OBSERVATIONS AND MODELING OF GROWTH OF IMMOBILIZED MICROCOLONIES OF LUMINOUS ESCHERICHIA-COLI

Growth of recombinant luminous E. coli immobilized in alginate beads r evealed a novel observation: pellets with a low initial cell density m ay yield higher final density than those of high initial density. Obse rvations of growth were combined with bioluminescence measurements tha t reflect the product of oxygen concentration and cell density distrib ution in a spherical gel pellet. To account for this behavior a model for growth of immobilized cells in the form of microcolonies was const ructed and the behavior was simulated in a deterministic and stochasti c (cellular automata) forms. Growth in the form of microcolonies was o bserved in this study as well as in other studies. Analytical and appr oximate solutions for zero or first-order kinetics predict that the fi nal total cell density and the final thickness of active biomass layer vary with the initial cell density as a -1/6 power. This exponent des cribes well the experimental results. Stochastic simulations revealed similar qualitative dependence. A pseudohomogeneous model of growth ca nnot account for this behavior.