武汉东湖周丛原生动物生态

作者于1963年12月—1964年12月对东湖Ⅳ、Ⅴ两个采样站的聚草、金鱼藻、黄丝草上周丛原生动物进行了周年的定性和定量的观察。共观察到175种周丛原生动物,其中真周丛原生动物占62.9%,伪周丛原生动物占37.1%。两个采样站、三种水草上原生动物数量周年变动均有共同的趋势,即在低温的冬季出现数量高峰,左右数量变动的优势种类是钟形钟虫,占周丛原生动物总数的80—90%。在Ⅴ站同期进行人工基质上周丛原生动物生态比较,表明其优势种类与水草上相同,但群集速度却以水温高的8—9月份为最快。通过金鱼藻生物量、金鱼藻上和人工基质上原生动物数量三者关系的分析,认为影响周丛原生动物数量变动的重要因子是水草本身的生长情况。文中分析了周丛原生动物与水体污染程度的关系,指出着生原生动物是迅速监测水体污染程度的优良指示生物。       

Assessment of potential sources of protozoan contamination between two avian feeding guilds in a conservation area

Occasional screening of food and water quality available to organisms in protected areas could be beneficial to their successful conservation. This is important for areas receiving regular human visitors and exhibiting activities that may be detrimental to ecosystem health. This study determined the intestinal protozoan species harboured by insectivorous and granivorous birds within the Jos Wildlife Park, Nigeria and whether the two avian feeding guilds are more susceptible to protozoan infection through water or food (grass seeds and insects). Special boxes were used to collect faecal samples from trapped birds. Samples were later analysed in the laboratory for protozoans. Both food and water utilised by the birds in the area were microscopically screened. The composition and abundance of intestinal protozoans between the two feeding guilds did not show significant differences. However, considering parasite species individually, the degree of infection by protozoans such as Giardia lamblia was highly related to the range of infection sources that a feeding guild was exposed to. The composition of parasites observed in the two feeding guilds was strongly linked to both water bodies and avian diet obtainable in the Park. These observations showed that birds in the Park are orally susceptible to infection with protozoans, some of which have been reported to cause health implications in birds. Thus, any measure to curtail environmental contamination by the parasites may improve ecosystem health and survival of avian species in the Park.     

Using a green fluorescent protein gene-labeled p-nitrophenol-degrading Moraxella strain to examine the protective effect of alginate encapsulation against protozoan grazing

A gfp-labeled p-nitrophenol-degrading Moraxella strain G21 was used to study grazing of a Tetrahymena thermophila strain in liquid medium. This allowed visualization of the feeding process. Under an epifluorescent microscope, individual G21 fluorescent cells could be seen in vacuoles within the protozoans. Most of the G21 cells appeared to be lysed by T. thermophila and green fluorescent protein released from the bacteria yielded brightly fluorescent food vacuoles inside the protozoans, Examination of population dynamics of a mixed culture of T. thermophila and Moraxella sp. G21 showed that the protozoan reduced the bacterial density from 7.6 to 5.8 log CFU/ml in 2 days. Encapsulating the bacteria in alginate prevented grazing by the protozoans and the density of G21 cells in the beads increased steadily from about 8.3 to 8.9 log CFU/ml in 15 days regardless of the presence of the protozoans.     

