Aerotaxis of two sulphate‐reducing bacteria, the freshwater strain Desulfovibrio desulfuricans CSN (DSM 9104) and the marine strain Desulfovibrio oxyclinae N13 (DSM 11498), was studied using capillary microslides, microscopy and oxygen microsensors. The bacteria formed ring‐shaped bands in oxygen diffusion gradients surrounding O 2 bubbles, which were placed into anoxic sulphate‐free cell suspensions in capillary microslides. The radial expansion of the oxic volume by diffusion was stopped by aerobic respiration. Bands were formed by cells avoiding high O 2 levels near the O 2 bubble, as well as by cells entering from the surrounding anoxic zone. At the inner edge of the bands, O 2 levels of up to 20% air saturation (50 μM O 2 ) were found, while the outer edge always coincided with the oxic–anoxic interface. Ring diameters and O 2 concentrations
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