Experimental Mycology最新文献

Balaji, B., Poulin, M. J., Vierheilig, H., and Piché Y. 1995. Responses of an arbuscular mycorrhizal fungus, Gigaspora margarita, to exudates and volatiles from the Ri T-DNA-transformed roots of nonmycorrhizal and mycorrhizal mutants of Pisum sativum L Sparkle. Experimental Mycology 19, 275-283. Transformed root cultures were established from the nonmycorrhizal (Myc^-) and mycorrhizal (Myc⁺) Pisum sativum L Sparkle mutants to study the biochemical factors necessary for initiating and maintaining the arbuscular mycorrhizal (AM) symbiosis. Root exudates produced by both the Myc^- and the Myc⁺ mutants inhibited the hyphal growth of Gigaspora margarita, whereas root volatiles from these mutants stimulated the hyphal growth significantly in the precolonization stage. Carbon dioxide is the principal volatile compound necessary for the elongation of hyphae from both the Myc^- and the Myc⁺ transformed roots. The addition of quercetin, a flavonol compound, to the medium with a Myc^- mutant enriched with an optimal CO₂ improved hyphal elongation and spreading as previously reported but did not cause Myc^- roots to become mycorrhizal. These results suggest that the root factors may stimulate or inhibit AM fungal growth and that they do not determine the mycorrhizal nature of P. sativum Sparkle mutants.

Henson, J. M., and Caesar-TonThat, T. C. 1995. Mitochondrial plasmids of the Gaeumannomyces-Phialophora complex and their detection by primed, in situ fluorescence labeling. Experimental Mycology 19, 263-274. Double-stranded, linear DNA mitochondrial plasmids were detected in most Gaeumannomyces graminis var. tritici and var. avenae isolates, but were infrequently detected in G. graminis var. graminis , and only detected once in other Gaeumannomyces or Magnaporthe species. Plasmids were 4-11 kb and were apparently blocked at their 5′ termini, as they were resistant to 5′ → 3′ exonuclease digestion. Two plasmids that shared homology were further characterized. Apparently they were not derived from the mitochondrial or nuclear genomes as they did not hybridize strongly to them. An internal fragment was cloned from one plasmid and used as a primer for primed, in situ labeling with cryosectioned hyphae. Plasmid-bearing strains had fluorescent signal in a pattern expected of a mitochondrial location for plasmids, whereas plasmid-less strains did not fluoresce. This is the first use of cryosectioned hyphae and mitochondrial probes with in situ fluorescence labeling in fungi.

Chalot, M., Finlay, R. D., Ek, H., and Söderström, B. 1995. Metabolism of [¹⁵N]alanine in the ectomycorrhizal fungus Paxillus involutus. Experimental Mycology 19, 297-304. Alanine metabolism in the ectomycorrhizal fungus Paxillus involutus was investigated using [¹⁵N]alanine. Short-term exposure of mycelial discs to [¹⁵N]alanine showed that the greatest flow of ¹⁵N was to glutamate and to aspartate. Levels of enrichment were as high as 15-20% for glutamate and 13-18% for aspartate, whereas that of alanine reached 30%. Label was also detected in the amino-N of glutamine and in serine and glycine, although at lower levels. Preincubation of mycelia with aminooxyacetate, an inhibitor of transamination reactions. resulted in complete inhibition of the flow of the label to glutamate, aspartate, and amino-N of glutamine, whereas [¹⁵N]alanine rapidly accumulated. This evidence indicates the direct involvement of alanine aminotransferase for translocation of ¹⁵N from alanine to glutamate. Alanine may be a convenient reservoir of both nitrogen and carbon.

Nadeau, M. P., Dunphy, G. B., and Boisvert, J. L. 1995. Effects of physical factors on the development of secondary conidia of Erynia conica (Zygomycetes: Entomophthorales), a pathogen of adult black flies (Diptera: Simuliidae). Experimental Mycology 19, 324-329. The effects of selected physical factors on the development of secondary type 2 conidia of Erynia conica was studied in vitro and in situ. Conidial germination and sporulation occurred without exogenous nutrients and was not influenced by substratum hardness or hydrophobicity but was influenced by pH, temperature, and charge of the substrata. Germination and sporulation occurred throughout the pH range of 5.5 to 8.0 and temperatures ranging between 5 and 30°C. Both germination and sporulation had the same optimum pH (7.5-8.0) and optimum temperature (10-20°C). The effect of temperature on the pattern of germination of conidia was similar in vitro and in situ. The infective stages of appressorial formation and penetration (observed only in situ) were more affected by temperature than was conidial germination.

