month-Old Child

ABSTRACT A Marseillevirus (giant virus of amoeba) has been found in the blood and stool samples of individuals who otherwise appear to be healthy. During an attempt to define a serological cutoff for Marseillevirus by enzyme-linked immunosorbent assay (ELISA) in children, we serendipitously detected high antibody responses to Marseillevirus in an 11-month-old boy suffering from adenitis. Marseillevirus DNA was then found in his blood using PCR and with a unique sequence. We identified Marseillevirus in a lymph node using fluorescence in situ hybridization (FISH) and immunohistochemistry, and the lymph node was removed surgically. The child was declared to be cured 1 year later. We conclude that adenitis during early childhood may be caused by Marseillevirus.

Toward reconfigurable associative architecture for high speed communication operators

The renewed interest in the new associative organization is driven by advances in technologies and the increase in the need for intelligent and real-time application complexity, based on complex data structures. This paper presents a novel and practical architecture pointing to the feasibility of a structured addressable associative memory related to high speed communication protocols. This organization provides a maximum of flexibility in the mapping of the associative memory according to the need of application context in an efficient manner. In this respect, several techniques have been investigated and developed in order to solve problems inherent in many previous CAM architectures. Results of tests, allowing the architecture validation using SYMOPSYS tool and FPGA experimental board, are presented.