Mukund told us that bacteria in the stationary phase can de-repress the repressor. So Urs and I decided we need to check to see if the overnight cultures were fluorescing green. First, Urs made quickly a torch with LEDs at specific wavelengths.
So it does turn out that when we dilute the bacterial growth culture, and compare it with equally turbid pond water, the arsenic GFP tube appears green fluorescent when excited with UV LEDs either 380 or 390nm.
The original wild type GFP from jelly fish has two excitation peaks, and 395nm (390nm LED) should give best signal of the 3 wavelengths on the torch (and indeed it was). For those of you who want scientific literature, more on GFP here in the classic review by Tsien, R.Y. 1998. The Green Fluorescent Protein. Annu. Rev. Biochemistry 67: 509-544.
We don’t know if this is because the water is already contaminated (can’t rule this out without some arsenic standards, and double confirming with analysis for arsenic) – or if it is indeed ArsR de-repressing. We could take the growth phase culture and compare, which we have not done yet. We also did not check or adjust the pH. This was a quick and crude check.
Regardless, we decided to make a sound-output for the UV input to see if we can hear the green color. I had some light to frequency sensors, so we had a chance to hear the process of how Urs and Ron think about circuit design for such things.
I soldered the piezo and the transistors, resistors, and the LED…and we went to get some bamboo from the NCBS campus to make the housing. We tested some filters, placing the light to frequency meter 90 degrees from the line of LED illumination, and to use a filter to have only the green signal. But so far, no sound differences to at least, our ears.
So far, this is a work in progress – let’s see. There are also DIY fluorescent microscopes published…which directions to take?