Search

The carrying capacity for microflora and nematofauna was manipulated (using a bactericide, a fungicide, manure or a growing millet plant) in a poor tropical soil, in order to identify relationships between the soil microbes and nematodes and to assess the influences of these organisms on nitrogen flux. The experiment was conducted for 4 months in containers under greenhouse conditions, with analyses of soil, nematofauna and microbial characteristics at regular intervals. Manure input and initial bactericide application led to a significant increase in bacterial-feeding and fungal-feeding nematodes of coloniser-persister classes 1 and 2, respectively, whereas high manure input stimulated omnivorous nematodes (i.e. Microdorylaimus rapsus) which became the dominant trophic group. Changes in abundance of the different bacterial-feeding nematode taxa between treatments seemed to be more related to changes in the structure of the microbial communities than to the total amount of micro-organisms, as suggested by the RISA fingerprint analysis of the bacterial communities. Canonical analysis of nematode feeding guilds, combined with soil microbial and mineral nitrogen parameters as well as multiple regression showed that the bacterial-feeding nematodes influenced the inorganic N content in the soil whereas microbial biomass was determined by total nematode abundance and not by any specific trophic group. (C) 2004 Elsevier Ltd. All rights reserved.

Cantharellus garnierii sp. nov. est décrit à partir de sept récoltes provenant des maquis miniers nickélifères de Nouvelle-Calédonie. Il est signalé comme associé à Acacia spirorbis, Casuarina coltina et Nothofagus balancae au sein d'un cortège assez classique et diversifié de champignons ectomycorhiziens comprenant, entre autres, les genres Russula, Lactarius, Inocybe, Suillus, Boletus, Cantharellus... Ce taxon est caractérisé par la taille moyenne de ses carpophores, qui sont d'un jaune à jaune orangé uniforme, sa croissance le plus souvent fasciculée, sur des sols nickélifères ultrabasiques, ses spores de taille moyenne, son médiostrate relativement différencié, et enfin ses hyphes bouclées à paroi distinctement épaissie au niveau de l'épicutis. Aucune autre espèce décrite au niveau mondial ne se rapproche de C. garnierii.

20 ref. Doi: 10.1016/S0959-1524(03)00007-6; International audience; Several key compounds for the final beer flavour (higher alcohols, esters, vicinal diketones) are produced during the alcoholic fermentation phase. The paper demonstrates the possibility of obtaining various desired final aroma profiles and reducing the total process time using dynamic optimisation of three control variables: temperature, top pressure and initial yeast concentration in the fermentation tank. The optimisation is based on a sequential quadratic programming algorithm, on a dynamic model of the alcoholic fermentation and on an aroma production model. The robustness of the optimal control profile with respect to model uncertainty is discussed.

La paroi du champignon filamenteux A. fumigalus conditionne la croissance et est responsable du maintien de l'intégrité cellulaire lors de l'infection. Les protéines de la paroi de ce champignon filamenteux n'avaient pas été étudiées jusqu'à présent alors qu'elles semblent jouer un rôle essentiel dans la structuration de la paroi de la levure modèle S. cereviciae. Une approche essentiellement biochimique a permis de caractériser les protéines associées à la paroi de A..fumigatus. La majorité des protéines pariétales chez A. fumigatus sont des protéines solubles. Une seule protéine est relarguée à partir de la paroi par un traitement f3- (1 .3) glucanase : c'est une phosphatase acide qui possède une ancre GPl et dont l'expression est réprimée en présence de phosphate inorganique. Par ailleurs, une étude des protéines GPl chez A. fumigatus par génomique comparative a montré que les protéines GPI décrites comme associées de façon covalente à la paroi chez la levure n'ont pas d'homologue chez A. fumigatus. Ainsi. l'organisation des protéines au sein de la paroi de A..fumigatus est différente de celle de la levure : les protéines pariétales ne semblent pas avoir un rôle essentiel dans l'élaboration de la paroi. Ensuite, une nouvelle famille de glycoprotéines portant un N-glycane lié à un galactofuranose en position terminale a été décrite. Cette famille comprend une phospholipase C, une phosphatase alcaline et une phytase. Enfin, une analyse morphologique de deux mutants chitine synthase et gluconosyltransférase a permis d'associer la réduction de la croissance à un hyper-branchement du mycélium et à une diminution de la taille de la cellule apicale sans que l'organisation globale des polysaccharides pariétaux et le taux de croissance spécifique soient affectés.

Three thermophilic fungal strainsRhizopus homothallicus 13a,Rhizomucor pusillus S5 andRhizomucor pusillus S8 were grown in solid state fermentation on sugar cane bagasse-olive cake mixture (50% each) at 47°C for 48 h. Humidity and pH increased during fermentation, from 5.1–5.2 to 5.5–6.1 and from 64% to 69% respectively. For all strains, O2 uptake rates reached a maximum of 1.7–2.2 ml/h/g IDM (initial dry matter) at an early stage of cultivation (7.5–9 h) and high respiratory activities (μr) were obtained (1.2–1.4 h-1). The maximal O2 uptake at 48h of culture was 28.1, 31 and 33.2 ml/g IDM for strains 13a, S5 and S8 respectively. All strains produced lipolytic activities, which varied from 15 U/g IDM for strain S8 to 47 U/g IDM for strain 13a when olive oil was used as enzyme substrate. The lipolytic activity of crude enzyme extracts from strain S 8 was specific of mid-chain length fatty acid esters. There was evidence of lipase activity (active on long chain fatty acid esters) and esterase activity (active on short chain fatty acid esters) for strain 13a. The latter one was present at 24h but not at 48h of culture. The specificity pattern of strain S5 extract looked similar to that of strain 13a. After incubation in n-heptane for 8 days at 37°C., the enzyme extracts retained 65%, 66% and 84% of initial activity for strains 13a, S5 and S8 respectively.

