Werner Reisser

Viruses and virus-like particles of freshwater and marine eukaryotic algae ― a review

Summary Viruses and virus-like particles of eukaryotic algae represent a rather neglected field of phycology. Neither their taxonomy nor their way of propagation and their ecological impact on aquatic ecosystems are known in detail. In this presentation a survey is given on available data of algal viruses as to ultrastructure, biochemistry, infection mechanisms and putative taxonomic affiliation. Aspects and prospects of future research are discussed such as the role of virus caused diseases in algae (phycopathology) and algal viruses as tools for genetic engeneering.

Die stoffwechselphysiologischen Beziehungen zwischen Paramecium bursaria Ehrbg. und Chlorella spec. in der Paramecium bursaria-Symbiose

Symbiotic Chlorellae have been isolated from Paramecium bursaria Ehrbg. and cultivated under conditions of nitrogen deficiency. Reinfection of Chlorella-free Paramecium bursaria with these nitrogen-deficient algae resulted in a complete regeneration and multiplication of the algae within the host cells. The endosymbiotic algal cells of the Paramecium bursaria-symbiosis can be supplied by their host with nitrogen.The inhibition of photosynthesis by 3-(3,4-Dichlorophenyl)-1,1-dimethylurea (DCMU) leads in green Paramecium bursaria to a breakdown of the symbiotic steady state-system resulting in a loss of algal cells. Obviously the endosymbiotic algae cannot be fed heterotrophically by their host to such an extent that a stable symbiosis is maintained.The application of 3-(3,4-Dichlorophenyl)-1,1-dimethylurea (DCMU) can be used as a new method for culturing Chlorella-free Paramecium bursaria.ZusammenfassungInfektionsexperimente algenfreier Paramecium bursaria mit aus diesen isolierten und unter Stickstoffmangel-Bedingungen vorkultivierten Algen deuten darauf hin, daß die Versorgung der endosymbiontischen Algen mit stickstoffhaltigen Verbindungen durch ihren Wirt in einem zu gutem Wachstum und Vermehrung der Alge ausreichendem Maße möglich ist. Die Bedeutung dieser stoffwechselphysiologischen Beziehung für die Symbiosepartner wird diskutiert.Die Vergiftung der Photosynthese der endosymbiontischen Chlorella durch 3-(3,4-Dichlorphenyl)-1,1-dimethylharnstoff (DCMU) führt in grünen Paramecium bursaria durch Beeinflussung des Kohlenstoff-Stoffwechsels zu einer Entkoppelung des symbiontischen steady state-Systems und damit zur Auflösung der Symbiose. Eine ausreichende heterotrophe Ernährung der Alge durch das Paramecium ist in der Symbiose offenbar nicht möglich.Die Anwendung von 3-(3,4-Dichlorphenyl)-1,1-dimethylharnstoff (DCMU) kann als neue Methode zur Züchtung algenfreier Paramecium bursaria dienen.: Symbiotic Chlorellae have been isolated from Paramecium bursaria Ehrbg. and cultivated under conditions of nitrogen deficiency. Reinfection of Chlorella-free Paramecium bursaria with these nitrogen-deficient algae resulted in a complete regeneration and multiplication of the algae within the host cells. The endosymbiotic algal cells of the Paramecium bursaria-symbiosis can be supplied by their host with nitrogen. The inhibition of photosynthesis by 3-(3,4-Dichlorophenyl)-1,1-dimethylurea (DCMU) leads in green Paramecium bursaria to a breakdown of the symbiotic steady state-system resulting in a loss of algal cells. Obviously the endosymbiotic algae cannot be fed heterotrophically by their host to such an extent that a stable symbiosis is maintained. The application of 3-(3,4-Dichlorophenyl)-1,1-dimethylurea (DCMU) can be used as a new method for culturing Chlorella-free Paramecium bursaria.

Evidence of de novo synthesis of maltose excreted by the endosymbiotic Chlorella from Paramecium bursaria.

The endosymbiotic Chlorella sp. from Paramecium bursaria excretes maltose both in the light and in the dark. Experiments on photosynthetic 14CO2 fixation and 14CO2 pulse-chase experiments show that maltose is synthesized in the light directly from compounds of the Calvin cycle, whereas in the dark it results from starch degradation.

Zur Taxonomie einer auxotrophen Chlorella aus Paramecium bursaria Ehrbg

An auxotrophic Chlorella has been isolated from Paramecium bursaria Ehrbg. and cultivated in mass culture in an inorganic medium supplied with vitamins B1 and B12. With regard to its physiological properties it is not identical with either one of the so far known Chlorella species. It belongs, however, to the group of Chlorella vulgaris f. tertia Fott et Novaková and Chlorella vulgaris var. vulgaris Beijerinck.ZusammenfassungAuf Grund der physiologischen Merkmale einer in Paramecium bursaria Ehrbg. auftretenden Chlorella ergibt sich eine systematische Zuordnung in den Formenkreis um Chlorella vulgaris f. tertia Fott et Nováková und Chlorella vulgaris var. vulgaris Beijerinck. Hiervon abweichende Befunde anderer Autoren werden diskutiert.

