Gordon Beakes | Newcastle University (original) (raw)
Papers by Gordon Beakes
Oomycete Genetics and Genomics
y phylogenetic speculations, valueless though these are considered to bey.may stimulate studies i... more y phylogenetic speculations, valueless though these are considered to bey.may stimulate studies in the life-history, cytology, morphology etcy. and clear the way for laying the foundations of a more logical system of classification.-E. A. Bessey (1935),
Handbook of the Protists, 2017
Handbook of the Protists, 2017
Mycologia, 2000
Haptoglossa heteromorpha sp. nov. is an aplanosporic species isolated from Rhabditis nematodes fo... more Haptoglossa heteromorpha sp. nov. is an aplanosporic species isolated from Rhabditis nematodes found in cow dung samples from northeast England. Video microscopy was used to re<;ord sporangia! development and spore release. The thalli were distinguishable from previously described Haptoglossa species because they produced one or more broad dome-shaped exit papillae. The thalli were also unusual in having a series of regularly spaced vacuolar regions which appeared to collapse several minutes before spore release. The aplanospores were released from sporangia in an explosive rush from the apex of the broad dome-shaped papillae. The spores initially aggregated together in an irregular clump but later dispersed. The aplanospores were found to be of two distinct sizes (3.5 and <10.5 1-1m diam), and the resulting infection cells were morphologically distinct, even though the sporangia that produced them were morphologically indistinguishable. Small infection cells were elongate with a wide bilobed base and a narrow tapered vacuolate apex, and there was a distinct pad-like protrusion on the ventral side of the spore. The large aplanospores produced typical Haptoglossa infection cells (gun cells) which had a broad vacuolate basal region and curved sharply to a beaked apex. This is the first record of an aplanosporic species of Haptoglossa consistendy producing heteromorphic infection cells that are likely to have different mechanisms of infection.
Microbiology, 1980
Streptomycin inhibited growth and sporulation of Saprolegnia species, although variations in sens... more Streptomycin inhibited growth and sporulation of Saprolegnia species, although variations in sensitivity were recorded. In sporulating colonies, streptomycin increased both the length of the post-induction lag phase and the proportion of gemmae. Antibiotic concentrations (> 100 pg ml-l) which resulted in the leakage of potassium ions from sporulating colonies also correlated with the condensation of hyphal cytoplasm into lysed segments. In vegetative colonies grown in > 500 pg streptomycin ml-l, changes were seen in the organization of endoplasmic reticulum, mitochondria and nuclei. These inhibitory effects could be counteracted by the addition of calcium ions. Some observed effects were consistent with an impairment of normal mitochondria1 function, but others, particularly in sporulating colonies, were possibly the result of interference with cellular functions regulated by calcium or other divalent cations.
Mycological Research, 2000
Two species of Haptoglossa isolated from nematodes from cow manure from N.E. England are describe... more Two species of Haptoglossa isolated from nematodes from cow manure from N.E. England are described. H. erumpens sp. nov., infecting Bunonema nematodes, is aplanosporic, the cysts being released after rupture of the nematode cuticle in the absence of an evacuation tube. H. dickii sp. nov. is zoosporic, infecting several species of rhabditid nematodes. Aplanospores and zoospore cysts germinated to produce secondary spores (gun cells) with which to infect further nematode hosts. Some key ultrastructural features in both species have been included. Haptoglossa (Drechsler, 1940) comprises obligately endoparasitic fungi which infect nematodes and rotifers. There are presently six species, four of which are zoosporic and two of which are aplanosporic (
Mycological Research, 1990
The morphology and physiology (temperature-growth relationships) of seventeen isolates of Saprole... more The morphology and physiology (temperature-growth relationships) of seventeen isolates of Saprolegnia from fish hatcheries in Japan were compared. A linear relationship between the number of hairs per bundle against bundle length, on secondary zoospore cysts, was found. One isolate of S. parasitica, a particularly strong pathogen, from silver salmon, had a secondary zoospore cyst ornamentation consisting of separate bundles of long, short and intermediate length hairs. This feature was also seen to a lesser extent in other isolates, including a strong pathogen from brown trout in the U.K. Using the Japanese isolates, temperature-growth relationships at 30 °C distinguished isolates of S. parasitica, from rainbow trout, from those from other fish. A mutant of one of the rainbow trout isolates showed differences in growth rates compared with the parent isolate, the possible ecological significance of which is discussed.
