Dynamics Of Protozoa Research Articles

Bacterial and protozoan dynamics upon thawing and freezing of an active layer permafrost soil.

The active layer of soil overlaying permafrost in the Arctic is subjected to annual changes in temperature and soil chemistry, which we hypothesize to affect the overall soil microbial community. We investigated changes in soil microorganisms at different temperatures during warming and freezing of the active layer soil from Svalbard, Norway. Soil community data were obtained by direct shotgun sequencing of total extracted RNA. No changes in soil microbial communities were detected when warming from -10 to -2 °C or when freezing from -2 to -10 °C. In contrast, within a few days we observed changes when warming from -2 to +2 °C with a decrease in fungal rRNA and an increase in several OTUs belonging to Gemmatimonadetes, Bacteroidetes and Betaproteobacteria. Even more substantial changes occurred when incubating at 2 °C for 16 days, with declines in total fungal potential activity and decreases in oligotrophic members from Actinobacteria and Acidobacteria. Additionally, we detected an increase in transcriptome sequences of bacterial phyla Bacteriodetes, Firmicutes, Betaproteobacteria and Gammaproteobacteria-collectively presumed to be copiotrophic. Furthermore, we detected an increase in putative bacterivorous heterotrophic flagellates, likely due to predation upon the bacterial community via grazing. Although this grazing activity may explain relatively large changes in the bacterial community composition, no changes in total 16S rRNA gene copy number were observed and the total RNA level remained stable during the incubation. Together, these results are showing the first comprehensive ecological evaluation across prokaryotic and eukaryotic microbial communities on thawing and freezing of soil by application of the TotalRNA technique.

Spatial and temporal distribution of free-living protozoa in aquatic environments of a Brazilian semi-arid region

Free-living protozoa organisms are distributed in aquatic environments and vary widely in both qualitative and quantitative terms. The unique ecological functions they exhibit in their habitats help to maintain the dynamic balance of these environments. Despite their wide range and abundance, studies on geographical distribution and ecology, when compared to other groups, are still scarce. This study aimed to identify and record the occurrence of free-living protozoa at three points in Pianco-Piranhas-Acu basin, in a semi-arid area of Rio Grande do Norte (RN) state, and to relate the occurrence of taxa with variations in chlorophyll a, pH and temperature in the environments. Samples were collected in the Armando Ribeiro Goncalves Dam, from two lentic environments upstream and a lotic ecosystem downstream. Sixty-five taxa of free-living protozoa were found. The Student's t-test showed significant inter-variable differences (p <0.05). Similar protozoan species were recorded under different degrees of trophic status according to chlorophyll a concentrations, suggesting the organisms identified are not ideal for indicating trophic level. We hypothesize that food availability, the influence of lentic and lotic systems and the presence of aquatic macrophytes influenced protozoan dynamics during the study period.

Trophic role and carbon budget of metazoan microplankton in northwest Mediterranean coastal waters

We determined the feeding rates, trophic effect, and growth efficiencies of natural assemblages of metazoan microplankton from a coastal site in the northwest (NW) Mediterranean over a seasonal cycle in laboratory incubations. Micrometazoans, i.e., multicellular heterotrophic plankters between 20 and 200 µm, were mainly constituted by invertebrate larval stages. Copepod nauplii and copepodites dominated the community, except in April, when polychaete larvae dominated. We analyzed the grazing pressure of micrometazoans on chlorophyll a (Chl a; total and &gt; 10 µm), nanoflagellates, phototrophic nanoflagellates, dinoflagellates, diatoms, and ciliates. Micrometazoans grazed on all the prey groups, with carbon‐specific ingestion rates ranging from 0.31 to 1.24 d−1. The gross growth efficiencies for the entire metazoan microplankton community, calculated as the slope of the linear regression relating specific growth rates vs. specific ingestion rates, varied between 0.27 and 0.39. The respiratory carbon losses of micrometazoans depended on temperature and ranged from 0.16 to 0.36 d−1, with a Q10 = 2. The average net growth efficiency, 0.41, was independent of temperature and food availability. Overall micrometazoans have higher specific growth rates than, but similar food conversion efficiencies to, mesozooplankton. The grazing effect on the standing stock of the different prey was &lt; 1% d−1 for Chl a (total and &gt; 10 µm) and &lt; 2.5% d−1 for the other studied prey, which seems insufficient to exert relevant control on phytoplankton and protozoan dynamics. The inclusion of micrometazoans did not change appreciably our current view of the role of metazooplankton in marine trophic webs of NW Mediterranean coastal waters.

