The response of benthic rhizopods to sediment disturbance does not support the intermediate disturbance hypothesis

Disturbance is one of the mechanisms which counteract competitive exclusion of populations in resource-limited communities, thereby facilitating coexistence and maintaining community species diversity. The intermediate disturbance hypothesis predicts maximum diversity at intermediate disturbance intensities and frequencies. This paper reports results of an experimental test of this hypothesis using a coastal benthic community of rhizopods (Protozoa: Rhizopoda), and experimental sediment resuspension as a simulated natural disturbance. We carried out two experiments of 5 d duration which focussed on the effects of resuspension intensity and frequency, respectively, on the abundance, species richness and on the Shannon-Weaver diversity index of rhizopod communities in surface sediments of natural sediment cores from the coastal southern Baltic. Care was taken to adjust the experimental treatments to the natural disturbance regime in this area.
Twenty-four and 28 rhizopod species were present during the intensity and frequency experiment, respectively. Small bacterivorous rhizopods of the Vannellidae, Cochliopodidae, Paramoebidae and Rhizopoda incertae sedis dominated the communities during both experiments. Rhizopod abundance, species richness and diversity increased towards the end of the intensity experiment, but they did not show effects of disturbance intensity. Similarly, no effects of disturbance frequency were found during the frequency experiment. Our results indicate that coexistence and community diversity maintenance in benthic rhizopod communities, and probably in benthic heterotrophic protistan communities in general, may rely on different mechanisms than intermediate disturbance, such as trophic niche separation and high rates of dispersal and colonisation.     

Induced cell fusion inForaminifera

Summary The fusion of cells of the monothalamous foraminiferMyxotheca arenilega (Protozoa, Rhizopoda) is described. The fusion process is induced by the separation of the extracellular organic shell from the cell body. As several cells can fuse either stepwise or simultanously, a giant cell of some millimeters in diameter can be formed.     

5S ribosomal RNA sequence of Pneumocystis carinii and its phylogenetic association with "Rhizopoda/Myxomycota/Zygomycota group"

The cytoplasmic 5S ribosomal RNA sequence from Pneumocystis carinii was determined and compared with those of 382 eukaryotes and an evolutionary tree was constructed to establish the phylogenetic position of Pneumocystis. The data suggest that Pneumocystis is associated with the Rhizopoda/Myxomycota/Zygomycota group but not with common fungi, such as Ascomycota or Basidiomycota, nor with other protozoa.     

Remarks on the ecology of Pyxidicula operculata (Agardh) Ehrenberg

The rhizopod fauna of two artificial ponds near Bonn was investigated. By means of the analysis of the colonization of both natural and artificial substrates data were collected about the ecology of Pyxidicula operculata (Rhizopoda testacea). Results give evidence for the wide temperature range under which this animal can develop and suggest that the species shows the typical characteristics of an r-strategist.     

On Soil Rotatoria from a Lithotelma near Halali Lodge in Etosha National Park in N-Namibia,South Africa

A soil sample out of a dried rockpool (lithotelma) on a dolomit hill in the Etosha National Park, Namibia, was investigated for possible occurence of rotifers. Besides a numerous and rich microfaunae, e.g. Zooflagellata, Rhizopoda. Acari, Nematoda, Tardigrada and Copepoda, 24 rotifers were found. Until today, four so far unknown Bdelloidea could be described: Dissotrocha decembullata n. sp., Dissotrocha hertzogi aculeata n. ssp., Otostephanos jersabeki n. sp. and Philodina foissneri n. sp.     

First evidence for diploidy and genetic recombination in free-living amoebae of the genus naegleria on the basis of electrophoretic variation

Electrophoretic variation for 15 enzyme-coding genes was studied in various Naegleria (Rhizopoda, Vahlkampfiidae) species. The occurrence of complex banding patterns provided the first evidence of a diploid structure of the genome of these amoebae. The putative loci identified were found not to be linked and the genotypic distribution suggested chromosomal recombination for one species (Naegleria lovaniensis).     

