Figure 1. Bench-top experiment of settling behavior of bioreduced smectite (BS) in Tube A and non-reduced control (NC) suspensions in Tube B. Following 48 h incubation of S. oneidensis with nontronite (NAu-1), a substantial color change of BS occurred in TubeA as compared to NC in Tube B, suggestingmicrobial reduction of structural Fe(III) in the clay. Clay suspensions in Tubes A and B were observed for 80 min after being shaken homogeneously. The BS suspensions are flocculated and settled faster while the NC suspensions remained dispersed in the water column (see arrows showing the boundary of suspension).