Des échantillons de sol ont été prélevés à l'aide d'une tarière autour de quatre légumineuses arborescentes de dix ans cultivées en couloirs dans la station agroforestière de Thiénaba, au Sénégal. Les échantillons ont été collectés à cinq profondeurs et à trois distances du tronc des arbres. Pour déterminer le potentiel mycorhizien des sols, un essai biologique a été conduit en serre avec du mil. Un échantillonnage de sols a été également effectué au nord (Tunisie) et au sud (Sénégal) du Sahara. L'effectivité de souches de Rhizobium et de champignons endomycorhiziens a été testée en pépinière sur Prosopis juliflora, Prosopis chilensis et deux provenances d'Acacia raddiana. Pour toutes les parcelles, les plants élevés sur les sols prélevés en surface (0-25 cm) sont plus grands et sont plus infectés que ceux élevés sur les sols prélevés en profondeur. Le taux d'infection des plants est plus élevé pour les sols prélevés sous Acacia raddiana et près du tronc, contrairement aux autres espèces. L'infection mycorhizienne ne dépend ni du climat, ni des formations végétales. Par contre, elle diminue avec les perturbations du sol. La réponse à l'inoculation des espèces arborescentes est très variable. Cependant, les courbes de nodulation et d'infection mycorhizienne sont similaires pour les deux provenances d'Acacia raddiana. Soil cores were sampled from around four leguminous tree species in 10-year-old alley cropping plots at Thiénaba, Senegal. Samples were collected from five depths and at three distances from the trunk. To determine the inoculum potential of the soils, mycorrhizal biossay was conducted in the greenhouse using millet seedling. Soil sampling was also conducted in the North (Tunisia) and the South (Senegal) of the Sahara desert. In order to test the effectiveness of rhizobial and mycorrhizal inocula, an experiment was conducted with Prosopis juliflora, Prosopis chilensis and two provenances of Acacia raddiana. For all plots, seedlings grown in soils from the surface (0-25 cm) were larger and formed higher levels of infection than those grown in soils from 25 to 50 cm depth. Mycorrhizal infection of the seedlings was greatest in soil from Acacia raddiana plots and, unlike the other tree species, also the greatest in soil collected near the tree. Mycorrhizal infection depended neither on climate nor on plant cover. In contrast, it decreased with soil disturbance. Inoculation test showed great variation between the tree species. However, nodulation and mycorrhizal infection of the two provenances of Acacia raddiana were similar.

Nous avons effectué des inoculations ponctuelles sur le système racinaire de Medicago laciniata, cultivée in vitro La bactérie symbiotique Sinorhizobium meliloti et le champignon mycorhizien arbusculaire Glomus sp. S043 ont été utilisés. Nous avons étudié la réponse chimique du tissu racinaire en présence et en l'absence de la bactérie ou du champignon par observation en microscopie visible et à épi-fluorescence. L'inoculation ponctuelle de Sinorhizobium meliloti ou Glomus sp. S043 induit une accumulation de flavonoïdes localisée autour du point d'inoculation. Les autres zones de la racine ne présentent aucune accumulation de flavonoïdes. Il n'a été observé d'accumulation de tannins ni chez le contrôle ni dans les racines inoculées. Le rôle de ces flavonoïdes est discuté.

97 ref.; International audience; Perturbations of the yeast cell wall trigger a repair mechanism that reconfigures its molecular structure to preserve cell integrity. To investigate this mechanism, we compared the global gene expression in five mutant strains, each bearing a mutation (i.e. fks1, kre6, mnn9, gas1, and knr4 mutants) that affects in a different manner the cell wall construction. Altogether, 300 responsive genes were kept based on high stringency criteria during data processing. Functional classification of these differentially expressed genes showed a substantial subset of induced genes involved in cell wall construction and an enrichment of metabolic, energy generation, and cell defense categories, whereas families of genes belonging to transcription, protein synthesis, and cellular growth were underrepresented. Clustering methods isolated a single group of ∼80 up-regulated genes that could be considered as the stereotypical transcriptional response of the cell wall compensatory mechanism. The in silico analysis of the DNA upstream region of these co-regulated genes revealed pairwise combinations of DNA-binding sites for transcriptional factors implicated in stress and heat shock responses (Msn2/4p and Hsf1p) with Rlm1p and Swi4p, two PKC1-regulated transcription factors involved in the activation genes related to cell wall biogenesis and G1/S transition. Moreover, this computational analysis also uncovered the 6-bp 5′-AGCCTC-3′ CDRE (calcineurin-dependent response element) motif in 40% of the co-regulated genes. This motif was recently shown to be the DNA binding site for Crz1p, the major effector of calcineurin-regulated gene expression in yeast. Taken altogether, the data presented here lead to the conclusion that the cell wall compensatory mechanism, as triggered by cell wall mutations, integrates three major regulatory systems: namely the PKC1-SLT2 mitogen-activated protein kinase-signaling module, the “global stress” response mediated by Msn2/4p, and the Ca2+/calcineurin-dependent pathway. The relative importance of these regulatory systems in the cell wall compensatory mechanism is discussed.

