Analysis of aerotactic band formation by Desulfovibrio desulfuricans in a stopped-flow diffusion chamber

Aerotactic band formation by Desulfovibrio desulfuricans (DSM 9104) was studied in a stopped-flow diffusion chamber. This chamber allowed us to create reproducible, steep oxygen gradients in a flat capillary, time-lapse video recordings and spatio-temporal analysis of band formation. The cells formed two types of bands. Bands of the first type evolved quickly after starting the experiment and were located near the oxic-anoxic interface. Bands of the second type typically appeared several minutes later and a few millimeters inside the initially anoxic volume of the capillary. Band formation depended on metabolism and could be stimulated by lactate addition, and thus appears to be energy taxis. Mathematical modeling of oxygen diffusion and respiration within the chamber revealed that bands formed preferentially at oxygen concentrations close to 4% air saturation. The swimming speed of the cells was determined by digital single-cell tracking and found to be highest (up to 58 mum s(-1)) close to the oxic-anoxic interfaces. Motility patterns were influenced by surfaces, at which cells accumulated. Bioconvection sometimes occurred if very dense bands had formed. The ecological implications of these two phenomena are unknown.