Physiology of organic nitrogen acquisition by ectomycorrhizal fungi and ectomycorrhizas

Abstract Ectomycorrhizal fungi are symbiotically associated microorganisms which ecological importance has been repeatedly demonstrated. There has been a considerable amount of research aimed at assessing the ability of ectomycorrhizal fungi and ectomycorrhizas to utilize organic nitrogen sources. The fate of soil proteins, peptides and amino acids has been studied from a number of perspectives. Exocellular hydrolytic enzymes have been detected and characterized in a number of ectomycorrhizal and ericoid fungi. Studies on amino acid transport through the plasma membrane have demonstrated the ability of ectomycorrhizal fungi to take up the products of proteolytic activities. Investigations on intracellular metabolism of amino acids have allowed the identification of the metabolic pathways involved. Possible intracellular compartmentation of amino acids will be examined by immunocytochemistry. Further translocation of amino acids in symbiotic tissues has been established by experiments using isotopic tracers, although the exact nature of the nitrogenous compounds transferred at the symbiotic interface remained unclear. One of the main future challenges in the physiology of organic nitrogen acquisition is to determine the nature, the regulation and the location of N-compound transporters at the soil-fungus and fungus-plant interfaces. The molecular approach which is just emerging in this particular research area will greatly improve our knowledge. Future research should also address the extent of competition between different ectomycorrhizal species and between different microbial populations for organic nitrogen. z 1998 Federation of European Microbiological Societies. Published by Elsevier Science B.V

HIV-1-infected patients from the French National Observatory experiencing virological failure while receiving enfuvirtide

Objectives We studied gp41 mutations associated with failing enfuvirtide salvage therapy. Methods This multicentre study involved patients with HIV-1 plasma viral load (pVL) > 5000 copies/mL after at least 3 months of uninterrupted enfuvirtide therapy and with plasma samples available at inclusion (T0), at initial enfuvirtide failure (T1) and at last follow-up visit during continued failing enfuvirtide therapy (T2). The HR-1 and HR-2 domains of the gp41 gene were sequenced at T0, T1 and T2. Results Ninety-nine patients were enrolled. At baseline, the median pVL and CD4 cell count were 5.1 log copies/mL and 72 cells/mm3, respectively. Based on the ANRS Resistance Group algorithm, the proportion of patients harbouring viruses with enfuvirtide resistance mutations increased significantly between T0 and T1. In the HR-1 domain, the V38A/M, Q40H, N42T, N43D and L45M mutations wereselected (P < 0.02). In the HR-2 domain, no mutations were significantly selected during the follow-up. None of the mutations was associated with a CD4 cell count increment. Conclusions Mutations selected during failing enfuvirtide salvage therapy are mainly located in the HR-1 domain of the gp41 gene, between codons 38 and 45. No mutations were associated with an increase in the CD4 cell coun

How Should Staphylococcal Food Poisoning Outbreaks Be Characterized?

Staphylococcal food poisoning is one of the most common food-borne diseases and results from the ingestion of staphylococcal enterotoxins (SEs) preformed in food by enterotoxigenic strains of Staphylococcus aureus. To date, more than 20 SEs have been described: SEA to SElV. All SEs have superantigenic activity whereas only a few have been proved to be emetic, representing a potential hazard for consumers. Characterization of staphylococcal food poisoning outbreaks (SFPOs) has considerably progressed compared to 80 years ago, when staphylococci were simply enumerated and only five enterotoxins were known for qualitative detection. Today, SFPOs can be characterized by a number of approaches, such as the identification of S. aureus biovars, PCR and RT-PCR methods to identify the se genes involved, immunodetection of specific SEs, and absolute quantification by mass spectrometry. An integrated gene-to-protein approach for characterizing staphylococcal food poisoning is advocated

Périgord black truffle genome uncovers evolutionary origins and mechanisms of symbiosis

