Norbert Hülsmann

Protist transport via ballast water — biological classification of ballast tanks by food web interactions

Summary Ships ballast waters and sediments serve as a vector in the transportation of marine organisms, including toxic dinoflagellates, parasitic labyrinthulids and other potentially harmful species. These exotic organisms have caused major ecological changes, as well as concern over effects on human health, fishing and aquaculture. Heterotrophic protozoans may be inadvertently introduced when their trophic or resting stages are discharged with the ballasttank waters and sediments. This survey describes the protist communities present in ballast tanks of cargo vessels arriving in Israeli Mediterranean ports. 362 records of living protozoan species, identified to at least 198 species belonging to 82 heterotrophic genera, were made in this study. The tanks examined exhibited a remarkable uniformity of protist communities, enabling us to classify food web interactions, ranging from bacteria-grazing protozoans, predatory unicells, and more intricate associations including parasites and metazoans.

The Genome of the Foraminiferan Reticulomyxa filosa

BACKGROUND Rhizaria are a major branch of eukaryote evolution with an extensive microfossil record, but only scarce molecular data are available. The rhizarian species Reticulomyxa filosa, belonging to the Foraminifera, is free-living in freshwater environments. In culture, it thrives only as a plasmodium with thousands of haploid nuclei in one cell. The R. filosa genome is the first foraminiferal genome to be deciphered. RESULTS The genome is extremely repetitive, and the large amounts of identical sequences hint at frequent amplifications and homologous recombination events. Presumably, these mechanisms are employed to provide more gene copies for higher transcriptional activity and to build up a reservoir of gene diversification in certain gene families, such as the kinesin family. The gene repertoire indicates that it is able to switch to a single-celled, flagellated sexual state never observed in culture. Comparison to another rhizarian, the chlorarachniophyte alga Bigelowiella natans, reveals that proteins involved in signaling were likely drivers in establishing the Rhizaria lineage. Compared to some other protists, horizontal gene transfer is limited, but we found evidence of bacterial-to-eukaryote and eukaryote-to-eukaryote transfer events. CONCLUSIONS The R. filosa genome exhibits a unique architecture with extensive repeat homogenization and gene amplification, which highlights its potential for diverse life-cycle stages. The ability of R. filosa to rapidly transport matter from the pseudopodia to the cell body may be supported by the high diversification of actin and kinesin gene family members.

Protists — A Dominant Component of the Ballast-Transported Biota

Ship’s ballast water and sediments serve as a main vector in the transportation and spreading of protists: toxic dinoflagellates, parasitic labyrinthulids and other potentially harmful and harmless unicellular beings. The omnipresence of protists in the sea means that photo- and heterotrophic protists invariably occur in ballast water and sediments. Ballast tanks — especially in container vessels with a high turnover of ballast water — serve as mesocosms supporting rich assemblages of heterotrophic protists. We estimate that more than 250 protist taxa are commonly present in a ballast tank, since their size and diet favour survival in there. As protists form an important part of the marine food web, otherwise harmless protists may be indirectly involved in the successful transport of bioinvaders by increasing the chances of survival of entrained filter-feeding and biofilm-grazing metazoans. Furthermore, we suggest that ballast-transported protists, harmless in their native habit ts, may modify or trigger changes in native assemblages, or may affect them by wholly outcompeting or partially displacing native taxa. Of momentous concern is whether protists, that are harmless in their native habitats, may become toxic after ballast-mediated spreading into the microbial associations of a recipient area, or vice versa, that the introduction of bacteria may start toxin production in formerly harmless eukaryotes.

Comparative Fine Structural Investigations of Interphase and Mitotic Nuclei of Vampyrellid Filose Amoebae

The nuclei of trophozoites and digestive cysts as well as mitotic nuclei of several species of the vampyrellids Vampyrella, Gobiella, Hyalodiscus, Arachnula, and Leptophrys were investigated by electron microscopy. Except for some species of the genus Hyalodiscus, the vampyrellids are generally multinucleate. The nuclei of the trophozoite stage are in interphase. These nuclei are spherical, except for the genus Arachnula, which reveals elongated nuclei. In digestive cysts of all vampyrellids the nuclei enlarge and the pars granulosa of the nucleoli becomes prominent. Karyokineses take place synchronously in older digestive cysts, which transform into reproductive cysts. The nuclei divide by closed intranuclear orthomitosis. In telophase the old nuclear envelope disintegrates and a new one is rearranged. Only in the genus Leptophrys the nuclear envelope decomposes before telophase. Neither centrioles nor MTOC‐plaques have been found in any stage of mitosis. After karyokinesis the cell divides inside the cyst or when leaving the cyst.