Salinity and fish effects on Salton Sea microecosystems: zooplankton and nekton

The Salton Sea is the largest inland lake in California. Currently (1997) the salinity of the lake is about 44 g l-1 and is increasing gradually as a result of continued agricultural wastewater inflows, high evaporation rates, and lack of an outlet. A microcosm experiment was carried out to determine the effects of salinity (30, 39, 48, 57, and 65 g l-1) on Salton Sea algae and invertebrates in outdoor aquatic microcosms. The experiment was also designed to assess the effects of tilapia ( Oreochromis mossambicus) on this community at two of these salinities (39 and 57 g l-1). Fiberglass tanks containing Salton Sea water were adjusted to the appropriate salinity by the addition of salts, identically inoculated with organisms from the Salton Sea and other saline water bodies in the region, and monitored for 15 months. Planktonic and nektonic invertebrates were sampled monthly at night from the upper part of the water column. The dominant invertebrates present were Gammarus mucronatus, Artemia franciscana, Trichocorixa reticulata, and an assemblage of ciliate protozoans. Gammarus decreased and Trichocorixa increased with increasing salinity. Artemia was present only at the two highest salinities. Rotifers, harpacticoid and cyclopoid copepods, barnacle larvae, and protozoans all showed marked and varied responses. During the latter half of the experiment, the invertebrate assemblage was dominated by Gammarus at 30 and 39 g l-1, by protozoans at 48 g l-1, and by protozoans and Trichocorixa at 57 and 65 g l-1. The presence of tilapia caused a 99 percent reduction in Gammarus at 39 g l-1 and a 70–90 percent decrease in Trichocorixa at 57 g l-1. These were accompanied by substantial increases in rotifers, copepods, and certain protozoans, and decreases in other protozoans. As the salinity of the Salton Sea continues to increase, large changes in the invertebrate populations are expected. This study suggests that the principal change would be an increase in Trichocorixa densities, the loss of Gammarus, and the appearance of Artemia at about 60–70 g l-1, when both fish and invertebrate predators are likely to be scarce or absent. Protozooplankton abundance is likely to increase when tilapia declines and later decrease when and if large Artemia populations develop. This revised version was published online in July 2006 with corrections to the Cover Date.     

Rotifers as predators on components of the microbial web (bacteria,heterotrophic flagellates,ciliates) — a review

Recent investigations have shown that processes within the planktonic microbial web are of great significance for the functioning of limnetic ecosystems. However, the general importance of protozoans and bacteria as food sources for rotifers, a major component of planktonic habitats, has seldom been evaluated. Results of feeding experiments and the analysis of the food size spectrum of rotifers suggest that larger bacteria, heterotrophic flagellates and small ciliates should be a common part of the food of most rotifer species. About 10–40 per cent of rotifers' food can consist of heterotrophic organisms of the microbial web. Field experiments have indicated that rotifer grazing should generally play a minor role in bacteria consumption compared to feeding by coexisting protozoans. However, according to recent experiments regarding food selection, rotifers should be efficient predators on protozoans. Laboratory experiments have revealed that even nanophagous rotifers can feed on ciliates. Preliminary microcosm and chemostat experiments have indicated that rotifers, due to their relatively low community grazing rates compared to the growth rates of bacteria and protozoans, should generally not be able (in contrast to some cladocerans) to suppress the microbial web via grazing, though they may structure it. Filter-feeding nanophagous rotifers (e.g. brachionids) seem to be significant feeders on the smaller organisms of the microbial web (bacteria, flagellates, small ciliates), whereas grasping species (e.g. synchaetids and asplanchnids) seem to be efficient predators on larger organisms (esp. ciliates). Another important role of rotifers is their feedback effect on the microbial web. Rotifers provide degraded algae, bacteria and protozoans to the microbial web and may promote microbial activity. Additional experimental work is necessary for a better understanding of the function of rotifers in aquatic ecosystems.     

On the Importance of Planktonic Protozoans in the Eutrophication Process of the Baltic Sea

Analysing the results of various authors recent studies in the pelagic region of the Baltic revealed that protozoan biomass is in the same range or even higher than metazooplankton biomass. The dominant groups of planktonic protozoans are heterotrophic pico- and nanoflagellates (various taxonomic groups), large heterotrophic flagellates (mainly dinoflagellates) and ciliates. Regularly the spring bloom of phytoplankton is accompanied by a maximum of protozoan biomass which declines in early summer as a result of intensive grazing pressure by metazooplankton and changing food conditions. The analysis of results from different stations indicated that biomasses of protozoans increase with an increasing degree of eutrophication. Several trophic levels within the microbial web should be added to the traditional view on the pelagic food web of the Baltic. Our knowledge regarding the quantitative aspect of the microbial matter flux of the Baltic is very limited up to now and complex ecological (and taxonomical) studies using standardized methods including all protozoan components are necessary. Protozoans (various trophic groups and levels), besides bacteria, should be viewed as the metabolically most active heterotrophic component in the pelagic region of the Baltic, their activity should increase with an increasing degree of eutrophication.     

