Ultrastructural Studies of the Free Zoospore of the Rumen Phycomycete Neocallimastix frontalis

Munn, E. A.; Orpin, C. G.; Hall, F.J.

doi:10.1099/00221287-125-2-311

Cited by 18 publications

(14 citation statements)

References 17 publications

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“…On the basis of thallus morphology, general life cycle, and zoospore ultrastructure the genus was formally assigned to the Spizellomycetales in the Chytridiomycetes ). Assignment to the Chytridiomycetes was consistent with earlier data from Orpin and his colleagues (Munn et al 1981;Orpin 1975Orpin , 1977 but it is clear, as recently pointed out by Munn et al,' that the genus differs in many ways from other members of the Spizellomycetales. The highly specialized rumen environment is likely to lead to both physiological and morphological adaptations which could obscure features indicative of common ancestry with organisms from more general aquatic environments.…”

Section: Introductionsupporting

confidence: 83%

Mitosis and the phylogeny of the genus Neocallimastix

Heath¹,

Bauchop²

1985

Can. J. Bot.

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HEATH, 1. B., and T. BAUCHOP. 1985. Mitosis and the phylogeny of the genus Neocc~llirna.stix. Can. J. Bot. 63: 1595-1604. Ultrastructural details of mitosis in species of the anaerobic chytridiomycete rumen fungal genus Neocallirnastix are described in an attempt to clarify the phylogeny of the genus. Mitosis and spindle formation arc entirely intranuclear and start with a group of kinetochores subtending a differentiated region of the nuclear envelope adjacent to extranuclear nucleusassociated 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. HEATH, 1. B., et T. BAUCHOP. 1985. Mitosis and the phylogeny of the genus Neocalli~na~stix. Can. J. Bot. 63: 1595-1604.Dans une tentative pour clarifier la phylogknie du genre, les auteurs dtcrivent les dktails ultrastructuraux de la mitose chez les esp&ces fongiques du genre Neocallimnstix, des chytridiomycktes anakrobies du rumen. La mitose et la formation du fuseau sont complktement intranuclkaires et commencent avec un groupe de cinttochore; sous-tendant une region diffkrencike de l'enveloppe nuclkaire adjacente aux organelles extranuclkaires associks au noyau. A la suite de la duplication des organelles extranuclkaires associks au noyau, un fuseau binuclkaire se%dCveloppe au sein des cinttochores et s'allonge a mesure que les organelles extranuclCaires associks au noyau se skparent. A la mktaphase, les cinktochores sont ktalks le long du fuseau et

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Section: Introductionsupporting

confidence: 83%

Mitosis and the phylogeny of the genus Neocallimastix

Heath¹,

Bauchop²

1985

Can. J. Bot.

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“…The xylan was from oat spelts; the starch, soluble starch. Zoospores were harvested using the methods of Munn et al (1981).…”

Section: Methodsmentioning

confidence: 99%

Polysaccharide-degrading enzymes formed by three species of anaerobic rumen fungi grown on a range of carbohydrate substrates

Williams¹,

Orpin²

1987

Can. J. Microbiol.

119

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The range of polysaccharide-degrading enzymes formed by three anaerobic rumen fungi (Neocallimastix patriciarum, Piromonas communis, and an unidentified isolate (F] was monitored following growth on seven mono-, di-, and poly-saccharide carbohydrate substrates. Enzymes capable of degrading a variety of alpha- and beta-glucans, beta-galactans, galactomannan, and hemicellulosic arabinoxylans were present in all three isolates. Although reducing saccharides were released from pectin, polygalacturonic acid was not degraded by the preparations. Enzyme activity was present in both the zoospore and vegetative stages of the life cycle and was also detected extracellularly in culture supernatants after vegetative growth. The specific activities of the polysaccharidases were affected by the growth substrate, being lowest in preparations grown on mono- and di-saccharides, whereas polysaccharidic growth substrates resulted in increased activity of the corresponding polysaccharidases. The enzymes were, however, formed after growth on all substrates. Oligomers and monosaccharides were produced as a result of polysaccharide breakdown by the unfractionated enzyme preparations. Studies on hemicellulose (arabinoxylan) breakdown by unfractionated vegetative preparations of the three isolates indicated that their modes of action, pH optima, substrate affinities, and response to potential inhibitors were similar.

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“…Electron transport components such as cytochromes and menaquinone have not been detected in anaerobic fungi (J. Macy, personal communication) and microscopic studies suggest that mitochondria are absent [18,22]. It therefore appears that these organisms are wholly dependent upon fermentative processes for growth.…”

Section: Cellulose Fermentation By Ru-men Anaerobic Fungimentioning

confidence: 99%

The rumen anaerobic fungi

Mountfort

1987

FEMS Microbiology Letters

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The anaerobic fungi represent a new group of organisms inhabiting the rumen ecosystem and possess a life cycle alternating between a motile flagellated form (zoospore) and a non‐motile vegetative reproductive form (thallus). In vivo studies show extensive colonization of plant material suspended in the rumen indicating the fungi have a role in fiber digestion. Pure cultures of anaerobic fungi ferment cellulose to give lactate, acetate, CO2 and H2 as the major products. Ethanol and formate may also be produced. Fermentation of cellulose by the fungi in coculture with H2‐utilizing methanogens results in a shift in the fermentation pattern favouring the production of H2 (utilized in the formation of CH4) and acetate at the expense of the electron‐sink products, lactate and ethanol. It is postulated that the methanogens in reducing the partial pressure of H2, facilitate an increased passage of reducing equivalents towards the production of H2 via a pyridine‐nucleotide (PN)‐linked hydrogenase reaction. H2 is believed to be produced in microbodies of the fungi called hydrogenosomes which possess all of the enzymes necessary for this function including PN‐linked hydrogenase. Absence of mitochondria and key electron transport components in these organisms indicate a dependence wholly on fermentative processes for growth. Anaerobic fungi also participate in hemicellulose and starch degredation but it is not yet clear whether they have a role in the degradation of lignin. Simple sugars (mono‐ and disaccharides) are readily utilized and their uptake is subject to similar regulatory constraints such as is found with other micro‐organisms. Enzymological studies have revealed that anaerobic fungi release substantial amounts of endo‐acting cellulase and protease, possibly giving them a competitive advantage over rumen bacteria in the degradation of plant structural material.

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Ultrastructural Studies of the Free Zoospore of the Rumen Phycomycete Neocallimastix frontalis

Cited by 18 publications

References 17 publications

Mitosis and the phylogeny of the genus Neocallimastix

Mitosis and the phylogeny of the genus Neocallimastix

Polysaccharide-degrading enzymes formed by three species of anaerobic rumen fungi grown on a range of carbohydrate substrates

The rumen anaerobic fungi

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