Étude des variations du nombre et de la répartition des muscles longitudinaux chez Phoronis psammophila Cori

In 21 samples, staggered over 18 months, 1725 composite muscle formulae have been established for Phoronis psammophila Cori. The study of variations of the number and distribution of longitudinal muscle bundles demonstrates the increase of the muscle number (3 or 4) with the age of the animals. This increase is displayed with difficulty because of the interactions of many phenomena, especially reproduction and so statistical tests have not indicated significance. The general and especially mean formulae of different samples do not indicate the increase of the number of muscle bundles with time, as proposed by Emig.     

Transmission experiments with pike fry (Esox Indus L.) rhabdovirus

Experimental infection of fertilized pike eggs with 'red-disease' virus produced 100% mortality in the fry. This mortality was associated with a disease that had previously been described as hydrocephalus internus, indicating that 'red-disease' and hydrocephalus are different manifestations of the same disease. The name pike fry rhabdovirus disease (PFRD) is suggested for the disease complex, and the name pike fry rhabdovirus (PFR) for the causative agent. Exposure of PFR to a Wescodyne * solution containing 25 ppm of iodine resulted in an inactivation of at least 99–99% of viral activity within 30 sec. Experimental egg transmission of PFR could be interrupted by disinfecting the eggs in a Wescodyne solution, suggesting that the virus was located on the egg surface. Conclusive evidence of a naturally occurring vertical transmission in pike culture is still lacking because, using FHM cells as a detection system, PFR could not be found in spawners and their sexual products. The susceptibility of pike fry to PFR rapidly decreases at increasing age.     

Effect of 50 S subunit proteins L5, L18 and L25 on the fluorescence of 5 S RNA-bound ethidium bromide

Among the three Escherichia coli 50 S subunit proteins L5, L18 and L25, which have an affinity for 5 S RNA, only protein L18 exerts a strong effect on the fluorescence of 5 S RNA-ethidium bromide complexes, without changing the quantum yield of the fluorescence. Proteins L5 and L25, although they have little effect on the fluorescence, have a strong stabilizing influence on the 5 S RNA-L18 complex. The results are discussed in terms of the secondary and tertiary structures of 5 S RNA in relation to ribosomal protein binding.     

The AMA1-RON complex drives Plasmodium sporozoite invasion in the mosquito and mammalian hosts

Plasmodium sporozoites that are transmitted by blood-feeding female Anopheles mosquitoes invade hepatocytes for an initial round of intracellular replication, leading to the release of merozoites that invade and multiply within red blood cells. Sporozoites and merozoites share a number of proteins that are expressed by both stages, including the Apical Membrane Antigen 1 (AMA1) and the Rhoptry Neck Proteins (RONs). Although AMA1 and RONs are essential for merozoite invasion of erythrocytes during asexual blood stage replication of the parasite, their function in sporozoites was still unclear. Here we show that AMA1 interacts with RONs in mature sporozoites. By using DiCre-mediated conditional gene deletion in P. berghei, we demonstrate that loss of AMA1, RON2 or RON4 in sporozoites impairs colonization of the mosquito salivary glands and invasion of mammalian hepatocytes, without affecting transcellular parasite migration. Three-dimensional electron microscopy data showed that sporozoites enter salivary gland cells through a ring-like structure and by forming a transient vacuole. The absence of a functional AMA1-RON complex led to an altered morphology of the entry junction, associated with epithelial cell damage. Our data establish that AMA1 and RONs facilitate host cell invasion across Plasmodium invasive stages, and suggest that sporozoites use the AMA1-RON complex to efficiently and safely enter the mosquito salivary glands to ensure successful parasite transmission. These results open up the possibility of targeting the AMA1-RON complex for transmission-blocking antimalarial strategies.     

