We check them of course, but in an interesting way… read on!
Extra measures to ensure we provide you with a viable glycerol stock of your clone!
We grow your clones in a red broth that includes phenol red as a growth indictor. Phenol red is a dye that is bright fuschia at pH 8.2 and above, as its pKa is 8.00 at 20 degrees C. As bacteria grow in culture broth, the pH will drop. Phenol red will indeed be red from pH 8.0 down to around pH7.2, but as the pH continues to drop, the broth begins to turn orange and then yellow as the pH drops to pH 6.8 and below. This process does not apply to our GIPZ, TRIPZ or Precision LentiORF collections, but we do check their viability another way.
Why would the color change as cultures grow?
As the E. coli are growing, they give off CO2 from the breakdown of glucose, which in turn decreases the pH of an unbuffered broth and this pH drop results in the color change. We don't ship it to you until the product turns a yellow-ish color, and we know the clone is viable. This bright color-coding system helps us to do a visual double-check so we don't ship something out that won't grow. This reduces the chance that you'll get a dud!