Large Protozoa Research Articles

Effects of pore size of nylon bags and dilution rate on fermentation parameters in a semi-continuous artificial rumen

Incubation trials were carried out with the rumen simulation technique (RUSITEC) to study the effects of bag pore size (40, 100 and 200 μm) and dilution rate (2.3%/h and 3.5%/h) on the fermentation parameters and number of protozoa when a high forage diet was incubated. The lower dilution rate resulted in a decrease in pH and an increase in the molar proportion of butyrate, but the disappearance of the diet from the bags was not affected. Protozoal counts were not affected by dilution rate, but holotrichs disappeared completely at low dilution rate as a consequence of low pH. Disappearance of the diet from the bags was higher with 100 μm than with 40 μm bags, but this could not be explained by higher washing losses. Numbers of protozoa were lower with 40 μm than with 100 μm bags, and large protozoa were not present when 40 μm bags were used. There was no difference in protozoa counts between pore sizes of 100 μm and 200 μm and large protozoa were present with both of them. However, disappearance of the diet from the bags and methane and acetate productions were higher ( P < 0.05) with 100 μm bags than with those of 200 μm. Our results indicate that pore size of the bags in RUSITEC affects not only the disappearance of the diet, but also the microbial population in the system and therefore the fermentation.

Modelling the production of dimethylsulfide during a phytoplankton bloom

Dimethylsulfide (DMS) is an important sulfur‐containing atmospheric trace gas of marine biogenic origin. DMS emitted from the oceans may be a precursor of tropospheric aerosols and cloud condensation nuclei (CCN), thereby affecting the Earth's radiative balance and possibly constituting a negative feedback to global warming, although this hypothesis is still somewhat controversial. The revised conceptual model of the marine pelagic food web gives a central role to planktonic bacteria. Recent experiments have shown that consumption of dissolved DMS by microbial metabolism may be more important than atmospheric exchange in controlling its concentration in surface waters and hence its ventilation to the atmosphere. In this paper we investigate the effect of the marine food web on cycling of dissolved DMS in surface waters during a phytoplankton bloom episode. A nitrogen‐based flow network simulation model has been used to analyze the relative importance of the various biological and chemical processes involved. The model predictions suggest that the concentration of DMS in marine surface waters is indeed governed by bacterial metabolism. Environmental factors that affect the bacterial compartment are thus likely to have a relatively large influence on dissolved DMS concentrations. The ecological succession is particularly sensitive to the ratio of phytoplankton to bacterial nutrient uptake rates as well the interaction between herbivore food chain and the microbial loop. Importantly for the design of field studies, the model predicts that peak DMS concentrations are achieved during the decline of the phytoplankton bloom with a typical time lag between peak DMS and peak phytoplankton biomass of 1 to 2 days. Significantly, the model predicts a relatively high DMS concentration persisting after the phytoplankton bloom due to excretion from large protozoa and zooplankton, which may be an additional explanation for the lack of correlation between DMS and chlorophyll a field measurements. Comparison of the model predictions has been made with tank algal bloom experiments.

The Meiobenthos Along a Mediterranean Deep‐Sea Transect off Calvi (Corsica) and in an Adjacent Canyon

Abstract. Meiobenthos densities (excluding hard‐shcllcd foraminifcrans) were compared along a Mediterranean deep‐sea transect off Calvi (Corsica) and in an adjacent canyon. Chloroplastic Pigment Equivalent values (CPE) provided an estimate of the amount of primary production reaching the bottom.The stations along the transect were characterized by a low CPE content of the sediment, decreasing with increasing station depth. CPE values in the canyon were much higher, which probably resulted from import of material from the adjacent bay of Calvi. Similarly, meiobenthos densities along the transect were much lower than at comparable depths along the canyon.Meiobenthos density was significantly and positively correlated with CPE values.Nematodes were the most abundant taxon at all stations, followed by copepods + nauplii and the soft‐shelled foraminiferans. The meiobenthos was most abundant in the upper half centimeter. Nematode and foraminiferan densities tended to decline less rapidly with increasing depth into the sediment. Specimens belonging to the recently described phylum Loricifera, larvae of the parasitic crustacean class Tantulocarida, and fragments of an infaunal Xenophyophoria (large protozoans) are reported for the first time from the Mediterranean.

