Pseudodifflugia klarae nov. spec., Bereczkya minuta nov. gen. nov. spec. and Paramphitrema muelleri nov. spec.: Three New Filose Testate Amoebae from the Plankton of the River Danube

Three new, minute testate amoeban species smaller than 15 μm, including one new genus, are described from the plankton of the River Danube (Hungary) using high resolution video micrography. Pseudodifflugia klarae nov. spec. is characterised by an oval/pyriform, rigid, slightly compressed, scarcely or densely agglutinated test with a length of 8–14 μm. Its aperture is irregular in outline and inconspicuous; the nucleus contains one nucleolus and a few bent rods in the nucleoplasm. Bereczkya nov. gen., an incertae sedis cercozoan, has a minute spherical cell enclosed in a thin, rigid, more or less agglutinated organic test that is filled entirely by the cytoplasm. Its test bears an irregular and inconspicuous aperture. A collar-like ectoplasmic rim is situated in the aperture, from which a pseudopodial stem with filopodia is erected. The nucleus is slightly irregular, without a central nucleolus, but it contains rod-shaped granules in the nucleoplasm. Bereczkya minuta nov. spec. (test length: 3.5–8 μm, the diameter of the ectoplasmic rim: 0.8–2.3 μm) has a spherical test with asymmetric swellings and depressions, agglutinated with refractile mineral and other flat or irregularly-shaped xenosomes that may sometimes be almost entirely absent. Paramphitrema muelleri nov. spec. has a tubular or lemon-like test (length: 13–17 μm), which tapers towards the rigid apertures. The test is rigid, agglutinated and ism circular in cross section. The nucleus is vesicular. Thin filopodia, as well as 1–2 thick, straight, unbranched, tubular pseudopodia are produced

Sequential colonization of river periphyton analysed by microscopy and molecular fingerprinting

1. An artificial glass substratum was incubated in the River Danube for a period of 28 days in order to detect the sequential colonization of microorganisms. 2. Light and fluorescent microscopy showed that microalgae and the picoalgal fraction on the slides increased rapidly over the first 2 weeks of colonization. Diatoms were numerically the most abundant component of the periphyton and their species richness and diversity increased rapidly in the early phase of colonization whereas diversity subsequently increased moderately. 3. Evenness of the diatom community was initially high, lower in the intermediate phase and again higher later on. Succession involving early, intermediate and late colonizer species was observed. Community composition during the first 5 days of colonization was very different from later stages whereas there were only minor changes subsequently. 4. Molecular community analysis by means of terminal restriction fragment length polymorphism analysis of PCR amplified 16S rRNA and 18S rRNA genes pointed to even larger differences between the composition of samples obtained early and late in the period. 5. The number of 18S rRNA and 16S rRNA terminal restriction fragments (T-RF-s) was variable over the colonization period and the fragment patterns of both the bacterial and eukaryotic portion of the microbial community were variable, with most T-RF-s unique to a single sample, suggesting a wide diversity and dynamic properties of periphytic organisms