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Hypnocysts of toxic Alexandrium tamarense (Lebour) Balech collected during a bloom in the North Sea near Scotland (UK) have been investigated ultrastructurally. Details of cell wall morphology and a cell wall covering, not mentioned previously in the literature, are given. The presence of intracellular bacteria has been shown by means of transmission electron microscopy. These bacteria were present in early and mature hypnocysts, but absent in flagellated vegetative cells found in the same region. The evidence for the transmission of toxic bacteria via hypnocysts and their inoculation into the environment by excysted dinoflagellates is discussed.

A strain of Amoeba proteus was isolated from a fresh-water aquarium with tropical fish. The amoebae were identified as A. proteus due to a honey comb structure underneath their nuclear envelope and several other features. Optimal growth of the amebae was observed at 22 C. In the cells two different intracellular bacteria were observed. the bacteria were visible in fixed cells after staining with lacto-aceto orcein or DAPI. One of the bacteria was rod shaped and straight (ro bacteria), whereas the other one was spiral-shaped (sp bacteria). Electron microscopy of thin sectarian revealed a Gram-negative appearance of both bacteria. Ro bacteria appeared to be naked in the host cytoplasm - not encircled by host membranes ; sp bacteria were encircled by two membranes. To get first information about the phylogenetic position of the bacteria fluorescence in situ hybridisation was performed using appropriate oligonucleotide probes. Both bacteria appeared to belong to the Y- subgroup of proteobacteria.