Wechselwirkungen zwischen der antarktischen Eisdiatomee Amphiprora kufferathii MANGUIN und epiphytischen Bakterien unter besonderer Berücksichtigung des Oxidationsschutzes

Abstract

The Antarctic ice diatom Amphiprora kufferathii is covered by epibacteria in its natural environment. This community is maintained under culture conditions. In my work the physiological interactions between the diatom and the bacteria were investigated with special regard to their antioxidative defense systems. The experiments were carried out with bacterized and axenic cultures of the diatom.The bacteria were identified by isolation and cloning of total 16S rRNS of the bacterized diatom culture. Phylogenetic analysis showed that A. kufferathii is covered by alphaproteobacteria of the genera Octadecabacter and Sulfitobacter as well as by members of the bacteriodetes phylum of the genera Cellulophaga and Psychroflexus. Most of the free living bacteria were classified as gammaproteobacteria of the genera Colwellia. Quantitative fluorescence in situ hybridization showed a 70% coverage of the diatom by Octadecabacter. Bacteriodetes and gammaproteobacteria showed a maximal abundance of 10% to 13%. The epibacteria stimulate the growth of A. kufferathii. Experiments under nutrient limitation showed that this effect can be explained by the remobilization of nitrogen and silicate by the bacteria. The epibacteria have also effects on A. kufferathii under osmotic and temperature stress. Physiologic investigations demonstrate that the epibacteria are participated in the antioxidative defense of A. kufferathii by scavenging hydrogen peroxide produced by the diatom.I investigated the most common antioxidative enzmes of the diatom and the isolated bacteria. In A. kufferathii two superoxide dismutases and two glutathione reductases were found, whereas catalase was not detected.Several isoenzymes of superoxide dismutse have been identified in Cellulophaga and Sulfitobacter but not in Colwellia. Catalase and Glutathione reductase were detected in all isolated bacteria.