Ethanol production by anaerobic thermophilic bacteria: Kinetics in fed-batch cultures ofClostridium thermohydrosulfuricum

Summary Fed-batch fermentations ofClostridium thermohydrosulfuricum are carried out using medium rich in nitrogen source and with glucose as growth limiting factor. The ethanol/lactate yield increases as the specific growth rate and specific rate of consumption of glucose diminish. Under the experimental conditions chosen here this yield attained 3.66 moles. mole^–1 with a maximal ethanol concentration of 12 g.l^–1. In batch fermentation, the maximum concentration of ethanol did not exceed 8 g.l^–1, independent of the concentration in glucose or nitrogen source applied.     

Influence of substrate carbon on the metabolism of Clostridium thermohydrosulfuricum

The concentration of carbon sources has a significant influence on the growth, carbohydrate uptake and metabolite distribution in Clostridium thermohydrosulfuricum. The growing concentrations of glucose or starch increase the production of ethanol and lactate, the intracellular fructose-1,6-diphosphate (FDP) and the specific activity of lactate dehydrogenase (LDH), but decrease the ethanol/lactate ratio.     

Ethanol production by anaerobic thermophilic bacteria: regulation of lactate dehydrogenase activity in Clostridium thermohydrosulfuricum

Summary The enzyme lactate dehydrogenase (LDH) in Clostridium thermohydrosulfuricum is controlled by the type and the concentration of the substrate. In batch fermentations an increase of the initial concentration of glucose leads to an increase in the activity of LDH. This increase in activity is related to the accumulation of fructose 1,6-diphosphate (F 1,6-DP), an intermediate of the Embden-Meyerhof-Parnas (EMP) pathway, which stimulates the enzyme by increasing its affinity for pyruvate and NADH. The K _mvalues of LDH for pyruvate and NADH, which are 2.5×10^-3 M and 9.1×10^-5 M respectively in absence of F 1,6-DP, fall considerably in the presence of this substrate. In presence of 0.2 mM of F 1,6-DP we observed a K _mof 3.3×10^-4 M for pyruvate and 4.1×10^-5 M for NADH.