SUMMARY: Colonies of Pseudomonas fluorescens growing on glucose salts agar with low concentrations of glucose (0.1 to 0.1%) exhibit ‘transition points’ or times at which the initial diameter increase changes to a second and slower linear rate. As the concentration of glucose was lowered, the colonies had slower rates of diameter increase and earlier transition points. Growth of the colonies after the transition point was shown to be limited by the rate of diffusion of glucose and by its availability to the colony. The transition point occurred when the amount of glucose available to the colony by extension (growth) of the colony started to decrease and when there was a minimum value for the total amount of glucose available per viable organism in the colony.
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