Ken J. Clarke
Freshwater Biological Association
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Featured researches published by Ken J. Clarke.
Nature | 1999
Bland J. Finlay; Ken J. Clarke
The biosphere supports astronomical numbers of free-living microorganisms that belong to an indeterminate number of species. One view is that the abundance of microorganisms drives their dispersal, making them ubiquitous and resulting in a moderate global richness of species. But ubiquity is hard to demonstrate, not only because active species have a rapid turnover, but also because most species in a habitat at any moment in time are relatively rare or in some cryptic state. Here we use microbes that leave traces of their recent population growth in the form of siliceous scale structures to show that all species in the chrysomonad flagellate genus Paraphysomonas are probably ubiquitous.
European Journal of Protistology | 1988
B. J. Finlay; Ken J. Clarke; Andrew J. Cowling; Ruth M. Hindle; Andrew Rogerson; Ulrike-G. Berninger
We have examined and quantified the protozoa living in a productive freshwater pond during a 2-day period in June 1987. Over 90 species were recognised. The planktonic and benthic communities were dominated by ciliates and heterotrophic flagellates although the large amoeba Pelomyxa palustris was abundant (102 ml(-1)) in anaerobic sediments. Picoplankton averaged 1.4 × 10(7) ml(-1), phototrophic nanoplankton 0.8 × 10(5) ml(-1), heterotrophic nanoplankton 0.9 × 10(5) ml(-1) and planktonic ciliates 1.3 × 10(2) ml(-1). Numbers were about two orders of magnitude higher in the sediment. Protozoan biomass ranged from 3% to 61% of the total plankton biomass. Heterotrophic flagellates were the principal grazers of the picoplankton. Planktonic ciliates fed mainly on phototrophic nanoplankton but they probably also ingested heterotrophic flagellates. Benthic ciliates were predominantly bactivorous. Competition between ciliate species was minimised by both spatial and food niche separation. Ten species of planktonic ciliates appeared to contain algal symbionts: one species (Strombidium viride) contained structures resembling sequestered chloroplasts. These findings concerning the diversity and abundance of protozoa in a freshwater pond are consistent with the consensus opinion expressed in the marine literature that protozoa play a fundamental role in microbial food webs within aquatic ecosystems.
Protist | 2001
Bland J. Finlay; Genoveva F. Esteban; Ken J. Clarke; José L. Olmo
Free-living microbes are by far the most abundant group of organisms in the biosphere, yet estimates of global species richness remain nebulous, and there is no consensus regarding the likely geographical distribution of species. Both uncertainties are addressed by the suggestion that the vast abundance of microbes may drive their ubiquitous random dispersal; for this would also make it likely that global species richness is relatively low. Here we test the idea of ubiquitous dispersal of testate amoebae and ciliates living in soil. We analysed their abundance and species richness in 150 soil samples collected from the one-hectare grassland site at Sourhope in Scotland, and in comparable published data from 1500 soil samples collected worldwide. Following taxonomic revision and removal of synonyms, there remained a total of 186 taxa (91 testate and 95 ciliate) recorded from both Sourhope and other places in the world. A fundamental pattern of random spatial distribution of species was revealed in species that are relatively rare. This probably arises from random dispersal, for when localised population growth occurs, the distributions become aggregated, as in virtually all metazoan species. We find no evidence for geographically-restricted protozoan morphospecies at spatial scales of 4 m2, 10,000 m2, or worldwide. Species that are locally rare or abundant are similarly rare or abundant on a global scale. Approximately one third of the global diversity of soil protozoa was found at the one-hectare grassland site in Scotland, but this is a minimum figure, for recorded species richness is proportional to sampling effort, as shown here.
Protist | 1999
Bland J. Finlay; Ken J. Clarke
Evidence is presented for the ubiquity of protist species. Using the example of protists that leave traces (siliceous scales) of their recent population growth, we show that most - perhaps all species in the genus Paraphysomonas, are ubiquitous. Of the species recorded in surveys carried out worldwide, we have identified 78% of their number in 0.1 cm2 of sediment collected from a freshwater pond (total area 10(8) cm2) in England. Moreover, the pond appears to act like a microcosm of aquatic environments in general, for species that are globally rare or abundant, are likewise rare or abundant in the pond. We assume that the rate of neutral migration to the pond is greatest for the globally abundant species. As these species are probably capable of growth in a broad range of conditions, they will more frequently encounter the environment they require for population growth. Thus globally abundant species are also locally abundant in the pond - a pattern that will be amplified by periodic cyst production. Ubiquitous dispersal is probably driven by very high absolute abundance of individuals, and the water column of the pond was estimated to support >10(14) Paraphysomonas individuals. Ubiquity will dampen rates of speciation, and the evidence presented here indicates that global species richness of Paraphysomonas is indeed modest - perhaps close to what is already known.
