Epiphytic bacteria associated with different parts of the fronds (blade or meristem) of the sublittoral brown algae Laminaria hyperborea, L. digitata and L. saccharina were investigated by cultivation and cultivation-independent techniques. Each Laminaria species was sampled from both inter- and sub-tidal zones of the island Helgoland, North Sea. Preliminary characterization of the bacterial communities was performed by DAPI staining as well as by community-level physiological profiling using BIOLOG Eco plates. For bacterial cultivation, agar plates were prepared from extracts of the particular algal species. The cultivated isolates were fingerprinted using repPCR and the 16S rRNA genes of different isolates were subsequently sequenced.Laminaria-associated bacterial communities have to prevail over other competing bacteria. One strategy might be the production of secondary metabolites with bioactivity to defend their position within the particular association. Therefore, isolates were investigated by chemical screening and bioassays with a defined battery of test organisms (bacteria, algae and fungi) were used. From the three Laminaria, 36 isolates could be cultivated of which 24 cultures display unique fingerprints. Several of them show middle to high bioactivity against either Bacillus subtilis, Staphylococcus aureus, Streptomyces viridochromogenes, Escherichia coli, Candida albicans or Mucor miehei.To compare the number of cultivates with the in situ diversity, additionally, bacterial DNA was isolated directly from the algae for subsequent DGGE analysis based on 16S rDNA sequences. Results of DGGE analyses indeed suggest differences in both composition and diversity of associated bacteria, with respect to specific algal species, frond parts and sampling sites.
Helmholtz Research Programs > MARCOPOLI (2004-2008) > CO2-Coastal diversity - key species and food webs