Interactions between Diatoms and Bacteria from phototrophic Biofilms of the littoral Zone of Lake Constance

In this report we describe different combinations of physical separation and antibiotic treatment to remove associated bacteria from freshwater diatoms. Diatoms were purified either from natural epilithic biofilms or from uni-algal cultures. We found that for most strains different purification procedures have to be combined individually. In a new approach we show that for some diatom strains the substitution of associated aquatic bacteria by an antibiotic sensitive E. coli strain and subsequent treatment with antibiotics may be a successful approach to obtain axenic diatom cultures.