An unusual pattern of product inhibition: Batch acetic acid fermentation

The limited tolerance of microorganisms to their metabolic products results in inhibited growth and product formation.The relationship between the specific growth rate, p , and the concentration of an inhibitory product has been described by a number of mathematical models.'In most cases, p was found to be inversely proportional to the product concentration and invariably the rate of substrate utilization followed the same pattern.In this communication, we report a rather unusual case in which the formation rate of a product, acetic acid, increased with a decreasing growth rate of the microorganism, Acetobacter aceti.Apparently, a similar behavior was mentioned in a review report with respect to Clostridium thermocellum in a batch culture but was not published in the freely circulating literature.2The fermentation of ethanol to acetic acid, C,H,OH + 0, = CH,COOH + H 2 0