Noctiluca scintillans is one of the largest species of marine dinoflagellates. A small fraction of these bloom forming algae was reported to be turbid due to endocytic bacteria. The diversity of these endocytic bacteria living in turbid Noctiluca cells was investigated by denaturing gradient gel electrophoresis (DGGE). The results indicate the occurrence of 1 dominant group of endocytic bacteria and some other groups of less dominance. DGGE profiles were compared between the endocytic bacterial populations of cultivated and non-cultivated turbid Noctiluca cells; the latter were directly collected from the North Sea. DGGE profiles displayed no differences between them. In contrast, the comparison of band patterns of endocytic bacteria and free-living marine bacteria were different, indicating the development of a specific bacterial population within N. scintillans. The DGGE bands identified by DNA sequencing were assigned to the species Marinobacter PCOB-2, to the Pseudoalteromonas group, and the Vibrio group, all members of the γ subdivisions of Proteobacteria. Another DGGE band was identical to the 18S ribosomal gene of N. scintillans itself. Furthermore, 16 bacterial isolates derived from single Noctiluca cells were characterized by 16S rRNA phylogenetic analysis. Data revealed that these bacteria belong to several different phylogenetic groups. Most of the isolates (14 strains) belong to several groups of the γ subdivision of Proteobacteria; 2 isolates are related to the Vibrio group and 1 isolate to Moraxella. The other isolates were assigned to the following groups of the γ subdivision: Colwellia group, Stenotrophomonas and Pseudoalteromonas group. Two of them were closely related to sequences obtained from DGGE bands (Pseudoalteromonas group, and Marinobacter PCOB-2). Two isolates were assigned to the phylum of Grampositive bacteria. KEY WORDS: Endocytic bacteria · Noctiluca scintillans · DGGE · DiversityResale or republication not permitted without written consent of the publisher Aquat Microb Ecol 25: 229-235, 2001 turable bacteria (0.2 to 10%, Hoppe 1978). Molecular tools allow the detection of non-culturable bacteria, and several techniques have been developed to determine the genetic diversity of microbial communities (i.e. DNA reassociation experiments, Torsvik et al. 1990; DNA/DNA hybridization, Lee & Fuhrman 1991; different cloning strategies, Giovannoni et al. 1990, Fuhrman et al. 1993 and DGGE, Muyzer et al. 1995, Nübel et al. 1996, Ferris & Ward 1997.Originally, DGGE was used to detect single-base changes (Fischer & Lerman 1983, Myers et al. 1985, 1987, Sheffield et al. 1989). However, it has been proved to be a fast, sensitive and direct approach to describe bacterial communities. The technique has been recently applied to study microbial communities of microalgae, bacterial mats and biofilms (Muyzer et al. 1993, Ferris & Ward 1997, Kirchner et al. 1999, hot springs in the marine environment (Muyzer et al. 1995), rhizospheres (Heuer et al. 1997) and soil (Felske et al.1998, Jens...

Yeasts are potential antagonists of microorganisms in the phyllosphere. Due to their osmotolerance, they should also be able to colonize apple flowers. In field experiments, we applied yeast agents against fireblight at two different sites in the southern part of Germany. They showed efficiencies 0–20% below Plantomycin (streptomycin). Co‐culture experiments in liquid basal media with synthetic nectar resulted in suppression of Erwinia amylovora by yeast. This effect could not be confirmed with population studies of yeasts and E. amylovora in flower clusters. Field and laboratory experiments indicated that yeasts have antagonistic properties against fireblight but further research is needed to investigate this potential.

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