Diversity Of Protozoa Research Articles

The Study of Diversity of Ciliate Protozoa in Ghizel Sheep Fed in Pasture and Nourished by Dried Grape by-Product

Problem statement: Ciliate protozoa are one of the normal microorganisms that found in rumen of both domestic and wild ruminants. Several factors seem to influence the concentration and composition of the protozoal fauna in the rumen. The aim of the present study was to determine the rumen ciliates protozoa diversity in Ghizel sheep of East Azerbaijan province and evaluate effects of alfalfa replacement by multiple level of dried grape by-product (0, 15, 30 and 45% of diet) on ciliate protozoa population. Approach: In the first experiment, samples of rumen fluids were collected from 16 mature sheep. Selected sheep were belonged to 4 pure herds of Ghizel sheep in east Azerbaijan province. In the second experiment, sixteen mature Ghizel wether sheep of live weight 34 kg (±1.5) were used. Data obtained from study was subjected to ANOVA as a completely randomized design with 4 replicates by the GLM procedure and treatment means were compared by the Duncan test. Results: In experiment 1, different geographical locations affect total number of rumen ciliated protozoa (p<0.05), Entodinium spp. and Dasytricha spp. In experiment 2, the concentrations of Entodinium spp., Diplodinium spp., Holotricha spp. and Opharyoscolex species were higher when 15% dried grape by-product (DGB) was included in the diet. With increasing DGB in diets the number of Epidinium spp. and Euodiplodinium spp. reduced in treatments 2 (15% of diet replaced by DGB) and 3 (30% of diet replaced by DGB) (p<0.05). Conclusion: The different geographical locations affected total number of rumen ciliated protozoa, Entodinium spp. and Dasytrisha spp. The concentration of Diplodinium was observed to increase when sheep were fed with dried grape by-product.

Rumen protozoal diversity in the Spanish ibex ( Capra pyrenaica hispanica) as compared with domestic goats ( Capra hircus)

Rumen protozoal diversity in the Spanish ibex (SI) was studied in males ( n=4), females ( n=7) and young ( n=4) from the Maestrazgo (Spain) and contrasted with domestic goats ( n=3; DG) of the same region. There were no differences among SI types in protozoal concentration or in the number of protozoal species. Only protozoa from the genus Entodinium were observed in SI (seven species), the highest numbers corresponding to E. damae, E. ovibos and E. parvum. DG harboured threefold more species than SI. Nine to 10 Entodinium spp. were observed, but E. ovibos was absent from the rumen of DG, and E. damae was in only one animal. E. caudatum ( caudatum, dubardi and lobospinosum morphotypes) occurred in the highest percentage, and E. dubardi, E. exiguum and E. parvum were quite abundant. Four genera of the subfamily Diplodiniinae and the genera Isotricha and Dasytricha from the family Isotrichidae were detected in DG. Epidinium (two DG) and Ophryoscolex (one DG) were also observed. Denaturing gradient gel electrophoresis analysis agreed with microscopic classification, showing up to 8 and 16 bands in SI and DG samples, respectively. The three DG clustered together (similarity index over 0.84), and separately from SI (similarity index over 0.86), with only 0.58 similarity between host species.

Effects of C60fullerene nanoparticles on soil bacteria and protozoans

Nanotechnology should produce numerous new materials in the coming years. Because of the novel design of nanomaterials with new physicochemical characteristics, their potential adverse impact on the environment and human health must be addressed. In the present study, agglomerates of pristine C60 fullerenes (50 nm to microm-size) were applied to soil at 0, 5, 25, and 50 mg/kg dry soil to assess their effect on the soil microbiota by measuring total respiration; biomass, number, and diversity of bacteria; and total number and diversity of protozoans during 14 d. Respiration and microbial biomass were unaffected by the fullerenes at any time, whereas the number of fast-growing bacteria was decreased by three- to fourfold just after incorporation of the nanomaterial. Protozoans seemed not to be very sensitive to C60, because their number decreased only slightly in the beginning of the experiment. With polymerase chain reaction and denaturing gradient gel electrophoresis analysis of eubacteria and kinetoplastids from the soil, however, a difference between the fullerene treatments and nonamended controls was demonstrated. The fullerenes did not induce more than 20 to 30% of relative dissimilarity (with both bacteria and protozoans) between treatments, but this effect was persistent throughout the experiment. It therefore is recommended that fullerene nanomaterial not be spread deliberately in the environment and that their ecotoxicology be further clarified.

