Juergens, K. Max Planck Institute for Limnology, juergens@mpil-ploen.mpg.de
Langenheder, S. Max Planck Institute for Limnology, langenheder@mpil-ploen.mpg.de
Pernthaler, J. Max Planck Institute for Marine Microbiology, jperntha@mpi-bremen.de
Amann, R. Max Planck Institute for Marine Microbiology, ramann@mpi-bremen.de

 
CHANGES IN MORPHOLOGY AND TAXONOMIC COMPOSITION OF PLANKTONIC BACTERIAL COMMUNITIES DUE TO ENHANCED PROTOZOAN GRAZING
 
The appearance of morphologically grazing-resistant planktonic bacteria such as filaments and aggregates is often correlated to peak abundances of bacterivorous protozoans. To study this phenomenon, we performed enclosure experiments in eutrophic ponds where we experimentally enhanced protozoan grazing pressure by removing metazooplankton. Resulting changes in bacterial morphology and composition were analyzed by fluorescence in situ hybridization with group-specific rRNA-targeted oligonucleotides. Freely suspended, small bacteria which grew up after removal of Daphnia belonged nearly exclusively to the beta subclass of the Proteobacteria and the Cytophaga-Flavobacterium cluster. The major part of this bacterial peak was consumed by nanoflagellates, and afterwards cells, resistant to protozoan grazing dominated the bacterial assemblage. In one experiment these were mainly filamentous bacteria belonging to different phylogenetic groups. Bacteria of the alpha subclass of the Proteobacteria were most successful in resisting high grazing pressure. Initially they accounted for less than 1 % of total bacteria, but after 72 h they became the dominant group, likely due to their elongated cell form. In other experiments, detrital aggregates proved to be important spatial refuges, harboring bacteria of all phylogenetic groups. The experiments revealed that predation can be a major structuring force for the phenotypic and taxonomic composition of planktonic bacteria.
 
Day: Tuesday, Feb. 2
Time: 11:30 - 11:45am
Location: Hilton of Santa Fe
 
Code: SS40TU1130H