Development and dynamics of Pseudomonas sp biofilms

Pseudomonas sp, strain B13 and Pseudomonas putida OUS82 were genetically ta gged,vith the green fluorescent protein and the Discosoma sp, red fluoresce nt protein, and the development and dynamics occurring in flow chamber-groa n two-colored monospecies or mixed-species biofilms were investigated by th e use of confocal scanning laser microscopy, Separate red or green fluoresc ent microcolonies were formed initially, suggesting that the initial small microcolonies were formed simply by growth of substratum attached cells and not by cell aggregation. Red fluorescent microcolonies containing a few gr een fluorescent cells and green fluorescent microcolonies containing a few red fluorescent tells were frequently observed in both monospecies and two- species biofilms, suggesting that the bacteria moved between the microcolon ies. Rapid movement of P. putida OUS82 bacteria inside microcolonies was ob served before a transition from compact microcolonies to loose irregularly shaped protruding structures occurred. Experiments involving a nonflagellat ed P, putida OUS82 mutant suggested that the movements between and inside m icrocolonies were flagellum driven. The results are discussed in relation t o the prevailing hypothesis that biofilm bacteria are in a physiological st ate different from planktonic bacteria.