Measurement of manganese amelioration of cadmium toxicity in Chlorella pyrenoidosa using turbidostat culture.

Cadmium (Cd) toxicity and amelioration of Cd toxicity by Mn were measured in Chlorella pyrenoidosa, using turbidostat culture. The responses were measured in terms of the maximum specific growth rate, mu max, of the populations. In turbidostat culture mu max 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 microM Cd. Toxicity was expressed after a 5 generation lag and resulted in a mu max 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 microM Mn which caused a rapid, immediate increase in mu max followed by linear increase until a steady-state plateau was reached at a mu max 90% of control. The ameliorative response spanned 20 culture generations. After addition of Mn (10.4 microM), 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 microM Mn. Possible mechanisms of the amelioration are discussed.