Differences of the protozoan biomass and grazing during spring and summer in the Indian sector of the Southern Ocean

The dynamics of protozoa were investigated during two cruises in the Indian sector of the Southern Ocean: the early spring ANTARES 3 cruise (28 September to 8 November 1995) and the late summer ANTARES 2 cruise (6 February to 8 March 1994). Biomass and feeding activity of protozoa were measured as well as the biomass of their potential prey – bacteria and phototrophic flagellates – along the 62°E meridian. The sampling grid extended from the Polar Frontal region to the Coastal and Continental Shelf Zone in late summer and to the ice edge in spring, crossing the Antarctic Divergence. Protozoan biomass, although low in absolute terms, contributed 30% and 20% to the total microbial biomass (bacteria, phytoplankton and protozoa) in early spring and late summer, respectively. Nanoprotozoa dominated the total protozoan biomass. The geographical and seasonal distribution of protozoan biomass was correlated with that of phototrophic flagellates. However, bacterial and phototrophic flagellate biomass were inversely correlated. Phototrophic flagellates dominated in the Sea Ice Zone whereas bacteria were predominant at the end of summer in the Polar Frontal region and Coastal and Continental Shelf Zone. Furthermore, bacteria were the most important component of the microbial community (57% of the total microbial biomass) in late summer. Phototrophic flagellates were ingested by both nano-and microprotozoa. In contrast, bacteria were only ingested by nanoprotozoa. Protozoa controlled up to 90% of the daily bacterial production over the period examined. The spring daily protozoan ingestion controlled more than 100% of daily phototrophic flagellate production. This control was less strong at the end of summer when protozoan grazing controlled 42% of the daily phototrophic flagellate production.

Hazard evaluation of lead effects using marine protozoan communities

Protozoan communities developed in laboratory microecosystems were used to evaluate the toxic effects of lead ion. The lead was added as lead acetate in different concentrations (50 μg · l−1, 20 μg · l−1, 10 μg · l−1 and 1 μg · l−1). The protozoans were taxonomically identified and classified into functional groups according to their common nutritional type. The population dynamics of protozoa has been studied. In the control the most frequent groups were bacterivore-detritivores and photosynthetics (more than 75% of abundance). Noticeable lead effects were observed after 24 hours of exposure to metal in all fractions. In general, the lead caused reductions in the number taxa, in total protozoan abundance and in protozoan biomass. The diversity values decreased in more than two nep respect to control in the different fractions. At the end of assay, the protozoan communities structure was simplified in the fractions with lead and some species of little flagellates were dominant. The information provided by this microecosystems of protozoan community was more complex than the one provided by single-species bioassays. Community protozoan bioassays may give more information about the toxic effects to compare with actual ecosystems.

Regulation of Fusarium oxysporum population introduced into soil: the amoebal predation hypothesis

Inoculation of fungi into soil has been suggested for biological control of plant diseases. The aim of our work was to test the ability of protozoa to reduce the density of introduced fungal populations. The survival of Fusarium oxysporum in non-sterile soil was studied after introduction at densities of: 1 × 10 4, 1 × 10 6 and 5 × 10 7 cfu/g soil. The dynamics of protozoa were also followed. The fungal populations remained close to the initial inoculation densities and did not induce the growth of indigenous protozoa. A bacterial population ( Enterobacter aerogenes) was used to promote and stimulate the predatory activity of amoebae. Then, after simultaneous inoculation with bacteria and fungi, the density of protozoa increased but this had no effect on the fungal population, although some amoebae are able to feed on small fungal propagules such as conidia. The physiological state of Fusarium in soil and intraspecific competition seem to be more important in regulating introduced fungal populations than amoebal predation. We conclude that the regulation of bacterial and fungal populations in soil depend on different mechanisms.

Regulation of Fusarium oxysporum populations introduced into soil: the amoebal predation hypothesis

Inoculation of fungi into soil has been suggested for biological control of plant diseases. The aim of our work was to test the ability of protozoa to reduce the density of introduced fungal populations. The survival of Fusarium oxysporum in non-sterile soil was studied after introduction at densities of: 1 × 104, 1 × 106 and 5 × 107 cfu/g soil. The dynamics of protozoa were also followed. The fungal populations remained close to the initial inoculation densities and did not induce the growth of indigenous protozoa. A bacterial population (Enterobacter aerogenes) was used to promote and stimulate the predatory activity of amoebae. Then, after simultaneous inoculation with bacteria and fungi, the density of protozoa increased but this had no effect on the fungal population, although some amoebae are able to feed on small fungal propagules such as conidia. The physiological state of Fusarium in soil and intraspecific competition seem to be more important in regulating introduced fungal populations than amoebal predation. We conclude that the regulation of bacterial and fungal populations in soil depend on different mechanisms.

