Yesterday I scored the results of Wednesday's test. I had incubated competent H. influenzae cells with magnetic beads, using both DNA-coated beads and control beads that had gone through the same treatment without DNA. Then I had washed the unattached cells away from the beads, taking samples for plating at every step so I could track the progress of the three washes. I added DNase I to the beads after the last wash, so I'd be counting the total number of attached cells rather than the number of beads that had cells on them. Then I plated all the samples, and later counted the colonies.
There were ten times more cells on the DNA-coated beads than on the control beads (about 10^5 vs 10^4). This is good, but because I used about 10^8 beads, it means that, at best, only about one bead in 1000 had a cell attached. I hadn't measured how much DNA was on these beads, lazily hoping that they had as much DNA as the similarly treated polystyrene beads. Now I need to repeat the experiment with better-characterized beads.
Subrahmanyan Chandrasekhar: A study in fortitude and rigor
1 day ago in The Curious Wavefunction