ESTIMATION OF THE ENERGETIC BIOMASS YIELD AND EFFICIENCY OF OXIDATIVE-PHOSPHORYLATION IN CELL-RECYCLE CULTURES OF SCHIZOSACCHAROMYCES-POMBE

The energetics of growth of the fission yeast Schizosaccharomyces pomb e was studied in continuous high-cell concentration cultures using a c ell-recycle fermentor. Under non-02-limited conditions, steady-states were obtained at various specific growth rates (partial cell-recycle) with purely oxidative (glucose limitation) or respiro-fermentative (gl ucose excess) metabolic behaviour. The stoichiometry of biomass synthe sis was established from the elemental composition of the cells and me asurements of all the specific metabolic rates, i.e. consumption of gl ucose and O2 and production of CO2, ethanol and other products. The th eoretical yield factor for biomass on glucose was Y(G,X) = 0.85 C-mol . C-mol-1 and maintenance requirements were negligible. Assuming a con stant coupling between energy generation and biomass formation for bot h respirative and respiro-fermentative breakdown of glucose, the bioma ss yield from ATP (Y(ATP)) and the efficiency of oxidative phosphoryla tion (P/0 ratio) could be determined as 9.8 g biomass.mol ATP and 1.28 mol ATP . atom of O2, respectively.