European Journal of Protistology | 1993
Ken J. Clarke; B. J. Finlay; Genoveva F. Esteban; Guhl Be; T.M. Embley
A new ciliate species (Cyclidium porcatum) is the first freshwater anaerobic scuticociliate to be cultured and described. It contains a unique tripartite structure consisting of hydrogenosomes (confirmed by cytochemical staining for hydrogenase), interspersed with methanogens (confirmed by auto fluorescence and in situ hybridisation with an archaeobacterial 16S rRNA-specific probe) and unidentified eubacteria (confirmed with a eubacterial 16S rRNA-specific probe). This complex structure is stable and persistent, indicating that it is an anaerobic symbiotic consortium incorporating three functional partners.
European Journal of Protistology | 1991
Bland J. Finlay; Ken J. Clarke; Eduardo Vicente; Maria Rosa Miracle
We have examined and quantified the anaerobic ciliates living in the hypolimnion of a 14 m deep sulphide-rich (up to 0.73 mM) solution lake in Spain. At least seven ciliate species were found, numbering up to 50 ml-1 in total and reaching maximum abundance close to the sediment. Caenomorpha medusula, Lacrymaria elegans, L. sapropelica and Lagynus sp. were the most abundant species. Their vertical distributions were not related to the sulphide profile. Most ciliates were dependent on the sedimentation of cryptomonads, photosynthetic bacteria (especially Chromatium and Oscillatoria) and other bacteria from their sites of production in closely-juxtaposed mid-water plates. All anaerobic ciliates contained at least one type of symbiotic bacterium which showed methanogen autofluorescence. C. medusula, Lagynus sp. and Lacrymaria sapropelica also contained a large, non-fluorescing rod-shaped bacterium. In C. medusula, the methanogens and the non-fluorescing rods were both attached to the hydrogenosomes. In this ciliate alone, a third bacterial type was attached to the external ventral surface of the ciliate. Digestion of sulphide-oxidising bacteria by ciliates which harbour methanogenic bacteria provides a short bridge between the anaerobic sulphur and carbon cycles. Theoretical considerations of the rate of ciliate consumption of microbial carbon in the anoxic hypolimnion indicate that it is significant and that it may amount to 4 × 10(-5) g cm(-2)d(-1).
Environmental Microbiology | 2009
Genoveva F. Esteban; Bland J. Finlay; Ken J. Clarke
We report aerobic eukaryotic microbial life in the dimly lit anoxic water layer of a small freshwater lake. The microbial eukaryote is the ciliated protozoon Histiobalantium natans. Electron microscopy of thin sections shows that the cytoplasm of the ciliate harbours sequestered chloroplasts and sequestered mitochondria. The sequestered chloroplasts are attached or in very close proximity to the ciliates own mitochondria. The sequestered mitochondria also seem to be associated with host-ciliate mitochondria. We suggest that the oxygenic photosynthetic activity of sequestered chloroplasts, perhaps enhanced by respiration in sequestered mitochondria, contributes to servicing the respiratory oxygen requirements of the ciliate host in its anoxic habitat. Our observations are novel, with the discovery of an aerobic microbial eukaryote capable of thriving and completing its life cycle in an anoxic environment, fuelled by oxygen generated by sequestered chloroplasts. The acknowledged flexibility and functional diversity within eukaryotic microbial communities still have many secrets to release.
Fems Microbiology Letters | 1994
Bland J. Finlay; Genoveva F. Esteban; Ken J. Clarke; Alan G. Williams; T. Martin Embley; Robert P. Hirt
Protist | 2000
Bland J. Finlay; Helaina I.J. Black; Susan Brown; Ken J. Clarke; Genoveva F. Esteban; Ruth M. Hindle; José L. Olmo; Alison Rollett; Keith Vickerman
Applied Soil Ecology | 2006
Genoveva F. Esteban; Ken J. Clarke; José L. Olmo; Bland J. Finlay