Austral winter distributions of large tintinnid and large sarcodinid protozooplankton in the ice-edge zone of the Weddell/Scotia Seas

Seasonal distribution and abundance data for large sarcodinid protozooplankton (Radiolaria, Foraminifera, Acantharia and the heliozoan Sticholonche spp.) and larger tintinnid ciliates (e.g., Laackmaniella spp.) are necessary for evaluating their roles in food webs and particle fluxes. As part of the Antarctic Marine Ecosystem Research in the Ice Edge Zone (AMERIEZ) project, we sampled these large (≥ 50 μm) protozooplankton in the winter ice edge zone of the Scotia/Weddell Seas. Organisms alive at the time of capture were counted in large volume (60 1) water samples from 5 paired depths in the upper 210 m from 17 stations. Relationships between abundances and environmental factors in ice-covered, ice edge, and open waters were assessed with correlation, cluster, and multidimensional scaling analyses. Mean abundances of large tintinnids were less than 3150 per m 3, and mean abundances of the individual sarcodine groups were generally less than 1000 per m 3. The most pronounced distributional patterns were related to depth. In general, large tintinnids were more abundant in the colder waters from 0–85 m, a zone encompassed by the mixed layer and the euphotic zone. Acantharians were more abundant in this upper zone only in ice-covered waters. Radiolaria (predominantly phaeodarians) and the heliozoan Sticholonche spp. were more abundant from 115 to 210 m, a zone of warmer, more saline water. Foraminiferan distributions showed little pattern with depth. Results of the cluster analyses also suggested that depth was the most significant effect determining similarity among assemblages of large protozooplankton at the 17 stations. The few correlations between abundances of the groups and chlorophyll a probably reflect relationships more complex than grazing. Abundances of large tintinnids were higher in surface waters under the ice than at the ice edge or in open water. This could result from their feeding on algal cells released from the base of the ice or it may be a result of higher populations in the outflow of Weddell Sea water. There were no consistent abundance patterns among large sarcodines that could be related to ice cover. It is suggested that the combination of low winter productivity, a dynamic environment, and slower growth rates of these large protozoans may prevent them from responding to local enhanced production with increased abundances in the winter ice edge zone. Furthermore, although there is enhanced productivity at the ice edge, this signal may not reach the protozooplankton groups most abundant in the water layer below the euphotic zone.

Abundance and feeding ecology of Antarctic phaeodarian radiolarians

Phaeodarian radiolarians were sampled from the upper 200 m along a transect through the ice-edge zone in the Weddell Sea in the austral autumn (March 1986) and at several stations in the western Antarctic Peninsula region in the austral winter (June 1987). Abundances of phaeodarians reached 3 132 m-3 and were similar to or higher than maximum abundances of polycystine radiolarians, foraminiferans, and acantharians, and similar to or less than those of the heliozoan Sticholonche sp. Phaeodarians varied in abundance and species composition both seasonally and/or geographically. In contrast to the more numerous ciliates and flagellates that were most abundant in the upper 100 m, phaeodarians were most abundant from 100 to 200 m and showed no distinct pattern related to the ice edge. Electron microscopical examination of food vacuoles showed that phaeodarians are omnivorous generalists, feeding on a variety of food ranging in size from bacteria to large protozoans in both regions and seasons. Algal cells consumed in addition to diatoms and dinoflagellates included Chlorella-like cells and members of the recently described chrysophyte order Parmales. Scales of prasinophytes were common. Phaeodarians are consumed by the non-selective particlefeeding salp Salpa thompsoni. Thus, phaeodarians link microbial food webs to macrozooplankton and increase the complexity of the Antarctic food web.

Selective defaunation of Mastotermes darwiniensis and its effect on cellulose and starch metabolism

The feeding of Mastotermes darwiniensis on starch resulted in the death of the four large protozoan species ( Mixotricha paradoxa, Deltotrichonympha operculata, Deltotrichonympha nana and Koruga bonita) and the loss of C x cellulase activity in the hindgut. Starch-fed termites died when transferred to a cellulose diet unless refaunated with the large protozoa. The acetate content of starch-fed termites was about 70% of that of cellulose-fed termites, but was apparently sufficient for the termites' needs since the starch-fed termites survived for over a year. Enterobacter cloacae and Streptococcus sp. isolated from the hindgut were able to grow anaerobically on maltose as a carbon source in monoculture and produced acetate. Starch feeding caused an increase in the number of the hindgut bacteria; a decrease in numbers to normal values occurred when the termites were transferred to a cellulose diet. During the course of starch feeding C x cellulase activity in the salivary glands, foregut and midgut declined and was stimulated if the starch-fed termites were transferred to a cellulose diet, even though the xylophagous protozoa were dead. Amylase activity in both starch-fed and cellulose-fed termites underwent little change.

Kinetics of large ciliate protozoa in the rumen of cattle given sugar cane diets.

