Microcalorimetric studies of bacterial growth

Abstract

Klebsiella aerogenes has been grown in carbon-limited chemostats and the heat output of different steady states measured by pumping the culture through an LKB flow microcalorimeter. Initially the flow time between fermentor and microcalorimeter cell was 5 minutes during which time the steady-state conditions of the chemostat were disturbed and the measured heat output was less than that in the fermentor. To minimise this problem a specially designed fermentor was fitted into the airbath of the microcalorimeter, thus providing temperature control and reducing the flow time between fermentor and microcalorimeter to 1 minute. This design was adequate providing only one dilution rate was used in each experiment. If different dilution rates were used in the same experiment the fermentor contents could not be maintained at 37C and inaccurate heat outputs were recorded. It is believed that with modifications this design may be used to accurately determine the energy changes occuring in chemostat cultures. K. aerogenes has been grown in batch culture in media limited by carbon or nitrogen. Characteristic heat output-time records were obtained for each medium. As growth proceeded the heat output increased steadily until oxygen became limiting whereupon the rate of heat output decreased. During the stationary phase endogenous metabolism occurred in the carbon-limited media and slow degradation of excess carbon in the nitrogen-limited media both of which gave rise to relatively large heat outputs.The total heat output of nitrogen-limited cultures was greater than that of carbon-limited cultures. When glycine replaced ammonium sulphate as nitrogen source the total heat output was increased. Very inefficient growth occurred when glycine provided both the carbon and nitrogen source. The heat output of all cultures changed with changes in oxygen tension, pH, biomass and flow rate between fermentor and microcalorimeter.