Molecular cloning of a gene encoding a Chlamydia psittaci 57-kDa protein that shares antigenic determinants with ca. 60-kDa proteins present in many Gram-negative bacteria

In order to develop reagents to study the immune response of guinea pigs to infection by Chlamydia psittaci guinea pig inclusion conjunctivitis strain (GPIC), we constructed a plasmid clone bank with C. psittaci DNA. One of the recombinant clones isolated produced large amounts of a 57-kilodalton (kDa) protein that was immunoreactive with sera from GPIC infected guinea pigs. While investigating this recombinant protein, we discovered that all the Gram-negative bacteria analyzed so far have immunoreactive proteins of similar size. This protein seems to be a 'common antigen' already described in various Gram-negative bacteria.     

Mycobacterium smegmatis laminin-binding glycoprotein shares epitopes with Mycobacterium tuberculosis heparin-binding haemagglutinin

Mycobacterium tuberculosis, the causative agent of tuberculosis, produces a heparin-binding haemagglutinin adhesin (HBHA), which is involved in its epithelial adherence. To ascertain whether HBHA is also present in fast-growing mycobacteria, Mycobacterium smegmatis was studied using anti-HBHA monoclonal antibodies (mAbs). A cross-reactive protein was detected by immunoblotting of M. smegmatis whole-cell lysates. However, the M. tuberculosis HBHA-encoding gene failed to hybridize with M. smegmatis chromosomal DNA in Southern blot analyses. The M. smegmatis protein recognized by the anti-HBHA mAbs was purified by heparin-Sepharose chromatography, and its amino-terminal sequence was found to be identical to that of the previously described histone-like protein, indicating that M. smegmatis does not produce HBHA. Biochemical analysis of the M. smegmatis histone-like protein shows that it is glycosylated like HBHA. Immunoelectron microscopy demonstrated that the M. smegmatis protein is present on the mycobacterial surface, a cellular localization inconsistent with a histone-like function, but compatible with an adhesin activity. In vitro protein interaction assays showed that this glycoprotein binds to laminin, a major component of basement membranes. Therefore, the protein was called M. smegmatis laminin-binding protein (MS-LBP). MS-LBP does not appear to be involved in adherence in the absence of laminin but is responsible for the laminin-mediated mycobacterial adherence to human pneumocytes and macrophages. Homologous laminin-binding adhesins are also produced by virulent mycobacteria such as M. tuberculosis and Mycobacterium leprae, suggesting that this adherence mechanism may contribute to the pathogenesis of mycobacterial diseases.     

Enhanced bacterial virulence through exploitation of host glycosaminoglycans

Present in the extracellular matrix and membranes of virtually all animal cells, proteoglycans (PGs) are among the first host macromolecules encountered by infectious agents. Because of their wide distribution and direct accessibility, it is not surprising that pathogenic bacteria have evolved mechanisms to exploit PGs for their own purposes, including mediating attachment to target cells. This is achieved through the expression of adhesins that recognize glycosaminoglycans (GAGs) linked to the core protein of PGs. Some pathogens, such as Bordetella pertussis and Chlamydia trachomatis, may express more than one GAG-binding adhesin. Bacterial interactions with PGs may also facilitate cell invasion or systemic dissemination, as observed for Neisseria gonorrhoeae and Mycobacterium tuberculosis respectively. More-over, pathogenic bacteria can use PGs to enhance their virulence via a shedding of PGs that leads to there lease of effectors that weaken the host defences.The exploitation of PGs by pathogenic bacteria is thus a multifaceted mechanistic process directly related to the potential virulence of a number of microorganisms.     

A method to estimate acetylcholinesterase-active sites and turnover in insects

Acetylcholinesterase is the primary target of organophosphorous and carbamate insecticides. Quantitative changes in acetylcholinesterase are suspected to confer resistance to these insecticides, but a method to estimate the amount in insect is not available. A method using irreversible inhibitors has been developed. Among the irreversible inhibitors tested, 7-(methylethoxyphosphinyloxy)-1-methylquinolinium iodide, chlorpyrifos-ethyl-oxon, and coumaphos-oxon were found to be sufficiently potent and specific.     

Gene function and expression level influence the insertion/fixation dynamics of distinct transposon families in mammalian introns

Background  

Transposable elements (TEs) represent more than 45% of the human and mouse genomes. Both parasitic and mutualistic features have been shown to apply to the host-TE relationship but a comprehensive scenario of the forces driving TE fixation within mammalian genes is still missing.     

Using stable isotopes to trace origin and host plants of an African polyphagous pest and an European beneficial insect

Crop protection against insect pests requires first a good knowledge of the biology and ecology of the different pest species and the associated beneficials, in particular the spatial distribution of the populations. But the movement of insect populations in the landscape remains often poorly known and in some cases does not make it possible to know the role of the various cultivated and wild habitats in the dynamics of pest and useful insects. Stable isotopes are a tool contributing to the knowledge of host plants (13carbon/12carbon) as well as geographical origin of insects (1hydrogen/2hydrogen). The analysis of stable isotopic ratios has been performed in south-western France on populations of the hoverfly Episyrphus balteatus, one of the most important predators of the cereal aphids in Europe and on West African populations of the bollworm Helicoverpa armigera, an important polyphagous pest attacking cotton and vegetables in the Old World. Methodology, preliminary results and perspectives given by stable isotopes are presented here.