Academic literature on the topic 'Chytridiomycetes'

The endosymbiotic marine protist Nephromyces was first classified as a chytridiomycete by Giard in 1888, yet its taxonomic affinities with chytridiomycetes, as well as with other groups traditionally considered fungi, remain in doubt. To supplement the morphological data on which taxonomic inferences have been based, we assayed Nephromyces for chitin, using three methods: chromatographic assays of acid hydrolysates of alkali-resistant cell residues; infrared spectral analysis; and observations of N-acetylglucosamine-specific lectin-binding properties of the surfaces of living cells. All three assays indicate the presence of chitin in Nephromyces. The possible phylogenetic implications of this finding are discussed.

The Chytridiomycete Allomyces macrogynus generates new membranes for cleavage furrow and nuclear-cap formation during gametogenesis and zoosporogenesis. Transmission electron microscopy after impregnation with a mixture of zinc iodide and osmium tetroxide clearly demonstrated changes in the endoplasmic reticulum. Endoplasmic reticulum was intensely stained but did not appear to contribute to the formation of the unstained flagellar membranes or cleavage furrows. However, the relative cytoplasmic volume of endoplasmic reticulum decreased as positively stained nuclear-cap membrane formed. These observations are consistent with the hypothesis that flagellar membranes and cleavage furrows are derived from trans-Golgi equivalents, whereas the nuclear-cap membrane is derived from the endoplasmic reticulum. Key words: Allomyces macrogynus, Chytridiomycetes, endoplasmic reticulum, gametogenesis, zoosporogenesis.

Ultrastructural details of mitosis in species of the anaerobic chytridiomycete rumen fungal genus Neocallimastix are described in an attempt to clarify the phylogeny of the genus. Mitosis and spindle formation are entirely intranuclear and start with a group of kinetochores subtending a differentiated region of the nuclear envelope adjacent to extranuclear nucleus-associated organelles. Following duplication of the nucleus-associated organelles, a bipolar spindle develops among the kinetochores and elongates as the nucleus-associated organelles separate. At metaphase the kinetochores are spread along the spindle; heterochromatin is associated with them and also lies throughout the nucleoplasm remote from the spindle. During anaphase the kinetochore microtubules shorten and the two interdigitating arrays of nonkinetochore microtubules slide apart. Karyokinesis involves medial constriction of the nucleus and the persistent nucleolus. Mitotic nuclei in young thalli bear discoidal nucleus-associated organelles which are replaced by a variable number of centrioles in older thalli. These features are dissimilar from other described chytridiomycete mitoses and indicate either a distant relationship between the Neocallimasticaceae and other chytridiomycetes or substantial changes induced in the mitotic apparatus by the specialized environment of the organisms.

The extracellular proteolytic enzymes of eight saprophytic, eucarpic, and monocentric isolates from two genera of the order Spizellomycetales and from one genus of the order Chytridiales (Chytridiomycetes) have been partially characterized. The isolectric points of the proteases were estimated from zymograms and demonstrate the existence of three types of proteolytic activity in most isolates. The proteases were tested against synthetic chromogenic peptide substrates and a selection of cations and more complex compounds, and the results suggest that parts of the extracellular proteolytic activities are due to proteases from two groups: the Ca2+ stabilized proteases and the alkaline serine proteases.Key words: serine proteases, metalloproteases, Chytridiomycetes, isoelectric focusing, chromogenic peptide substrates.

Vegetative thalli, developing sporangia, and zoospores of two new uniflagellate anaerobic chytridiomycete gut fungi, Piromyces mae sp. nov. and Piromyces dumbonica sp.nov., isolated from manure derived from the hindgut of the horse and elephant, respectively, were examined by light and electron microscopy. Piromyces mae differs from Piromyces communis by having papillae-like structures on the sporangium. Piromyces dumbonica differs from P. communis by its C-shaped elongated circumflagellar ring and characteristic organelle distribution in the zoospores. The circumflagellar rings in both new species are tilted at about 10° towards the spur in both prereleased and free zoospores. Three struts in both species connect the circumflagellar ring to the skirt and connective (a newly described perikinetosomal structure) surrounding the kinetosome opposite to the skirt. The connective interconnects the strut, skirt, scoop, kinetosome, and spur. A general model of the kinetosome and perikinetosomal apparatus is proposed for the gut fungi. This model attempts to unify and clarify previous descriptions of the apparatus in these fungi and shows the limited range of variations reported. Key words: gut fungi, Chytridiomycetes, kinetosomes, perikinetosomal apparatus.

Because ultrastructural features of zoospores are considered primary characters in Chytridiomycete systematics, computer-aided three-dimensional reconstructions of serial sections were used to analyze zoospore fine structure of Rhizophlyctis harderi, a questionable member of the genus Rhizophlyctis. A secondary centriole was parallel to the kinetosome, but the nucleus was not structurally or spatially associated with the kinetosomes. Mitochondria and cisternae associated with vesicles bounded a ribosomal aggregation in which the nucleus was partially embedded. The peripheral cytoplasm between the plasma membrane and ribosomal aggregation contained α-glycogen particles, vacuoles with osmiophilic globules, vesicles with clear matrices, and vesicles with electron-dense cores. A new, compound form of microbody – lipid globule complex (MLC) was identified. This type of MLC incorporated posteriorly located lipid globules associated with rumposomes and anteriorly located lipid globules associated with simple cisternae, microbodies, and highly branched mitochondria. Based on these and other recent observations, the concept of the type 1 MLC was redefined. Sources for variation in ultrastructural features of zoospores are discussed. Zoospore ultrastructure of R. harderi is different from that described for other chytrid zoospores. Key words: Chytridiomycetes, microbody – lipid globule complex, Rhizophlyctis, taxonomy, ultrastructure, zoospore.

