Klaus Hausmann

Extrusive Organelles in Protists

Publisher Summary This chapter discusses the extrusive organelles in protists. Extrusive organelles are membrane-bounded structures of protists, usually located in the cortical cytoplasm of these cells. Although they have different type-specific structures and functions, they all exhibit one general characteristic: they are readily discharged when subjected to a wide range of stimuli. This chapter describes the structural and functional diversity of extrusomes in protozoa. Some have a wide distribution in flagellates as well as in ciliates; others are restricted to small systematic groups, for example, the discobolocysts of the flagellate order Chrysophyceae or the cnidocysts of a few species of dinoflagellates. Some enigmatic similarity exists between extrusomes and organelles of systematically widely differing organisms such as ejectisomes of algae and the R bodies of the bacterial symbionts of Paramecium or the toxicysts of ciliates and the nematocysts of cnidarians.

Large-scale patterns in biodiversity of microbial eukaryotes from the abyssal sea floor

Eukaryotic microbial life at abyssal depths remains “uncharted territory” in eukaryotic microbiology. No phylogenetic surveys have focused on the largest benthic environment on this planet, the abyssal plains. Moreover, knowledge of the spatial patterns of deep-sea community structure is scanty, and what little is known originates primarily from morphology-based studies of foraminiferans. Here we report on the great phylogenetic diversity of microbial eukaryotic communities of all 3 abyssal plains of the southeastern Atlantic Ocean---the Angola, Cape, and Guinea Abyssal Plains---from depths of 5,000 m. A high percentage of retrieved clones had no close representatives in genetic databases. Many clones were affiliated with parasitic species. Furthermore, differences between the communities of the Cape Abyssal Plain and the other 2 abyssal plains point to environmental gradients apparently shaping community structure at the landscape level. On a regional scale, local species diversity showed much less variation. Our study provides insight into the community composition of microbial eukaryotes on larger scales from the wide abyssal sea floor realm and marks a direction for more detailed future studies aimed at improving our understanding of deep-sea microbes at the community and ecosystem levels, as well as the ecological principles at play.

Demonstration of tubulin, actin and α-actinin by immunofluorescence in the microtubule-microfilament complex of the cytopharyngeal basket of the ciliate Pseudomicrothorax dubius

Abstract The feeding organelle (cytopharyngeal basket) of the ciliate Pseudomicrothorax dubius contains a highly complex pattern of microtubular lattices closely associated with microfilamentous web-like material. Indirect immunofluorescence microscopy on cell ‘ghosts’ and isolated cytopharyngeal baskets with antibodies against brain tubulin and mammalian muscle proteins show the presence of not only tubulin but also actin and α-actinin within this organelle. These findings demonstrate a special microtubule-microfilament complex and suggest the participation of contractile elements in conjunction with microtubules in the complex movement phenomena observed during the feeding process.

Bilateral symmetry in the cnidocil-nematocyst complex of the freshwater medusaCraspedacusta sowerbii Lankester (Hydrozoa, Limnomedusae)

Abstract We have investigated the fine structure of the cnidocil apparatus and the nematocyst in the hydrozoan Craspedacusta sowerbii using both light and electron microscopy. The structures are intimately connected and form a highly polarized, bilaterally symmetrical structure, the cnidocil-nematocyst complex. The cnidocil apparatus consists of a modified cilium, about 12 stereocilia, and an inner ring of short microvilli surrounding the nematocyst and cnidocil. The stereocilia enclose the cnidocil circularly in its distal region but in a crescent-like pattern in the proximal region; thus the nematocyst is not encompassed by the stereocilia, but only by the inner ring of short microvilli. We present a new reconstruction of the cnidocil apparatus and discuss the physiological significance of the various elements of the cnidocil-nematocyst complex.

Arrangement and structure of plates in the cortical alveoli of the hypotrich ciliate, Euplotes vannus

Each alveolus of the pellicle of Euplotes vannus contains a plate about 40 nm thick. Each plate consists of three layers of electron-dense material interconnected by ill-defined, irregular bridges. The margins of each plate appear strengthened. The entire cell is covered by a layer of these plates, interrupted only at the site of emergence of the dorsal bristles, cirri, and membranelles. At these sites specific modifications of the plates are apparent. These plates appear to give the cell rigidity, but otherwise their function is obscure.

Composition of benthic protozoan communities along a depth transect in the eastern Mediterranean Sea

The benthic protozoans were investigated along a transect in the eastern Mediterranean Sea from the Ionian to the Levantine Sea. Sediment samples were taken during Meteor cruise 25/1 in May and June 1993 at water depths of between 156 and 4617 m with a box corer and a multiple corer. A semi-quantitative cultivation technique was applied by placing sediment in petri dishes and diluting with sterile biotope water. Microscopic analyses of the protozoan taxa were conducted immediately after sampling, and then daily after enrichment with organic substrate. A total of 134 protozoan morphospecies were recorded, including 87 flagellates, 12 naked amoebae and 35 ciliates. 58% of the species could be attributed to genera known from shallow waters, demonstrating the wide distribution of these taxa. The number of recorded species per location ranged from 0 to 35 and decreased with increasing water depth. At stations deeper 1300 m very low species numbers as well as low potential abundances were recorded. Qualitative changes in the taxonomic composition with increasing depth were recorded as a decrease in the proportion of amoebae and euglenid flagellates and as an increase in the proportion of dinoflagellates. Ciliates were found down to a depth of 4260 m. The number of species was also dependent on the chloroplastic pigment equivalent (CPE), indicating a dependency on sedimented phytodetritus. The observed species included picophagous species, which feed mostly on bacteria, as well as nano- and microphagous species, which generally feed on protists, suggesting the existence of several trophic levels within the deep sea microbial food web.