Molecular Evolutionary Analyses of Nuclear-Encoded Small Subunit Ribosomal RNA Identify an Independent Rhizopod Lineage Containing the Euglyphina and the Chlorarachniophyta

The Rhizopoda comprise a diverse assemblage of protists which depend on lobose or filose pseudopodia for locomotion. The biochemical and morphological diversity of rhizopods has led to an uncertain taxonomy. Ribosomal RNA sequence comparisons offer a measure of evolutionary relatedness that is independent of morphology and has been used to demonstrate a polyphyletic origin of the Lobosea. We sequenced complete small subunit ribosomal RNA coding regions from the filose amoebae, Euglypha rotunda and Paulinella chromatophora (Euglyphina) to position these taxa in the eukaryote phylogeny. The neighbor-joining analyses show that E. rotunda and P. chromatophora share a monophyletic origin and are not closely related to any lobose amoebae in our analyses. Instead, the Euglyphina form a robust sister group to the Chlorarachniophyta. These results provide further evidence for the polyphyly of the Rhizopoda and support the creation of a new amoeboid lineage which includes the Euglyphina and the chlorarachniophyte algae; taxa with tubular mitochondrial cristae and filose or reticulate pseudopodia.     

四川九寨沟自然保护区浮游动物调查

2002年5～6月、7～8月和2003年7月分3次对九寨沟自然保护区四条主沟的浮游动物多样性进行了调查。结果表明：九寨沟主要水体浮游动物由3门、5纲、11目、20科、34属、71种组成。区系特点以原生动物种类最丰富,有34种,占浮游动物种类组成的47．8％,其中根足纲种类最多,达29种,占全部浮游动物的40．8％;其次为节肢动物有21种,占29．6％;种类最少的类群属轮虫,仅16种,占22．5％。分布以长海、熊猫海、珍珠滩种类最多,数量最大。     

Small subunit ribosomal DNA suggests that the xenophyophorean Syringammina corbicula is a foraminiferan

Xenophyophorea are giant deep-sea rhizopodial protists of enigmatic origins. Although species were described as Foraminifera or sponges in the early literature, the xenophyophoreans are currently classified either as a class of Rhizopoda or an independent phylum. To establish the phylogenetic position of Xenophyophorea, we analysed the small subunit (SSU) rRNA gene sequence of Syringammina corbicula Richardson, a newly described xenophyophorean species from the Cape Verde Plateau. The SSUrDNA analyses showed that S. corbicula is closely related to Rhizammina algaeformis, a tubular deep-sea foraminiferan. Both species branch within a group of monothalamous (single-chambered) Foraminifera, which include also such agglutinated genera as Toxisarcon, Rhabdammina, and Saccammina, and the organic-walled genera Gloiogullmia and Cylindrogullmia. Our results are congruent with observations of similar cytoplasmic organisation in Rhizammina and Syringammina. Thus, the Xenophyophorea appear to be a highly specialised group of deep-sea Foraminifera.     

Pneumocystis carinii: Freeze-fracture study of stages of the organism

The morphology and life cycle of Pneumocystis carinii were studied in cortico-steroid-treated rats by ultrathin section and freeze-fracture electron microscopy. The following stages of P. carinii were noted: trophic, precyst, and cyst. The crescent-shaped cysts appeared to be intermediate forms between precyst and cyst. The cell wall of the trophic stage showed membrane structures suggestive of protozoan endocytosis, whereas the surface of the precyst stage was smooth. The cell wall of the cyst lacked the specialized structural differentiation of yeasts and resembled that of Plasmodium spp. We conclude that P. carinii belongs to the Protozoa, and is presumably Rhizopoda.     

A revised classification of the Gymnamoebia (Protozoa: Sarcodina)

A revised classification of the naked amoebae is proposed on the basis of a synthesis of many kinds of information presently available for taxonomic purposes above the species level. These amoebae, constituting the subclass Gymnamoebia within the class Lobosea, superclass Rhizopoda, include not only strictly lobose amoebae but also those with more or less filose subpseudopodia produced from a broader hyaline lobe. The subclass is divided into the orders Amoebida, Schizopyrenida, and Pelobiontida, and suborders are recognized within the order Amoebida. Although the Gymnamoebia are undoubtedly heterogeneous and polyphyletic and the proposed classification is intended chiefly as a practical system with a logical basis, there are a few suggestions of natural relationships.     

