Effect of naphthalene and aqueous crude-oil extracts on the green flagellate Chlamydomonas angulosa. VI. Phosphate uptake and retention

Abstract

Chlamydomonas angulosa when grown in normal Bold's basal medium (BBM) (1.7 mM Pi) has a very high cell P content (120 fg-at. P∙cell−1) and low C: P atomic ratio (35: 1) and is only able to show net Pi uptake in media with Pi concentrations higher than 0.1 mM when grown in the light. The presence of light enhances net phosphate uptake or decreases net phosphate loss under all external Pi concentrations. Cells transferred to low-Pi media will, however, grow rapidly while reducing their cell P to almost 1/10 of the initial level, indicating that most of the cell P in cells grown in high-P media represents reserve P, probably in the form of polyphosphates. The presence of naphthalene and crude-oil components in the culture media decreases net uptake of Pi at high external Pi concentrations and increases the rate of Pi loss at low external concentrations. Naphthalene present at 100% saturation level in BBM causes rapid loss of a large fraction of cell P under all conditions tested. The phosphorus lost appears as reactive phosphorus in the medium, suggesting that cell polyphosphates are rapidly converted to Pi, which then leaks out of the cells in response to the presence of saturating naphthalene concentrations in the medium. BBM with 50% naphthalene saturation causes much less loss of cell P under most of the incubation conditions, and net uptake can take place at the highest external Pi concentrations tested in the light. Media saturated with crude oil are even less effective than 50% naphthalene saturated media in causing P efflux, or in reducing net Pi uptake, although at low external P concentrations, uptake of P is decreased compared with the control.