Ciliate protozoa of the forestomach of llamas (Lama glama) and alpacas (Vicugna pacos) from the Bolivian Altiplano

Protozoal diversity in the forestomach of South American camelids (SAC) was studied in eight llamas and six alpacas from the Parque Natural Condoriri (3900 to 4100 m altitude, Departamento La Paz, Bolivia). Total protozoal concentrations were 3.6 times higher (P &lt; 0.001) in the stomach contents of alpacas (39.6 x 10 4 ml -1 and 143.8 x 10 4 ml -1 in llamas and alpacas, respectively). Four to 11 species, all from the genus Entodinium, were observed in llamas, whereas from eight to nine species of Entodinium and minor proportions of Diplodinium (D. anisacanthum, D. dogieli, D. rangiferi), Eudiplodinium (E. bovis, E. maggii, E. neglectum) and Epidinium (E. ecaudatum) were observed in alpacas. The presence of Epidinium species in the alpaca is a new host record. The vestibuliferids, Dasytricha and Isotricha were absent from the forestomach of SAC, as well as other species such as Caloscolex genus, Diplodinium cameli and Entodinium ovumrajae, commonly found in Old World camelids.

Comparative study of protozoan communities in full-scale MWTPs in Beijing related to treatment processes

The potential influence of process principles and system conditions on shaping protozoan community structures in eight full-scale municipal wastewater treatment systems in Beijing, including four process types, i.e., anaerobic/anoxic/aerobic or anoxic/anaerobic/aerobic process (A2O), anoxic/aerobic or anaerobic/aerobic process (AO), oxidation ditch (OD) and sequencing batch reactor (SBR), was evaluated with the aid of cluster analysis and principal components analysis (PCA). The species richness and abundance distribution of protozoa varied significantly with the process types: the A2O ecosystems harbored more diverse protozoan communities with higher relative abundance of crawling and sessile ciliates than the other systems. Cluster analysis revealed that the protozoan community structures were in high coordination with the process types, i.e., different systems with the same process principles exhibited similar community structures. The A2O processes displayed a distinctively higher similarity of protozoan community structures than the AO processes, suggesting that the A2O ecosystems were more stable than those of AO. The PCA analyses demonstrated that swimming and carnivorous ciliates were correlated with poor settleability of sludge, and that amoebae were sensitive to DO level. We therefore concluded that protozoan community structures were primarily shaped by treatment process principles, whilst they were also modified by system conditions in terms of operational properties and water quality.

Microfauna associated with amoebic gill disease in sea‐farmed Atlantic salmon, Salmo salar L., smolts

A study of microfauna, associated with pathological changes in the gills of Atlantic salmon, Salmo salar L., was conducted over 2001-2002. Monthly samples of 1(+) salmon smolts were taken, protozoan populations were quantified and gill health was assessed histologically. Protozoan densities were correlated with pathological changes, in order to determine their possible role in lesions in the gills. The most severe gill tissue changes were observed in summer/autumn and the least in spring. A diverse polyphyletic protozoan community was observed colonizing the gills, including Neoparamoeba sp., other amoebae, scuticociliates, Ichthyobodo-like flagellates, trichodinid ciliates and prostomatean ciliates. The earlier gill tissue changes in the gill were not always associated with the presence of these microorganisms, whereas amoebae (other than Neoparamoeba sp.), Ichthyobodo-like flagellates and trichodinid ciliates correlated with augmenting gill lesions. Neoparamoeba sp. was present, but its abundance did not correlate with the disease. This study suggests that a diversity of protozoans including Ichthyobodo-like flagellates, trichodinid ciliates and amoebae other than Neoparamoeba sp. are involved in the aetiology of amoebic gill disease in the Irish situation.

Pro- and anti-apoptotic activities of protozoan parasites

During infection, programmed cell death, i.e. apoptosis, is an important effector mechanism of innate and adaptive host responses to parasites. In addition, it fulfils essential functions in regulating host immunity and tissue homeostasis. Not surprisingly, however, adaptation of parasitic protozoa to their hosts also involves modulation or even exploitation of cell death in order to facilitate parasite survival in a hostile environment. During recent years, considerable progress has been made in our understanding of apoptosis during parasitic infections and there is now convincing evidence that apoptosis and its modulation by protozoan parasites has a major impact on the parasite-host interaction and on the pathogenesis of disease. This review updates our current knowledge on the diverse functions apoptosis may fulfil during infections with diverse protozoan parasites including apicomplexans, kinetoplastids and amoebae. Furthermore, we also summarize common mechanistic themes of the pro- and anti-apoptotic activities of protozoan parasites. The diverse and complex effects which parasitic protozoa exert on apoptotic cell death within the host highlight fascinating interactions of parasites and their hosts. Importantly, they also stress the importance of further investigations before the modulation of host cell apoptosis can be exploited to combat parasitic infections.

