ABSTRACT
The pattern of glucose repression in most Kluyveromyces marxianus strains does not correlate with fermentative behaviour; however, glucose repression and fermentative metabolism appear to be linked to the kinetics of sugar uptake. In this work, we show that lactose transport in K. marxianus CCT 7735 by lactose-grown cells is mediated by a low-affinity H+-sugar symporter. This system is glucose repressed and able to transport galactose with low affinity. We also observed the activity of a distinct lactose transporter in response to raffinose. Regarding glucose uptake, specificities of at least three low-affinity systems rely on the carbon source available in a given growth medium. Interestingly, it was observed only one high-affinity system is able to transport both glucose and galactose. We also showed that K. marxianus CCT 7735 regulates the expression of sugar transport systems in response to glucose availability.
