CALORIMETRIC INVESTIGATIONS OF BACTERIAL-GROWTH ON PHENOL-EFFICIENCY AND VELOCITY OF GROWTH AS A FUNCTION OF THE ASSIMILATION PATHWAYS

Aromatic compounds (e.g. phenol) are known to be assimilated via two p athways initiated by the cleavage of the ring structure in the intradi ol (ortho) or extradiol (metal position of catechol intermediate. Ther e is some biochemical and physiological evidence that the ortho pathwa y is energetically more efficient than the meta pathway, i.e. the form er results in higher growth yield than the latter. Alcaligenes eutroph us JMP 134 (now, Ralstonia eutropha) possesses both possibilities. As the growth efficiency corresponds to the heat production, calorimetric measurements can help determine (i) which of the two pathways is acti vated under what conditions and (ii) whether or not the upper limit of carbon conversion into biomass is reached. To answer these questions, a feeding system for a fermentation calorimeter was constructed which allowed to adjust dilution rates, the concentration of substrates and the composition of feed as a function of time. It was shown that duri ng chemistatic growth A. eutrophus uses the ortho pathway up to a dilu tion rate of 0.25 h(-1). At this point the rate of heat production cha nged, indicating a shift to the meta pathway. Phenol can be used as a sole source of carbon and energy for growth. But the energy, which can be made available, does not reach to assimilate the phenol-carbon con sumed. This means that phenol is deficit in energy. Formate can balanc e the carbon/energy ratio and provides energy to increase phenol-carbo n conversion. By adding formate, the yield coefficient grew from 0.56 g dry mass/g phenol to 1.03 g/g, and in the end it was found that the net gain of energy from the formate is not constant. (C) 1998 Elsevier Science B.V.