Some properties of a photodynamic pigment from Blepharisma

1. A pigment can be extracted from Blepharisma undulans by heat treatment of a concentrated suspension of the deeply pigmented animals. 2. In the presence of this pigment, various colorless protozoans are sensitized to light and killed if exposed long enough. The protozoans show a differential sensitivity, some being much more sensitive than others. 3. Bleached colorless blepharismas are not sensitized to their own pigment even after prolonged exposure in the most concentrated solutions available. 4. Blepharisma is also less sensitive than any of the protozoans tested to such photodynamic dyes as rose bengal. 5. The pigment is not extracted from wet blepharismas by non-polar solvents, but is readily extracted into such polar organic solvents as the alcohols. 6. When the alcohol extract is dried, the amorphous residue is readily soluble in a variety of organic solvents, but not in the most non-polar. 7. The pigment is highly stable in alcohol extract and has been kept in the dark for years. 8. The pigment is bleached by light in a photooxidation. 9. Absorption maxima are found at wave lengths 5800, 5400, 4800, and 3300 A, the latter being the largest. Similar peaks are found in alcohol and water solutions, although the heights are not exactly the same. In both alcoholic and aqueous solutions pH had an effect on the absorption spectrum. Heat has little effect but illumination with intense visible light or exposure to ultraviolet light bleaches the pigment with decreases in the characteristic peaks. 10. Preliminary absorption column experiments indicate a single pigment in the alcohol extract. 11. Experiments on the migration of zoopurpurin in agar and gelatin gels indicate that it diffuses at about the same rate as eosin and is therefore probably not a large molecule.     

Trade-Offs between Competition and Defense Specialists among Unicellular Planktonic Organisms: the “Killing the Winner” Hypothesis Revisited

Summary: A trade-off between strategies maximizing growth and minimizing losses appears to be a fundamental property of evolving biological entities existing in environments with limited resources. In the special case of unicellular planktonic organisms, the theoretical framework describing the trade-offs between competition and defense specialists is known as the “killing the winner” hypothesis (KtW). KtW describes how the availability of resources and the actions of predators (e.g., heterotrophic flagellates) and parasites (e.g., viruses) determine the composition and biogeochemical impact of such organisms. We extend KtW conceptually by introducing size- or shape-selective grazing of protozoans on prokaryotes into an idealized food web composed of prokaryotes, lytic viruses infecting prokaryotes, and protozoans. This results in a hierarchy analogous to a Russian doll, where KtW principles are at work on a lower level due to selective viral infection and on an upper level due to size- or shape-selective grazing by protozoans. Additionally, we critically discuss predictions and limitations of KtW in light of the recent literature, with particular focus on typically neglected aspects of KtW. Many aspects of KtW have been corroborated by in situ and experimental studies of isolates and natural communities. However, a thorough test of KtW is still hampered by current methodological limitations. In particular, the quantification of nutrient uptake rates of the competing prokaryotic populations and virus population-specific adsorption and decay rates appears to be the most daunting challenge for the years to come.     

Effects of mosquito larvae removal with Bacillus thuringiensis israelensis (Bti) on natural protozoan communities

The protein crystals produced by Bacillus thuringiensis israelensis (Bti) are used against the larvae of pestiferous flood-water mosquitoes in ephemeral wetlands. Although mosquito larvae are considered important predators on protozoans and bacteria, it is not known how a distinct reduction of mosquito larvae density in natural wetlands caused by application of Bti may indirectly affect these microbial communities. Here we show, in a large scale experiment in six natural wetlands, that the densities of heterotrophic protozoans was on an average 4.5 times higher in wetland areas treated with Bti than in control areas. In addition, the taxonomic richness of heterotrophic protozoans increased on an average of 60% in areas with Bti application compared to control areas. The increase in protozoan density and richness was fairly consistent among sites of different wetland habitats. We discuss the potential implications of our results for other parts of the ecosystem. Handling editor: K. Martens     

Metabolic level and size scaling of rates of respiration and growth in unicellular organisms

