Predation rates of flagellate and ciliated protozoa on bacterioplankton in a river

Abstract Predation rates of flagellate and ciliate protozoa on the bacterioplankton of Butrón River (Spain) were determined from FLB (fluorescently labelled bacteria) uptake rates. Bacterial and ciliate protozoa counts were higher when higher water temperature was recorded. Flagellate counts did not show this pattern, which suggested predation of flagellates by other organisms, or some other different nutritional mode besides phagotrophy. Average individual ciliate predation rates were up to 40-times higher than those of flagellates. These results were compared with similar data obtained from other authors in several aquatic systems. However, the population predation rates of flagellate protozoa were on average 6-times higher than that of ciliate protozoa, due to the low population numbers of the latter. Thus, flagellate protozoa can be considered as more important bacterial consumers than ciliates in this aquatic system.     

Export of species to islands from sources of differing maturity

Export of species from sources (epicenters) of differing ages and complexities was examined using laboratory microcosms. Polyurethane foam (PF) artificial substrates were colonized by protozoans for different time periods in a small pond. Substrates were returned to the laboratory and used as epicenters for protozoan colonization of barren PF islands in initially sterile microcosms. Islands were exposed to epicenters for either 24 h or continuously for 28 d. Islands from pairs of microcosms exposed to epicenters of identical ages were sampled on 1, 3, 7, 14, 21, 28 and 46 d after initial epicenter exposure. Colonization parameters were estimated by fitting numbers of colonizing species to the MacArthur-Wilson equilibrium model. Islands exposed continuously to epicenters were colonized by significantly more species than those exposed for only 24 h. Islands exposed to immature, species poor epicenters were colonized by a greater proportion of the source community than those exposed to more mature, species rich epicenters. All islands were depauperate compared to epicenters except those exposed to the most immature (1 d old) epicenter. Colonization continued at a reduced rate in spite of the absence of the epicenter. Results from communities with rapid species turnover and rapidly reproducing species suggest that the continuous presence of a species source is less important for colonization of a new habitat. Dispersal of potential colonists occurs rapidly in these communities. Less mature communities dominated by pioneer forms are more effective at producing colonists than more mature communities.     

Studies on ciliated protozoa in eutrophic lakes: 2. Field and laboratory studies on the effects of oxygen and other chemical gradients on ciliate distribution

An investigation into the spatial distribution of hypolimnetic ciliates in three small eutrophic lakes during the period of summer stratification was carried out. Peak ciliate densities were found to occur at the oxic/anoxic boundary, ciliate numbers declining with increasing depth within the hypolimnion. The ciliates only occurred in aerobic water where oxygen levels were less than about 0.5 mgl^–1 Laboratory experiments demonstrated that the ciliates swim upwards under anaerobic conditions but swim rapidly downwards under aerobic conditions. Further laboratory experiments showed that although the bulk of the population occured within anaerobic water, the hypolimnetic ciliates are aerobes and cannot survive indefinite anoxia. Despite the demonstrable toxicity of high levels of ammonia and sulphide, it was probably excesive distance from an available source of oxygen that excluded the ciliates from the lowest levels of the hypolimnion. Possible mechanisms which allowed these aerobic ciliates to colonise anaerobic water are considered.     

Protein phylogeny of translation elongation factor EF-1α suggests microsporidians are extremely ancient eukaryotes

Partial regions of the mRNA encoding a major part of translation elongation factor 1 (EF-1) from a mitochondrion-lacking protozoan,Glugea plecoglossi, that belongs to microsporidians, were amplified by polymerase chain reaction (PCR) and their primary structures were analyzed. The deduced amino acid sequence was highly divergent from typical EF-1's of eukaryotes, although it clearly showed a eukaryotic feature when aligned with homologs of the three primary kingdoms. Maximum likelihood (ML) analyses on the basis of six different stochastic models of amino acid substitutions and a maximum parsimony (MP) analysis consistently suggest that among eukaryotic species being analyzed,G. plecoglossi is likely to represent the earliest offshoot of eukaryotes. Microsporidians might be the extremely ancient eukaryotes which have diverged before an occurrence of mitochondrial symbiosis. Sequence availability: The nucleotide sequence data reported here appear in the GSDB, DDBJ, EMBL, and NCBI databases with the accession number D32139     

A comparative study of ciliated protozoa communities in activated-sludge plants

Abstract: Ciliated protozoa present in ten activated sludge plants at Madrid (Spain) were identified. The abundance of key groups of ciliates was determined at each plant; attached ciliates made up the most abundant and representative group. Multivariate statistical analysis was employed to study relationships between ciliates and both the physico-chemical and operational parameters of the plants. Partial correlation analysis revealed: (1) The indicator value of attached ciliates in assessing management and performance of the activated sludge process, (2) the relationship of swimming ciliates with short-aged sludges and lower quality effluents and (3) the direct association between swimming-crawling ciliates and bad settlement conditions of the sludge. Factor analysis showed the associations of the most frequent species of ciliates with the operational parameters of the plants, suggesting the indicator value of some of the species: Vorticella striata was related with poor quality of effluent; Aspidisca cicada with stable plant conditions, and Litonotus lamella with a deficiently settling sludge.     

Microbial-feeding nematodes and protozoa in soil: Their effectson microbial activity and nitrogen mineralization in decomposition hotspots and the rhizosphere

Food web studies from a range of ecosystems have demonstrated that the fauna contributes about 30% of total net nitrogen mineralization. This results mainly from the activities of microbial-feeding microfauna (nematodes and protozoa). Microbial and microfaunal activity is concentrated at spatially discrete and heterogeneously distributed organic substrates, including the rhizosphere. The dynamics of microfauna and their effect on nutrient cycling and microbial processes at these sites is reviewed. The potential manipulation of microfauna, either as an experimental tool to further understand soil microbial ecology or as a practical means of managing nutrient flows in agroecosystems, is discussed.     

