Definition of grams of wet weight cells
Cell pellets shrink significantly after freezing and thawing
While some researchers completely process cells (i.e. proceed to lysis) on the day that they harvest them, others harvest, pellet and freeze cell samples, planning to thaw and lyse them at a future date. We have noticed that pellets shrink significantly if re-centrifuged after thawing, for example during a washing process after thawing. For example, if a 5 g pellet (with an approximate volume of 5 ml) is frozen overnight and subsequently thawed and re-centrifuged, it will shrink to a volume of approximately 3ml and will weigh approximately 3 g. The ATCC Mycology Culture Guide attributes this type of phenomenon to cells losing water due to osmosis during freezing.
We provide optimized ratios of wet weight of cells to buffer to beads, with the aim of assisting our customers in developing their own protocols for creating yeast lysate. It is important to note that we define wet weight of cells as the weight before freezing. So, in the example above, the pellet is always regarded as weighing 5 g, even if it has shrunk. The rationale is that the number of cells present has remained the same. We further recommend that if customers wish to employ our optimized ratios, they should re-suspend the shrunken pellets such that they have the same volume as before. So, in the example above, 2 ml buffer would be added to the 3 ml pellet after washing, returning it to a 5 ml volume.
Some researchers have reported that they find it advantageous to freeze and re-suspend pellets, as it allows them to greatly increase the ratio of buffer to cells, without increasing the overall volume.