Intragenomic spliced leader RNA array analysis of kinetoplastids reveals unexpected transcribed region diversity in Trypanosoma cruzi

The spliced leader RNA gene ( SL RNA) repeat is present in large multicopy arrays and has been used as a marker for the diversity of kinetoplastid protozoans. Intra-array variation could affect conclusions made using a randomly isolated repeat as a marker. We examined the Leishmania major (Friedlin) and Trypanosoma cruzi (CL Brener) genome projects for SL RNA repeat sequences in order to assess their homogeneity and the possible effects of sequence variation on taxonomic interpretation. Of the dozens of distinct sequence classes examined, no single copy would bias clustering analyses with regard to other closely related species or isolates. Six dimorphic sites within the T. cruzi transcribed region were found to be linked and are predicted to yield a heterogeneous SL RNA population. The variation that exists among the repeats paints a picture of the broad mechanisms of array maintenance and evolution where site-specific mutations in a single repeat may be spread throughout the array and recombined with existing repeats to create new sequence classes, all occurring under selective pressure to maintain or increase the fitness of the cell line in which these events occur.

Experimental studies of the relative effects of leaf litter from four hardwood trees on protozoan community productivity

Leaf litter is an important source of organic matter as nutrients for aquatic and terrestrial microbial communities. Biogenic decomposition of leaf litter contributes substantially to atmospheric CO2, possibly producing global warming, and comprises an important part of the terrestrial carbon cycle. Small‐scale variability in terrestrial protozoan communities may be attributed to localized variations in leaf matter. This study examined the effect of aqueous leaf extracts from four trees (beech, maple, red oak, and white oak) on the abundance and diversity of protozoa in laboratory aquatic and soil cultures. Beech leaf extract was the most productive followed in the descending order by white oak, red oak, and maple in both aquatic and soil microcosm cultures. Dilution experiments indicated that concentration‐related inhibitory substance(s) in the maple and red oak leaves contribute to lower productivity. Removal of tannins by treatment with activated charcoal (Norit®) improved productivity especially for red oak leaf extracts, suggesting that tannins may contribute to the inhibition of protozoan standing stock. To determine if the lower productivity was mainly due to the inhibition of protozoan excystment, aliquots of thoroughly dried soil were inoculated into maple and red oak leaf extracts. A comparable growth of protozoa occurred in these treatments as in aliquots from moist soil indicating that inhibition of excystment is not a likely explanation for reduced productivity of the protozoan communities.

Molecular and phylogenetic characterization of syntaxin genes from parasitic protozoa.

Vesicular transport is an integral process in eukaryotic cells and the syntaxins, a member of the SNARE protein superfamily, are a critical piece of the vesicular transport machinery. We have obtained syntaxin homologues from diverse protozoan parasites (including Entamoeba, Giardia, Trichomonas and Trypanosoma), determined the paralogue affinity of the homologues by molecular phylogenetics and compared functionally critical amino acid sites identified in other syntaxins. Surprisingly, three sequences deviate at the signature glutamine residue position, conserved in all previously identified syntaxin homologues. It is known that, despite conserved structure and function of both the syntaxins and the proteins of the regulatory SM superfamily, the various syntaxin paralogues bind their respective SM partners at different regions of the syntaxin molecule. These sites of interactions have been identified down to the individual residues. The pattern of conservation at these residues, in our evolutionarily diverse sampling of syntaxin paralogues, is therefore used to gain further insight into the interaction of these proteins. Phylogenetic analysis confirms and extends previous conclusions that the syntaxin families are present in diverse eukaryotes and that the syntaxin sub-families diverged early in eukaryotic evolution. This result is expanded with the inclusion of new homologues for previously sampled taxa, newly sampled taxa, and newly sampled syntaxin sub-families. Because of their integral role in membrane trafficking, the syntaxin genes represent a valuable potential molecular marker for the experimental study of the endomembrane system of disease-causing protists.

