Oxygen dynamics at the base of a biofilm studied with planar optodes

The 0, dynamics at the base of biofilms was studied using planar optodes Biofllms were grown directly on the optodes and the 2-dimensional distnbution of O2 at the base of biofilms was resolved at a spatial resolution of 30 X 30 pm, using a CCD camera The average 0, saturahon at the base decreased and the heterogeneity increased as blofllms developed In mature blofilms heterogeneous 0, distributions were caused by clusters of high biomass which had low O2 saturations surrounded by 0,-nch voids and channels The O2 distribution at the base of biofilms was highly dependent on the free flow veloclty above the biofilm e g m a 400 pm thick biofllm the average 0, saturation increased from 0 to 23 1 % air saturation as the free flow velocity increased from 6 2 to 35 1 cm S ' Addition of glucose to a concentrat~on of 2 n1M in the water phase at maximum flow velocity caused the 0, consumption rate to increase and the base of the blofilm to go anoxlc The insertion of an O2 microelectrode into a biofdm caused the 0, saturation at the base of the biofiln~ to increase by approximately 25 pM This effect, presumably caused by hydrodynamic disturbances, typically extended several mm away from the position of the mcrosensor tip The presented data show for the first tune the true distnbution of O2 at the basis of heterogeneous biofilms and demonstrate the great potential of planar optodes for the study of solute d y n a m c s within biofllms at a very high spabal and temporal resolution