Liu, W.-Z., Boucias, D. G., and McCoy, C. W. 1995. Extraction and characterization of the insecticidal toxin hirsutellin A produced by Hirsutella thompsonii var. thompsonii. Experimental Mycology 19, 254-262. Hirsutellin A (HtA) produced by Hirsutella thompsonii var. thompsonii (strain JAB-04) was extracted and purified using a combination of ion-exchange, gel-permeation, and immunoaffinity chromatography. The identity of the purified HtA was confirmed by amino acid analysis and N-terminal sequencing. Monoclonal antibodies prepared against HtA were capable of detecting 25-50 ng of HtA by direct sandwich ELISA. In addition, utilizing Western blot methods, the antibodies were shown to be specific to HtA. The production of HtA was monitored during submerged fermentation. The peak level of exocellular HtA (13-14 μg/ml) was during the late exponential growth phase (39-45 h), determined by utilizing a combination of densitometric analysis of the 16.3-kDa bands on SDS-PAGE gels and ELISA. HtA production was directly correlated with mycelial growth. Twenty-one-hour culture filtrates were highly toxic to larvae of the greater wax moth. Pure HtA at a final concentration of 40 pmol was highly toxic to Galleria mellonella larvae.

Imbert-Bernard, C., Valentin, A., Mallie, M., and Bastide, J.-M. 1995. Involvement of Candida albicans cell wall proteins in the adherence of blastospores to human buccal epithelial cells. Experimental Mycology 19, 247-253. The adherence of Candida albicans to epithelial cells is one of the first steps in the development of candidiasis and therefore could constitute an interesting target for the prevention of infection. A yeast cell wall extract was prepared by using a C. albicans isolate (IVP 1453) highly adherent to buccal epithelial cells (BECs). This cell wall extract was separated by concanavalin A-affinity chromatography into two fractions referred to as Fr1 (proteic fraction) and Fr2 (mannoproteic fraction). The adhesion activity was mostly associated with the proteic fraction. This fraction was therefore retained and further fractionated by ion-exchange chromatography into two other fractions, referred to as Fr1a and Fr1b. The adhesion activity was mostly associated with the Fr1b fraction (56.4% adherence inhibition); it was not specific to the C. albicans isolate used during the cell wall extract preparation. The Fr1b fraction contained four major proteins with molecular masses of 30, 38, 47, and 54 kDa. Among these four proteins, those with molecular masses of 38 and 54 kDa could be involved in adherence mechanisms of C. albicans to human BECs.

Lamboy, J. S., Staples, R. C., and Hoch H. C. 1995. Superoxide dismutase: A differentiation protein expressed in Uromyces germlings during early appressorium development. Experimental Mycology 19, 284-296. Germlings of the bean rust fungus Uromyces appendiculatus detect penetration sites on the surface of the host leaf by thigmosensing topographical features. Within 2-4 min after the apex of a urediospore germ tube encounters the cuticular lip of a stomate, the germling ceases polarized growth and begins to swell over the aperture. The mechanism by which the cells detect topographical signals is not understood; however, previous experiments indicated that the initiation process does not involve de novo gene expression. In order to detect posttranslational modifications, the protein profiles of induced and noninduced germlings were compared at the earliest stages of appressorium formation, and a 21-kDa differentiation protein was identified by a shift in isoelectric point. The N-terminal amino acid sequence exhibited homology with superoxide dismutase (SOD), and antibodies to a synthetic peptide fragment of the respective sequence recognized cooper/zinc isozymes of SOD in electroblots of native gels. Electroelution of the active enzyme bands and separation by SDS-PAGE indicated that the 21-kDa protein is a component of a tetrameric 85-kDa SOD.

Murayama, T., Fujisawa, Y., and Okano, Y. 1995. A suppressor mutation which suppresses adenylyl cyclase mutations in Neurospora crassa. Experimental Mycology 19, 320-323. A spontaneous suppressor mutant, hah, which suppressed the colonial growth of adenylyl cyclase mutants (cr-1) was isolated. The morphology of cr-1 hah was filamentous, but slightly different from that of wild type on solid medium. The hah strain formed many high aerial hyphae, but did not form any conidia. The expression levels of an adenylyl cyclase gene, nac, in both hah and cr-1 hah were much higher than those in wild type or in cr-1. The level of cAMP in cr-1 was very low but returned to close to the wild-type level in the cr-1 hah suppressed strain, whereas that in the strain carrying hah alone was similar to or a little higher than that in wild type. The hah gene was located 13.3 map units from inl on the right arm of the linkage group V. The hah mutation was recessive and allele specificity of hah for the suppression of cr-1 mutations was weak.

Davis, R. H., and Ristow, J. L. 1995. Osmotic effects on the polyamine pathway of Neurospora crassa. Experimental Mycology 19, 314-319. In bacteria, mammals, and certain plants, the induction of the polyamine synthetic enzyme, ornithine decarboxylase (ODC), and the accumulation of its product, putrescine, follows osmotic manipulations of cells. In at least some of these cases, this response is indispensable for survival. We wished to determine whether the polyamine pathway of Neurospora crassa was regulated in response to hyper- or hypoosmotic conditions. Unlike ODC of most other classes of organisms, the N. crassa enzyme and the accumulation of putrescine appears to be relatively indifferent to these conditions, either during sudden transitions or in steady-state. We conclude that other mechanisms of osmotic adjustment or tolerance have evolved in N. crassa and perhaps other fungi that obviate the need for putrescine accumulation.