Mycological Research, 1989
The ultrastructural architecture of the oospore-oogonium walls of Phytophthora megasperma was stu... more The ultrastructural architecture of the oospore-oogonium walls of Phytophthora megasperma was studied in the soybean (f. sp. glycinea ) and alfalfa (f. sp. medicaginis ) isolates with the major objective of elucidating changes that occur during oospore germination. For comparison, ultrastructural changes in isolated oogonium-oospore walls brought about by digestion with various β-glucanases were also examined. Major emphasis was placed on determining the structure of the conspicuous inner oospore wall (IOW). This thick (2–3 μm) layer showed little staining by any of the procedures used, including staining for polysaccharides by the Thiery procedure. There were only minor differences in electron density across the IOW. Observations on sections of whole oospores and mechanically fractured, or partially digested, walls indicated that the IOW contains microfibrils embedded in an amorphous matrix which tend to be oriented parallel to the plasma membrane. During oospore germination, the IOW is extensively eroded in a characteristic ‘scallop’ pattern that creates numerous cavities separated by radial strands of undigested wall. The electron dense outer oospore wall (OOW) remained intact and unaltered and probably confines the activity of the wall digesting enzymes to the IOW. In the digested cavities, removal of the wall matrix exposed the network of underlying microfibrils together with some electron dense globular material. Treatment of isolated oogonium-oospore walls with exo-β-1,3 glucanase or a mixture of endo-β-1,3-glucanases caused substantial digestion of the oogonium wall matrix and the IOW. Following enzymatic digestion, both the IOW and, in particular, the oogonium walls showed greater reactivity with the Thiery procedure. The observed patterns of wall digestion indicate that the amorphous β-1,3-glucan component of the IOW is extensively consumed during germination and is probably the main supply of carbon and energy for germination. No evidence of a pre-formed germination wall layer in the oospore was found. As the innermost layers of the oospore wall became digested, a new wall was produced internal to the IOW.
This review discusses the taxonomy, patterns of sporogenesis and modes of infection of a group of... more This review discusses the taxonomy, patterns of sporogenesis and modes of infection of a group of little studied holocapic pathogens of bactivorous nematodes (and rotifers) from terrestrial and marine habitats. These holocarpic obligate parasites have been traditionally placed within the "Iagenidiaceous oomycetes" although Haptoglossa had been placed in the Saprolegniales. The nematode pathogens that will be discussed fall within the genera C/amydomyzium, Gonimocheate, Haptoglossa and Myzocytiopsis. The patterns of asexual and sexual sporogenesis will be described in detail in the light of recent ultrastructural studies that we have undertaken. We conclude by discussing the main infection strategies employed by these organisms which we categorise into active and passive types. In the former, zoospores actively locate their host (by chemotaxis) and encyst on the host surface immediately prior to infection. In the latter types, the zoospores or aplanospores rapidly germinate...
Mycological Research, Oct 1, 2000
Environmental Conservation, Jun 1, 2000
![Research paper thumbnail of Corrigendum to “Ultrastructural morphogenesis of dimorphic arcuate infection (gun) cells of Haptoglossa erumpens an obligate parasite of Bunonema nematodes” [Fung. Genet. Biol. 37 (2002) 250–262]](https://attachments.academia-assets.com/73527983/thumbnails/1.jpg)
](Fungal Genet Biol, 2004
Corrigendum to ''Ultrastructural morphogenesis of dimorphic arcuate infection (gun) cells of Hapt... more Corrigendum to ''Ultrastructural morphogenesis of dimorphic arcuate infection (gun) cells of Haptoglossa erumpens an obligate parasite of Bunonema nematodes'' [Fung. Genet. Biol. 37 (2002) 250-262] q
Transactions of the British Mycological Society, 1978
Cytoplasmic changes accompanying oospore maturation in Saprolegnia furcata Maurizio have been fol... more Cytoplasmic changes accompanying oospore maturation in Saprolegnia furcata Maurizio have been followed using light and electron microscopy. The occurrence of a brief wallless stage following oosphere formation is demonstrated. Changes in the distribution within the oosphere and oospore of two reserve products, droplets of neutral lipid and membrane bound dense-body vesicles are described. At a late stage in outer oosphere wall formation, the neutral lipid becomes centrally concentrated in the cytoplasm and the dense-body vesicles move towards the periphery. Later, during the accretion of the thick inner wall these storage components briefly intermix before the dense-body granules coalesce and expand to form a prominent central vacuole, the ooplast. During its formation, the ooplast is transparent, but on maturation the dense-body granules are released into Brownian motion, giving the ooplast a characteristically granular appearance. Oospore maturation is accompanied by a reduction in the amount of endoplasmic reticulum and in the number of mitochondria and ribosomes. Golgi dictyosomes and peripheral wall vesicles are lost completely. Oospore development in Saprolegnia is compared with that in other oomycetes and the taxonomic implications are discussed.
