Biological reduction of iodate: From research history to recent findings

Abstract

Iodine (¹²⁷I) is an essential trace element for humans and animals as a component of thyroid hormone, while radioactive iodine-129 (¹²⁹I) released from nuclear fuel reprocessing plants and nuclear accidents is a significant risk factor. Together with its volatilization and oxidation, iodine reduction is one of important processes in the global iodine cycling, whose details are still unknown. Iodine exists mainly as inorganic iodate (IO₃⁻) and iodide (I⁻),although iodate is thermodynamically more stable than iodide in seawater. Nevertheless, up to 50% of total iodine are observed as iodide in surface seawater. This apparent thermodynamic disequilibrium is thought to be due to the activity of iodate reduction by algae and marine bacteria in ocean surface. In particular, a hypothesis that iodate is reduced by nitrate reductase of marine organisms has been paid attention. This article summarizes the research history of biological iodate reduction, and also introduces recent findings on enzymes potentially involved in iodate reduction in nature.