Towards a new perspective in protozoan evolution

Summary As in other biological disciplines, in protozoology the field of phylogenetically oriented systematics is currently experiencing a vital popularity. This is not only caused by the discovery of new species with attributes or features of missing links or by the elaboration of ultrastructural and molecular features of little-known protozoa during the last 20 years, but mainly by the recent establishment of new quantitative approaches and methods of classification and of phylogeny reconstruction. Among them, the concepts of cladistic taxonomy appear most notable. They allow us to differentiate between homologous characters developed in different historical horizons and to evaluate their impact on the development of new strategies.

Lateromyxa gallica N. G., N. Sp. (Vampyrellidae) : a filopodial amoeboid protist with a novel life cycle and conspicuous ultrastructural characters

ABSTRACT. A large, uni‐ or multinucleate vampyrellid rhizopod, Lateromyxa gallica n. g., n. sp., has been isolated several times from two lakes in central France between September 1973 and August 1989 and cultivated for several months or years under laboratory conditions. No essential variations of feeding behaviour were found over the time; all isolated strains invade the trichomes of the green alga Oedogonium and move, divide and encyst inside the vanished plant cells. Penetration is performed by attacking the cross walls and only primary attacks are directed against the lateral cell walls of the algae. These findings contrast with the behaviour, life cycles and fine structure of all known species of the genera Vampyrella, Hyalodiscus, Arachnula and Gobiella. The establishment of a new genus, Lateromyxa, with the type species Lateromyxa gallica is therefore proposed.

Karyological investigations on the vampyrellid filose amoeba Lateromyxa gallica Hülsmann 1993

The nuclei of the vampyrellid filose amoeba Lateromyxa gallica were investigated in trophozoites, early digestive cysts, reproductive cysts, and in developing resting cysts. Trophozoites possess numerous, minute, spherical nuclei in interphase. In early digestive cysts the nuclei enlarge and the morphology of the nucleolus changes. The digestive cysts develop into reproductive cysts. Karyokinesis takes place synchronously. The spindle is intranuclear and acentrical. In metaphase, the chromosomes are arranged in a distinct equatorial plate. The nuclear envelope remains intact at least until telophase. Shortly after karyokinesis the trophozoites leave the cysts. Cytokinesis regularly takes place when the trophozoites invade cells of Oedogonium. Under unfavorable conditions the trophozoites as well as the digestive cysts are able to form resting cysts. Nuclei of digestive cysts which begin to develop into resting cysts were found in the pachytene phase of meiosis, proved by synaptonemal complexes. Karyokinesis, probably the second meiotic division, was detected when the resting cyst was almost fully developed. From the results of our investigations, the vampyrellid filose amoebae can be regarded as sexual.

The Biological Efficacy of Open Ocean Exchange — Implications for Ballast Water Management

The urgent need to control ballast-mediated bioinvasions prompted the maritime industry and the legislators to adopt open-ocean ballast water exchange without rigorously testing its effectiveness in terms of eliminating ballast-entrained biota. A review of recent studies of biota entrained in ballast water and sediments following open-ocean exchange raised questions as to the reliability of the procedure as an effective control measure.

Dracomyxa pallida gen. et sp. nov.: a new giant freshwater foraminifer, with remarks on the taxon Reticulomyxidae (emend.).

Reticulomyxids are organotrophic freshwater foraminifers typically placed within the radiation of early monothalamous Foraminifera. Though ubiquitous, reticulomyxids are rarely reported, which may be due both to their concealed life style and to inappropriate isolation techniques. Their taxonomic position is largely based on developmental stages of the life cycle. Here, we describe a new freshwater species, Dracomyxa pallida gen. nov. et sp. nov., isolated from submersed plant material. It has two possible life cycles including small cells, large plasmodia and encysted stages. Both types of development occur simultaneously in cultures derived from a single cell as well as in crude cultures. We amplified and sequenced a short sequence fragment of the 18S rRNA gene of the new isolate. Comparative phylogenetic analysis and molecular characterization indicate that it is a new reticulomyxid species, with Reticulomyxa filosa Nauss, Haplomyxa saranae Dellinger and Wobo gigas Hülsmann as the closest relatives. Unique features such as tripodal pediculated cysts and the lack of cleansing process justify the erection of a new genus.

Induction of lobopodia and lamellipodia in a filopodial organism (Vampyrella lateritia)

Summary The normally filopodial motor system of Vampyrella lateritia was modified by chemical agents that promote cell adhesion and spreading and by mechanical stimuli. Large lobopodia arose by cell surface blebbing between the filopodia. The cortical cytoskeletal layers periodically detached from the plasma membrane at the growing tips of lobopodia and moved backwards. Combined chemical and mechanical stimuli sometimes resulted in the development of lamellipodia, which were either circular as characteristic of cell spreading, or intensely expanded in one direction as usual in locomotion. Lamellipodia arise from filopodia by their swelling and fusion. After retraction they leave behind a reconstructed filopodial system. In general, in Vampyrella as in some other motile cells, lobopodia arise and function independently of filopodia, whereas the lamellipodia and filopodia are related by their origin and may be transformed one into another.