![Research paper thumbnail of Corrigendum to ?Ultrastructural morphogenesis of dimorphic arcuate infection (gun) cells of an obligate parasite of nematodes? [Fung. Genet. Biol. 37 (2002) 250?262]](https://attachments.academia-assets.com/73527985/thumbnails/1.jpg)
](Fungal Genet Biol, 2004
Corrigendum to ''Ultrastructural morphogenesis of dimorphic arcuate infection (gun) cells of Hapt... more Corrigendum to ''Ultrastructural morphogenesis of dimorphic arcuate infection (gun) cells of Haptoglossa erumpens an obligate parasite of Bunonema nematodes'' [Fung. Genet. Biol. 37 (2002) 250-262] q
Botany, 1995
The origin and structure of cyst surface components in oomycete fungi are described in relation t... more The origin and structure of cyst surface components in oomycete fungi are described in relation to evaluating their use as taxonomic markers. The ontogeny, biochemistry, and morphological variations in the populations of peripheral vesicles that occur in the zoospores of members of the Peronosporomycetidae and Saprolegniomycetidae, which are discharged upon encystment to give rise to spore surface components, are reviewed. The use of the ornamentation of the cyst coat to define genera within the Saprolegniomycetidae and as an indicator of geographical and host-specific clones within a species of Saprolegnia are reviewed. The cyst coat of the fish pathogen Saprolegnia parasitica shows considerable morphological diversity that appears to be independent of the geographic origin of isolates. There is an indication that a group of isolates with variable, relatively short, spines form a separate clone from those with larger hooped bundles. The monoclonal antibody probes that have been generated to spore surface components of Saprolegnia parasitica, Pythiwn aphanidermatum, and Phytophthora cinnamomi are summarized and their use in defining taxonomic groups reviewed. The antibodies show different levels of specificity ranging from isolate- to order-specific reactions. The degree of specificity can be influenced in some cases by the immunoassay method used. These studies indicate that surface structures and molecules provide extremely versatile and valuable markers for use in oomycete taxonomy and phylogeny. Key words: Saprolegnia, Phytophthora, Achlya, oomycete, zoospore, cysts, ultrastructure, monoclonal antibodies, taxonomy.
Botany, 1988
... Sections were poststained in 2% uranyl acetate for 40 min and Reynold's lead citrate... more ... Sections were poststained in 2% uranyl acetate for 40 min and Reynold's lead citrate for 10 min in an LKB automatic stainer before examination in either a CORA or JEOL 100S electron microscope operated at 60 kV with 25-/Ш1 apertures. ...
Transactions of the British Mycological Society, 1984
Oomycete Genetics and Genomics
y phylogenetic speculations, valueless though these are considered to bey.may stimulate studies i... more y phylogenetic speculations, valueless though these are considered to bey.may stimulate studies in the life-history, cytology, morphology etcy. and clear the way for laying the foundations of a more logical system of classification.-E. A. Bessey (1935),
Handbook of the Protists, 2017
Handbook of the Protists, 2017
Mycologia, 2000
Haptoglossa heteromorpha sp. nov. is an aplanosporic species isolated from Rhabditis nematodes fo... more Haptoglossa heteromorpha sp. nov. is an aplanosporic species isolated from Rhabditis nematodes found in cow dung samples from northeast England. Video microscopy was used to re<;ord sporangia! development and spore release. The thalli were distinguishable from previously described Haptoglossa species because they produced one or more broad dome-shaped exit papillae. The thalli were also unusual in having a series of regularly spaced vacuolar regions which appeared to collapse several minutes before spore release. The aplanospores were released from sporangia in an explosive rush from the apex of the broad dome-shaped papillae. The spores initially aggregated together in an irregular clump but later dispersed. The aplanospores were found to be of two distinct sizes (3.5 and <10.5 1-1m diam), and the resulting infection cells were morphologically distinct, even though the sporangia that produced them were morphologically indistinguishable. Small infection cells were elongate with a wide bilobed base and a narrow tapered vacuolate apex, and there was a distinct pad-like protrusion on the ventral side of the spore. The large aplanospores produced typical Haptoglossa infection cells (gun cells) which had a broad vacuolate basal region and curved sharply to a beaked apex. This is the first record of an aplanosporic species of Haptoglossa consistendy producing heteromorphic infection cells that are likely to have different mechanisms of infection.