Forty-four fungal strains capable of growing at temperatures above 50 C were isolated from different samples of soil and coconut residues collected in Mexican tropical and subtropical regions. These thermophilic and thermotolerant fungal strains were identified by microscopical analysis using standard procedures. Three species were identified: Rhizomucor pusillus (Lindt)Schipper (19 strains), Rhizopus microsporus van Tieghem (6 strains), and Aspergillus fumigatus Fresenius (19 strains). Four strains identified as Rhizopus microsporus were ascribed to the variety rhizopodiformis; however, the other two strains showed new characteristics which require further analysis, such as a homothallic sexual reproduction. Aspergillus fumigatus was found in coconut residues as a common contaminant during the isolation of other thermophilic species. Strains were isolated from samples containing a high content of lipids (mainly from coconut coprah), and accordingly extracellular lipase biosynthesis was directly confirmed in Petri dishes for every strain.

Le bois possède une structure très complexe. Les particularités de son organisation cellulaire, sa composition chimique et l'identité génétique de chaque espèce conditionnent ses propriétés parmi lesquelles sa sensibilité vis-à-vis des agents biologiques. Champignons et insectes attaquent le bois, brisant sa structure cellulaire en altérant ses caractéristiques physiques et esthétiques. Les champignons de pourritures cubique, fibreuse ou molle, en utilisant les différents constituants du bois comme source carbonée, engendrent sa dégradation en provoquant des altérations profondes et irréversibles de toutes ses propriétés, couleur, dureté, propriétés mécaniques. Ces propriétés catalytiques fondamentales au bon fonctionnement de la plupart des écosystèmes terrestres représentent une nuisance grave pour les bois mis en service. Mieux connaître les organismes impliqués dans ces dégradations afin de s'en protéger pour assurer la durabilité du bois mis en service doit permettre de déterminer l'exacte quantité du pesticide requis pour une préservation du bois efficace et respectueuse de l'environnement. Pour cela, le CIRAD-Forêt a entrepris une caractérisation moléculaire des 800 souches de sa collection de champignons lignivores. Ainsi, les régions de l'ADN ribosomique nucléaire comprenant les parties ITS1, ITS2 et 5,8S de 103 Aphyllophorales ont été amplifiées par PCR en utilisant les amorces ITS1 et ITS4. L'analyse des poids moléculaires des amplifiats a permis de mettre en évidence un polymorphisme de longueur de cette région permettant de définir deux principaux groupes d'isolats: un premier avec un ITS ayant une longueur voisine de 635 paires de bases et un second avec une longueur voisine de 725 paires de bases. L'utilisation d'enzymes de restriction a permis de préciser la caractérisation de ces isolats et d'en révéler la diversité. Enfin, le séquençage des amplifiats obtenus avec les amorces ITS1 et ITS4 a été réalisé sur 69 souches parmi les 103 initialement étudiées. Les comparaisons de ces séquences entre-elles et avec des séquences de la base de données NCBI ont permis de mettre en évidence des variabilités inter et intraspécifiques importantes, de nature à remettre en cause la détermination des souches ou la systématique de certains groupes comme tes Spongipelis spp. et les Antrodia spp. Par ailleurs, le positionnement phylogénétique de ces différents groupes met en évidence des clusters de souches de pourriture cubique distinct des clusters de souches de pourritures fibreuses. (Texte intégral)

Comparative analyses of volatile aroma compounds of the Pleurotus ostreatus JMO.95 fruit-body and its corresponding mycelium grown in liquid, on agar surface, or on solid support cultures have been carried out by dynamic headspace concentration using GC/MS and GC/sniffing. The aroma of the fruit-body was due essentially to the presence of octan-3-one and, in a lesser extent, to the presence of octan-3-ol. Other compounds, such as oct-l-en-3-ol, oct-l-en, 2-methylbutanol and a-pinene were also present in low concentrations. The comparison of the aromatic spectra of the fruit-body with the aromatic spectra of mycelia obtained under different culture conditions indicated that the main aromatic compounds present in the P. ostreatus fruit-body were also produced by the mycelium and generally in the same proportions, except for culture under submerged conditions.

