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

The O-2 dynamics at the base of biofilms was studied using planar optodes. Biofilms were grown directly on the optodes and the 2-dimensional distribution of O-2 at the base of biofilms was resolved at a spatial resolution of 30 x 30 mu m, using a CCD camera. The average O-2 Saturation at the base decreased and the heterogeneity increased as biofilms developed. In mature biofilms heterogeneous O-2 distributions were caused by clusters of high biomass which had low O-2 saturations surrounded by O-2-rich voids and channels. The O-2 distribution at the base of biofilms was highly dependent on the free flow velocity above the biofilm, e.g. in a 400 mu m thick biofilm the average O-2 saturation increased from 0 to 23.1% air saturation as the free flow velocity increased from 6.2 to 35.1 cm s(-1). Addition of glucose to a concentration of 2 mM in the water phase at maximum flow velocity caused the O-2 consumption rate to increase and the base of the biofilm to go anoxic. The insertion of an O-2 microelectrode into a biofilm caused the O-2 saturation at the base of the biofilm to increase by approximately 25 mu M. This effect, presumably caused by hydrodynamic disturbances, typically extended several mm away from the position of the microsensor tip. The presented data show for the first time the true distribution of O-2 at the basis of heterogeneous biofilms and demonstrate the great potential of planar optodes for the study of solute dynamics within biofilms at a very high spatial and temporal resolution.