Field of Science

GFAJ-1 growth curves in limiting phosphate

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?).


  1. I am enjoying myself (astrobiology interest) with catching up on #arseniclife, well #noarseniclife now, and have to pitch in with others yet again with hearth felt thanks for doing this (and in public)! Looking forward to see the Brevia publication.

  2. I just stumbled across your blog through the article currently posted on the Nature website (which I now plan to follow), so I am not completely up to date on your results and approach to looking at this issue, but I am curious to know if you are use the same reagents (brand, catalog #, etc) as the authors of the article in science?

    I ask because I am currently conducting growth studies pertaining to potassium in a halophilic archaeon and have found that my minimal obtainable potassium concentration in my medias vary widely with the brand of high-purity salts I use. For example, with Fluka high-purity NaCl (>99.9999% by trace metal analysis) I still have a final potassium concentration of approximately 8mM. Could this be the reason you aren't seeing growth without the addition of 3uM phosphate and they did? Perhaps you are using higher purity reagents?

    Just a thought.

    1. The Nature article was wrong - I do see growth in AML60 medium without added phosphate. I think I'd better do a new post about this concern.

    2. Forgot to say: Wolfe-Simon et al. didn't provide any information about their reagents, so I used ordinary reagent-grade chemicals from our usual suppliers (Fisher, Sigma, whatever we had on our shelves). As my new post explains, our media did appear to have less phosphate contamination than theirs did, which is why I added an additional 3 µM phosphate to my 'P-' cultures.


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