Croissance de la biomasse azotée du Phaeodactylum tricornutum (Bacillariophyceae) en cultures discontinues dialysante et non dialysante

Abstract

The unique conditions associated with discontinuous (batch) dialysis culture of the diatom Phaeodactylum tricornutum elicit different nutritional responses from those observed in nondialysis culture. Simultaneous determinations of the nitrogen biomass concentration and of the nitrogen nutrients (NO3− + NO2−) in the culture chamber, as well as in the seawater nutrient medium at the entrance and exit of the dialyzer, revealed that nitrogen-biomass production in dialysis cultures is achieved mainly (>90%) during postexponential growth, when the concentration of nutrients is limiting (smaller than Michaelis-Menten constant). Almost half of this biomass is produced at the diffusion limit of the apparatus, i.e., when the mass transfer of nutrient substrates, which determines the total uptake activity of the culture, reaches a maximum. In contrast, in nondialysis discontinuous cultures, in which the postexponential growth phase is short, most of the total cellular nitrogen is accumulated during active growth. Certain physiological indices relating to the active uptake and assimilation of inorganic nitrogen are consistent with the different nutritional responses elicited by these two types of culture techniques and explain the high biomass levels obtained in dialysis culture. Key words: dialysis culture, diatom, nitrogen metabolism.