Results and conclusion
The image shows the oxygen concentration and redox potential as a function of depth in the wild-type P. aeruginosa colony biofilm and a phenazinenull mutant (no phenazine production). The oxygen gradient in the wildtype and mutant biofilms decreased similarly from the surface and down into the biofilm. The redox potential in the wild-type biofilm decreased with depth whereas the redox potential in the mutant remained the same throughout the biofilm. The decrease of redox potential in the wild type indicated reduction of the phenazines. The decline in oxygen concentration was seen right from the surface of the wild-type biofilm whereas the decline in redox potential was mostly pronounced at around 50 µm depth.