Kinetics of lactose transport inKluyveromyces fragilis grown in a chemostat on diluted whey permeate

Abstract

Lactose transport was studied inKluyveromyces fragilis grown in lactose-limited chemostat cultures. Kinetic parameters were determined using a method based on genetic population evolution. Lactose transport was carried out via three carriers characterized respectively byK _m of 0.1 mM, 3 mM and 15.5 mM. The synthesis of these lactose carriers and their capacity (V _max) are dependent on the dilution rate (D). At D=0.12 h⁻¹, the high affinity transporter is prominent. For intermediate dilution rate, only the high and the medium affinity systems are present. In cells growing at D=0.4 h⁻¹, these carriers are absent but instead, the low affinity transporter is present. The effect on lactose transport of such metabolic inhibitors as CCCP, a proton ionophore, and Antimycin A, an energy inhibitor, were also investigated. The high affinity system is the most sensitive to the effect of these inhibitors. Lactose transport through this carrier is probably a mechanism dependent on the proton motive force.