The BioScreen is a wonderful time-saver. Over the weekend it did growth curves using media with 9 different concentrations of phosphate, each with 10 replicates, taking readings every 20 minutes for 46 hr!
This data tells me that my choice of 3 µM added phosphate was good; it gives about four times as much growth as no added phosphate, and twice as much as 1 µM, so the unsupplemented medium probably has about 1 µM contaminating phosphate.
The big surprise is that cells reach higher densities with a moderate amount of phosphate (70 µM) than they do with 250 µM or with the 1500 µM used by Wolfe-Simon et al. I don't think this has any serious implications for our analysis.
I was also surprised to see that the cultures with the higher amounts of phosphate were still growing at the end of the time course. I'm going to replicate these results with another time course, and this time I'll run it for longer (3 days? 4 days?).
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