Isothermal microcalorimetry of the metabolically versatile bacterium Rhodobacter sphaeroides

The life cycle of the bacterium Rhodobacter sphaeroides was investigated by isothermal microcalorimetry using two different procedures based on the use of a static ampoule and a flow cell, respectively. In the static ampoule method it is possible to follow the growth phase and also the death phase which cannot be revealed by total biomass based techniques like turbidimetry. However, different cellular metabolisms, possibly due do the oxygen limitation occurring during the bacterial life cycle, produce complex behavior in the experimental curves. In the stop-flow cell mode this limitation is overcome as the bacteria are grown outside the calorimeter under well-defined aerobic conditions and aliquots of cell suspension are transferred in the calorimeter at different time intervals. The complex behavior shown in the static ampoule mode was successfully analyzed by a population evolution model based on a Fujikawa modified logistic equation which provides a quantitative description of the process.