The lipid composition of an obligately anaerobic bovine rumen fungus Neocallimastix frontalis, belonging to the Neo-callimasticaceae of the Chytridiomycetes, has been investigated. It consisted of 44% neutral lipids (triacylglycerol, fatty acid, and sterols) and 56% polar lipids. The fatty acid composition of this unusual fungus differed markedly from that of other members of Chytridiomycetes by the absence of long-chain polyenoic fatty acids and by the presence of a large proportion (48%) of a series of cis-monoenoic fatty acids between 14:1 and 24:1. The absence of polyunsaturated fatty acids is explained by the anaerobic life style of this organism. However, the formation of the large proportions of monoenoic fatty acids under anaerobic conditions constitutes a major difference which cannot be explained by known pathways of fatty acid biosynthesis in fungi. This result indicates that N. frontalis differs from other fungi in possessing an anaerobic pathway for monoenoic fatty acid biosynthesis.

Blastocladiella emersonii é um fungo aquático da classe dos quitridiomicetos, notável pelas mudanças morfogenéticas que ocorrem durante o seu ciclo de vida. Neste trabalho isolamos 8.495 seqüências expressas (ESTs) deste fungo, que representam 3.226 seqüências únicas putativas. Destas seqüências, 37% foram classificadas segundo o processo biológico onde estariam envolvidas, de acordo com o sistema de anotação do Gene Ontology (GO). Analisamos os perfis de expressão in silico das ESTs usando estatística Bayesiana e os resultados obtidos foram validados por Northern blot para sete perfis de expressão selecionados. Pudemos encontrar boa correlação entre vários padrões de expressão e determinados processos biológicos. Foram selecionadas algumas seqüências potencialmente envolvidas com a esporulação do fungo para melhor caracterização. Analisamos a expressão de dois genes codificando centrinas (BeCenl e BeCen2) pertencentes a subfamílias distintas. Centrinas são proteínas ligantes de cálcio envolvidas em diferentes processos como o direcionamento do aparelho flagelar e a duplicação dos centros organizadores de microtúbulos (MTOCs). Observamos que os níveis da proteína BeCenl, que não havia sido descrita em fungos, apresentam um máximo aos 150 min da esporulação, defasado do pico de expressão do seu mRNA que ocorre aos 90 min deste estágio. A proteína BeCen2 está presente em níveis constantes durante todo a ciclo de vida do fungo, embora o seu mRNA apresente um pico de expressão aos 120 min da esporulação. Experimentos de imunofluorescência localizaram a proteína BeCenl no citoplasma e no corpo basal do zoósporo. Estes dados sugerem que BeCenl atue na re-orientação e movimento dos corpos basais e BeCen2 na duplicação dos MTOCs. Investigamos também a expressão de dois genes codificando proteína-quinases dependentes de ciclina putativas (BeCdkl e BeCdk2). Apenas uma Cdk (Cdkl) foi descrita em fungos como diretamente envolvida no controle do ciclo celular. Ambos os genes apresentam expressão diferencial, com níveis máximos de mRNA para os dois casos aos 90 min da esporulação. Por outro lado, a proteína BeCdkl está presente durante todo o ciclo de vida do fungo e foi localizada no núcleo e no capacete nuclear dos zoósporos. Um transportador putativo de hexose (Bemst) foi também analisado, com base na regulação por glicose de genes envolvidos com o ciclo celular observada em eucariotos. Verificou-se que os níveis do mRNA de Bemst diminuem drasticamente durante a esporulação, mas glicose ou outras hexoses não afetaram a expressão de Bemst.
Blastocladiella emersonii is an aquatic fungus that belongs to the class of chytridiomycetes, notable for the morphogenetic processes which occur during its life cycle. In this work we have isolated 8,495 expressed sequence tags (ESTs) from this fungus, representing 3,226 putative unigenes. From these unigenes, 37% were classified into a biological process, as a result of Gene Ontology (GO) annotation. Furthermore, we analyzed the expression profile in silico of each transcript using Bayesian Statistics and seven of these profiles were validated by Northern blot analysis. In addition, we found a good correlation between several of these expression patterns and certain biological processes. Some ESTs potentially involved in the sporulation of the fungus were selected to be further characterized. We analyzed the expression of two genes encoding two centrins (BeCenl and BeCen2) of distinct subfamilies. Centrins are calcium-binding proteins involved in different processes such as basal body orientation and duplication of the microtubuleorganizing centers (MTOCs). The amount of BeCenl, a centrin ortholog not previously described in fungi, presents a maximum at 150 min of sporulation, whereas the peak of its mRNA occurs at 90 min of this stage. Protein BeCen2 presents constant levels during the entire life cycle of the fungus, even though its mRNA shows a peak of expression at 120 min of sporulation. In addition, immunofluorescent studies localized BeCenl in the cytoplasm and the basal body of zoospores. These results suggest that BeCenl plays a role in re-orientation and movement of basal bodies and BeCen2 in MTOCs duplication. We also investigated the expression of two genes encoding putative cyclin-dependent protein kinases (BeCdkl and BeCdk2). Only one type of Cdk (Cdkl) directly involved in cell cycle control has been described in other fungi. Both genes were found to be differentially expressed, with maximum mRNA levels being detected in either case at 90 min of sporulation. In contrast, BeCdk1 is present throughout the life cycle of the fungus and was immunolocalized in the nuc1eus and the nuclear cap of zoospores. A putative hexose transporter (Bemst) was also investigated, taking into account the regulation by glucose of cell cycle controlled genes in eukaryotes. We found that Bemst mRNA levels decrease drastically during sporulation, but glucose and other hexoses had no effect on Bemst expression.