Field of Science

What does MIV do that inosine and cAMP don't?

I've done several more tests of how cAMP and the presence of inosine inluence competence development.  All these experiments used wildtype cells and the 'mixture' medium RM.  In each case I grew the cells in RM plus inosine for at least several hours at low density, so that competence was very low.   I then transferred them to different media that I thought would affect their competence (keeping the cell density about the same), and took samples.

Here's a graph of the results of the latest experiment.   The bottom (blue) line is the negative control: cells were put into fresh RM medium with inosine.  They continued to grow and became a bit ore competent as the culture got denser, but competence was still much lower than that of dense cultures.  The top (purple) line is the positive control: cells were put into the starvation medium MIV, which caused them to become very competent very quickly.  As I recall, cells transferred from rich medium to MIV take longer - I should look up some data.

The red line is cells transferred from RM plus inosine ('RM+') to RM minus inosine ('RM-').  The cells can still grow in this medium (with a variable lag), but there's a rapid (though modest) increase in competence.  (Hmm, I've been thinking that this competence is much higher than that of cells that were growing continuously in RM-, mainly because that was true the first time I did this transfer.  But I need to check my data for continuous growth in RM-, and maybe do more controls.)

Cells became tenfold more competent if they were instead transferred to RM+ with cAMP (teal line), and the combination of RM- and cAMP induced even higher competence (green line), up about 1000-fold from cells in RM+.  But this is still 100-fold lower than the MIV-induced competence.  How come?

The difference is probably because of something that RM- has and MIV lacks.  It shouldn't be the amino acids from casamino acids, as both media contain these (MIV has less), but RM has a lot of other ingredients that come from the RPMI component.  I wonder how much competence would be induced by transfer from RM+ to cMMB without inosine but with cAMP?  Perhaps I'll do a series of tests of adding different RM components to MIV.

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