F. Plihon et al., OXYGEN EFFECT ON LACTOSE CATABOLISM BY A LEUCONOSTOC-MESENTEROIDES STRAIN - MODELING OF GENERAL O-2-DEPENDENT STOICHIOMETRY, Biotechnology and bioengineering, 49(1), 1996, pp. 63-69
Lactose metabolism of a Leuconostoc mesenteroides strain was studied i
n batch cultures at a pH of 6.5 and 30 degrees C in 10 L of a modified
MRS (De Man, Rogosa, Sharp) broth. The end products of this heterolac
tic bacterium were D-lactate, acetate, ethanol, and carbon dioxide. To
test the effect of oxygen on their synthesis, the medium was sparged
with different gases: nitrogen, air, and pure oxygen. When oxygen was
available, oxygen uptake occurred, which caused a modification in acet
ate and ethanol production but not in lactate or carbon dioxide produc
tion; acetate plus ethanol together were produced in constant amounts,
which were independent of the level of aeration. The influence of oxy
gen on end-product formation could be summed up by the general equatio
n: lactose + x O-2 --> 2 D-lactate + (x + 0.1) acetate + (2 - x) ethan
ol + 2 CO2. Maximal oxygen uptake (x = 2) was reached under a 120 Vh f
low rate of pure oxygen. In addition, this equation provided useful in
formation on the possible pathway of galactose catabolism by a heterof
ermentative microorganism. (C) 1996 John Wiley & Sons, Inc.