CO2 UPTAKE MECHANISM IN EREMOSPHAERA-VIRIDIS

Electrophysiological measurements of the acidophilic alga Esemosphaera viridis De Bary explored the effects of low CO2 levels on both membra ne potential and resistance. This procedure incorporates a double-barr eled microelectrode and suction pipette system, coupled with an approx imately CO2-free environment. A key requirement is an artificial pond water perfusion media that has been purged of dissolved inorganic carb on by being boiled and bubbled with nitrogen gas. Both membrane potent ial and resistance were measured at pH 5 in both low-CO2 conditions (2 mu M) and high-CO2 conditions (14 mu M) in both light, where CO2 tran sport is known to be active, and dark, where CO2 transport is not acti ve. To avoid dissolved inorganic carbon contamination of the perfusion media, a special chamber was constructed, featuring a laminar flow of nitrogen gas over the solution, which allowed for the manipulation of cells while preventing any contamination by CO2 from the air. Results indicate that the uptake of CO2 by the alga is electrically silent an d, therefore, not the result of a symport or antiport cotransport syst em that would ''drive'' CO2 uptake by coupling it to the electrochemic al gradient of ions such as protons or sodium. The uptake is most like ly facilitated by a transporter directly coupled with ATP hydrolysis.