Abundance, distribution and diversity of planktonic Planctomycetes in coastal zones

Abstract

Members of the bacterial phylum Planctomycetes are reported in marine water samples worldwide but quantitative information is scarce. In this thesis the abundance, distribution and phylogenetic diversity of Planctomycetes were investigated in different coastal systems, the German North Sea island Helgoland, the Tyrrhenian coastal lake Lago di Paola and the adjacent marine coastal waters. Seawater was collected in different seasons at the station "Kabeltonne" near the island Helgoland. An increase in Planctomycetes absolute numbers was registered in spring showing a positive correlation with phytoplankton blooms. The analysis of size-fractionated seawater samples and of macroaggregates showed that ~ 90% of the Planctomycetes reside in the > 3µm size fraction. At Lago di Paola Planctomycetes increased in summer - during stratification - in surface waters and mainly responded to chlorophyll a concentrations confirming their suggested role in the degradation of algal biomass. Abundances were higher in the coastal lake than in the adjacent marine waters. With both studies 224 almost full length 16S rRNA gene sequences of Planctomycetes have been added to the database and six coastal clades have been defined. At Helgoland the clade-specific counts revealed a seasonal succession which might be linked to phytoplankton blooms. At Lago di Paola, cell numbers indicated the simultaneous presence of all clades in the surface and bottom water in similar abundances. In clone libraries from Lago di Paola, 20 almost full length 16S rRNA gene sequences affiliated with Chlamydiales were retrieved, two main clusters were identified and two oligonucleotide probes were designed. It was possible to visualize high numbers of individual environmental chlamydiae as well as chlamydiae inside a host, presumably a protist.