1.  Metabolic rate is conventionally assumed to scale with body mass to the 3/4-power, independently of the metabolic level of the organisms being considered. However, recent analyses in a variety of animals and plants indicate that the power (log–log slope) of this relationship varies significantly with metabolic level, ranging from c . 2/3 to 1.
2.  Here I show that the scaling slopes of rates of respiration and growth are related to the metabolic level of a variety of unicellular organisms, as similarly occurs for respiration rates in multicellular organisms.
3.  The recently proposed 'metabolic-level boundaries hypothesis' provides insight into these effects of metabolic level. As predicted, the scaling slopes for resting (endogenous) respiration rate in prokaryotes, algae and protozoans are negatively related to metabolic level; and in protozoans, the scaling slope increases with starvation. Also as predicted, the scaling slopes of growth rate in algae and protozoans are negatively related to growth level. Unexpectedly, opposite effects of starvation on the metabolic scaling slopes of unicellular prokaryotes (compared to that of eukaryotes) may be a spurious result of respiration measurements that did not adequately consider the effects of rapid cell multiplication in prokaryotes with extremely short generation times.
4.  Analyses of both unicellular and multicellular organisms show that there is no universal metabolic scaling relationship, and that variation in metabolic scaling relationships is systematically and possibly universally related to metabolic level.     

Predation on Protozoa: its importance to zooplankton

Protozoa are an important component of both the nano- and microplanktonin marine and freshwater environments and are preyed upon byzooplankton, including suspension-feeding cope pods, some gelatinouszoopiankters and some first-feeding fish larvae. The clearancerates of suspension-feeding zooplankton for ciliates, in particular,are higher than for most phytoplankton. For at least some suspension-feedingzooplankton, protozoans are calculated to be quantitativelyan important component of the diet during certain seasons. Inlaboratory studies, protozoan components in the diet appearto enhance growth and survival of certain life-history stagesor enhance fecundity. These data suggest that protozoans arequalitatively as well as quantitatively important in the dietsof marine zooplankton. Most studies of predation on Protozoahave focused on the euphotic zone in nearshore waters. Predationon Protozoa is expected, however, to be particularly importantboth quantitatively and qualitatively in marine environmentsand seasons in which primary production is dominated by cells<5 µm in size, such as nearshore environments afterthe spring phytoplankton bloom, in oligotrophic waters, andin environments dominated by detritus-dominated food webs, suchas the deep sea. In detritus-dominated food webs, Protozoa maybe a source of essential nutrients and may thus facilitate utilizationof bacterial and detrital carbon by metazoan plankton.     

Ancient weapons for attack and defense: the pore-forming polypeptides of pathogenic enteric and free-living amoeboid protozoa

Pore-forming polypeptides have been purified from several amoeboid protozoans that are well-known human pathogens. Obligate enteric parasites, such as Entamoeba histolytica, and free-living but potentially highly pathogenic species, such as Naegleria fowleri, contain these cytolytic molecules inside cytoplasmic granules. Comprehensive functional and structural studies have been conducted that include isolation of the proteins from their natural sources, monitoring of their biological activity towards different targets, and molecular cloning of the genes of their precursors. In the case of the most prominent member of the protein family, with respect to protozoans, the three-dimensional structure of amoebapore A was solved recently. The amoebic pore-forming polypeptides can rapidly perforate human cells. The antibacterial activity of amoebapores and of related polypetides from free-living protozoa points to a more vital function of these molecules: inside the digestive vacuoles they combat growth of phagocytosed bacteria which are killed when their cytoplasmic membranes are permeabilized. The concommitant activity of these proteins towards host cells may be due to a coincidental selection for an efficient effector molecule. Nonetheless, several lines of evidence indicate that these factors are involved in pathogenesis of fatal diseases induced by amoeboid protozoa.     

Glycosidases in mucin-dwelling protozoans

A range of protozoans were tested for the presence of glycosidases using p-nitrophenyl sugars as substrates. Some of the organisms were mucin dwellers whereas others were blood borne parasites. It had been hypothesized that glycosidase production would be significantly higher in the mucin dwellers. The results obtained demonstrated that the urogenital protozoans Tritrichomonas foetus and Trichomonas vaginalis produced a vast range of glycosidases which included those required for mucin breakdown. The gut dwelling protozoans Giardia lamblia and Entamoeba histolytica both produced β-N-acetylglucosaminidase. G.lamblia also had detectable β N-acetylgalactosaminidase activity, and small amounts of β mannosidase were found in the extracts from E. histolytica. In contrast, little or no glycosidase activity was detected under the same experimental conditions in Leishmania donovani, Trypanosoma brucei or T. cruzi. The mucin dwelling protozoans all produce β-N-acetylglucosaminidase but only the Trichomonads produced the range of enzymes required for complete breakdown of mucin. This seems to suggest that mucin breakdown is not a characteristic of all mucin dwelling protozoans. This revised version was published online in November 2006 with corrections to the Cover Date.     

