Growth kinetics ofPseudomonas fluorescens microcolonies within the hydrodynamic boundary layers of surface microenvironments.

Computer-enhanced microscopy (CEM) was used to study the growth kinetics of bacterial microcolonies attached to the wall of a continuous-flow slide culture. Image processing increased effective microscope resolution and quantitated colony growth at 10 min intervals. Three growth parameters were used to determine growth rate: the time required for cell fission, the specific rate of increase in cell number, and the specific rate of increase in cell area. Growth rate was initially constant regardless of colony size, as assumed previously in deriving colonization kinetics. However, at low substrate concentrations growth rate varied depending on laminar flow velocity. Growth was flow-dependent at a glucose concentration of 100 mg/liter and flow-independent at a concentration of 1 g/liter. This indicated that the surface microenvironment became substrate-depleted in the absence of sufficient laminar flow velocities and that glucose rather than oxygen was rate limiting.