Results
3.1 Growth of diatoms
We have shown previously[24] that Amphora coffeaeformis grows in ASP2 medium with a generation time of 12 h at 25–28 °C. The organism can grow heterotrophically (dark growth) and mixotrophically (stimulation of light-limited growth) on D-glucose, D-fructose, L-glutamate and yeast extract. Navicula sp.l, on the other hand, has an autotrophic generation time of 32 h, is heterotrophic only on 0.05% yeast extract and mixotrophic on 0.5 mM D-glucose or L-glutamate.
3.2 Extraction of putative diatom polymers
The extracts of fresh and lyophilized diatoms were of very different composition. Table 1 shows that a much larger amount of both protein and carbohydrate reacting material was extracted from the lyophilized cells than from the cells in a fresh state. When samples of these cells were stained with Sytox Green and examined microscopically, the percentage with compromised membranes was found to be 11% (n = 633) for the fresh cells and 100% (n = 300) for the lyophilized cells. Microscopic examination of footpads, shown in Fig. 1, indicated that they were soluble in hot (90 °C) bicarbonate solution.