74 ref.; Plants are continuously exposed to attack by potential phytopathogens. Disease prevention requires pathogen recognition and the induction of a multifaceted defense response. We are studying the non-host disease resistance response of parsley to the oomycete, Phytophthora sojae using a cell culture-based system. Receptor-mediated recognition of P. sojae may be achieved through a thirteen amino acid peptide sequence (Pep-13) present within an abundant cell wall transglutaminase. Following recognition of this elicitor molecule, parsley cells mount a defense response, which includes the generation of reactive oxygen species (ROS) and transcriptional activation of genes encoding pathogenesis-related (PR) proteins or enzymes involved in the synthesis of antimicrobial phytoalexins. Treatment of parsley cells with the NADPH oxidase inhibitor, diphenylene iodonium (DPI), blocked both Pep-13-induced phytoalexin production and the accumulation of transcripts encoding enzymes involved in their synthesis. In contrast, DPI treatment had no effect upon Pep-13-induced PRgene expression, suggesting the existence of an oxidative burst-independent mechanism for the transcriptional activation ofPR genes. The use of specific antibodies enabled the identification of three parsley mitogen-activated protein kinases (MAPKs) that are activated within the signal transduction pathway(s) triggered following recognition of Pep-13. Other environmental challenges failed to activate these kinases in parsley cells, suggesting that their activation plays a key role in defense signal transduction. Moreover, by making use of a protoplast co-transfection system overexpressing wild-type and loss-of-function MAPK mutants, we show an essential role for post-translational phosphorylation and activation of MAPKs for oxidative burst-independentPR promoter activation.

Comparative analyses of the production of volatile compounds by Pleurotus ostreatus JMO.95 fruit body and its corresponding mycelium grown in liquid, on agar surface, and on solid support cultures were carried out by dynamic headspace concentration using gas chromatography/mass spectrometry and gas chromatography sniffing. The aroma produced by fruit body was owing essentially to the presence of octan-3-one and, to a lesser extent, to octan-3-ol. Other compounds, such as oct-1-en-3-ol, oct-1-en, 2-methylbutanol, and alpha-pinene were also present in low concentrations. Comparison of aromatic spectra of the fruit body with that of mycelia obtained under different culture conditions indicated that the main aromatic compounds present in the P. ostreatus fruit body and mycelium were produced in the same proportions on agar surface and on solid support culture, but not under submerged conditions.

In the traditional popular culture there are over ten different varieties of mushrooms growing in the Polish territory that are in use. A few of them used to be utilised as medicines. The official science doesn't reflect this use. Only four species of mushrooms are described in seven studied polish pharmacopoeias from the MX and XX centuries: two polypores, medicinal yeast and ergot. In the first Polish pharmacopoeia - Pharmaopoeia Regni Poloniae published in 1817 Boletus igniarius and Boletu...

International audience; Selected strains of ectomycorrhizal fungi can be inoculated in forest nurseries to improve survival and growth of seedlings or cuttings after field transplantation. The survival of the American strain Laccaria bicolor S238N on Douglas fir cuttings was evaluated in nursery and field conditions three years after outplanting using morphological and PCR/RFLP of nuclear rDNA spacers. The comparison of the mycorrhizal status of Douglas fir cuttings at the end of the nursery phase and two years after outplanting shown several behaviours among the ectomycorrhizal fungi naturally occurring in the nursery or artificially introduced. The naturally occurring Rhizopogon type disappeared after outplanting, while the inoculated strain Laccaria bicolor S238N and an unknown type (1/2 ITS ribotype) survived and competed with the naturally occurring fungi of the outplanting site. Only one indigenous type (1/3 ITS ribotype) seemed occurring in the outplanting site where Cenococcum geophilum was almost completely absent.; Des souches sélectionnées de champignons ectomycorhiziens peuvent être inoculées en pépinières forestières afin d'améliorer la survie et la croissance des plants après transplantation en forêt. La survie de la souche fongique américaine Laccaria bicolor S238N associée à des plants de Douglas issus de boutures a été évaluée en pépinière et trois ans après la transplantation sur un site de reboisement par description morphologique et utilisation d'outils moléculaires (PCR/RFLP de l'ADN ribosomal nucléaire). La comparaison du statut mycorhizien des plants de Douglas à la fin de la phase de pépinière et trois ans après la transplantation a permis de mettre en évidence plusieurs différences de comportement entre les espèces fongiques naturelles ou introduites de la pépinière. Le Rhizopogon naturellement présent en pépinière disparaît après transplantation, alors que la souche inoculée Laccaria bicolor S238N et un type inconnu (ribotype 1/2 ITS) survivent et montrent une bonne capacité de compétition avec les espèces fongiques naturelles du site de plantation. Seul un ribotype indigène semble avoir une capacité de compétition importante sur le site de plantation où Cenococcum geophilum est presque complètement absent.