1. Experiments were undertaken to examine the kinetics of large ciliate protozoa in the rumen of cattle on sugar-cane diets. 2. Three Zebu bulls were fed once daily on a diet of sugar cane and wheat bran. The diurnal patterns of volatile fatty acids and ammonia concentrations, and the numbers of protozoa in rumen fluid were determined. The numbers of protozoa reached values of 5 X 10(4)/ml for holotrichs (large ciliates) mainly Isotricha and Dasytricha spp and 4 X 10(5) for smaller protozoa, mainly Entodinia (small ciliates). 3. A method was developed which allowed large ciliate protozoa in rumen fluid to be separated from plant material and bacteria and concentrated in a relatively uncontaminated form. Analysis of these protozoa indicated that 1.8 X 10(5) large ciliates contained 1 mg nitrogen and approximately 32 mg dry matter. 4. A labelled preparation consisting mainly of large ciliates (principally Isotricha spp.) was obtained by incubating isolated protozoa in rumen fluid (free of plant materials) containing [14C-methyl]choline and then isolating them by sedimentation and differential centrifugation. 5. A portion of the preparation containing labelled protozoa was incubated in vitro with rumen fluid to determine the turnover of 14C-labelled metabolites. There was no apparent dilution of the label in the protozoa over a 22 h period. 6. A major portion of the preparation containing labelled protozoa was returned to the rumen of each of the donor cattle as a single injection. The specific radioactivity in the large protozoa (microCi/mg N) was monitored frequently for over 30 h, and thereafter daily for a further 12 d. The kinetics of tracer dilution were analyzed to give estimates of the size of the pool of these large ciliates in the rumen (24-46 g N), and of their apparent rate of turnover. 7. In contrast to the slow turnover of the large ciliates, the rate of turnover of the rumen fluid pool (approximately 54 1), estimated from the rate of dilution of polyethylene glycol, was considerably faster. Large ciliates were therefore selectively retained within the rumen.

Biological Control Agents of Sewage Bacteria in Marine Habitats

The introduction of Escherichia coli into natural seawater results in a direct response from the natural microbial parasites and predators, which increase in number and rapidly destroy the alien coliform bacteria. In a predictable successional sequence, the decline in numbers of E. coli was followed by a reduction in the parasite and predator populations resulting from the absence of suitable host organisms and from predation by larger protozoa. E. coli numbers declined more rapidly in seawater taken from near a sewage outlet, because the parasites and predators were enriched by the constant availability of host organisms. A slower rate of decline of E. coli numbers in seawater samples taken further from the outlet was attributed to lower initial populations of parasites and predators. Two common marine predators of E. coli, a fruiting myxobacter (Polyangium) and a small amoeba (Vexillifera), have been characterized.

Utilization of seagrass in the deep sea

Recent American photographic surveys of the deep-sea floor off the east coast of the United States and in the Caribbean have shown the occurrence of a sometimes large number of seagrass blades, particularly after hurricanes. Examination of considerable quantities of seagrass (mainly Thalassia testudinum Banks ex König) collected in 1973 by the Soviet R/V Akademik Kurchatov has revealed extensive utilization by deep-sea animals. Eight or nine kinds of sessile animals (including large protozoans, actinians, gastropods, and a tanaid crustacean) have used blades and/or rhizomes as a substrate. Fresh traces of gnawing activity on rhizomes and blades are abundant. A total of nine different, hitherto underscribed species were found inside Thalassia rhizomes (viz., a polychaete, an echiurid worm, a cocculinid gastropod, and six species of isopods). It is certain that at least the gastropod feeds on the marrow of the rhizomes. This is most probably also the case with the polychaete, the echiurid and one isopod species, as other specimens of these three species were found to feed on other kinds of plant material (of terrestrial origin). 45 out of a total of 55 specimens of a second isopod species were found still in situ inside rhizomes, indicating that this isopod may also utilize seagrass as a source of food. Presumably this is also the case with the remaining four isopod species, but they may just use the rhizomes as a convenient shelter.

Correlation of electrical and mechanical responses in nervous control of cilia.

ALTHOUGH cilia have many important functions in the majority of animal phyla, our knowledge about the mechanism by which their activity is controlled has been fragmentary1. Extensive electrophysiological studies of the ciliated cell, with intracellular microelectrodes, have been made only with the relatively large protozoans, principally Paramecium, where the ciliary activity has been shown to be closely associated with the electrical properties of the cell membrane2,3. Among the metazoans, some examples of nervous control of ciliary activity have been reported4, but, mainly because of technical difficulties, intracellular recording of the membrane potential from the ciliated cells has been made in only a few cases5,6; in no case has nervous control of cilia been studied by recording simultaneously the electrical and the mechanical events. Such recording is essential to understanding the mechanism of nervous control at the cellular level.

