APPROVAL

Biofilm research has been restricted to studies of undefined mixed microbial populations and to investigations of (defined) mono microbial populations. In the first case, the organisms are considered as a homogeneous mass, biomass, ignoring the properties of individual species, the sum of which determines the observed phenomena. The second case concentrates on the properties and processes of one microbial species ignoring the influence of the broader environment, eg. other microbial species, on this species. Goal of this research was to study a defined mixed microbial biofilm and to determine possible interactive effects between the species comprising the biofilm. Biofilm experiments were conducted with mono populations of Klebsiella pneumoniae and Pseudomonas aeruginosa and with binary populations of K. pneumoniae and P aeruginosa. Process rates and stoichiometric coefficients, determined for the mono population biofilms were compared with those found in the binary population biofilm. Results indicate that the specific cellular product formation rate of K. pneumoniae or P. aeruginosa in the binary biofilm is not affected by the presence of the other species. Similarly, the glucose-oxygen stoichiometric ratio of K. pneumoniae or P. aeruginosa in the binary biofilm is not affected by the presence of the other species. Many processes at the cellular level are performed faster by K. pneumoniae than by P. aeruginosa: eg. biofilm specific product formation rate and the maximum specific growth rate of K. pneumoniae are 5 times that rate of P. aeruginosa. Nevertheless, K. pneumoniae cell mass does not dominate the biofilm, possibly because of its non-motility and its product formation properties