The effects of simulated N deposition on the ectomycorrhizal and total macrofungal community in a subalpine Picea abies stand were investigated by adding 150 kg N ha-1year-1 as ammonium nitrate as a long-term fertilizer. Ectomycorrhizal diversity was studied 1) above-ground in terms of sporocarp production, including three years of recording before N addition, and 2) below-ground by PCR-RFLP analysis of the ITS region of rDNA extracted from single mycorrhizal root tips before and after one and two years of fertilization in treated and control plots. Sporocarp surveys revealed a strong impact of increased N input on the ectomycorrhizal community by drastically decreasing species diversity already one year after the start of N addition, whereas the saprobic fungal community was not affected. The impact of N addition on below-ground ectomycorrhizal diversity was less pronounced. No change in the number of ectomycorrhizal taxa and Simpson's index of diversity was found. However, ordination analysis as well as comparison of similarities among control and treated plots indicated a change in below-ground species composition two years after N addition. Significant changes in abundances of single species were observed in fertilized plots. Eleven out of 25 species which produced conspicuous sporocarps in the six years of survey were identified on the root system. These species accounted for approx. 25% of all sampled root tips. At least 44% of all ectomycorrhizas, comprising nine different RFLP-types, were formed by species belonging to the Thelephoraceae and Corticiaceae, taxa which produce inconspicuous sporocarps. Our data indicate that the abundance of these species on the root system increases at higher N concentrations, whereas the abundance of species which produce fewer sporocarps after N input decreases.

This paper presents evidence for strong biochemical weathering of basaltic outcrops induced by fungal communities in a cold environment. Weathering rind formation is considered to be a consequence of the biological activity. Comparisons between in vitro experiments and in situ observations allow a characterization of fungi effects on rocks and help to define the place of these microorganisms in the cold environment weathering chain. It is concluded that biological weathering is chronologically the first process of weathering, probably leading to the subsequent expression of cryogenic processes. Information presented here suggests the need for reconsideration of the traditional frost-driven morphogenetic system normally considered for sub-polar areas.

Undesirable protease production by Aspergillus niger Aa-20 in submerged culture and solid-state culture was evaluated using different concentrations of tannic acid as sole carbon source in a model system designed for tannase production. Protease production was found to be dependent on the culture system used (submerged culture or solid-state culture) and on the initial tannic acid concentration. Expression of protease activity in submerged culture was higher (up to 10 times) than activity obtained in solid-state culture, using identical culture medium composition. In submerged culture, the lowest final protease activity (0.13 IU) was obtained with the highest tannic acid concentration, while in solid-state culture protease activity was not affected by changes in initial substrate concentration. Absence of detectable proteolytic activity in solid-state culture is related to high production of tannase enzyme. Hence, the use of solid-state culture for fungal enzyme production may allow for higher and more stable enzyme titers present in culture extracts.

Filamentous fungi of the genus Cylindrocladium are known since many years to be partly responsible for root necrotic lesions that induce root breakage and toppling disease in banana cropping systems. Until now the implicated taxa have never been typed probably because species are difficult to identify in this genus. Consequently a multiphasic diversity study aimed at characterizing these species and developing a molecular diagnostic tool of Cylindrocladium species was undertaken. Phenotypic and biological analysis of Cylindrocladium isolates from the banana rhizosphere yielded a structuration according to 5 morphotypes with different geographical distribution. Isolates from MTl , MT3, MT4 and MT5 morphotypes could not be clearly identified by their phenotypic traits because of their similarity with different complexes of morphologically similar species. MT2 isolates seemed to be conspecific with the species Cy. spathiphylli. Analysis of ribosomal DNA spacers polymorphism pointed out the conserved nature of ITS region in the genus Cylindrocladium whereas the IGS region displayed polymorphism that can easily be used for discrimination of species. CAPS on the amplified intergenic spacer represent a rapid and reliable molecular diagnostic tool of Cylindrocladium species that can easily be transferred in banana producing zones. It revealed that MT2 and MT5 isolates are respectively conspecific with the species Cy. spathiphylli and Cy. gracile while MT3 and MT4 are related to the species Cy. scoparium and Cy. floridanum sensu lato. Despite their atypical phenotype, MTl isolates were shown to be closely related to the species Cy. gracile. RAPD markers revealed that they only have 60% genetic similarity with this species. Taking into account their overall characteristics, they were further recognized as a related undescribed species called Cy. macrogracile. Pathogenicity evaluation of these 5 taxa towards banana yielded that Cy. spathiphylli and Cy. macrogracile as respectively highly and moderately aggressive on the variety Grande-Naine (AAA). The 3 other species showed weak to no pathogenicity. Inoculation of 6 different banana genotypes revealed significant differences in susceptibility, but no true differential interactions between isolates and banana genotypes. RAPD markers also indicated a low genetic variation within the species Cy. spathiphylli and Cy. macrogracile therefore suggesting their possible clonal propagation in banana cropping systems. Within Cy. spathiphylli a partition according to host separated isolates originating from bananas to those coming from heliconias. This partition was illustrated at different levels by rDNA spacers polymorphism, RAPD markers and pathogenicity on bananas. This study offers many challenging research perspectives among which the possibility to develop from the IGS region species-specific PCR primers that could further simplify identification of these fungi and favour the development of detection tests from plant or soil samples.

Summary • The influence of two fluorescent pseudomonads strains (HR13 and HR26) on the ectomycorrhizal symbiosis between Pisolithus alba and Acacia holosericea is reported here. • We measured ectomycorrhizal establishment, fungal growth in the soil (by HPLC) and soil microbial biomass (using the fumigation–extraction method) in treatments with or without pseudomonads. • Bacteria inoculated with the fungal symbiont stimulated ectomycorrhizal formation and shoot or root biomass. Only HR13 significantly increased fungal biomass in the soil. The bacteria stimulated fungal growth and production of phenolic compounds. Sequence analysis of the two fluorescent Pseudomonas revealed 99% homologuey between HR13 and P. monteilii, and 98% between HR26 and P. resinovorans. • It is clear that some bacteria (Mycorrhiza Helper Bacteria) can stimulate the establishment of the ectomycorrhizal symbiosis in tropical conditions.

