When we paused last week, I had just noted the unexpected result that, in two of three tests (#1184 and #1189), GFAJ-1 cells in 3 µM PO4 + 40 mM AsO4 grew to a higher density than the cells in 3 µM PO4 (no AsO4), but the cells with more and with less phosphate didn't grow much at all. In the other test (#1188) the cells didn't grow at all in the arsenic cultures; I won't say anything more about these cultures unless I get more results like this. All cultures without arsenic grew as they had in previous experiments.
I left the #1189 arsenic cultures in the incubator while I was away, and over this ~225 hr incubation the 1.5 mM-phosphate' and no-added-phosphate cultures grew to densities close to those of their no-arsenate controls. I don't know why they grew so much slower than the 3 µM phosphate+arsenate culture.
I'm going to repeat these cultures once more. If I see the same results (fast high growth of cells in 3 µM phosphate + arsenate), I'll dilute the 3 µM phosphate cultures into 400 ml of the same medium ± arsenate, to get lots of cells for my first arsenate-grown DNA prep.
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