COLONY GROWTH OF UNICELLULAR MICROORGANISMS - A 2-DIMENSIONAL MODEL AND ITS EXPERIMENTAL TESTING

The growth dynamics of Pseudomonas fluorescens, Escherichia coli, Baci llus cereus, and Saccharomyces cerevisiae from a single cell to a macr ocolony on the surface of an agar medium was monitored. The maximum sp ecific growth rate on solid media was found to be 10 to 30% lower than in homogeneous media. The development of the colony was shown to proc eed in several phases: (1) exponential increase in the diameter of a m onolayer colony; (2) exponential increase in the diameter and height o f a multilayer colony; (3) linear increase in the colony diameter and height. During formation of a monolayer, B. cereus initially grew as a chain of cells and later as an association of filaments with long pro trusions. Cells of other microorganisms were arranged in a much tighte r pattern, ensuring the maximum possible contact between their surface s. The obtained results were approximated using a two-dimensional kine tic model that relates the dimensions of a single cell, the maximum sp ecific growth rate of the biomass of a monolayer colony, the number of its generations, the fraction of biomass contributing to the colony s ize increase, and the radial and vertical rates of colony growth in th e third phase.