Physico-chemical characteristics of a permanent Spanish hypersaline lake: La Salada de Chiprana (NE Spain)

La Salada de Chiprana Lake, located in the Ebro River basin, northeastern Spain, is the only permanent and deep water hypersaline ecosystem in all of western Europe. With a total surface of 31 ha and a maximum depth of 5.6 m, it has several basins bounded by elongated sandstone-bodies or ribbons which are paleochannels of Miocene age. Its salinity varied from 30 to 73 g 1^–1 during the 1989 hydrological cycle and the most abundant ions were magnesium and sulphate. Depth-time distributions of major physico-chemical variables demonstrated that the lake was stratified in two distinctive layers during most of the year. The chemocline disappeared only in October, with the complete overturn of the water column. In the deep water, three conditions occurred which allowed development of green sulphur bacteria populations: (1) oxygen depletion, (2) presence of hydrogen sulphide and (3) presence of light. Benthic microbial mats covered the sediments of shallow shores of moderate slope.     

Winter Ciliates in a British Columbian Fjord: Six New Species and an Analysis of Ciliate Putative Prey

ABSTRACT. This work provides the first study of North Pacific planktonic ciliates by quantitative protargol staining. Triplicate water bottle samples were collected at a depth of 2 m (above the shallow pycnocline) at six stations in Indian Arm, British Columbia, on February 15, 1990, and February 26, 1991. Thirty-six ciliate species were observed. Six new species are described from protargolstained specimens: Strombidium lynni n. sp., Strombidium taylori n. sp., Strombidium basimorphum n. sp., Slrombidiurn ventropinnum n. sp., Strobilidium undinum n. sp., and Urotricha cyrtonucleata n. sp.
Ciliate abundance varied significantly (ANOVA, α= 0.05) between sampling sites, ranging from 550 to 6,800 cells/liter in 1990 and from 1,800 to 7,900 cells/liter in 1991. Biomass also varied significantly (ANOVA, α= 0.05) ranging from 3.7 × 10⁵ to 3.3 × 10⁶ pg carbon/liter in 1990 and 3.04 × 10⁶− 6.97 × 10⁶ pg carbon/liter in 1991. Putative prey were enumerated in three size fractions (1.5–5 μm, 5–10 μm and 10–25 μm). The source of variation in ciliate abundance and biomass was not identified. Parameters of salinity, temperature, putative prey, chlorophyll a and pycnocline depth did not significantly correlate with ciliate biomass or abundance (α= 0.05).     

Actin and spectrin-like (Mr= 260–240 000) proteins in gregarines

In Gregarina blaberae a M_r = 47 000 and a M_r = 260–240 000 doublet polypeptides reacted in immunoblotting: i) with a polyclonal monospecific rabbit antibody to frog muscular actin, a monoclonal anti-actin antibody against chicken gizzard; and ii) with polyclonal and monoclonal antibodies to human erythrocyte β-spectrin, respectively. The M_r = 47 000 actin-like protein is associated with the ghost and a contractille cytoplasmic extract. The presence of an actin-like protein in Gregarina and Lecudina and its cellular distribution in the cortex indicated that the gliding movement might involve an actin-myosin system in contrast to previous studies. Immunofluorescence showed clear differences between the anterior part of Gregarina and Lecudina which illustrated the high cell polarity of these protozoa. The M_r = 260–240 000 doublet was detected in SDS-PAGE from G. blaberae trophozoite ghosts but not in the cytoplasmic extracts or in extracts from sexual stages, indicating that the presence of these spectrin-like proteins is stage-dependent. Visualization of the M_r = 260–240 000 by immunofluorescence showed clear species differences, with rings arranged perpendicular to the longitudinal narrow folds of G. blaberae, with longitudinal lines underlying the folds of L. pellucida and with lines separating the large folds of Selenidium pendula. The cellular distribution is consistent with a stabilizer function of the spectrin-like proteins in the scaffolding of the cortex of gregarines according to the high diversity of the cell-shape and the cell motility systems in gregarines. The presence of spectrin-like proteins in protozoa and particularly in parasites from primitive arthropods indicated that ancestral spectrin genes could the M_r = 260–240 000 form.     

The Physiological Ecology of Planktonic Sarcodines with Applications to Paleoecology: Patterns in Space and Time1

ABSTRACT. Planktonic sarcodines, suspended in the water column, are conveniently grouped into three categories based on functional morphology: (1) gymnamoebae and their relatives, which lack major living or nonliving compartmentalizing barriers, (2) foraminifera, and testate amoebae enclosed by a test or shell with one or more major openings, but lacking extensive cytoplasmic compartmentalizing barriers, and (3) radiolaria, which exhibit distinct compartmentalization of the cytoplasm into functional zones. Differences in feeding strategies and trophic activity of members in the three groups reflect in part these differences in functional morphology. Members of all three groups form symbiotic associations with Monera and protists, including algae, thus partially offsetting interspecific trophic competition among species occupying the same water mass. Physiological and morphological adaptations supporting a symbiotic association are presented. C¹⁴-labeling studies of endosymbiotic radiolarian species show a substantial contribution of carbon to the host. Rates of calcification (planktonic foraminfera) and silica deposition (radiolaria) are reported, based on morphometric analyses and isotopic labeling studies. Major distributional patterns in space and time for each of the three groups, and some ecological principles explaining these regularities, are presented as related to population growth dynamics, niche differentiation, water-mass properties, and the role of symbionts in supporting highly diverse communities of species within the same locale in the water column.