Density and diversity of protozoa in some arid Australian soils.

This is the first extensive study of soil protozoa of arid lands. Twenty-six samples from litters, soils, termitaria, and a cyanobacterial crust, collected from central and south Australian arid lands, were analyzed for numbers and species of gymnamoebae, ciliates, and testacea. Amoebae ranged from 1,000-5,000/g of material, and were two orders of magnitude more abundant than ciliates. Both groups increased in abundance and species richness from bare soils through spinifex to mulga to chenopod vegetations. Testacea ranged 900-5,000/g with similar species richness throughout vegetations, but reached 11,900/g with a doubling of species in a refugium in Kings Canyon. The most prevalent species of amoebae, ciliates, and testacea were taxa associated with ephemeral and disturbed habitats (r-selection). The cyanobacterial crust might be considered a micro-refugium because it contained a number of non-encysting protozoa, including Thecamoeba sp. and Nassula picta, feeding on cyanobacterial filaments. The numbers and species richness of protozoa under shrubs were greater than in bare soils, supporting the resource island hypothesis that desert plants create soil heterogeneity by localizing soil fertility under their canopies.

Protozoan Diversity in a productive fishpond of a tropical plateau

A survey of the Protozoan species diversity in a productive fishpond of the Jos Plateau, Nigeria was investigated at 7 day interval over a period of 11 months. Samples were collected from water column and sediment. Protozoans were found to compose of the flagellates sarcodines and cilliates. There was a significant variation (P < 0.05) between the sampling periods for the flagellates. In the water column, the flagellates ranged 38 - 1035 cells.l-1 in July (atmospheric temperature ranged from 22 - 240C and water temperature was 22 - 250C) while the sediment contained 5 - 860 cells.1-1 in August (atmospheric and water temperature coincided at a range of 22 - 260C). Sarcodina abundance showed significant variation (P < 0.05) between sampling period. The density ranged from 3 - 140 cells.l-1 in the water column of temperature range between 23 and 260C while atmospheric temperature was between 23 and 280C. In the sediment of the same sampling period (i.e. June - November) numbers ranged from 32 - 480 cells l-1. The cilliates showed no significant difference in abundance (P > 0.05) between the sampling period. The highest number ranged from 3 - 145 cells.l-1 in the sediment while the water column was 0 - 4 cells. l-1. The low numbers recorded for the sacodines and cilliates could have been due to predation by the planktivorous fish species in the pond. The study has revealed the dynamic nature of the pond ecosystem interacting to maintain an ecological balance through the contribution of the protozoans. Key words: Protozoa diversity, homestead fishpond, Jos Plateau. Journal of Aquatic Sciences Vol.17(2) 2002: 109-112

Exploring Leeuwenhoek's legacy: the abundance and diversity of protozoa.

Towards the end of the 17th century, Leeuwenhoek built "magnifying glasses" that enabled him to see and describe protozoa for the first time. Continued exploration of the natural history of protozoa during the past 300 years has progressed far beyond simply documenting morphospecies (global total probably <20,000). We now realize that protozoan 'biodiversity' is multi-faceted (e.g. sibling species, variant genotypes and syntrophic consortia). Realization of their extraordinary abundance has secured for protozoa the position of dominant phagotrophs and regenerators of nutrients within microbial food webs. And studies of protozoa in the natural environment have done much to effect a paradigm shift in our understanding of why specific microbes live where they do and how they got there in the first place. In particular, the hypothesis of ubiquitous dispersal of protozoan species does seem to be supported by the evidence provided by morphospecies, sibling species and even individual genotypes.

Stratification and dynamics of microbial loop communities in Lake Fryxell, Antarctica

1. Lake Fryxell, situated in the McMurdo Dry Valleys, Antarctica, offers the opportunity to study microbial loop processes in the absence of crustacean zooplankton and other higher organisms. This is the first study of Lake Fryxell to provide detailed temporal and vertical variations of microbial loop organisms. 2. Protozoan communities are concentrated around the chemocline (9–10 m) in Lake Fryxell. Phototrophic nanoflagellates (PNAN), heterotrophic nanoflagellates (HNAN) and ciliates formed deep maxima of 14 580, 694 and 58 cells mL−1 respectively. Although abundance and biomass at the chemocline was high, diversity of protozoa was low, Plagiocampa accounting for&gt; 80% of the total ciliate biomass. 3. In the mixolimnion (4.5–8 m), protozoa were less abundant, but more diverse, with 24 ciliate morphotypes being identified within this region of the water column. Inter‐annual variability of protozoan biomass and abundance was greater in the mixolimnion than at the chemocline due to more variable nutrient and prey concentrations. 4. Physicochemical gradients in Lake Fryxell were very stable because the perennial ice cover reduced wind driven currents. As a consequence, ciliate species occurred in distinct depth strata, Monodinium being most abundant directly beneath the ice cover, Askenasia having maximum abundance at 8 m and Plagiocampa dominating ciliate biomass at the chemocline. The lack of vertical mixing reduced seasonal successions of PNAN and ciliate species. Three cryptophyte species dominated the PNAN community at all times (&gt;79% of total biomass).

