Pronounced Effect of the Nature of the Inoculum on Biofilm Development in Flow Systems

Biofilm formation renders sessile microbial populations growing in continuous-flow systems less susceptible to variation in dilution rate than planktonic cells, where dilution rates exceeding an organism's maximum growth rate (mu(max)) results in planktonic cell washout. In biofilm-dominated systems, the biofilm's overall mu(max) may therefore be more relevant than the organism's mu(max), where the biofilm mu(max) is considered as a net process dependent on the adsorption rate, growth rate, and removal rate of cells within the biofilm. Together with lag (acclimation) time, the biofilm's overall mu(max) is important wherever biofilm growth is a dominant form, from clinical settings, where the aim is to prevent transition from lag to exponential growth, to industrial bioreactors, where the aim is to shorten the lag and rapidly reach maximum activity. The purpose of this study was to measure CO2 production as an indicator of biofilm activity to determine the effect of nutrient type and concentration and of the origin of the inoculum on the length of the lag phase, biofilm mu(max), and steady-state metabolic activity of Pseudomonas aeruginosa PA01 (containing gfp), Pseudomonas fluorescens CT07 (containing gfp), and a mixed community. As expected, for different microorganisms the lengths of the lag phase in biofilm development and the biofilm mu(max) values differ, whereas different nutrient concentrations result in differences in the lengths of lag phase and steady-state values but not in biofilm mu(max) rates. The data further showed that inocula from different phenotypic origins give rise to lag time of different lengths and that this influence persists for a number of generations after inoculation.