Controlling factors of bacterioplankton succession

Seasonal successions have been investigated in detail for all major planktonic organisms, but up to now only few data are available on the seasonal succession of bacterial populations, i.e. of different phylogenetic clades of 16 or 23S rRNA gene sequence types. Even less is known, how particular bacterial populations are affected by changes in grazing pressure and nutrient availability throughout the seasonal cycle in lakes. In the proposed project we plan to examine the impact of different intensities and species specific patterns of protistan grazing and of nutrient availability (phosphorus and carbon) on the seasonal dynamics of abundance and biomass of different bacterial groups. All investigations (three workpackages WP) shall be conducted in the oligo-mesotrophic Piburger See (Tyrol, Austria). - Methodological approach (WP1). During the first six months we will adapt existing and tested image analysis procedures to quantify the abundance and particularly the biomass of bacteria hybridized with rRNA targeted oligonucleotide probes. The efficiency and applicability of various rRNA targeted probes will be evaluated. - Descriptive approach (WP2). During one year, abundances and biomasses of major bacterial populations will be investigated in biweekly sampling intervals by applying fluorescence in situ hybridization followed by catalyzed reporter deposition (CARD-FISH). Bacterial parameters will be related to protistan grazing parameters and to a wide spectrum of biotic and abiotic limnological data, most importantly the seasonal composition of algal species - a potential key factor for the development of a so-called bacterial "satellite" assemblage. Results from this WP will indicate bacterial clades which will be analyzed in workpackage 3. - Experimental approach (WP3). In the third part of the project the impact of protistan grazing and limiting nutrients will be experimentally manipulated. Therefore, size fractionation and nutrient enrichment experiments will be conducted during selected periods throughout the year (mixis, phytoplankton spring bloom, stratification, ice- cover). CARD-FISH in combination with microautoradiography will be applied to investigate potential substrate uptake preferences.We hypothesize that specific, seasonally dominant phytoplankton species, the intensity of grazing as well as the actual composition and size selectivity of protistan grazers will impact the seasonal development of different bacterial populations.

Seasonal successions have been investigated in detail for all major planktonic organisms, but up to now only few data are available on the seasonal succession of bacterial populations, i.e. of different phylogenetic clades of 16 or 23S rRNA gene sequence types. Even less is known, how particular bacterial populations are affected by changes in grazing pressure and nutrient availability throughout the seasonal cycle in lakes. In the proposed project we plan to examine the impact of different intensities and species specific patterns of protistan grazing and of nutrient availability (phosphorus and carbon) on the seasonal dynamics of abundance and biomass of different bacterial groups. All investigations (three workpackages WP) shall be conducted in the oligo-mesotrophic Piburger See (Tyrol, Austria). Methodological approach (WP1). During the first six months we will adapt existing and tested image analysis procedures to quantify the abundance and particularly the biomass of bacteria hybridized with rRNA targeted oligonucleotide probes. The efficiency and applicability of various rRNA targeted probes will be evaluated. Descriptive approach (WP2). During one year, abundances and biomasses of major bacterial populations will be investigated in biweekly sampling intervals by applying fluorescence in situ hybridization followed by catalyzed reporter deposition (CARD-FISH). Bacterial parameters will be related to protistan grazing parameters and to a wide spectrum of biotic and abiotic limnological data, most importantly the seasonal composition of algal species - a potential key factor for the development of a so-called bacterial "satellite" assemblage. Results from this WP will indicate bacterial clades which will be analyzed in workpackage 3. Experimental approach (WP3). In the third part of the project the impact of protistan grazing and limiting nutrients will be experimentally manipulated. Therefore, size fractionation and nutrient enrichment experiments will be conducted during selected periods throughout the year (mixis, phytoplankton spring bloom, stratification, ice-cover). CARD-FISH in combination with microautoradiography will be applied to investigate potential substrate uptake preferences.We hypothesize that specific, seasonally dominant phytoplankton species, the intensity of grazing as well as the actual composition and size selectivity of protistan grazers will impact the seasonal development of different bacterial populations.