Hydrobiological analysis of a peat bog with emphasis on its planktonic diversity and population dynamics in Bumdeling Wildlife Sanctuary, eastern Bhutan

A pioneering limnological investigation was carried out in Bhutan in a small peat bog in the Trashiyangtse district (1950 m above sea level) from February 2000 to January 2002. The sampled pond water had low transparency (55.0–95.0 cm), was typically acidic (pH 5.69–6.58) with soft water (alkalinity, 11.0–36.0 mg/l; total hardness, 10.0–34.0 mg/l), and had low to moderate specific conductivity (17.0–62.0 μS/cm). Further, moderate Na (2.0–6.8 mg/l), K (1.8–13.5 mg/l), sulphate (0.85–2.99 mg/l), and silicate (2.5–15.0 mg/l) concentrations as well as low nutrient levels such as phosphate (0.006–0.170 mg/l) and nitrate (0.003–0.180 mg/l) characterize the water in the peat bog. The recorded net plankton comprised 27 species of phytoplankton and 49 species of zooplankton, with the latter indicating greater homogeneity and breaking down into Rotifera (23 species) > Cladocera (13 species) > Rhizopoda (8 species) > Copepoda (3 species) > Ostracoda = Nematoda (1 species each). On the other hand, the net plankton density ranged between 93 and 692 number/l (n/l) with numerical dominance by phytoplankton (68.5% ± 12%), of which Chlorophyceae were predominant (90 ± 63 n/l). Zooplankton showed moderately high diversity (2.745 ± 0.293) and evenness (0.925 ± 0.049) and exhibited almost equal abundance of four recorded groups, namely Cladocera (20 ± 15 n/l) > Rotifera (15 ± 6 n/l) > Copepoda (14 ± 7 n/l) > Rhizopoda (14 ± 4 n/l). While no significant impact of abiotic factors was recorded on zooplankton density, rainfall alone was the most important factor that influenced net plankton and various groups of phytoplankton. Comments on some comparative limnological attributes are also made with similar as well as different habitats in the nearby Himalayan countries.     

The moss dwelling testacean fauna of Île de la Possession

An ecological study of the moss dwelling testacean fauna (Protozoa, Rhizopoda) on Île de la Possession (Crozet Archipelago, sub-Antarctica) revealed 83 taxa, belonging to 21 genera. The moss flora was dominated by cosmopolitan and ubiquitous taxa, such as Trinema lineare, T. enchelys, Euglypha laevis and E. rotunda. A cluster analysis and a correspondence analysis identified three communities: (1) a Corythion dubium assemblage found in a drier, slightly acidic terrestrial moss vegetation, (2) the Arcella arenaria, and (3) the Difflugiella crenulata assemblages, both characteristic of wetter, circumneutral habitats. The latter typified submerged mosses growing in running water, while the A. arenaria assemblage seemed to prefer mosses in standing waterbodies. Moisture conditions appeared to play a key role in determining the distribution pattern of testacean communities, while pH was only a secondary factor. A logistic regression emphasised the effect of the habitat type in controlling the variance in testacean assemblages. Moreover, the close relationship between bryophyte species and habitat type had a significant influence on the distribution pattern of the testate amoebae. Weighted averaging and calibration were used to estimate moisture optima and tolerances of the testate amoebae.     

Testacean communities in perturbed soils: the influence of the wandering albatross

On Île de la Possession (Crozet Archipelago, sub-Antarctica), the testate amoebae (Protozoa, Rhizopoda) fauna in soils around abandoned and occupied nests of the wandering albatross (Diomedea exulans) was investigated. A comparison with control samples, a cluster analysis and several ordination techniques indicated that the presence of the breeding albatrosses induced modifications in physico-chemical soil characteristics and in the soil inhabiting testacean fauna. Only 11 testate species occurred frequently in the soils in the albatross’ zone. Soils around occupied nests had significantly higher moisture values, less acid pH values, an increased specific conductance and elevated phosphate and ammonium concentrations. Highly influenced testacean communities were characterised by high abundances of Difflugiella oviformis and extremely high abundances of Trinema lineare, resulting in a very low diversity and evenness within these communities. The intermediary situation of one abandoned nest indicated that soils around abandoned nests evolve gradually back to undisturbed soils. Although an overall negative influence on the testacean diversity, a limited albatross’ influence may increase the living fraction within the testacean soil communities.     