LetterInternational audienceThe Périgord black truffle ($Tuber\ melanosporum$ Vittad.) and the Piedmont white truffle dominate today's truffle market. The hypogeous fruiting body of $T.\ melanosporum$ is a gastronomic delicacy produced by an ectomycorrhizal symbiont endemic to calcareous soils in southern Europe. The worldwide demand for this truffle has fuelled intense efforts at cultivation. Identification of processes that condition and trigger fruit body and symbiosis formation, ultimately leading to efficient crop production, will be facilitated by a thorough analysis of truffle genomic traits. In the ectomycorrhizal $Laccaria\ bicolor$, the expansion of gene families may have acted as a 'symbiosis toolbox'. This feature may however reflect evolution of this particular taxon and not a general trait shared by all ectomycorrhizal species. To get a better understanding of the biology and evolution of the ectomycorrhizal symbiosis, we report here the sequence of the haploid genome of $T.\ melanosporum$, which at $\sim$125 megabases is the largest and most complex fungal genome sequenced so far. This expansion results from a proliferation of transposable elements accounting for $\sim$58% of the genome. In contrast, this genome only contains $\sim$7,500 protein-coding genes with very rare multigene families. It lacks large sets of carbohydrate cleaving enzymes, but a few of them involved in degradation of plant cell walls are induced in symbiotic tissues. The latter feature and the upregulation of genes encoding for lipases and multicopper oxidases suggest that $T.\ melanosporum$ degrades its host cell walls during colonization. Symbiosis induces an increased expression of carbohydrate and amino acid transporters in both $L.\ bicolor$ and $T.\ melanosporum$, but the comparison of genomic traits in the two ectomycorrhizal fungi showed that genetic predispositions for symbiosis $-$'the symbiosis toolbox'$-$ evolved along different ways in ascomycetes and basidiomycete

Chapitre quatre. De la recherche à la formation en didactique des mathématiques à l’école primaire

Ce texte propose deux formes possibles d’articulation de la recherche et de la formation à l’enseignement des mathématiques à l’école primaire. La première recherche exposée dans le texte s’appuie sur une méthodologie qui consiste à interroger et observer des élèves hors classe, dans le bâtiment scolaire. Grâce à cette recherche nous pouvons envisager dans la formation la reprise par les étudiants de démarches qui permettent de provoquer des données interprétables dans le cadre de la théorie ..

Design of Human Machine Interfaces for a trucks anti-rollover system using a video support

This article deals with the method developed to define and characterize the Human Machine Interfaces (HMI) and the support strategies of a driver support system to avoid truck’s on the road rollover. The design of this system is the purpose of the COROLA (COncrete mixer ROLlover Avoidance) project, currently funded with the help of the European Union FEDER2008. The COROLA system is based on anticipation of environmental data (satellite positioning, vehicle speed and navigation charts) and on vehicle usage profile (load, type of load, dynamic characteristics). A projective tool has been developed to facilitate access to the representations of rollover situations in the drivers. It is based on the dynamic video media on DVD. Several HMI of the system are illustrated through short video sequences, showing the curves crossing at different levels of rollover risk. The used strategies of information processing are global, with the situation presented as a "whole" (bend, roundabout, etc.) and/or analytical, with the indication of some components of the situation (speed, direction of the curve, etc.). This method has been used in a study involving 68 professional drivers. The results allowed determining a HMI for a first mockup of the COROLA system, that will be assessed in a driving simulator

Ammonia: a candidate for nitrogen transfer at the mycorrhizal interface

International audienceIn mycorrhizal associations, the fungal partner assists its plant host with nitrogen and phosphorus uptake while obtaining photosynthetically fixed carbon. Recent studies in mycorrhiza have highlighted the potential for direct transfer of ammonia from fungal to plant cells. This presents a new perspective on nitrogen transfer at the mycorrhizal interface, which is discussed here in light of recent progress made in characterizing a large array of membrane proteins that could fulfil the function of transporting ammonia