A comparison of the polycation receptors of Paramecium tetraurelia and Tetrahymena thermophila

Chemorepellents are compounds that cause ciliated protozoans to reorient their swimming direction. A number of chemorepellents have been studied in the ciliated protozoans, Paramecium and Tetrahymena. Chemorepellents, such as polycations, cause the organism to exhibit "avoidance behavior," a swimming behavior characterized by jerky movements and other deviations from normal forward swimming, which result from ciliary reversal. One well-characterized chemorepellent pathway in Tetrahymena is that of the proposed polycation receptor that is activated by lysozyme and pituitary adenylate cyclase activating polypeptide (PACAP). In this study, we compare the response of Paramecium to the chemorepellents lysozyme, vasoactive intestinal peptide (VIP), and PACAP to the previously studied polycation response in Tetrahymena. Our results indicate that lysozyme, VIP, and PACAP are all chemorepellents in Paramecium, just as they are in Tetrahymena. However, the signaling pathways involved appear to be different. While previous pharmacological characterization indicates that G-proteins are involved in polycation signaling in Tetrahymena, we present evidence that similar reception in Paramecium involves activation of a tyrosine kinase pathway in order for lysozyme avoidance to occur. Polycation responses of both organisms are inhibited by neomycin sulfate. While PACAP is the most effective of the three chemorepellents in Tetrahymena, lysozyme is the most effective chemorepellent in Paramecium.     

The importance of Protozoa in controlling the abundance of planktonic algae in lakes

Apart from ciliates, there are other protozoans which can form an important element in the herbivorous zooplankton of lakes.
The protozoans discussed in this paper feed on colonial algae. They can greatly reduce the numbers of certain Chlorophyta in Windermere, Esthwaite Water and Blelham Tarn, lakes in the English Lake District.
A very short period, often 7–14 days, can suffice for the destruction of more than 99% of an algal population.
Experiments with a species of Pseudospora showed that it would only ingest one out of six green algal species, although, in nature, Pseudosporae which are morphologically similar to this species have been observed in all these algae.
The importance of such protozoans, and of parasitic fungi, has been underrated or neglected in studies of the quantitative relationships between primary and secondary production in the plankton.     

Zooplankton biomass distribution patterns along the western Antarctic Peninsula (December 2002)

The phytoplankton [chlorophyll a (Chl a)], microzooplankton,mesozooplankton and macrozooplankton biomass and distributionwere studied as part of a multidisciplinary project (Tempano)along the Antarctic Peninsula during December 2002. Even thoughthe summer phytoplankton bloom was not yet developed in thearea, autotrophs dominated the plankton biomass. Phytoplanktonvertical distribution was, in general, homogeneous in the upper40–50 m of the water column, further decreasing with depth.Protozoans showed low biomass; their contribution to the totalplankton being one order of magnitude lower than that of autotrophs.The vertical distribution of protozoans was variable among stationswith marked peaks at depths ranging from 30 to 80 m. Mesozooplankton-integratedbiomass was generally low, although there was a notable increasesouthward near the ice marginal zone. Macrozooplankton distributionwas more variable without any clear zonal distribution pattern.The vertical distribution of meso- and macrozooplankton (>4mm) biomass showed clear peaks of abundance comprising differentspecies depending on the geographical area. Our biomass distributiondata suggest a food-web scenario in which macrozooplankton arepreying on mesozooplankton populations only in the northernerstations, and mesozooplankton are, in their turn, shaping theabundance of the emerging populations of microzooplankton. Phytoplankton,on the other hand, seem to be hardly controlled by grazing activity.     

Unexpected diversity and differential success of DNA transposons in four species of entamoeba protozoans

We report the first comprehensive analysis of transposable element content in the compact genomes (approximately 20 Mb) of four species of Entamoeba unicellular protozoans for which draft sequences are now available. Entamoeba histolytica and Entamoeba dispar, two human parasites, have many retrotransposons, but few DNA transposons. In contrast, the reptile parasite Entamoeba invadens and the free-living Entamoeba moshkovskii contain few long interspersed elements but harbor diverse and recently amplified populations of DNA transposons. Representatives of three DNA transposase superfamilies (hobo/Activator/Tam3, Mutator, and piggyBac) were identified for the first time in a protozoan species in addition to a variety of members of a fourth superfamily (Tc1/mariner), previously reported only from ciliates and Trichomonas vaginalis among protozoans. The diversity of DNA transposons and their differential amplification among closely related species with similar compact genomes are discussed in the context of the biology of Entamoeba protozoans.     

