The Growth of Continuous Cultures of the Phytoplankton Phaeodactylum Tricornutum


Abstract: Continuous cultures of Phaeodactylum tricornutum} (Bohlin) have been grown in a basic chemostat, that is, in a well-stirred, continuous flow, biochemical reactor. The effects of changes in dilution rate, nutrient concentration and illumination on the growth of the cultures have been studied by monitoring cell populations, chlorophyll fluorescence and nitrate-limited nutrient concentrations in the reactor. Three types of stationary state have been observed corresponding to light limitation and to two regimes of nutrient limitation analogous to bottom-up and top-down control in field experiments. In the first nutrient-limited regime, the phytoplankton share and consume all the available nutrient, whereas in the second regime the phytoplankton are removed from the euphotic zone before consumption is complete. Phytoplankton adapt to their environment, a process which takes a few hours when cell division is light limited but a few days when cell division is nutrient limited, partly by the modification of gene expression and partly through the preferential washout of dead cells from the chemostat.

Keywords: Phytoplankton growth, continuous culture, Phaeodactylum tricornutum

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