Sulfate Transport in Penicillium chrysogenum Plasma Membranes

Transport studies with Penicillium chrysogenum plasma membranes fused with cytochrome c oxidase lipo-somes demonstrate that sulfate uptake is driven by the transmembrane pH gradient and not by the trans-membrane electrical potential. Ca21 and other divalent cations are not required. It is concluded that the sulfate transport system catalyzes the symport of two protons with one sulfate anion. One of the transport processes which plays an important role in the biosynthesis of penicillins by filamentous fungi is the uptake of sulfate. Current penicillin production processes yield final penicillin titers which are more than 500 times higher than those obtained with the parental Penicillium chrysogenum strain NRRL 1951 (9). Sulfate is the primary sulfur source in industrial production of penicillin and is the precursor of cys-teine that together with valine forms the backbone of the penicillin molecule (9, 15). Therefore, the strongly increased demand for cysteine during penicillin production requires an elevated rate of sulfate uptake from the environment. Studies of the mechanism of sulfate uptake by P. chrysogenum, related filamentous fungi, and yeasts have led to the conclusion that this process occurs through active transport (1, 6, 8, 12–14, 16, 17). It has been suggested that in Penicillium notatum, sulfate is taken up in symport with one proton and one calcium ion (2). According to such a mechanism, the driving forces for sulfate uptake would be the transmembrane electrical poten-tial (DC), the transmembrane pH gradient (DpH), and the chemical gradient of calcium ions (DmCa21/F). Although sulfate transport was shown to promote uptake of Ca21, a stoichio-metric coupling could not be demonstrated. It has been sug-gested that the sulfate transport system exchanges SO