Two new terricolous spathidiids (Protozoa, Ciliophora) from tropical Africa: Arcuospathidium vlassaki and Arcuospathidium bulli

Soil protozoa of the tropics are poorly known. However, the few data available indicate that tropical soils are inhabited by a highly diverse protozoan community. In the present paper, some of the many new ciliate species (about 300) that I discovered in African soils are described. Descriptions are based on standard methods, i.e. living and silver-impregnated specimens. Arcuospathidium vlassaki was discovered in a highly saline soil from the margin of the Etosha Pan in Namibia, Southwest Africa. It differs from congeneric species mainly by its rod-shaped macronucleus, fusiform micronuclei, and oblanceolate extrusomes. Arcuospathidium bulli was discovered in a savanna soil of Rwanda, East Africa. It is similar to Arcuospathidium cultriforme Penard in most features, but has a second contractile vacuole in the anterior body half.

Ciliates and heterotrophic dinoflagellates in the marginal ice zone of the central Barents Sea during spring

Diversity and biomass of ciliates and heterotrophic dinoflagellates were analysed at six stations on a south–north transect (mimicking a time span of months in the biological succession during the Arctic spring–summer) from open water through drift ice and into fast ice (72°30′N 76°32′N) during spring 1993 in the open Barents Sea. A pycnocline was observed beneath the sea ice at 40–50 m. A diatom spring bloom beneath the ice with chlorophyll-a maximum &gt;10 μg l−1 and a diverse protozoan community with a peak biomass of 34 μg C l−1 was associated with this bloom. Maximum biomass of tintinnids (1 μg C l−1), athecate dinoflagellates (8 μg C l−1) and thecate dinoflagellates (26 μg C l−1) were found associated with the chlorophyll-a maximum in the upper 10 m of the water column beneath the sea ice at the northern stations. In contrast, the protozooplankton community was dominated by naked ciliates at the southern open water stations. Here chlorophyll-a was low (&lt;1 μg l−1) and the maximum biomass of protozooplankton was 10 μg C l−1 of which naked ciliates accounted for &gt;50%.Cell sizes and estimated carbon content of cells &gt;11 μm, as well as depth by depth biomass of 12 species/types of naked ciliates, 12 tintinnids, 12 athecate dinoflagellates and 24 thecate dinoflagellates, are presented. The community of naked ciliates was dominated by Strombidium spp. and Strobilidium spp., the tintinnids were dominated by Parafavella spp., Ptychocylis, Leprotintinnus, Acanthostomella and Tintinnopsis. The very small gyro-/gymnodinoid cells and Gyrodinium cf. spirale dominated the athecate dinoflagellates and the thecate dinoflagellates by the heterotroph Protoperidinium spp. generally accounted for the major part of the protozooplankton biomass along the transect. The Margalef diversity index revealed lowest diversity of ciliates and heterotrophic dinoflagellates in the open water and higher at ice-associated stations. The overall diversity was coupled with prey availability in terms of food concentration, but already saturated at 0.1 μg chlorophyll-a l−1.

The effect of substratum roughness and river flow rate on the development of a freshwater biofilm community

This study assessed the effects of substratum roughness, using two grades of silicon carbide sandpaper coupons, and river flow rate on the colonisation dynamics of bacteria, hetero‐trophic flagellates and algae over a 16 week incubation period in the River Conder, UK. In the short‐term i.e. up to 2 weeks, a combination of substratum roughness and high river flow significantly increased bacterial biomass on the coupons, but did not affect any of the numbers cm‐2 of other organisms. In the long‐term i.e. up to 16 weeks, neither parameter appeared to affect the development and maintenance of the mature biofilms. Evidence of a diverse protozoan community within the biofilms was recorded, thereby highlighting the need to consider the effect of these primary consumers on biofilm dynamics in future studies.