The role of endosymbiotic algae in photoaccumulation of green Paramecium bursaria

The endosymbiotic unit of Paramecium bursaria with Chlorella sp. photoaccumulates in white, blue-green, and red light (λ<700 nm), whereas alga-free Paramecia never do. The intensity of photoaccumulation depends on both the light fluence rate and the size of the symbiotic algal population. Photoaccumulation can be stopped completely with 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea (DCMU), an inhibitor of photosynthetic electron transport. Hence the photosynthetic pigments of the algae act as receptors of the light stimulus for photomovement and a close connection must exist between photosynthesis of the algae and ciliary beating of the Paramecium.

The metabolic interactions between Paramecium bursaria Ehrbg. and Chlorella spec. in the Paramecium bursaria-symbiosis

The rates of the photosynthetic oxygen production of the green Paramecium bursaria and of the symbiotic Chlorella spec. isolated from it were measured at various CO2-concentrations in the incubation medium. Due to the respiration of the ciliate the amount of CO2 offered to the symbiotic algae in situ is higher than in water under normal atmospheric conditions. So the algae within the symbiotic unit show a higher rate of photosynthetic oxygen production than in the isolated state and thus guarantee the supply with oxygen for the Paramecium. In the green Paramecium the rate of photosynthetic oxygen production is increased by the addition of glucose. In the dark the incubation with glucose increases the rate of respiratory oxygen consumption in alga-free Paramecium bursaria to a much greater extent than in green Paramecia.

Extracellular DNA in aquatic ecosystems may in part be due to phycovirus activity

In a eutrophic lake, a crash of the algal population was followed by a significant increase in the number of virus-like particles (from ca. 1 106 ml−1 to ca. 26 106 ml−1), and soon thereafter by an increase of the amount of extracellular DNA (from ca. 20 µg l−1 to ca. 40 µg l−1). The same pattern of correlation between decrease of algae and increase of viruses and extracellular DNA could be demonstrated by an in vitro experiment with a Chlorella-virus-system. Lysis of algae by viruses increased both the number of viruses and the amount of DNA in the culture medium. Extracellular DNA mainly consisted of material with a molecular weight below 500 bp.The Chlorella-virus-system is discussed. It could be used as a model-system for studying the dynamics of interaction of viruses and algae in aquatic ecosystems.

Comparative studies on photosynthetic enzymes of the symbiotic Chlorella from Paramecium bursaria and other symbiotic and non-symbiotic Chlorella strains

The activities of ribulose 1,5-bisphosphate carboxylase and of carbonic anhydrase were studied in cell-free extracts of two symbiotic Chlorella strains isolated from Paramecium bursaria and from Spongilla sp., and of two nonsymbiotic strains of Chlorella (Chlorella fusca and Chlorella vulgaris) cultivated at varied CO2-concentrations. The symbiotic Chlorella of Paramecium bursaria differs distinctly from the other Chlorella strains by a higher activity of ribulose 1,5-bisphosphate carboxylase, which is independent of the actual CO2-concentration, and by a lack of carbonic anhydrase activity. These properties are discussed with respect to their ecological significance.

Freeze-Fracture Evidence of Differences between Membranes of Perialgal and Digestive Vacuoles in Paramecium bursaria

Abstract Measurements of particle densities on the two freeze-fracture faces of digestive and perialgal vacuole membranes in green and aposym biotic Paramecium bursaria Ehrbg. show distinct differences between the P-faces of both membrane types. The distribution of particle densities is more homogenous on the P-faces of perialgal vacuole membranes than on the P-faces of digestive vacuole membranes. Possibly homogeneity among peri algal vacuole membranes reflects the stability of perialgal vacuoles during their life cycle. Perhaps lysosomes cannot fuse with them.

Zytologische Analyse der Endosymbioseeinheit von Paramecium bursaria Ehrbg.und Chlorella spec.: II.Die Regulation der endosymbiontischen Algenzahl in Abhängigkeit vom Ernährungszustand der Symbiosepartner

Summary The activity of acid phosphatase was analysed by histochemical methods in green and algafree Paramecium bursaria with regard to its dependence on the nutritional conditions of the ciliate and to its significance for the regulation of the endosymbiotic algal population. In green Paramecia the activity of the acid phosphatase in food vacuoles increases after feeding with Enterobacter cloacae.The internal supply with carbohydrates by the symbiotic Chlorellae does not exclude the uptake of external food.The lack of an external food supply results in a low level of enzymatic activity in organisms cultured in both light and dark. A model is discussed referring to the regulation of the endosymbiotic algal population.Its size is not regulated by digestion of the Chlorellae, but depends on the division rates of the symbiotic partners.In the dark, the division rate of algal cells is diminished due to the lack of photosynthetic activity, which cannot be compensated by a heterotrophic food supply.If the culture medium is devoid of suitable food, the number of algal cells soon decreases to reach a constant level, finally the whole symbiotic unit dies.Sufficient external food supply raises the division rate of the Paramecium, to such an extent that the number of algal cells per Paramecium is statistically diminished resulting in alga-free Paramecia.