NEW PATTERNS OF MIXED-SUBSTRATE UTILIZATION DURING BATCH GROWTH OF ESCHERICHIA-COLI K12

Microbial growth on mixtures of substrates is of considerable engineer ing and biological interest. Most of the work until now has dealt with microbial growth on binary mixtures of sugars or polyols. In these ca ses, it is often found that no matter how the inoculum is precultured, only one of the two substrates is consumed in the first growth phase, leading to the diauxic growth pattern. The goal of the experiments re ported here is to investigate growth on mixtures containing at least o ne organic acid. These experiments show that the substrate utilization patterns in such mixtures are qualitatively different from the diauxi c growth pattern. For instance, during growth of Escherichia coil K12 on certain binary mixtures of organic acids, the two substrates are ut ilized simultaneously, and the mixed-substrate maximum specific growth rate exceeds the single-substrate maximum specific growth rate on eit her one of the two constituent substrates. Furthermore, the very same mixed-substrate maximum specific growth and substrate uptake Fates are observed no matter how the inoculum is precultured. On the other hand , in a mixture of glucose and pyruvate, the maximum specific growth ra te seems to depend on the preculturing conditions, thus suggesting the existence of multiple physiological quasi-steady states. (C) 1997 Joh n Wiley & Sons, Inc.