International audience

Studies were carried out to evaluate solid-state fermentation (SSF) for the upgradation of the nutritional quality of coffee husk by degrading the caffeine and tannins present in it. SSF was carried out by Aspergillus niger LPBx in a glass column fermenter using factorial design experiments and surface response methodology to optimize bioprocess parameters such as the substrate pH and moisture content and aeration rate. The first factorial design showed that the moisture content of the substrate and aeration rate were significant factors for the degradation of toxic compounds, which was confirmed by the second factorial design too. The kinetic study showed that the degradation of toxic compounds was related to the development of the mold and its respiration and also to the consumption of the reducing sugars present in coffee husk. From the values obtained experimentally for the oxygen uptake rate and CO(2) evolved, the system determined a biomass yield (Y(x/o)) of 3.811 (g of biomass).(g of consumed O(2))(-1) and a maintenance coefficient (m) of 0.0031 (g of consumed O(2)).(g biomass of biomass)(-1).h(-1). The best results on the degradation of caffeine (90%) and tannins (57%) were achieved when SSF was carried out with a 30 mL.min(-1) aeration rate using coffee husk having a 55% initial moisture content. The inoculation rate did not affect the metabolization of the toxic compounds by the fungal culture. After SSF, the protein content of the husk was increased to 10.6%, which was more than double that of the unfermented husk (5.2%).

Studies were performed to appreciate the presence of micro-organisms able to degrade OLA, in earthworms casts or in the surroundings. Worms were grown in biosynthesol, an artificial soil. The counting of bacteria and fungi in earthworms casts and in biosynthesol without earthworms suggested that earthworms ate some of the micro-organisms. The main filamentous fungi genera found were Aspergillus, Trichoderma, Fusarium and Penicillium. Previous results in the literature have shown that some species from the Aspergillus and Fusarium genera were able to degrade OLA and other aliphatic esters. It could be suggested that these two genera and some bacteria were responsible for the pre-degradation of OLA, and that earthworms might eat them. Já mostramos que a minhoca Eisenia andrei é capaz de bioassimilar o OLA (oligomeros de ácido lático), uma vez que este último tenha sido pré-digerido por microorganismos. A fim de verificar a presênça de microorganismos capazes de degradar os oligomeros de ácido láctico (OLA), as minhocas foram criadas num solo artificial, o biosintesol. O número de bactérias e fungos nas fezes de minhocas e no biosintesol sem minhoca foi estimado, assim como o gênero dos fungos filamentosos presentes. O resultado mostra uma fraca diminuição do número de microrganismos após sua passagem no instestino das minhocas, sugerindo que as minhocas digerem alguns deles. Os principais fungos filamentosos encontrados foram Aspergillus, Trichoderma, Fusarium e Penicillium. Resultados anteriores mostraram que algumas espécies dos gêneros Aspergillus e Fusarium são capazes de degradar o OLA e outros ésteres alifáticos. Sugere-se que esses 2 gêneros e algumas bactérias são responsáveis pela pré-degradação do OLA, antes que as minhocas os comam.

*INRA UMR Sécurité et Qualité des Aliments d'Origine Végétale, Centre d'Avignon Diffusion du document : INRA UMR Sécurité et Qualité des Aliments d'Origine Végétale, Centre d'Avignon Diplôme : Dr. d'Université

Les champignons pathogènes ont été les premiers organismes reconnus responsables des maladies des plantes. Ils sont nombreux à l'origine des maladies de feuilles, de racines, de fruits ou des maladies systémiques provoquant des dépérissements généralisés. L'identification des champignons a longtemps reposé sur des critères morphologiques, ce qui était insuffisant. Des critères plus fins ainsi que des critères physiologiques ou la compatibilité sexuelle ont permis d'affiner la distinction des espèces fongiques. La variabilité génétique, incluant la variabilité du pouvoir pathogène, au sein d'une même espèce est d'un intérêt de plus en plus grand. Les maladies bactériennes n'ont été découvertes que bien plus tard, de même que les maladies à phytoplasmes, à virus et encore plus récemment à viroïdes. Les nématodes comptent aussi parmi les agents pathogènes des maladies des cultures pérennes tropicales. Enfin, des dépérissements dont on a tout lieu de penser qu'ils sont des maladies en raison de leur symptomatologie et de leur schéma de propagation, restent encore d'étiologie inconnue. Outre cette diversité d'agents pathogènes eux-mêmes, il est intéressant de noter la variabilité au sein de chaque espèce, variabilité biologique, sérologique, moléculaire, se traduisant souvent par des variations de l'agressivité. Les études étiologiques doivent s'accompagner de recherche sur les modes de propagation du parasite, en particulier quand la vection se fait par un insecte, un nématode ou encore un champignon

This work was carried out to determine the influence of the duration of fallow and of physico-chemical components of soils on the distribution of endomycorrhizal fungal spores and the mycorrhizal soil infectivity. The mycorrhization of indigenous plants from the fallows was examined and it was concluded that, except for Cassia obtusifolia, fungal colonization was poorly developed. No correlation was established between spore populations and duration of fallow or between grazed and fenced areas. The relationships between abundance of mycorrhizal spores and the physico-chemical characteristics of the soils were markedly variable among species of mycorrhizal fungi. The results did not provide evidence of a beneficial effect of increased length of fallowing on mycorrhizal soil infectivity, but they did demonstrated the positive effect of preventing grazing on the re-establishment of vegetation during the fallow period.

