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The cell fixation of Pseudomonas aeruginosa, Citrobacter amalonaticus, and Methanosarcina barkeri to lipid-free glass slides was investigated under anaerobic conditions using cell number, protein content, and ATP level as the biomass parameters. Energy substrates stimulated the attachment of P. aeruginosa and C. amalonaticus significantly as compared to the fixation behaviour in basal medium without substrates. The fixation exhibited characteristic kinetics of attachment and detachment of the cells. Cells of M. barkeri obtained from pure cultures did not adhere at all. In mixed cultures with C. amalonaticus, significant fixation of M. barkeri cells was observed. Light micrographs gave rise to the assumption that M. barkeri was "incorporated" into already existing biofilms. This mechanism is supposed to be important for retaining methanogenic biomass in anaerobic biofilms. The results could help to reduce the start-up periods of biofilm reactors and to enhance methanogenic activities in this environment. This assumption was supported by experiments performed with methanogenic mixed cultures fixed to ceramic particles in biofilm reactors.

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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.