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[Drosophila] overseeding

Mark Thorson via dros%40net.bio.net (by nospam from sonic.net)
Fri Nov 16 17:19:20 EST 2012

Leif Søndergaard wrote:
> I am pretty sure that your problem comes from what we in our lab call "crumble infection". It is an infection of wild yeast or another fungus which dries out the medium.

I'm not having problems with the medium being too dry.
Until I started adding calcium propionate, the
cultures were so close to being liquid that I sometimes
had trouble with the medium spilling out when the
flies were harvested.

> You can save infected cultures, at least partly, by adding a few drops of water.
> To get rid of the infection you have to transfer flies to fresh vials a dozen times or so with one-two hour intervals.
> Sometimes we seed our vials with dry bakers yeast (=live yeast) just before we use them and we rarely see "crumble infection" in such vials. But if this is a universal cure we have not investigated.

For every batch of medium, I'm using 0.25 oz (0.8 g)
of active dry yeast.  I use the medium immediately
after making it up.  The yeast produces lots of
trapped gas bubbles and the medium roughly doubles
in size before settling back down.

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