The colonization dynamics of the black truffle in an artificial field were assessed through analyses of microsatellite and RAPD markers. The truffle field was composed of three tree species and mycelial inoculum of three different origins, and was monitored for the first three years of truffle production. We found very low levels of genetic diversity. Isolation by distance was detected only at the between-tree level. This could be interpreted as local colonization around each tree facilitated by the presence of the tree root system. At the larger spatial scale of the European range, the absence of isolation by distance corroborates the hypothesis of an impact of glaciation on genetic variation, followed by rapid postglaciation demographic expansion. In addition, genetic variation of harvested truffles was explained by neither inoculation origin, nor tree species. Our study questions the real impact of man-made inoculation of tree root systems with fungal mycelia.

Après avoir été déposés par les glaciers, les sédiments morainiques subissent une dégradation météorique plus ou moins lente, plus ou moins intense. Parmi lesprocessus de destruction, l'altération biochimique peut jouer un rôle non négligeable, à côté voire antérieurement aux processus mieux reconnus et plusétudiés dans les milieux froids : gélifraction ou microgélifraction. Cette étude se propose de décrire certains des agents biologiques (micro-champignons) en action sur les surfaces détritiques au sud de l'Islande et de déterminer leurs effets sur les minéraux des roches basaltiques en comparant observations de terrain etexpérimentations en laboratoire.

Studies were carried out on detoxification of coffee husk in solid state fermentation using three different strains of Rhizopus, Phanerochaete, and Aspergillus sp. Fungal strains were selected by their ability to grow on a coffee husk extract-agar medium. Using R. arrizus LPB-79, the best results on the degradation of caffeine (87%) and tannins (65%) were obtained with pH 6.0 and moisture 60% in 6 days. When P. chrysosporium BK was used, maximum degradation of caffeine and tannins were 70.8 and 45%, respectively, with coffee husk having 65% moisture and pH 5.5 in 14 days. The Aspergillus strain, isolated from the coffee husk, showed best biomass formation on coffee husk extract-agar medium. Optimization assays were conducted using factorial design, and surface response experiments with Aspergillus sp. The best detoxification rates achieved were 92% for caffeine and 65% for tannins. The results showed good prospects of using these fungal strains, in particular Aspergillus sp., for the detoxification of coffee husk.

Functional compatibility between thirteen tropical fruit trees (Afzelia africana Smith., Adansonia digitata L., Aphania senegalensis Radlk., Anacardium occidentale L., Cordyla pinnata (Lepr. ex A. Rich.) Milne-Redhead, Dialium guineensis Wild., Landolphia heudelottii A.DC., Sclerocarya birrea (A.Roch.) Hochst., Saba senegalensis (A. DC.) Pichon and four reference hosts Balanites aegyptiaca (L.) Del., Parkia biglobosa (Jacq.), Tamarindus indien L. and Zizyphus mauritiana Lam.) and two arbuscular mycorrhizal fungi (AMF) (Glomus aggregatum Schenck and Smith emend. Schenck and Glomus intraradices Schenck and Smith), was investigated. Marked differences were found between them in terms of mycorrhizal formation, root colonization, relative mycorrhizal dependency (RMD) and phosphorus concentrations in shoot tissues. A. africana, L. heudelottii and S. senegalensis did not form symbiotic associations, and the growth of A. africana decreased following mycorrhizal inoculation, while L. heudelottii and S. senegalensis showed no dependency. In contrast, A. digitata, A. senegalensis, A. occidentale, B. aegyptiaca and S. birrea were well colonized with AMF, but did not significantly increase in biomass production. Five fruit trees did, however, show dependency by a positive interaction with G. aggregatum, the most effective AMF. Z. mauritiana was found to be very highly dependent (RMD > 75%), T. indica was highly dependent (50-75% RMD), and D. guineensis, P. biglobosa and C. pinnata were moderately dependent (25-50% RMD). Phosphorus absorption probably contributed to this dependency more than the absorption of potassium. These results indicate that some tropical fruit trees do derive benefits from AM inoculation, while others do not.

