When transforming cells I tend to use 100 ul of cells and a non-saturating amount of DNA (usually around 1ul of 1 ng/ul). For recovery I add 900 ul of medium and afterwards plate 50 ul. My question is, in this case, should the dilution factor be 50/(900+100+1) or should it only take into account the cells + DNA making it 50/(100+1)?
I ask this because recently I had to do some transformations using 200 ul of cells (prepared by a different method) whilst reducing the medium to 800 ul as advised by my PI. Since the total volume remais the same, I am unsure whether any diferences I observe are due to the method itself or simply due to a higher volume of cells.
From your question it seems you are talking about transforming bacterial cells eg E. coli. If so the transformation efficiency would be calculated based on the number of competent cells you use for transformation and the DNA amount used.
For example if youre using 1 ng of bacterial plasmid and transform 100ul E.coli cells (10e6 cells) and obtain 1000 transformants you would calculate 1000 transformants/ng plasmid.