A microcalorimetric study of energy changes during bacterial growth
Thermal events accompanying the growth of K. aerogenes in batch culture in C- and K+-limited salts media were recorded using a flow-microcalorimeter; growth parameters (biomass, CO2, pO2 and pH) were also continuously monitored. Calorimetric data is discussed in terms of i) the power-time trace profile and ii) enthalpy changes associated with formation of cells and utilization of C-source. Standard experimental and cultural conditions, which affect the measured thermal events, were established; at P = 0.05 the reproducibility of the heat output was 3%. The reproducibility of other growth parameters were similar. The p-t trace accompanying aerobic growth in glucose-limited media consisted of a single peak, the maximum power output coincided with the cessation of exponential growth and exhaustion of glucose; at this point the CO2 output was a maximum and pO2 a minimum. The total heat output increased linearly with glucose concentration. The enthalpy change for anabolic growth processes depends on the temperature and glueose-concentration. Generally the rate of heat output exceeded those for biomass and CO2 production. Maintenance coefficients for batch growth in glucose- and a-methyl glucoside-limited media are calculated. Addition of a second carbon source to cells growing in glucose had a characteristic effect on the p-t trace depending on its carbon content. The p-t trace of glucose-trained cells in media containing a-MG showed that it was metabolized in the presence of glucose. Results of thermal data for cells trained for growth in a-MG and mixed glucose/a-MG media are discussed in terms of known metabolic pathways. The effects of metabolic inhibitors on thermal, events are discussed in terms of their mode of action; azide inhibited growth in glucose but not in alpha-MG.