The use of turbidostat culture in investigations of algal heavy metal toxicity and rotifer population dynamics

Turbidostat culture is a form of continuous culture by which, through maintaining constant density of an organism or its food, the maximum specific growth rate of the population, {dollar}usb{lcub}rm max{rcub}{dollar}, becomes a dependent variable. This aspect of turbidostat culture allows unique measurements to be made of responses by populations to toxins and different environmental conditions.; Using the green alga Chlorella pyrenoidosa Chick, the heavy metals selenium (Se) as selenate, cadmium (Cd), cadmium + manganese (Mn) and cadmium + zinc (Zn) were investigated to assess their toxicity in terms of changes in {dollar}usb{lcub}rm max{rcub}{dollar}. It was shown that increases of sublethal concentrations of Se produced a near linear decrease in {dollar}usb{lcub}rm max{rcub}{dollar}. A {dollar}usb{lcub}rm max{rcub}{dollar}IC{dollar}sb{lcub}50{rcub}{dollar} was calculated to be 10.1 {dollar}u{dollar}M Se (0.80 ug Se ml{dollar}sp{lcub}-1{rcub}{dollar}). A concentration of 1.8 {dollar}u{dollar}M Cd (as CdCl{dollar}sb2{dollar}) produced a 62% decrease in {dollar}usb{lcub}rm max{rcub}{dollar} after 2 generating lag. A recovery of {dollar}usb{lcub}rm max{rcub}{dollar} (amelioration) was observed when MnCl{dollar}sb2{dollar} (10.4 {dollar}u{dollar}M Mn) or ZnCl{dollar}sb2{dollar} (4.08 {dollar}u{dollar}M Zn) was added to the medium in which populations were experiencing sublethal Cd toxicity. The amelioration responses were incomplete with regard to full recovery of {dollar}usb{lcub}rm max{rcub}{dollar} and last 20 generations for the Cd-Mn exposure and 7 generations for the Cd-Zn exposure. Measurement of {dollar}usb{lcub}rm max{rcub}{dollar} is turbidostat culture was shown to provide a very sensitive measure of toxicity.; For the first time, a metazoan, the rotifer Brachionus calyciflorus Pallas, was grown in turbidostat culture and maintained near its {dollar}usb{lcub}rm max{rcub}{dollar} for many generations. This study represents the first usage of the turbidostatic method to regulate population growth rate by regulating its food concentration. It was discovered that {dollar}usb{lcub}rm max{rcub}{dollar} was subject to selection in this species and increased 51% from 0.053 h{dollar}sp{lcub}-1{rcub}{dollar} to 0.080 h{dollar}sp{lcub}-1{rcub}{dollar} (doubling time = 8.7 h) over 8 mo at 25{dollar}spcirc{dollar}C. This strain was shown to be genetically distinct from the original strain. The increase in {dollar}usb{lcub}rm max{rcub}{dollar} was hypothesized to be the result of a trade-off between reproduction and growth-maintenance, whereby fecundity was shifted to younger age classes and life span, egg production time, and egg and adult size were reduced.; The fast-growing rotifer strain was compared to a control field population in terms of various population variables and its population dynamics were evaluated by a growth model based on saturation kinetics. Important deviations from the model were hypothesized to be caused by shifts between carbon and non-carbon limited growth.