Studies on N-limited growth of diatoms in dialysis culture

N-limited growth of Skeletonema costatum (Grev.) Cleve in dialysis culture has been studied. The division rate of exponentially growing cells was independent of the nitrate concentration in the growth medium in the range from 886 down to 0.25 μM N-salt, while no growth beyond one division took place in cultures to which no nitrogen salt was added. The half saturation constant, K₃, for growth must, therefore, be in the range 0–0.13 μM, provided the growth-nutrient relationship is hyperbolic for S. costatum.Contrary to growth rate, cellular chlorophyll and protein were markedly reduced in media poor in nitrogen salts. A dialysis culture chamber was used to demonstrate that the measurement of half saturation constants for S. costatum was influenced by stirring, the stirred culture growing almost twice as fast as the unstirred control under identical conditions. The ability of diatoms to grow rapidly at low nitrogen levels was used to remove nutrients from sewage enriched media. Removal efficiencies corresponding to 80 and 90 % were obtained for nitrate and ammonia, respectively, using the diatom Phaeodactylum tricornutum Bohlin. It was found that both this diatom and S. costatum as well as Thalassiosira pseudonana Hust (Hasle) tolerated ammonia up to at least 450 μM with no deleterious effects on growth rate.