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

Growth and detachment rates of Aeromonas hydrophila and Pseudomonas aeruginosa were measured to determine if nutrient depletion causes detachment of attached cells. A glass parallel plate, continuous observation flow cell placed on a phase contrast microscope was used to monitor bacterial behaviour on the surface under defined flow and mass transfer conditions. Shear stress was held constant at 3 N m−2. Images were taken every 15 minutes, and digital image analysis was used to quantify specific growth, detachment and accumulation rates for the attached organisms. An observable parameter proportional to the nutrient depletion at the surface was used to determine the effect of nutrient depletion on detachment rates. Increases in the depletion parameter corresponded with increases in detachment rate after the cells were rod, but the depletion parameter was not scaleable between different experiments. These experiments showed that as nutrients were depleted, detachment increased. If the detachment mechanism postulated in this work is more universal and applicable to other microbial species, new methods of detachment control through dynamic changes of nutrient supply might be devised.