Symbiosis and Rumen Protozoa

O ne of the most intriguing concepts opposing survival of the fittest is the concept of cooperation for survival as demonstrated by the organisms that inhabit the intestinal tract of invertebrates and vertebrates. While the work of Cleveland and his classical studies on the large termite flagellates is often cited for classroom use, the difficulty in obtaining his extensive references on these organisms is limiting. The availability of agricultural permits and monies for living termites which are fragile and of limited durability further compound the problems of using these organisms for the laboratory animals of choice for the demonstration of animal associations. Over the years I have found that the availability and diversity of the protozoans that inhabit the rumen of the large grazing mammals that we call ruminants provide me with large protozoans in which students can view internal and external structures without an electron microscope. These can be obtained in unlimited amounts without a seasonal limitation or a geographical or monetary restriction in obtaining a ready supply. As a laboratory experience in protozoology to stress animal associations other than parasitic I have used the following guide lines for a limited approach to the complex taxonomy of the large and marvelous group of protozoa that inhabit the rumen of cattle. The following two paragraphs are presented as a hand-out sheet when the film Rumen Ciliate Protozoa is used. The sheet is intended to indicate the source of the protozoan supply and to stimulate the method of collection of rumen ciliates when live animal sources are unavailable. K)~~~~~A

Electron Microscopy of the Longitudinal Fibrillar Bundle and the Contractile Fibrillar System in Spirostomum ambiguum

SYNOPSIS. A study of the ‘longitudinal fibrillar bundle’ (LFB) and the ‘contractile fibrillar system’ (CFS) of a large protozoan ciliate, Spirostomum ambiguum, has been performed by means of an electron microscope. A system of sub‐pellicular fibrils has been newly found and its function is discussed. Each LFB runs parallel with a longitudinal row of ciliary bases. It seems to be identical with the so‐called kinetodesma. It is composed of tubular fibrils arranged in layered sheets, each of which contains 13 to 35 fibrils with the same diameter as the intra‐ciliary fibrils and has a close connection to each of the ciliary bases. The CFS lies on a transitional plane between ectoplasm and endoplasm of the organism and forms a cobweb‐like system of myofibrils as a whole. It stands in an intimate relationship with a characteristic vacuolar system. In a peristomial field, the fibrous structures are interrupted and somewhat thickened. A sub‐pellicular system is composed of minute fibrils 20 to 26 mμ in diameter. The fibrils run parallel with each other in an antero‐posterior direction, immediately beneath the inner pellicular membrane.

The cultivation and metabolism of oligotrich Protozoa from the sheep's rumen.

SUMMARY: Suspensions of the oligotrich protozoan, Metadinium medium, were extracted from whole rumen contents by allowing the large protozoa to settle out from the bulk of the rumen liquor and concentrating by pouring off the supernatant. The settled protozoa were separated from the associated rumen debris by incubation with maltose, when a bacterial fermentation set in with a vigorous production of gas which carried most of the rumen debris to the surface for removal by gentle suction. After repeated washing of the protozoa by resuspension in buffer and removal of the supernatant, M. medium was cultivated on powdered cotton-wool (0·05%) and powdered hay (0·05%) in buffer at pH 6·8. These oligotrich protozoa remained alive and dividing for 12 days. A species of Entodinium, concentrated from rumen liquor and washed by centrifugation, after the larger protozoa had settled out, was kept alive for 12-14 days under similar conditions in the presence of rice starch grains instead of powdered cotton-wool. Streptomycin (560 μg./ml.) was used to prepare cultures of protozoa which were bacteriologically sterile when tested by streaking agar plates containing yeast extract, starch and glucose or cellobiose. Under these conditions, Entodinium spp. disappeared within 24 hr. and M. medium in 3 or 4 days. This suggests that these organisms are dependent on bacteria for some of their metabolic processes. It is concluded that the species of Metadinium studied here contained symbiotic cellulolytic bacteria which were destroyed by streptomycin, but that the protozoa continued at least for some time to draw on their polysac-charide reserves after treatment with the antibiotic. Rumen oligotrichs may be of use to the sheep by acting as ‘reservoirs' of polysaccharide and so preventing rapid bacterial breakdown. The relationship between the protozoa and the ruminant is considered to be a true symbiosis.

Effects of High Frequency Sound Waves on Protoplasm.

The observations described in the following preliminary report were made by subjecting animal cells to the action of sound waves produced by a rapidly vibrating quartz crystal. The oscillating current was generated by a 250 watt tube connected in a modified Hartley circuit. The crystal lay between a heavy lower electrode and a light upper electrode of copper gauze in a crystallizing dish containing the dielectric liquid, usually xylene. The crystal vibrated at the rate of approximately 750,000 times per second.Effects in Vitro. In this type of experiment the animals were placed in a test tube or similar vessel containing water and dipped into the dielectric over the vibrating crystal. Free-swimming Triturus larvae are rapidly killed, the gill filaments being torn away and areas of denuded surfaces exposed. Confirming the findings of Wood and Loomis,1 the larger protozoa are killed by this method, while the smaller protozoa, being able to swim between the nodes of the stationary wave system set up in the w...