Aerotaxis in Desulfovibrio

Aerotaxis of two sulphate-reducing bacteria, the freshwater strain Desulfov ibrio desulfuricans CSN (DSM 9104) and the marine strain Desulfovibrio oxyc linae N13 (DSM 11498), was studied using capillary microslides, microscopy and oxygen microsensors. The bacteria formed ring-shaped bands in oxygen di ffusion gradients surrounding O-2 bubbles, which were placed into anoxic su lphate-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 mu M O-2) were found , while the outer edge always coincided with the oxic-anoxic interface. Rin g diameters and O-2 concentrations at the inner edge of the band depended o n the cell density and the strain used in the suspension. Band formation di d not occur in the absence of an electron donor (5 mM lactate) or when N-2 gas bubbles were used. Both strains were highly motile with velocities of a pproximate to 32 mu m s(-1) during forward runs, and 7 mu m s(-1) during ba ckward runs respectively. Within the bands, cells moved in circles of about 20 mu m diameter, while cells outside the band exhibited straighter or onl y slightly bent traces. It is concluded that the capacity of respiration at high rates and the positive and negative aerotactical responses of Desulfo vibrio provide an efficient strategy for removing O-2 from the habitat in s ituations where sufficient electron donors and high cell densities are pres ent.