Nutrition experimentale: Problemes methodologiques lies a l'utilisation des microorganismes comme source trophique

The present study deals with technical problems encountered under lab conditions in studies of trophic relations between deposit-feeding invertebrates and microorganisms. Using 2 pure cultures of Pseudomonas and Navicula , it was shown that these microorganisms will attach to artificial (glass beads) and natural (sand grains) substrates. Best microbial attachment was observed on sand (up to 4.8 x 10 super(8) cells.g super(-1) dry wt.). The radioactive labelling of the microorganisms depends not only on the form under which the isotope ( super(14)C) is supplied to the cultures, but also on the time and the duration of the labelling. 70% of the isotope was incorporated in a stable manner by the diatoms. The bacteria incorporated, at most, 34% of the super(14)C available in the cultures, an very rapidly lost and important fraction of their label when they were transferred to sea water.