International audience

Recherche de molécules possedant une activité anti-auxinique dans les hyphes des champignons ectomycorhiziens n'accumulant pas d'hypaphorine

Six methods to determine the activity of tannase produced by Aspergillus niger Aa-20 on polyurethane foam by solid state fermentation, which included two titrimetric techniques, three spectrophotometric methods and one HPLC assay were tested and compared. All methods assayed enabled the measurement of extracellular tannase activity. However, only five were useful to evaluate intracellular tannase activity. Studies on the effect of pH on tannase extraction demonstrated that tannase activity was considerably under-estimated when its extraction was carried out at pH values below 5.5 and above 6.0. Results showed that the HPLC technique and the modified Bajpai and Patil methods presented several advantages in comparison to the other methods tested.Seis métodos para determinar a atividade de tannase produzida por Aspergillus niger O Aa-20 em espuma de polyuretano por fermentação em estado sólido foram estudados. Duas técnicas titulométricas , três métodos spectrofotométricos e um método por HPLC foram testados e comparados. Todos os métodos testados permitiram determinar a atividade da tannase produzida extracelularmente. Entretanto, somente cinco se mostraram úteis para avaliar a atividade da tannase produzida intracelularmente. Os estudos do efeito do pH na extração de tannase demonstraram que a atividade de tannase era consideravelmente subestimada quando sua extração foi executada em valores de pH inferiores a 5.5 e superior a pH 6.0. Os resultados demostraram que a técnica de HPLC o método Bajpai and Patil modificado apresentam várias vantagens em comparação aos outros métodos testados.

Des maladies de toute nature sont transmises ou favorisées par les insectes. Ils sont indispensables dans le cas de maladies à agents pathogènes intraphloémiques : les phytoplasmes, certains virus, les bactéries et les trypanosomides. Les insectes peuvent jouer un rôle dans la vection ou dans le développement d'autres organismes tels que les nématodes, voire les champignons. La mise en évidence puis l'étude de ces divers vecteurs sont d'une grande importance car, dans la majorité des cas, ils entrent dans la politique générale de lutte contre les maladies. La lutte peut se faire de différentes manières grâce à des traitements chimiques bien ciblés et souvent par des moyens strictement biologiques à l'aide de parasitoïdes. Des techniques culturales peuvent permettre de réduire, voire d'éliminer, un vecteur. Le piégeage des insectes vecteurs peut contribuer également pour une large part à la réduction de l'impact d'une maladie

This study compares the origin and activities of glycolytic enzymes present in the gut contents of some geophagous adult earthworms and demonstrates that all the species did not develop mutualistic relationships with the ingested microorganisms to digest soil organic matter. Although the glycolytic activities were rather weak in the earthworms studied, they possess quite a complete enzymatic system that allows to degrade root and fungal substrates available in soils. #Millsonia anomala$ Omo. from Lamto (Côte d'Ivoire) and #Hormogaster elisae$ Alvarez from El Molar (Madrid) developed a strong mutualistic earthworm-microflora digestion system for hydrolysing cellulose : cellulase produced by inested microflora is able to degrade cellulose to cellobiose, cellobiase released by the worm itself breaks down cellobiose into D-glucose. Both enzymes found in intestinal contents of #Pontoscolex corethrurus$ Müll. from Palma Sola, Veracruz (Mexico) were produced by ingested soil microflora since they were not found in gut tissue culture. On the contrary, #Polypheretima elongata$ Perr. from Sainte Anne (Martinique), #Hyperiodrilus africanus$ Bedd. and #Dichogaster terrae nigrae$ Omo. et Vld. from Lamto (Cîte d'Ivoire) possess a complete enzymatic system for hydrolyzing cellulose. They could synthesize cellulolytic enzymes, i.e. cellulase and cellobiase by themselves. In the course of their digestion, geophagous earthworms seem to display variable adaptive characters which are undoubtedly linked to the different ecological categories and niches. (Résumé d'auteur)

L'Institut de Recherche pour le Développement (IRD) a pour objectif la conduite de recherches avec des partenaires scientifiques des pays du Sud sur des thèmes importants pour le développement de ces pays. Depuis une quinzaine d'années, la dépollution et la valorisation des déchets agricoles et agro-industriels constituent l'un des trois principaux thèmes de recherche des microbiologistes regroupant leurs activités au sein d'un Programme de l'IRD intitulé "Utilisation de la biodiversité microbienne pour la valorisation des ressources tropicales". Ces recherches sont orientées d'une part vers les activités microbiennes anaérobies et la méthanisation, et d'autre part vers les processus microbiens dits de "fermentation en milieu solide" (FMS) impliquant principalement des champignons et des groupes bactériens tels que les bactéries lactiques. Ces deux orientations conditionnent le classement en trois grands groupes des résidus agricoles et agro-industriels pouvant constituer une source de pollution importante dans les pays du Sud et du Nord. Différents exemples de projets de recherche achevés ou en cours sont résumés en indiquant pour chacun d'eux (1) la nature du problème, (2) l'approche microbiologique du problème et (3) l'état de la valorisation pratique de ces résultats. Les recherches à l'IRD sur la méthanisation de sous-produits agricoles et agro-industriels tropicaux ont initialement été orientées vers la biodépollution. Les premiers travaux ont utilisé des consortiums microbiens non définis provenant de différents écosystèmes et adaptés aux produits à dépolluer. Ce n'est que récemment qu'un inoculum caractérisé a été utilisé avec succès. Ces travaux ont débouché soit sur la valorisation en milieu industriel, soit sur des essais en cours à l'échelle pilote... (D'après le résumé d'auteur)