Oxidation-reduction processes in cultures of bacteria - I. The reducing power of Bact. lactis aerogenes

Abstract

Cultures of Bact. lactis aerogenes show a reducing power towards oxygen (as measured by a modification of the Thunberg methylene-blue test) which is a rather stable characteristic of the growth under specified conditions. During adaptation of cells to utilize a given carbon substrate the reducing power and the growth rate increase in parallel (over considerable ranges) to their respective optima. In general the reducing power of fully adapted cultures is nearly constant for a considerable variety of carbon sources (12 to 15 units) in spite of a nearly fourfold variation of optimal growth rates. The regularity is masked with certain substrates by abnormal enhancements or inhibitions occurring at high concentrations but reappears when the measurements are made in the low concentration range. The result suggests that there is normally a rate-limiting step in the part of the cell mechanism which consumes molecular oxygen. This is not altered by adaptation to a new carbon source, though when the cells are first transferred to a new medium the proportions of various enzymes are unsuitable for the optimum utilization of the substrate, and the amount of oxygen which can be consumed is far below the maximum. Until these proportions are finally readjusted growth rate and the degree to which the oxidizing mechanism can be used increase in parallel, a limit to the adaptive process being set by the relatively unchanging maximum oxygen uptake.