Dynamics of protozoa in the rumen of cattle.

1. The dynamics of protozoa were studied in two groups of rumen-fistulated cattle fed on a basal diet of molasses ad lib., with oaten chaff given at 6 or 18 g/kg live weight. This diet resulted in different mixtures of protozoal species in the populations in the rumen. 2. The rumen protozoa were studied by intrarumen injections of protozoa labelled in vitro with [14CH3]choline. An indication of protozoal death and fermentation of protozoal cell residues was obtained by measuring 14C loss via the methane pool. 3. After a single injection of labelled protozoa, the decline in the specific radioactivity (microCi/g nitrogen) of the protozoal pool in the rumen indicated that first-order kinetic processes applied. Conversely the specific radioactivity of protozoa, incubated in rumen fluid, remained constant indicating no growth in vitro, presumably owing to a rapid exhaustion of essential nutrients. 4. The protozoal populations in the rumen of cattle fed on the diet with the low level of oaten chaff were mainly small ciliates; but on the higher level of chaff in the diet, the large ciliates were a higher proportion of the total protozoal population present. 5. The mean pool size of protozoa in the rumen was significantly larger and the protozoal half-life tended to be longer for cattle fed on the higher level of chaff in the diet. The apparent production rate of protozoa in cattle fed on each diet was not significantly different and there were no differences in the production rate of methane. The percentage losses of label from protozoa in the rumen via the methane pool were not significantly different on the two diets and indicated that 74% of the protozoa that were apparently irreversibly lost from the rumen could be accounted for by death and lysis in the rumen and therefore only 26% of protozoa apparently entered the lower digestive tract.

The effects of monensin on the pool size and turnover rate of protozoa in the rumen of sheep

SummaryThe effects of including monensin in the diet on the dynamics of protozoa in the rumen of sheep were investigated using injections of protozoa labelled with14C-choline.The half time of rumen fluid was higher in sheep receiving monensin but neither the pool size nor the composition of protozoa species (mainly smaller entodiniomorph ciliates) was significantly affected.More protozoa passed out of the rumen as liquid outflow rate increased and there was a tendency for the apparent production rate of protozoa to be higher with the resulting increase in washout of protozoa.

Dynamics of protozoa in the rumen of sheep.

Protozoa were labelled by incubating 100 ml rumen fluid with [14C]choline for 1 h. The protozoa were concentrated by centrifugation and then washed with rumen fluid. This reduced residual 14C in the fluid medium to insignificant amounts while still retaining the viability of the labelled protozoa. Washing procedures using formal saline (40 g formaldehyde/1 saline (9 g sodium chloride/1)) and saline were developed to isolate protozoa for estimation of specific radioactivity. 2. The protozoal pool in freshly-collected rumen fluid incubated in vitro retained 90% of the radioactivity for up to 6 h following addition of 14C-labelled protozoa produced as indicated previously. The specific radioactivity of protozoa did not change during the incubation period. 3. Protozoa labelled with [14C]choline and then stored until they died rapidly lost 14C to methane when they were incubated in rumen fluid or were injected into the rumen. Some [14C]choline was salvaged under these conditions by the live protozoa present as they apparently incorporated up to 13% of the label from the dead protozoa. However, protozoal debris from the injected solution could also have been present in the isolated protozoa. 4. The in vitro results suggested that the protozoal preparations were viable, and that the incorporated choline did not have a turnover in excess of the turnover of nitrogen (i.e. specific radioactivity remained constant with time in vitro) suggesting that the dilution of specific radioactivity of protozoa following mixing of a 14C-labelled dose of protozoa represented the rate of irreversible loss and also replacement of protozoa in the rumen. 5. 14C-labelled protozoa had a half-life in the rumen which was greater than that of rumen fluid and in six animals the protozoal replacement rate was 1-4.1 mg N/min. 6. Losses of 14C from labelled protozoa in the rumen in methane or via abomasal digesta were 65 and 35% respectively. 7. The results suggest that protozoal growth may be as high as 32% of the total microbial protein synthesis in the rumen but that 65% of the protozoa die and are degraded in the rumen.