Structural differences between human proteins and aero- and microbial allergens define allergenicity

The current paradigm suggests that structural homology of allergenic proteins to microbial (particularly helminths) or human proteins underlie their allergenic nature. To examine systematically the structural relationships among allergens and proteins of pathogens (helminths, protozoans, fungi and bacteria) as they relate to allergenicity, we compared the amino acid sequence of 499 molecularly-defined allergens with the predicted proteomes of fifteen known pathogens, including Th2 inducing helminths and Th1-inducing protozoans, and humans using a variety of bioinformatic tools. Allergenicity was assessed based on IgE prevalences using publicly accessible databases and the literature. We found multiple homologues of common allergens among proteins of helminths, protozoans, fungi and humans, but not of bacteria. In contrast, 187 allergens showed no homology with any of the microbial genera studied. Interestingly, allergens without homologues or those with limited levels of sequence conservation were the most allergenic displaying high IgE prevalences in the allergic population. There was an inverse relationship between allergenicity and amino acid conservation levels with either parasite, including helminth, or human proteins. Our results suggest that allergenicity may be associated with the relative "uniqueness" of an antigen, i.e. immunogenicity, while similarity would lead to immunological tolerance.     

The role of quorum sensing mediated developmental traits in the resistance of Serratia marcescens biofilms against protozoan grazing

Resistance against protozoan grazers is a crucial factor that is important for the survival of many bacteria in their natural environment. However, the basis of resistance to protozoans and how resistance factors are regulated is poorly understood. In part, resistance may be due to biofilm formation, which is known to protect bacteria from environmental stress conditions. The ubiquitous organism Serratia marcescens uses quorum sensing (QS) control to regulate virulence factor expression and biofilm formation. We hypothesized that the QS system of S. marcescens also regulates mechanisms that protect biofilms against protozoan grazing. To investigate this hypothesis, we compared the interactions of wild-type and QS mutant strains of S. marcescens biofilms with two protozoans having different feeding types under batch and flow conditions. Under batch conditions, S. marcescens forms microcolony biofilms, and filamentous biofilms are formed under flow conditions. The microcolony-type biofilms were protected from grazing by the suspension feeder, flagellate Bodo saltans, but were not protected from the surface feeder, Acanthamoeba polyphaga. In contrast, the filamentous biofilm provided protection against A. polyphaga. The main findings presented in this study suggest that (i) the QS system is not involved in grazing resistance of S. marcescens microcolony-type biofilms; (ii) QS in S. marcescens regulates antiprotozoan factor(s) that do not interfere with the grazing efficiency of the protozoans; and (iii) QS-controlled, biofilm-specific differentiation of filaments and cell chains in biofilms of S. marcescens provides an efficient mechanism against protozoan grazing.     

Patterns of host specificity and transmission among parasites of wild primates

Multihost parasites have been implicated in the emergence of new diseases in humans and wildlife, yet little is known about factors that influence the host range of parasites in natural populations. We used a comprehensive data set of 415 micro- and macroparasites reported from 119 wild primate hosts to investigate broad patterns of host specificity. The majority (68%) of primate parasites were reported to infect multiple host species, including animals from multiple families or orders. This pattern corresponds to previous studies of parasites found in humans and domesticated animals. Within three parasite groups (viruses, protozoans and helminths), we examined parasite taxonomy and transmission strategy in relation to measures of host specificity. Relative to other parasite groups, helminths were associated with the greatest levels of host specificity, whereas most viruses were reported to infect hosts from multiple families or orders. Highly significant associations between the degree of host specificity and transmission strategy arose within each parasite group, but not always in the same direction, suggesting that unique constraints influence the host range of parasites within each taxonomic group. Finally characteristics of over 100 parasite species shared between wild primates and humans, including those recognised as emerging in humans, revealed that most of these shared parasites were reported from multiple host orders. Furthermore, nearly all viruses that were reported to infect both humans and non-human primates were classified as emerging in humans.