Microbial gradients in a turbid estuary: Application of a new method for protozoan community analysis

A method was developed to assess the planktonic flagellate, ciliate, and amoeboid populations across the transition from fresh to salt water in the upper St. Lawrence estuary. As in many estuarine environments the water is too turbid for examination by standard concentration and microscopy techniques. A combined system of fluorescence, Nomarski interference, and Utermohl sedimentation (FNU) allowed us to resolve a community of 57 protozoan species across the freshwater-salt-water gradient. Colorless nanoflagellate concentrations decreased from 4.1 × 106 cells liter−1 (247 × 106 µm3 liter− 1) in the freshwater zone to 1.7 × 106 cells liter−1 (139 × 106 µm3 liter−1) in the estuarine frontal region; on average this group contributed at least 45% of the total protozoan cell numbers. Nonpigmented ochromonads (Spumella spp.) were the consistent dominants. The heterotrophic picoplankton increased from 1.7 to 2.8 × 109 cells liter-1 across the salt-water gradient, whereas the autotrophic picoplankton decreased from 8.4 to 2.8 × 106 cells liter . The frontal region of maximum fish larval biomass contained a diverse protozoan assemblage and was a transitional zone of changing microbial food-web structure.

Analyses of heliozoan interrelationships: an example of the potentials and limitations of ultrastructural approaches to the study of protistan phylogeny

Concepts about specific relationships among various groups of protists are diverse and protist taxonomy is consequently unstable. In order to investigate the causes of this variety, data (mainly ultrastructural) relating to 198 characters of 25 species of heliozoa and other protozoa are analysed. Procedures are used which are compatible with numerical taxonomy (single linkage, complete linkage and group average cluster analyses), cladistic procedures (Camin–Sokal, Dollo and Wagner parsimony analyses) and evolutionary taxonomy (an intuitive tree). The results are presented as branching diagrams. There is no complete congruence among any of the techniques, but all give similar results in some important aspects. The Wagner and Dollo parsimony analyses give those results which are most credible. The results corroborate the view that several major traditional taxa of protozoa (the heliozoa, flagellates, amoebae and filose amoebae) are polyphyletic and require revision. All of the analyses identify the following clusters: actinophryid heliozoa, centrohelid heliozoa, chrysophyte flagellates, actinomonad and pedinellid flagellates and nucleariid filose amoebae. As there is no disagreement, these are confirmed as monophyletic taxa. There is a strong suggestion for a close relationship between dimorphid flagellates and desmothoracid heliozoa. There is some support for the suggestion that the actinophryid heliozoa are more closely related to actinomonad helioflagellates than to other heliozoa. The results are summarized as an unrooted ‘true tree'. The lack of agreement among the analyses appears not to be due to a lack of rigour in analytical procedures, but to an inadequate supply of data. The paucity of data cannot be compensated for by the application of repeatable techniques. Most relationships among high level protist taxa are likely to be (currently) obscured by similar limitations. Ultrastructural data are well suited to mapping out the diversity of protozoa. Electron microscopy currently appears to be the most valuable technique for investigating problems of evolutionary relationships of protists. Various hurdles to the development of a natural (phylogenetic) classification of protists are discussed.

The Extent of Algal and Bacterial Endosymbioses in Protozoa1,2

Long neglected has been the extensive and more or less intimate association of protozoa with a wide variety of other cells, either prokaryotic or eukaryotic in nature. Yet study of such relationships can provide important information concerning certain basic aspects of cellular evolution in general. A survey is offered here of the whole range of such symbiotic associations (i.e. with species of protozoa serving as hosts) with the purposes of drawing attention to the exciting possibilities of such research and of reviewing significant findings made to date. Because of the vastness of the overall field, examples and discussion are primarily limited to consideration of the following major studies: methanogenic bacteria in certain ciliates, bacterial endosymbionts of the large freshwater amoeba Pelomyxa palustris (itself an amazing organism from an evolutionary/phylogenetic point of view), the rod‐shaped bacteria found in Amoeba proteus, the “Greek‐letter” prokaryotes of Paramecium species, the xenosomes (sensu stricto) of the marine scuticociliate Parauronema acutum, and the diverse algal endosymbionts of similarly diverse protozoan taxa–ciliates, flagellates, radiolarians, acantharians, and foraminifera.