Microbiology, 1980
Streptomycin inhibited growth and sporulation of Saprolegnia species, although variations in sens... more Streptomycin inhibited growth and sporulation of Saprolegnia species, although variations in sensitivity were recorded. In sporulating colonies, streptomycin increased both the length of the post-induction lag phase and the proportion of gemmae. Antibiotic concentrations (> 100 pg ml-l) which resulted in the leakage of potassium ions from sporulating colonies also correlated with the condensation of hyphal cytoplasm into lysed segments. In vegetative colonies grown in > 500 pg streptomycin ml-l, changes were seen in the organization of endoplasmic reticulum, mitochondria and nuclei. These inhibitory effects could be counteracted by the addition of calcium ions. Some observed effects were consistent with an impairment of normal mitochondria1 function, but others, particularly in sporulating colonies, were possibly the result of interference with cellular functions regulated by calcium or other divalent cations.
Mycological Research, 2000
Two species of Haptoglossa isolated from nematodes from cow manure from N.E. England are describe... more Two species of Haptoglossa isolated from nematodes from cow manure from N.E. England are described. H. erumpens sp. nov., infecting Bunonema nematodes, is aplanosporic, the cysts being released after rupture of the nematode cuticle in the absence of an evacuation tube. H. dickii sp. nov. is zoosporic, infecting several species of rhabditid nematodes. Aplanospores and zoospore cysts germinated to produce secondary spores (gun cells) with which to infect further nematode hosts. Some key ultrastructural features in both species have been included. Haptoglossa (Drechsler, 1940) comprises obligately endoparasitic fungi which infect nematodes and rotifers. There are presently six species, four of which are zoosporic and two of which are aplanosporic (
Mycological Research, 1990
The morphology and physiology (temperature-growth relationships) of seventeen isolates of Saprole... more The morphology and physiology (temperature-growth relationships) of seventeen isolates of Saprolegnia from fish hatcheries in Japan were compared. A linear relationship between the number of hairs per bundle against bundle length, on secondary zoospore cysts, was found. One isolate of S. parasitica, a particularly strong pathogen, from silver salmon, had a secondary zoospore cyst ornamentation consisting of separate bundles of long, short and intermediate length hairs. This feature was also seen to a lesser extent in other isolates, including a strong pathogen from brown trout in the U.K. Using the Japanese isolates, temperature-growth relationships at 30 °C distinguished isolates of S. parasitica, from rainbow trout, from those from other fish. A mutant of one of the rainbow trout isolates showed differences in growth rates compared with the parent isolate, the possible ecological significance of which is discussed.
Mycological Research, 1989
The ultrastructural architecture of the oospore-oogonium walls of Phytophthora megasperma was stu... more The ultrastructural architecture of the oospore-oogonium walls of Phytophthora megasperma was studied in the soybean (f. sp. glycinea ) and alfalfa (f. sp. medicaginis ) isolates with the major objective of elucidating changes that occur during oospore germination. For comparison, ultrastructural changes in isolated oogonium-oospore walls brought about by digestion with various β-glucanases were also examined. Major emphasis was placed on determining the structure of the conspicuous inner oospore wall (IOW). This thick (2–3 μm) layer showed little staining by any of the procedures used, including staining for polysaccharides by the Thiery procedure. There were only minor differences in electron density across the IOW. Observations on sections of whole oospores and mechanically fractured, or partially digested, walls indicated that the IOW contains microfibrils embedded in an amorphous matrix which tend to be oriented parallel to the plasma membrane. During oospore germination, the IOW is extensively eroded in a characteristic ‘scallop’ pattern that creates numerous cavities separated by radial strands of undigested wall. The electron dense outer oospore wall (OOW) remained intact and unaltered and probably confines the activity of the wall digesting enzymes to the IOW. In the digested cavities, removal of the wall matrix exposed the network of underlying microfibrils together with some electron dense globular material. Treatment of isolated oogonium-oospore walls with exo-β-1,3 glucanase or a mixture of endo-β-1,3-glucanases caused substantial digestion of the oogonium wall matrix and the IOW. Following enzymatic digestion, both the IOW and, in particular, the oogonium walls showed greater reactivity with the Thiery procedure. The observed patterns of wall digestion indicate that the amorphous β-1,3-glucan component of the IOW is extensively consumed during germination and is probably the main supply of carbon and energy for germination. No evidence of a pre-formed germination wall layer in the oospore was found. As the innermost layers of the oospore wall became digested, a new wall was produced internal to the IOW.