Light and electron microscopic study of the bacterial adhesion to termite flagellates applying lectin cytochemistry

SummaryMany of the flagellates inhabiting the hindgut of lower termites are associated with ectobiotic, rod-like bacteria or spirochetes. Different types of attachment sites are present. Electron dense material underlies, e.g., the plasma membrane ofJoenia annectens at the contact site, whereas other attachment sites do not show any visible specializations. The host cells glycocalyx may, however, be reduced at the attachment sites as it is the case inDevescovina glabra. The thick glycocalyx ofStephanonympha nelumbium is not changed at the sites where bacterial rods attach, but spirochetes penetrate to a certain extent. Bacteria which colonize the extracellular surface structures ofMicrorhopalodina multinucleata express their own glycocalyx to mediate a contact. In this study we focussed on the examination of one common mode of interaction between bacteria and their host cells, i.e., adhesion via lectins and sugars. The sugar composition was analysed by light and electron microscopic labelling experiments using the lectins Con A, WGA and SBA. In general, only the posterior body surface ofJoenia which is colonized with bacteria is labelled. The demonstrated sugars are found in fibrous glycocalyx portions surrounding the attachment sites of the bacteria. Such glycocalyx fibres in combination with the electron dense material supporting the attachment sites seem to be the prerequisites for bacterial attachment. InD. glabra, however, a role for sugars in mediating the attachment could not be demonstrated. Removal of the ectobiotes using antibiotics revealed that the specialized contact sites ofJoenia are present in the absence of bacteria and thus possibly serve to attract bacteria. Nothing, however, remains of the former attachment sites in bacteria-freeDevescovina cells. Attachment sites in this case could be induced by bacterial contact. There is not one general mechanism for bacterial attachment to termite flagellates; rather, adhesion seems to follow different strategies.

Structural studies on Trichodina pediculus (Cilliophora, Peritricha): I. The locomotor fringe and the oral apparatus

The structure of the epizoitic clialte Trichodina pediculus from the freshwater medusa Craspedacusta wowerbii is described using light and transmission electron microscopy. The organism moves on the surface of the host using a basal locomotor fringe of cilia. This has three components: A sparsely ciliated anterior row of kinctosomes gives rise to the lateral cilia. Every other kinetosome of this row is connected to oblique bands of eight ciliated kinetosomes. These form the more substantial locomotor werath. A more basally located row of sparsely ciliated kinestosomes is separated from the locomoter wreath by a septum. This final row is intimately associated with the adhesive disc. The buccal cavity is located near the apical end of the cell. One haplokinety and one polykinety spiral around the apical end of the cell and pass down into the buccal cavity where further rows of cilia are apparent. Oral ribs pass from the haplokinety to the cytostome, and elongate viscles with structured contents are implicated in the supply of membranes for forming food vacuoles.

Description of Paramoeba atlantica n. sp. (Amoebozoa, Dactylopodida) – a Marine Amoeba from the Eastern Atlantic, with Emendation of the Dactylopodid Families

Summary. A strain of marine amoeba has been isolated and studied from the bottom sediments of the Great Meteor Seamount (Atlantic Ocean, 29°36.29′N; 28°59.12′W; 267.4 m deep). This amoeba has a typical dactylopodiid morphotype, a coat of delicate, boat-shaped scales, and a Perkinsela-like organism (PLO), an obligatory, deeply-specialized kinetoplastid symbiont near the nucleus. These characters allow us to include this species into the genus Paramoeba. However, it differs from its only described species, P. eilhardi, in the structure of scales. P. atlantica n. sp. is established therefore to accommodate the studied strain. SSU rRNA gene sequence analysis suggests that P. atlantica belongs to the Dactylopodida, and is sister to a monophyletic clade of P. eilhardi and all Neoparamoeba spp., branching separately from P. eilhardi. Therefore, the genera Paramoeba and Neoparamoeba, currently defined based on the cell surface ultrastructure, might be paraphyletic and probably should be synonymized, as further evidence is accumulated. Based on the data available we emend the families Vexilliferidae and Paramoebidae to make them more consistent with the current phylogenetic schemes.

Development of compound trichocysts in the ciliatePseudomicrothorax dubius

SummaryDuring the logarithmic growth of the ciliatePseudomicrothorax dubius associations between mitochondria, rough endoplasmic reticulum and dictyosomes have been observed. The Golgi apparatus is very active and it is suggested that, as a consequence of cytotic activity, the contents of the Golgi vesicles become incorporated into large irregular vacuoles as globular material. The large vacuoles develop into trichocysts and the dictyosome derived globules consolidate to ultimately form the rod-like arms of the trichocysts of theMicrothoracidae.