Detachment of Aeromonas hydrophila and Pseudomonas aeruginosa due to variations in nutrient supply

Growth and detachment rates of Aeromonas hydrophila and Pseudomonas aerugin osa were measured to determine if nutrient depletion causes detachment of a ttached cells. A glass parallel plate, continuous observation flow cell pla ced on a phase contrast microscope was used to monitor bacterial behaviour on the surface under defined flow and mass transfer conditions. Shear stres s was held constant at 3 N m(-2). Images were taken every 15 minutes, and d igital image analysis was used to quantify specific growth, detachment and accumulation rates for the attached organisms. An observable parameter prop ortional to the nutrient depletion at the surface was used to determine the effect of nutrient depletion on detachment rates. Increases in the depleti on parameter corresponded with increases in detachment rate after the cells were rad, but the depletion parameter was not scaleable between different experiments. These experiments showed that as nutrients were depleted, deta ch ment increased. If the detachment mechanism postulated in this work is m ore universal and applicable to other microbial species, new methods of det achment control through dynamic changes of nutrient supply might be devised .