Energy reserves and storage polymers in intact bacteria analyzed by metabolic calorimetry

Abstract

Bacteria grown under nitrogen limitation and excess carbon accumulate energy storage polymers such as PHB, poly β-hydroxybutyrate. On mixing 1 to 2 ml. suspensions of such cells (2–20 mg. of cells) with air but no additional carbon in a calorimeter large heats evolve until cellular internal energy reserves are consumed. Division of the overall heat by the specific heat content of monomer aerobic metabolism - estimated as (−)200 Kcal/mole PHB monomer - gives the apparent weight of energy reserve content of the cells. The calorimetric method is easier to carry out than conventional respirometric or oxygen uptake methods that require tight control of oxygen concentration baselines. In calorimetry any roughly set oxygen concentration suffices if there is an excess of oxygen sufficient to exhaust the storage materials residing in the cells.