I am trying to grow biofilm on the surface of gravels(~3mm), I chose P.aeruginosa PA01, and use 1/4 concentration of LB medium and 0.5 % of glucose. It is a continuous flow condition. The gravels are packed in a column (I.D.25mm, length 115mm), the feeding flow rate is 1.5ml/min. But the bacteria are in planktonic state, instead of biofilm state. Does anyone have experience?