Use of Percoll gradient centrifugation for the isolation of diatoms from Wadden Sea sediments; diatom yields, species recoveries and population diversity.

The technique of Percoll gradient centrifugation was applied to samples from Wadden Sea sediments of the shoreside near Dangast (German Bight). Experiments were also performed with Wadden Sea sediment inoculated with diatoms and with axenic and mixed diatom cultures. For axenic and mixed cultures, total recoveries ranged from 6 to 70% of the diatoms loaded onto the gradients, whereas the yields were less than 5% in most of the experiments with Wadden Sea sediments. The extraction of diatoms from mixed cultures and from sediment samples was not quantitative, neither in terms of biodiversity nor of total individuals extracted, because the rates of recovery varied for the different species. Diatom cells extracted by Percoll gradient centrifugation were devoid of sand grains and debris. The obtained material was suitable to be used in biochemical experiments, in cultural studies and for electron microscopy. The overall cell morphology and subcellular organelle organization was excellent and appeared to be unaffected by the purification procedure. The results and advantages and disadvantages of the technique are discussed.