The research was a modified version of the luria delbruck fluctuation test.
The idea behind the experiment was that the premise of the fluctuation test and most of the investigations that followed it had one flaw. They assumed that mutability for fixed for an individual cell during its life cycle. A quote from Luria and Delbruck's paper; \\
"The basic assumption of the mutation hypothesis is the assumption of a fixed small chance per time unit for each bacterium to undergo a mutation to resistance. The assumption of a fixed chance per time unit is reasonable only for bacteria in an identical state. Actually the chance may vary in some manner during the life cycle of each bacterium and may also vary when the physio- logical conditions of the culture vary, particularly when growth slows down on account of crowding of the culture. With regard to the first of these variations, the assumed chance represents the average chance per time unit, averaged over the life cycle of a bacterium"
My suspicion was that the jackpot number of colonies were an indication of simultaneous cell division, since the initial innocula was a small, and therefore they were dividing almost simultaneously.
Therefore, according to my premise, the jackpot colonies should appear once in every 20 minutes or so. Since I was plating one plate every two minutes, every 10th plate should have a jackpot colony if the mutation was directed. If it was random, there shouldn't have been any regular intervals.
However, the initial experiment yielded neither of these results. There were regular intervals, but instead of one jackpot colony every 20 minutes, the number of jackpot colonies increased after every 20 minute interval.
For example, if the first jackpot occurred in the first plate, the second and third were in platings 10 and 11, and the next was in 19, 20 and 21 and so on.
Then I suspected that cell division was not synchronous. My suspicions were confirmed by some literature (Given in the paper). I also confirmed this in a online cell cam where one could watch bacteria divide and grow in live time. I modified the experiment so that a set of 4-5 plates were done simultaneously, and a series of such sets were done in regularly spaced intervals.
The innocula for each plating were subject to the selection agent simultaneously. If the mutation was directed, then all the plates in a set would have similar number of mutations. If the mutation was pre-existing, then the jackpot colonies would be random (This is somewhat similar to what Luria and Delbruck predicted). And the results showed that the number of mutations in the different plates within a set were more or less same/similar.
This was the first part of the experiement.
Second Part of the Research
Next, I wanted to identify the mechanism. Now there have been several mechanisms proposed to explain directed mutagenesis, but these evidences for directed mutation could be easily explained on the basis of a darwinian mechanism.
I knew that for a proposed mechanism to be true (for directed mutation), it should be applicable to any organism, and not just prokaryotes or bacteria.
Skipping the intermediate parts of my reasoning, I theorized that the mechanism by which an external stress caused mutation during replication, would be through regulation of the energy available through hydrolysis of ATP.
But since I was not sure, I decided to test the influence of extra cellular ATP, ADP, AMP, and Adenosine (ADO). I repeated the same experiment, this time with the addition of these compounds. My theory was that addition of ATP would greatly increase the number of mutant colonies.
To my surprise, this was not the case. AMP was better at promoting mutation. The other surprise was that adenosine,a wild card entry, was very effective at suppressing mutation. A little more research indicated that magnesium ion, to which cellular ATP is bound before hydrolysis could be the actual reason for mutability during cell division.
I tested combinations of magnesium and adenosine and found that this was true.