Rhizosphere processes, among many others are crucial in determining the mobility and bioavailability of arsenic in soil-rice systems. Several studies have pointed to the role of iron plaque on rice root surface in modulating the dynamics of arsenic in soil-rice systems (Liu et al., 2004; 2006). It is well known that microbes are heavily involved in the oxidation and reduction of iron, but their role in iron plaque formation/dissolution, and thus arsenic bioavailability is not clear. In the past five years or so, our group has been investigating whether nitrate-dependent iron oxidizing bacteria and iron reducing bacteria are involved in arsenic sequestration and release in paddy soils, and rhizosphere soils in particular.