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Improvements in the poly(β-hydroxybutyrate) (PHB) productivity of Alcaligenes eutrophus can be achieved by using genetically engineered strains. Knowledge of their metabolic regulation can be obtained from fermentation experiments. Certain events may not be noticed owing to the typically low frequency of sampling. To avoid information gaps, a newly developed fermenter-calorimeter was used for batch experiments allowing comprehensive on-line monitoring of fermentations. PHB-producing strain HI 6 and PHB-lacking mutant PHB−4 were selected, since they are well characterized with respect to the metabolism of PHB. For both strains, the profiles of thermograms, oxygen dissolved in the medium, and carbon dioxide formation were in good agreement with the off-line analysis. The on-line measurements showed characteristic differences between strains PHB−4 and H16. During fed-batch cultivations of PHB-accumulating strain H16, rapid autolysis of the cells was observed.Key words: Alcaligenes eutrophus, PHB, fermentation, calorimetry, on-line analysis, growth efficiency.

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