Eureka, today yet another post about agar plates and Brettanomyces. This post is about the plating results from streaking some Wyeast’s #5112 Brettanomyces bruxellensis on Sabouraud agar. I first streaked some liquid directly taken from the Wyeast package on a plate and waited for colonies to arise. Then picked a colony after seven days and streaked it on another plate. Lets have a look at the first plate (directly from the package) after six days of incubation (Fig 1).
There are some bigger and smaller colonies to be observed (Fig 1). The bigger colonies were off-white colored, milky, raised, even and glossy. The smaller colonies might have formed out of less cells than the bigger ones. So I picked a bit of a big colony a day later and re-streaked it on another plate. I took a picture of this plate after an incubation of eleven days (Fig 2).
This time only one kind of colonies could be observed (Fig 2). Morphology like the one before (Fig 1). I added another picture of the same plate (Fig 3). It can be observed that the margins of the colonies get wavy. But the same happens in bigger colonies of Saccharomyces cerevisiae.
And yet another picture. The following one is the same plate as shown in Fig 1, but after 18 days of incubation.
It’s easy to observe that the smaller colonies in Fig 1, now become bigger ones as well.
As I did other Saccharomyces plates along with the shown ones, I tried to compare the colonies of Saccharomyces and the ones from the Brettanomyces. But I could not observe a real difference in the morphology of the colonies between the yeasts to be able to differ between one and another. For me a colony of Brettanomyces looks like one of Saccharomyces. This could all be due to the agar itself. Other beer bloggers posted about results where they used different types of agar and could differentiate between Saccharomyces and Brettanomyces. One example is BKYeast’s results about selective agar.
The only difference is the time the yeasts needed to form visible colonies. Normally, colonies of Saccharomyces are visible within days (assumed a reasonable amount of yeast is streaked), Brettanomyces colonies were visible after approximately one week. Maybe this can be used to differ between the two yeasts. I should streak the same amount of both yeasts side by side on plates and find out if colonies of Brettanomyces form after Saccharomyces. But now I know at least that Brettanomyces can grow on Sabouraud agar.
If I have some time in the future, I will streak the Brettanomyces on other agar media to try to get a different morphology of the colonies and hopefully be able to have a method available to differ between Brettanomyces and Saccharomyces. So stay tuned!
I usually attribute the colony differences to plating density, due to nutrient limitation in more densely plated areas. Colonies in the first heavy streak will be smaller since there are more cells trying to grow on approximately the same area, i.e. nutrients, compared to colonies in your most dilute streak where each colony has more nutrients to itself. To get a good idea of true colony morphology compare only isolated colonies.
From a fermenting culture there may be some cells sticking together but it is generally assumed that each colony arises from a single cell (especially the isolated ones in your tertiary streak).
Really enjoying reading through your yeast library. Great images! Thanks a bunch!
Thanks for commenting. Makes sense to me and I haven’t thought about it in this way yet.
Hi! So I work in a lab and have been plating out quite a few yeast strains so far, and recently came to plate some dregs of Orval beer (should be bretted with Brett B), hence why I’ve been looking through your posts! My question is what temperature you were incubating the plates at? I plated the dregs on YEPD Agar plates on Monday, and already have pretty fat colonies today (Wednesday), but this was with a 25ºC incubation. I’ve checked under the microscope, and have the same observation as you – they look a lot like any standard brewing yeast. I didn’t check for the black spot, hopefully I’ll do this tomorrow!
Hi there, I commonly incubate my plates at room temperature. As for your plates, judging from the time from streak to colonies, it is very unlikely Bretts what you have there. It takes a while longer for Bretts to form colonies (days to weeks at room temperature).