When reading the publication "Guo, X., Zhou, J., & Xiao, D. (2010). Improved ethanol production by mixed immobilized cells of Kluyveromyces marxianus and Saccharomyces cerevisiae from cheese whey powder solution fermentation. Applied biochemistry and biotechnology, 160(2), 532-538." I understood that authors found higher lactose consumption and ethanol production when a mixture of S. cerevisiae and K. marxianus cells where grown on a cheese-whey-powder medium, with respect to K. marxianus alone. I assume that higher lactose consumption and ethanol production is due to the simultaneous growth of both yeasts inoculated.
Then, my question is how it is possible for S. cerevisiae to growth on that medium with lactose as the only sugar initially present if this yeast is not able to degrade lactose, and beta-galactosidase of K. marxianus has an intracellular location, thus releasing glucose and galactose inside K. marxianus cells, as I am supossing that these monosacharydes will be metabolized by K. marxianus as soon as they are produced, and not released to external medium.
K. marxianus produces lactase to break lactose into galactose and glucose, both of which S. cerevisiae can utilize.
Dear Bilge, thank you for your answer
I understand that "K. marxianus produces lactase to break lactose into galactose and glucose, both of which S. cerevisiae can utilize", but my question (maybe I wasn´t clear enough) is
"how it is possible for S. cerevisiae to growth on that medium with lactose as the only sugar initially present if this yeast is not able to degrade lactose, and beta-galactosidase of K. marxianus has an intracellular location, thus releasing glucose and galactose inside K. marxianus cells, as I am supossing that these monosacharydes will be metabolized by K. marxianus as soon as they are produced, and not released to external medium."
Hi Julio
The Lactases of Kluyveromyces are highly active, if you want to degrade Lactose in milk, a commercial preparation of Kluyveromyces lactis is used.
Your argument is right, Kluyveromyces ( historicallly a "Saccharomyces" too) is able to use Glucose and Galactose too, the growth rate and metabolism of Saccharomyces cerevisae might be higher, so the biggest part of the Monosaccharides will be metabolized there, but you will have a consumption of Monosaccharids by Kluyveromyces too.
It should be possible to substitute the living Kluyveromyces marxianus with an aliquot of commercial lactase. You have a better control and you have a clean culture of Saccharomyces that is easier in handling than a mixed culture.
good luck
Dear Frank, thank you for your answer
It is an interesting alternative the one you mention of avoiding a mixed culture of the two yeasts. I'll keep it in mind.
With respect to the other part of your answer it clarifies the discussion, but in order to be possible for Saccharomyces cerevisiae to assimilate monosacharides released by lactase from Klyveromyces marxianus, as far as I understand it is necessary that
1) beta-galactosidase of K. marxianus were present in the extracelular medium or to be a membrane protein or
2) Galactose and glucose, once produced intracelullarly by lactose hydrolysis, can someway go outside the K. marxianus cells, maybe due to any sort of yeast regulation mechanism in order to keep homeostasis.
In that case, I think it is possible for monosacharydes to be available for S. cerevisiae
Is that correct? Isvalid any of the explanation given for the phenomena?
- Badges
- Science topic
- Similar topics
- Higher Education
- Universities