杭州湾滨海湿地不同植被类型沉积物磷形态变化特征

研究了杭州湾滨海湿地不同植被类型下0-5 cm和10-20 cm沉积物总磷(TP)、无机磷(IP)、有机磷(OP)及其形态变化特征,揭示湿地植被演替对沉积物磷形态的影响.结果表明,沉积物TP,互花米草(MC)显著高于其他植被类型.在IP中,可溶性松散态磷(Soluble and loosely bound P,SL-Pi)含量光滩(CK)最小、MC最大;还原态可溶性磷(Reductant soluble P,RS-Pi)含量芦苇(LW)和MC显著高于CK和海三棱藤草(BC);钙磷(Ca-Pi)含量CK和BC显著大于LW和MC.在OP中,活性有机磷( Labile Po,L-Po)含量最低、中等活性有机磷(Moderately labile Po,ML-Po)含量最高、非活性有机磷(Nonlabile Po,NL-Po)处于中间水平.IP是磷素的主要形态、占TP的74％ -89％,而Ca-Pi又是IP的主要形态、于湿地沉积物淤积初期通过吸附沉淀作用存留.杭州湾湿地植被自然演替过程中不同植物生物量积累和营养物质循环过程的变化导致沉积物中磷形态的差异.植被演替初期,BC显著改变0-5 cm沉积物磷形态,对10-20 cm沉积物无显著影响;植物演替后期的LW和MC促使0-5 cm沉积物有机磷快速积累、10-20 cm沉积物有机磷小幅增加,同时促进Ca-Pi向可溶性、活性态磷转变.     

Biochemical Taxonomy of Symbiotic Chlorella Strains from Paramecium and Acanthocystis*

Biochemical and physiological characters of 5 symbiotic Chlorella strains, 4 of them from Paramecium (Ciliata) and one from Acanthocystis (Rhizopoda, Heliozoa), were studied. Four strains (3 from Paramecium and one from Acanthocystis) belong to the same species. This is characterized by the presence of hydrogenase, no formation of secondary carotenoids, no growth on mannitol, requirements for thiamine and vitamin B₁₂, and a G + C content of the DNA of 66.4–68.4 mol%; the limits of growth are at pH 5.5, at up to 1% NaCl, and at 26–30°C. The strains are somewhat heterogeneous in their utilization of inorganic nitrogen sources: only two of them are able to use nitrate, whereas all can grow with nitrite and ammonium. Thus, in two strains the nitrate-reducing system — in contrast to nitrite reductase — seems to be defective. Another strain, which has been claimed to be from Paramecium, belongs to C. protothecoides.     

Accumulation of sediment-associated viruses in shellfish.

The present study focused on the importance of contaminated sediments in shellfish accumulation of human viruses. Epifaunal (Crassostrea virginica) and infaunal (Mercenaria mercenaria) shellfish, placed on or in cores, were exposed to either resuspended or undisturbed sediments containing bound poliovirus type 1 (LSc 2ab). Consistent bioaccumulation by oysters (four of five trials) was only noted when sediment-bound viruses occurred in the water column. Virus accumulation was observed in a single instance where sediments remained in an undisturbed state. While the incidence of bioaccumulation was higher with resuspended rather than undisturbed contaminated sediment, the actual concentration of accumulated viruses was not significantly different. The accumulation of viruses from oysters residing on uninoculated sediments. When clams were exposed to undisturbed, virus-contaminated sediments, two of five shellfish pools yielded viral isolates. Bioaccumulation of undisturbed sediments by these bivalves was considered marginal when related to the concentration of virus in contaminated sediments; they would only represent a significant threat when suspended in the water column. Arguments were advanced for water-column sampling in the region of the water-sediment interface to provide an accurate determination of the virological quality of shellfish harvesting waters.     

