Some characteristics of arsenate transport in a marine cyanobacterium, Synechococcus sp.

Abstract The mechanism of arsenate incorporation in the cells of a unicellular marine cyanobacterium, Synechococcus sp., was investigated. A lag period in arsenate incorporation, probably caused by an inhibitory effect of phosphate absorbed on the cell surface, was observed. Although arsenate incorporation into the cells of cyanobacterium was several times faster than that of phosphate, it was readily inhibited by addition of phosphate, also suggesting inhibition caused by phosphate. The Michaelis–Menten type of equation was employed for the simulation of incorporation, and a nonlinear fitting was applied for the estimation of the kinetic parameters in the equation. Analysis based on the assumption that arsenate is incorporated via the phosphate transport system in cells suggested that arsenate competes with phosphate for entry into cells and each species acts as a competitive inhibitor to each other. The affinity of arsenate with the transport system was much less than that of phosphate, but it was not low enough for elucidation of an almost complete inhibition of arsenate incorporation by phosphate, and another mechanism to block the approach of arsenate to the transport system was deduced to exist. The inhibitory effect of phosphate on arsenate incorporation seemed responsible for alleviation of the toxicity of arsenate in the cells. Copyright © 2001 John Wiley & Sons, Ltd.