ENDOGENOUS RESPIRATION AND CELL COMPONENT TURNOVER IN GROWING AND NONGROWING CULTURES OF PSEUDOMONAS-FLUORESCENS

A new method based on measurements of the rate of endogenous respirati on is proposed for determining the overall turnover rate of cell compo nents in a growing microbial culture. A chemostat culture of Pseudomon as fluorescens was grown on (C-14)glucose under conditions of limitati on by this source of energy and carbon. At some point, unlabeled subst rate was instantaneously substituted for the labeled substrate, and th e dynamics of (CO2)-C-14 evolution were followed. These data allowed t he turnover rate of cell biopolymeric components to be calculated. It was established that (1) the specific turnover rate amounted to about 20% of the true specific growth rate of microorganisms, a figure signi ficantly higher than previous estimates; (2) the rate of turnover was not constant and depended on the physiological state of cells in the c hemostat culture, increasing with the dilution rate; and (3) switching from limited growth to starvation did not affect the turnover rate of biopolymeric components. The obtained results demonstrate that the en ergy expenditures for resynthesis of biopolymers undergoing turnover c onstitute a major fraction of the total maintenance energy requirement s.