Genoveva F. Esteban

Local versus Global Diversity of Microorganisms: Cryptic Diversity of Ciliated Protozoa

Microbial species diversity. both global and local, is still poorly understood. In this study all species of ciliated protozoa were recorded microscopically from ∼1 cm 2 sediment collected from a small lake and from a marine shallow-water bay. Additional adjacent sediment samples (together representing <50 cm 2 ) then incubated under a variety of culture conditions to reveal cryptic species that are present as resting cysts or are too rare to be found microscopically. About 85 and of the total number of observed species from the limnic and marine sediment, respectively, were such cryptic species. In both cases the number of species found in < 50 cm 2 of sediment represented about 75% of all ciliate species ever recorded from these two previously well-studied habitats, and about 8% of all named free-living ciliates. These observations support the assumption that in the case of microorganisms everything is everywhere and that their global species diversity is relatively limited.

Freshwater protozoa: biodiversity and ecological function

The purpose of this article is to pull together various elements from current knowledge regarding the natural history of free-living protozoa in fresh waters. We define their functional role, set the likely limits of ‘biodiversity’, and explore how the two may be related. Protozoa are unicellular, phagotrophic organisms, and 16 phyla of protists contain free-living freshwater protozoan species. They are the most important grazers of microbes in aquatic environments and the only grazers of any importance in anoxic habitats. In sediments, ciliates are usually the dominant protozoans. Benthic ciliate biomass accounts for slightly less than 10% of total benthic invertebrate biomass, but ciliate production may equal or even exceed invertebrate production. Freshwater protozoan species are probably ubiquitous, although many may persist locally for long periods in a cryptic state – as ‘potential’ rather than ‘active’ biodiversity. As protozoa are among the largest and most complex of micro-organisms, it follows that bacteria and all other smaller, more numerous microbes are also ubiquitous. The number of protozoan species recorded in local surveys (232) is about 10% of the estimated global species richness (2390). The seedbank’ of protozoan (and microbial) species ensures that local microbial diversity is never so impoverished that it cannot play its full part in ecosystem functions such as carbon fixation and nutrient cycling.

Microbial diversity and activity in a Danish Fjord with anoxic deep water

Abstract Microbial diversity and activity were studied in a stratified basin of Mariager Fjord, Denmark in August 1994. The basin is about 30 m deep and the lower half of the water column is anoxic and sulphidic. The hydrographical and biological features of the system are described. Based on chemical gradient profiles and measurements of process rates, we found that the relative importance of sulphate reduction, denitrification and methanogenesis in terms of anaerobic terminal mineralisation was about 5:1:0.4. It is possible, however, that methanogenesis is underestimated because an unknown fraction of the methane production escaped by ebullition. It was estimated that 10–15 % of the net primary production is mineralised anaerobically. The mean residence time of methane, sulphide and ammonia beneath the chemocline is within the range 1.6–2.3 yrs. Chemolithotrophic production in the chemocline (sulphide oxidation and nitrification) accounted for about 3% of the net primary production of the system. Methan...

Dynamics of ciliated protozoa communities in activated sludge process

Abstract The purpose of this research is to describe and examine the importance of ciliated protozoan communities in the activated-sludge process. During this study a total number of 21 species of ciliates was recorded and 19 physico-chemical variables measured in the wastewater. The presence of the most common species of ciliates was related to plant operational parameters using multivariate statistical procedures. Principal Component Analysis with Varimax rotation performed on the total biological and non-biological set of data showed that six component factors explained 73% of the variability of the process. The first factor has a significant biological importance; it groups together the species of ciliates and explains 25% of the variability of the sewage plant. This study helps to understand the ecology of these organisms and the operational and control methods of the activated-sludge process.

Biodiversity of terrestrial protozoa appears homogeneous across local and global spatial scales.

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.

Protozoan diversity: converging estimates of the global number of free-living ciliate species.

Protozoa are the most abundant phagotrophs in the biosphere, but no scientific strategy has emerged that might allow accurate definition of the dimensions of protozoan diversity on a global scale. We have begun this task by searching for the common ground between taxonomy and ecology. We have used two methods - taxonomic analysis, and extrapolation from ecological datasets - to estimate the global species richness of free-living ciliated protozoa in the marine interstitial and freshwater benthos. The methods provide estimates that agree within a factor of two, and it is apparent that the species-area curves for ciliates must be almost flat (the slope z takes the very low value of 0.043 in the equation: [number of species] = [constant][area](z)). Insofar as independent ecological datasets can be extrapolated to show similiar, flat, species-area relations, and that these converge with an independent estimate from taxonomic analysis, we conclude that the great majority of freeliving ciliates are ubiquitous. This strengthens our recent claim that the global species richness of free-living ciliated protozoa is relatively low (∼3000).

Mixotrophy in ciliates.

Mixotrophy is the occurrence of phagotrophy and phototrophy in the same organism. In ciliates the intracellular phototroph can be unicellular green algae (zoochlorellae), dinoflagellates (zooxanthellae), cryptomonads or sequestered chloroplasts from ingested algae. An intermediate mixotrophic mechanism is that where the phagotroph ingests algal cells, maintains them intact and functional in the cytoplasm for some time, but the algae are afterwards digested. This seems to occur in some species of Mesodinium. Ciliates with phototrophic endosymbionts have evolved independently in marine and freshwater habitats. The enslaved algal cells or chloroplasts provide host cells with organic matter. Mixotrophs flourish in oxygen-rich, but also in micro-aerobic waters and in the complete absence of oxygen. In the latter case, the aerobic host retains aerobic metabolism, sustained by the oxygen produced by the phototrophic endosymbionts or the sequestered chloroplasts. Mixotrophic ciliates can attain spectacular abundances in some habitats, and entirely dominate the ciliate community.

Diversity of Free-Living Morphospecies in the Ciliate Genus Metopus

Summary This is a taxonomic revision of anaerobic free-living ciliates in the genus Metopus . It includes a rationalization of all nominal species described in the literature, and the allocation of the survivors to “morphospecies“. The revision is based on examination of cultured species together with an exhaustive comparison of the published descriptions of nominal species. All free-living Metopus can be allocated to one of five general morphological types. Each type contains several morphospecies (and their synonyms), each with conservative features. The seventy-six nominal species of Metopus are reduced to 22 morphospecies, and M. nivaaensis n. sp. is described.

Cyclidium porcatum n. sp.: a Free-living anaerobic scuticociliate containing a stable complex of hydrogenosomes, eubacteria and archaeobacteria

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.

Ciliated protozoa from a volcanic crater-lake in Victoria, Australia

We have investigated the ciliated protozoa living in the crater-lake of an extinct volcano in Australia. Our principal objective was to discover if such a habitat— geographically distant and isolated from Europe (the latter having provided most of the diversity on which ciliate taxonomy is based)— could yield species that were unusual, and perhaps new to science. Numerous samples were taken from the superficial layer of lake sediment, and examined fresh in the laboratory. Thereafter, the samples were manipulated to encourage growth of rare and cryptic ciliate species. Eighty-five species of ciliated protozoa were identified. None of these was new, all having been found previously in fresh-or brackish water, sea water, or soil. All, apart from one (Oxytricha salmastra), are already known from Europe. In order to test our ability to discover new ciliate species, we examined a variety of water samples from other lakes, including those known to harbour endemic algae. One new ciliate species (Lembadion curvatum) was discovered in a lake in Western Tasmania. We conclude that the ciliate fauna of Australia is remarkably similar to that in Europe and other parts of the world. This is supported by the example of those ‘endemic’ ciliate species described in the literature which have, in response to additional sampling, been found elsewhere in the world.