How to Grow Yeast

15/03/2018
 

INTRODUCTION

When working with any yeast strain, begin with a newly isolated colony to avoid the possibility of working with a contaminated culture.  Most strains can be streaked onto complete medium, YPD.  However, in cases where the strain is unstable, streak the cells onto a selective medium to retain the desired marker.

There are a couple of ways in which you can grow yeast cells.  You can either streak the cells onto a fresh agar plate or grow them in liquid media.

STREAK ONTO AN AGAR PLATE

(Adapted from Donna Kelis Lab, Washington University, St Louis)

Time required: less than 5 minutes to streak; 2-3 days for the colonies to grow

Use a flame-sterilised wire loop, disposable plastic loop, or sterile toothpick and pick up a slightly visible amount of yeast cells from another plate, a slant, or from a frozen glycerol stock.

1. To transfer the cells to a media plate, begin the streak at one edge of the plate. Press the side of the loop or toothpick containing the cells to the agar plate’s surface and quickly streak back and forth across part of the plate’s surface. The streaks should lie near one another, but should not cross over previous streaks.
2. Re-sterilise, or use a new tool for the next streaks. These streaks should start by crossing over the last streak, then proceeding as before into new areas of the agar plate.
3. Repeat in new territory on the agar plate. The cells will be distributed on the plate in decreasing concentration through the streaks, and no matter how many cells were on the toothpick to begin with, there should be an area on the streaked plate that will produce isolated colonies.
4. Cover the plate, invert it and incubate at 30 ˚C for 2-3 days. The plate should appear to have solid streaks of cells as well as isolated colonies. Pick a yeast colony well isolated from the others to use in subsequent work.
5. Check the plate after 2 to 3 days’ growth.

GROW IN LIQUID

Time required: less than 5 minutes to prepare; less than 1 day for the culture to grow

Dispense fresh liquid media into a test tube or a flask.

1. Use a flame-sterilised wire loop, disposable plastic loop, or sterile toothpick and pick up a slightly visible amount of yeast cells from a previously streaked plate.
2. Swirl the loop or toothpick in the liquid media to get as many cells off the loop as possible.
3. Discard the loop, and seal the test tube or flask with a cap or with a piece of aluminum foil.
4. Leave the tube or the at 30 ˚C shaker for no more than 1 day.
5. Collect the liquid culture when the cells reach the desired OD.