Effects of sediment pretreatment on the performance of sediment microbial fuel cells

In the present study, the effects of different pretreatment methods for sediments on the performance of sediment microbial fuel cells (SMFCs) were evaluated. Autoclaved (30 and 60 min), and heated (150 °C, 3 h) sediments demonstrated high power density, compared with control and heated (60 °C, 3 h) sediments. An SMFC with heated (60 °C, 3 h) sediment was found to easily form a biocathode. The power density of an SMFC with heated (150 °C, 3 h) sediment was 214 mW m(-2) on day 24. Furthermore, autoclaved (30 and 60 min) and heated (3 h, 60 and 150 °C) sediments accelerated the production of dissolved organic matter (DOM). The DOM in heated (60 °C, 3 h) sediments had larger molecular sizes. The present study demonstrates that SMFCs can have high power density and high loss on ignition removal efficiencies when produced from sediments by suitable pretreatment methods.     

Lipid Biomarkers of Suspended Particulate Organic Matter in Lake Bled (NW Slovenia)

Aquifer sediments from Norman, Oklahoma, were used to study the potential for microbial reduction of Cr(VI) to Cr(III). Black, clay-like sediments rapidly reduced Cr(VI) in both autoclaved and viable microcosms, indicating an abiotic mechanism. Lightcolored sandy sediments slowly reduced Cr(VI) only in viable microcosms, indicating a biological process. Cr(VI) reduction in these sediments had a pH optimum of 6.8 and temperature optima of 22°C and 50°C. Nearly complete inhibition of Cr(VI) reduction was observed when sandy sediments were shaken in the presence of oxygen. The addition of nitrate but not sulfate, selenate, or ferrous iron to sandy sediments inhibited Cr(VI) reduction. When electron acceptors were supplied in combinations with Cr(VI), reduction of Cr(VI) was greatest in the absence of nitrate. No loss of sulfate and no production of Fe(II) occurred in the presence of Cr(VI). The addition of molybdate to the microcosms did not affect Cr(VI) reduction in sandy sediments until very high concentrations (40 times the Cr[VI] concentration) were used. Interestingly, the addition of bromoethanesulfonic acid in amounts less than, or slightly greater than, the Cr(VI) concentration partially inhibited Cr(VI) reduction in sandy sediments. In the absence of this bacterial inhibitor, the sandy sediments produced methane. A methanogenic enrichment capable of reducing Cr(VI) during growth was obtained from sandy sediments. However, the enrichment produced methane only when Cr(VI) was absent, indicating that a shift in electron flow from methane production to Cr(VI) reduction may have occurred. These studies showed that Cr(VI) reduction in sandy aquifer sediments is a biologically mediated, anaerobic process that is inhibited by oxygen and partially inhibited by nitrate. The lack of sulfate reduction and sulfide production, as well as a lack of inhibition of Cr(VI) reduction by molybdate, argues against an indirect mechanism for Cr(VI) reduction, in which the sulfide produced during sulfate reduction would chemically reduce Cr(VI). Rather, Cr(VI) reduction may be mediated by a community of microorganisms that ordinarily use methanogenesis as the terminal electron-accepting process.     

Accumulation of sediment-associated viruses in shellfish

The present study focused on the importance of contaminated sediments in shellfish accumulation of human viruses. Epifaunal (Crassostrea virginica) and infaunal (Mercenaria mercenaria) shellfish, placed on or in cores, were exposed to either resuspended or undisturbed sediments containing bound poliovirus type 1 (LSc 2ab). Consistent bioaccumulation by oysters (four of five trials) was only noted when sediment-bound viruses occurred in the water column. Virus accumulation was observed in a single instance where sediments remained in an undisturbed state. While the incidence of bioaccumulation was higher with resuspended rather than undisturbed contaminated sediment, the actual concentration of accumulated viruses was not significantly different. The accumulation of viruses from oysters residing on uninoculated sediments. When clams were exposed to undisturbed, virus-contaminated sediments, two of five shellfish pools yielded viral isolates. Bioaccumulation of undisturbed sediments by these bivalves was considered marginal when related to the concentration of virus in contaminated sediments; they would only represent a significant threat when suspended in the water column. Arguments were advanced for water-column sampling in the region of the water-sediment interface to provide an accurate determination of the virological quality of shellfish harvesting waters.