Effect of oxygen transfer and carbon source composition on the growth of Corynebacterium melassecola

Corynebacterium melassecola, a glutamate producing bacteria, has been cultivated in a 4-l batch aerated fermentor with glucose and fructose mixtures of various proportions as carbon sources and mineral ammonium as nitrogen source. Experimental results are analysed in order to obtain the specific rates and the conversion yields. A data reconciliation technique is used to manage with the experiments performed in similar conditions. The redundant experimental informations are used to test the carbon, nitrogen, available electrons, phosphorus and protons balances. The measurement of dissolved oxygen tension and volumetric oxygen transfer coefficient indicates that oxygen was never a limiting substrate in the experimental device though the oxygen demand was up to 70 mmoles/l.h and the heterogeneity of the liquid phase. The highest specific growth rate (0.59 h^?1) and the highest biomass production yield (0.48 gX/gS) are obtained with glucose as the sole carbon source. These two parameters progressively decrease with the increase of the proportion of fructose in the medium down to 0.43 h^?1 and 0.38 gX/gS on fructose so that the specific carbon uptake rate remains constant and equal to 0.04 C-mole/gX h. From a metabolic point of view, this decrease of the carbon conversion efficiency into cellular material is correlated to a lower carbon flux through the pentose pathway as the fructose proportion is increased. This is correlated with an accumulation of fructose 1,6-biphosphate which further activates the lactate deshydrogenase resulting to lactate production though the metabolism remains strictly aerobic.