This review discusses the taxonomy, patterns of sporogenesis and modes of infection of a group of... more This review discusses the taxonomy, patterns of sporogenesis and modes of infection of a group of little studied holocapic pathogens of bactivorous nematodes (and rotifers) from terrestrial and marine habitats. These holocarpic obligate parasites have been traditionally placed within the "Iagenidiaceous oomycetes" although Haptoglossa had been placed in the Saprolegniales. The nematode pathogens that will be discussed fall within the genera C/amydomyzium, Gonimocheate, Haptoglossa and Myzocytiopsis. The patterns of asexual and sexual sporogenesis will be described in detail in the light of recent ultrastructural studies that we have undertaken. We conclude by discussing the main infection strategies employed by these organisms which we categorise into active and passive types. In the former, zoospores actively locate their host (by chemotaxis) and encyst on the host surface immediately prior to infection. In the latter types, the zoospores or aplanospores rapidly germinate...
Mycological Research, Oct 1, 2000
Environmental Conservation, Jun 1, 2000
Fungal Genet Biol, 2004
Corrigendum to ''Ultrastructural morphogenesis of dimorphic arcuate infection (gun) cells of Hapt... more Corrigendum to ''Ultrastructural morphogenesis of dimorphic arcuate infection (gun) cells of Haptoglossa erumpens an obligate parasite of Bunonema nematodes'' [Fung. Genet. Biol. 37 (2002) 250-262] q
Transactions of the British Mycological Society, 1978
Cytoplasmic changes accompanying oospore maturation in Saprolegnia furcata Maurizio have been fol... more Cytoplasmic changes accompanying oospore maturation in Saprolegnia furcata Maurizio have been followed using light and electron microscopy. The occurrence of a brief wallless stage following oosphere formation is demonstrated. Changes in the distribution within the oosphere and oospore of two reserve products, droplets of neutral lipid and membrane bound dense-body vesicles are described. At a late stage in outer oosphere wall formation, the neutral lipid becomes centrally concentrated in the cytoplasm and the dense-body vesicles move towards the periphery. Later, during the accretion of the thick inner wall these storage components briefly intermix before the dense-body granules coalesce and expand to form a prominent central vacuole, the ooplast. During its formation, the ooplast is transparent, but on maturation the dense-body granules are released into Brownian motion, giving the ooplast a characteristically granular appearance. Oospore maturation is accompanied by a reduction in the amount of endoplasmic reticulum and in the number of mitochondria and ribosomes. Golgi dictyosomes and peripheral wall vesicles are lost completely. Oospore development in Saprolegnia is compared with that in other oomycetes and the taxonomic implications are discussed.
Fungal Genet Biol, 2004
Corrigendum to ''Ultrastructural morphogenesis of dimorphic arcuate infection (gun) cells of Hapt... more Corrigendum to ''Ultrastructural morphogenesis of dimorphic arcuate infection (gun) cells of Haptoglossa erumpens an obligate parasite of Bunonema nematodes'' [Fung. Genet. Biol. 37 (2002) 250-262] q
Botany, 1995
The origin and structure of cyst surface components in oomycete fungi are described in relation t... more The origin and structure of cyst surface components in oomycete fungi are described in relation to evaluating their use as taxonomic markers. The ontogeny, biochemistry, and morphological variations in the populations of peripheral vesicles that occur in the zoospores of members of the Peronosporomycetidae and Saprolegniomycetidae, which are discharged upon encystment to give rise to spore surface components, are reviewed. The use of the ornamentation of the cyst coat to define genera within the Saprolegniomycetidae and as an indicator of geographical and host-specific clones within a species of Saprolegnia are reviewed. The cyst coat of the fish pathogen Saprolegnia parasitica shows considerable morphological diversity that appears to be independent of the geographic origin of isolates. There is an indication that a group of isolates with variable, relatively short, spines form a separate clone from those with larger hooped bundles. The monoclonal antibody probes that have been generated to spore surface components of Saprolegnia parasitica, Pythiwn aphanidermatum, and Phytophthora cinnamomi are summarized and their use in defining taxonomic groups reviewed. The antibodies show different levels of specificity ranging from isolate- to order-specific reactions. The degree of specificity can be influenced in some cases by the immunoassay method used. These studies indicate that surface structures and molecules provide extremely versatile and valuable markers for use in oomycete taxonomy and phylogeny. Key words: Saprolegnia, Phytophthora, Achlya, oomycete, zoospore, cysts, ultrastructure, monoclonal antibodies, taxonomy.
Botany, 1988
... Sections were poststained in 2% uranyl acetate for 40 min and Reynold's lead citrate... more ... Sections were poststained in 2% uranyl acetate for 40 min and Reynold's lead citrate for 10 min in an LKB automatic stainer before examination in either a CORA or JEOL 100S electron microscope operated at 60 kV with 25-/Ш1 apertures. ...
Transactions of the British Mycological Society, 1984