The lipopeptide antifungal agents, echinocandins, papulacandins, and pneumocandins, kill Candida albicans by inhibiting glucan synthesis. For this fungus, there is a good correlation of in vitro enzyme inhibition with in vitro assays of MICs. Semisynthetic lipopeptides such as cilofungin, LY303366,989,560 have activity in vivo against Aspergillus infections but appear to be inactive in broth dilution in vitro tests (MICs, > 128 ,ug/ml). To understand how compounds which lack activity in vitro can have good in vivo activity, we monitored the effect of pneumocandins on the morphology ofAspergillusf migatus and A. flavus strains by light microscopy and electron microscopy and related the changes in growth to inhibition of glucan synthesis.Pneumocandin Bo caused profound changes in hyphal growth; light micrographs showed abnormally swollen germ tubes, highly branched hyphal tips, and many cells with distended balloon shapes. Aspergillus electron micrographs confirmed that lipopeptides produce changes in cell walls; drug-treated germlings showed very stubby growth with thick walls and a conspicuous dark outer layer which was much thicker in the subapical regions. The rest of the hyphal tip ultrastructure was unaffected by the drug, indicating considerable specificity for the primary target. The drug-induced growth alteration produced very compact clumps in broth dilution wells, making it possible to score the morphological effect macroscopically. The morphological changes could be assayed quantitatively by using conventional broth microdilution susceptibility assay conditions. We defined the endpoint as the lowest concentration required to produce the morphological effect and called it the minimum effective concentration to distinguish it from the no-growth endpoints used in MIC determinations.The minimum effective concentration assay was related to inhibition of glucan synthase activity in vitro and may provide a starting point for development of susceptibility testing methods for lipopeptides.Echinocandins, pneumocandins, and papulacandins are antifungal agents which inhibit the synthesis of 1,3-p-D-glucan (22,39,43,44). ,B-Glucans are vital cell wall polymers in clinically important pathogenic fungi, including Candida and Aspergillus spp. (8). The proportion of this polysaccharide in the walls of different organisms varies, but at least 10% of the dry weight of the walls of these organisms is in the form of 1,3-p-D-glucan (4). This polysaccharide is synthesized by a membrane-associated activity which has been partially characterized in yeasts such as Candida albicans and Saccharomyces cerevisiae (31,40,46). The enzyme uses UDP-glucose as a substrate and catalyzes the polymerization of a linear polymer of 1,3-p-D-glucan reported to be 60 U (40) or as much as 700 U (35) long. The Km for UDP-glucose is approximately 2 mM, and the reaction is stimulated by nucleoside triphosphates, particularly GTP (31, 42). For both C. albicans and S. cerevisiae, the in vitro product, which is synthesized without a requirement for ...

No abstract

No abstract

Neocallimastix frontalis is an anaerobic herbivore gut inhabitant which occupies an uncertain taxonomic position, probably among zoospore fungi. It produces uninucleate zoospores which are bipartite with an organelle-free anterior portion and a posterior half bearing about 10 flagella and all organelles. The flagella are arranged primarily in two rows and beat as a unit. The flagellar roots are composed of two arrays of single microtubules, all of which emanate, in groups of about 14, from single kinetosome-associated spurs. The main array forms a divergent cone with which the microbodies (hydrogenosomes?) are intimately associated. The second group (the posterior fan) forms a fan-shaped array lying close to the posterior plasmalemma. Zoospores encyst, develop rhizoids, and can produce new zoospores at any stage in their subsequent development from a uninucleate to a multinucleate eucarpic thallus. Zoospore production involves intracytoplasmic flagellar vesicles, organelle clustering, and loss of the sporangium plasmalemma. Zoospore release follows nonlocalized dissolution of the entire sporangium wall. On these data, we assign the genus to a new family, the Neocallimasticaceae, in the Spizellomycetales of the Chytridiomycetes and thereby redefine these taxa to accommodate organisms producing polyflagellate zoospores.

No abstract

No abstract

No abstract

To clarify the phylogenetic relationships of the Chytridiomycota and the anaerobic fungi from the rumen and caecum of herbivorous animals, we analyzed the partial 18S rRNA sequences from 28 species ranging from protists to mammals and internal transcribed spacer 1 (ITS1) and its adjacent sequences from four gut fungi and one chytrid by using three algorithms from the Phylogeny Inference Package (PHYLIP). To get the confidence limits for each branch, we applied bootstrapping for each algorithm. Our analysis on partial 18S rRNA sequences shows that the Chytridiomycota are clustered with other fungi with 98, 76, and 30% confidences in the Fitch–Margoliash, neighbour-joining, and maximum parsimony algorithms. None of these three algorithms place any of 17 protists from 12 phyla with the fungi, including the chytrids. The same analysis also shows that the Spizellomycetales and Chytridiales cluster with the gut fungi but does not identify which order is closest to them. These results suggest that the Chytridiomycota, including the gut fungi, are indeed fungi but the gut fungi might not belong to the Spizellomycetales. The phylogenetic trees generated by the above three algorithms, plus the maximum likelihood algorithm, based on ITS1 and its adjacent regions show that Anaeromyces is more distant from Orpinomyces, Neocallimastix, and Piromyces. However, they failed to determine the relationships among the last three genera. Key words: Chytridiomycota, gut fungi, rumen fungi, phylogeny, rRNA sequences.