Measurement of manganese amelioration of cadmium toxicity inChlorella pyrenoidosa using turbidostat culture

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Abstract
Cadmium (Cd) toxicity and amelioration of Cd toxicity by Mn were measured inChlorella pyrenoidosa, using turbidostat culture. The responses were measured in terms of the maximum specific growth rate, μmax, of the populations. In turbidostat culture μmax is a dependent variable that can be measured continuously. Cd (as CdCl2· 2.5 H2O) was added to control populations at a concentration of 1.8 μM Cd. Toxicity was expressed after a 5 generation lag and resulted in a μmax steady state 62% lower than the initial control after 2 generations. With continued Cd exposure, Mn (as MnCl2 · 6H2O) was then added stepwise to a concentration of 10.4 μM Mn which caused a rapid, immediate increase in μmax followed by linear increase until a steady-state plateau was reached at a μmax 90% of control. The ameliorative response spanned 20 culture generations. After addition of Mn (10.4 μM), cellular Cd concentration did not change and cellular Mn concentration increased. Increase in mean cell size accompanied Cd exposure and was significantly decreased when supplemented with 10.4 μM Mn. Possible mechanisms of the amelioration are discussed.