Heat Production and Growth Kinetics of E. coli K12 from Flow Calorimetric Measurements on Chemostat Cultures

Abstract

The heat production of E. coli K12 growing aerobically in glucose limited chemostat cultures is determined in the range of specific growth rates μ ( = dilution rates D) from 0,058 h-1 to 0.852 h-1 for two different glucose concentrations Se in the instream of the chemostat. namely Se1=0.3182 g·1-1 and Se2 = 0.6364 g·1-1. Heat production Q and biomass production P per unit of culture volume show well correlated patterns for Se1 and Se2. For Se1 the highest value Q actually measured is 443-10-3 W·1-1 at D = 0.74 h-1 with P = 0.068 g·1-1·h-1 and for Se2 593·10-3 W·1-1 at D = 0.497 h-1 with P = 0.108 g·1-1·h-1. Heat production QB per unit of biomass appears to be independent of Se at least up to D - 0.5 h-1.At higher D there is strong indication that QB possesses a real maximum. The highest value of QB actually measured is 4.8 W·g-1 at D = 0.74 h-1. For Se1 and Se2 there were significantly higher specific growth rates verified in chemostat culture than μmax Batch= 0.717 h-1 which is the maximum specific growth rate in comparable, unlimited batch cultures. The real maximum of QB is estimated to be in the vicinity of μmax Batch. This suggests the hypothesis of a maximum principle for the growth in batch culture. For Se1 a closed analytical expression is derived for the relationship between μ and the substrate concentration S. μ[S] features a S-shaped characteristic with μmax Chemostat= 0.905 h-1; 1/2 μmax Chemostat is reached at S = 2.85·10-3 g·1-1. Three basic parameters which characterize the overall metabolism of the cells, namely the heat released per unit of substrate consumed, (Qs, the effective yield of biomass, Yeff, and μmax Chemostat are identified to depend on Se.