An assessment of the role of physiological adaptation in the transient response of bacterial cultures

The RNA‐limiting theory of transient response states that the primary physiological adaptation which occurs when microbial cultures are grown at specific rates less than their maximum is a decrease in the cellular level of RNA. It predicts that, as a result of this decrease, the response of the culture to a shift‐up in growth rate will be limited by its RNA level. In order to test the RNA‐limiting theory and to investigate the role physiological adaptation in transient response, experiments were performed in which steady‐state chemostat cultures of Pseudomonasputida grown at various specific rates were transferred to batch reactors containing sufficient carbon source (L‐lysine) and nutrients to remove all external growth restrictions. Samples were collected during the subsequent transient period for determination of the macromolecular composition and the maximum instantaneous oxygen uptake rate. The results indicated that, while decreases in the RNA level did significantly affect the nature of the transient response, other unidentified components varied with the steady‐state specific growth rate at which the culture had been grown prior to the shift‐up and that the levels of those components affected the nature of the subsequent transient response. This implies that the RNA‐limiting theory is inadequate for describing the transient responses of cultures grown over a wide range of specific growth rates.