Cucurbit Powdery Mildew: First Insights for the Identification of the Causal Agent and Screening for Resistance of Squash Genotypes (Cucurbita moschata (Duchesne ex Lam.) Duchesne ex Poir.) in Mendoza,Argentina

The cucurbit powdery mildew (CPM) caused by different fungal species is a major concern for cucurbit crops around the world. In Argentina CPM constitutes the most common and damaging disease for cucurbits, especially for squash crops (Cucurbita moschata). The present study displays initial insights into the knowledge of the disease in western Argentina, including the determination of the prevalent species causing CPM, as well as the evaluation of the resistance of squash cultivars and breeding lines. Fungal colonies were isolated from samples collected in Mendoza province, Argentina. A field trial was also performed to assess the resistance of five squash accessions, including commercial cultivars and breeding lines. The severity of CPM was analyzed and epidemiological models were built based on empirical data. The morphological determinations and analysis with specific molecular markers confirmed Podosphaera xanthi as the prevalent causal agent of CPM in Mendoza. The results od the field trial showed differences in the resistance trait among the squash accessions. The advanced breeding line BL717/1 showed promising results as source of CPM resistance for the future development of open pollinated resistant cultivars, a crucial tool for an integrative control of the disease.     

Microbiota within the perennial ice cover of Lake Vida, Antarctica

Lake Vida, located in the McMurdo Dry Valleys, Antarctica, is an 'ice-sealed' lake with approximately 19 m of ice covering a highly saline water column (approximately 245 ppt). The lower portions of the ice cover and the lake beneath have been isolated from the atmosphere and land for circa 2800 years. Analysis of microbial assemblages within the perennial ice cover of the lake revealed a diverse array of bacteria and eukarya. Bacterial and eukaryal denaturing gradient gel electrophoresis phylotype profile similarities were low (<59%) between all of the depths compared (five depths spanning 11 m of the ice cover), with the greatest differences occurring between surface and deep ice. The majority of bacterial 16S rRNA gene sequences in the surface ice were related to Actinobacteria (42%) while Gammaproteobacteria (52%) dominated the deep ice community. Comparisons of assemblage composition suggest differences in ice habitability and organismal origin in the upper and lower portions of ice cover. Specifically, the upper ice cover microbiota likely reflect the modern day transport and colonization of biota from the terrestrial landscape, whereas assemblages in the deeper ice are more likely to be persistent remnant biota that originated from the ancient liquid water column of the lake that froze.     

合理利用网络资源为《微生物学》教学服务

充分利用网络上的教学资源 ,经过整理、修正、补充之后应用到微生物学的教学中 ,提高微生物学的教学质量和教学效率。     

Genotypic characterization and species identification of Fasciola spp. with implications regarding the isolates infecting goats in Vietnam

Ribosomal RNA sequences (361 or 362 bp) of the second internal transcribed spacer 2 (ITS-2) and a portion of mitochondrial cox1 (423 bp) for Fasciola spp. obtained from specimens collected in indigenous and hybrid goats and sheep in Vietnam were characterized for genotypic status and hybridization/introgression. Alignment of 48 ITS-2 sequences (also those from goats and sheep in this study) indicates that F. gigantica and F. hepatica differ typically from each other at seven sites whereas one of these is a distinguishing deletion (T) at the 327th position in F. gigantica relative to F. hepatica. The isolates from the mountainous goats in the North of Vietnam (Yen Bai province) showed the ITS-2 composition relatively identical to that of F. hepatica. The ITS-2 sequences from populations of Fasciola isolates in goats had probably experienced introgression/hybridization as reported previously in other ruminants and humans. All Vietnamese goat-of-origin specimens had high pairwise percentage of mitochondrial cox1 sequences to F. gigantica (97-100%), and very low identity to F. hepatica (91-93%), suggesting their maternal linkage to be traced to F. gigantica. The presence of hybrid and/or introgressed populations of liver flukes bearing genetic material from both F. hepatica and F. gigantica in the goats/sheep in Vietnam, regardless of indigenous or imported hosts, appears to be the first demonstration from a tropical country.