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 opto des. 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 Satur ation at the base decreased and the heterogeneity increased as biofilm s developed. In mature biofilms heterogeneous O-2 distributions were c aused by clusters of high biomass which had low O-2 saturations surrou nded 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 b iofilm, e.g. in a 400 mu m thick biofilm the average O-2 saturation in creased from 0 to 23.1% air saturation as the free flow velocity incre ased 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 co nsumption rate to increase and the base of the biofilm to go anoxic. T he insertion of an O-2 microelectrode into a biofilm caused the O-2 sa turation at the base of the biofilm to increase by approximately 25 mu M. This effect, presumably caused by hydrodynamic disturbances, typic ally 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 p otential of planar optodes for the study of solute dynamics within bio films at a very high spatial and temporal resolution.