I have been struggling so far with my co-culture of Pichia stipitis BCRC 21777 and Kluyveromyces marxianus K-21. K-21 grows much faster than BCRC 21777, since I already co-cultured the two at the same time. The result of this experiment presented the fact that K-21 as a result of its faster growing time will suppress the growth of BCRC 21777. So as a result I seeked advice from a colleague who then told me the best stage of to inoculate the faster growing yeast is during the log phase of the slower growing yeast. I then repeated the experiment and inoculated K-21 12 hours during the fermentation of BCRC 21777 which is supposedly to be in/ almost at log phase, however, the result of the experiment still showed the suppressing activity of K-21. I am seeking advice as in to what stage should I do inoculation of the faster growing yeast, log or stationary phase?
The fermentation medium I used was basic ethanol fermentation medium with a combination of xylose and glucose.
I used YPD medium for the culturing of BCRC 21777 and YM medium for the culturing of K-21.
I am really looking forward to your expert advices.
Hi,
Firstly, you need to know if your yeasts have the same affinity to use these two carbon sources, xylose and glucose. Secondly, you need to check if your fast growing yeast produces any antimicrobial compounds. Thirdly, you would try to use different incoulation ratio (e.g 70% of the slow growing yeast with 30 % of the fast growing yeast) of your inoculum. Regards
Hi Dan,
Firstly, you can surface culture the yeasts together in a plate of YPD agar and check if there are any antagonistic activities present between them or not. Alternatively, you can follow Kirby-Bauers disc diffusion method to check the same. If you find that there are no antagonism present in between the two yeasts, then you culture them in broth medium as you earlier did. But you need to control the overgrowth of the fast growing yeast by reducing its inoculum volume, suppose fast to slow ratio is 1:10 or like that. Another thing is that yeast are known to use the carbon sources at very fast rates, so I would suggest that you should increase the concentration of glucose and xylose in your medium to eliminate any competition for substrate between the two yeasts. Co-culture systems can be really tricky sometimes.
Regards,
Shiladitya
Well I am working on bioethanol production from the green algae Ulva lactuca. The main sugars that can be found in this algae are Rhamnose, Glucose and Xylose. The yeasts strains that I am using are Pichia stipits and Kluyveromyces marxianus. K. marxianus is a faster growing yeast and is able to consume glucose quicker that P. stipitis. However, it cannot consume xylose and rhamnose as efficient as P. stipitis. Rhamnose is the most abundant sugar in my substrate and based on a few publication I read. P. stipitis is able to turn rhamnose into pyruvate, and once that process is done, then K. marxianus can turn pyruvate into ethanol.
Dr. Ghosh has very correctly pointed towards the fact that the pyruvate produced in the metabolic pathway of one microbe can not be used by another microbe as precursor of some other metabolite. This is surely not possible, at least not with any wild strains. In the present system described by Dan, I sense strong possibilities of occurrence of catabolite repression and competitive interaction between the two yeasts. In that case their use as co-culture needs to be more strategically designed.
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