Does fructose inhibit development of competence?

I gave a seminar at Michigan State yesterday, invited by the Microbiology graduate students (Thanks guys!).  While I was there I met with a research group that works on Actinobacillus succinogenes, a relative of H. influenze.  They were interested in improving the competence levels of this species, and I explained that induction of the H. influenzae competence regulon was controlled by CRP and cAMP, with cAMP levels determined by the availability of external fructose to the phosphotransferase system’ (PTS) sugar-uptake system.

The PI then asked me whether we’d tested the obvious prediction that adding frucose to the culture medium should inhibited the development of competence, and I was shocked to realize that we hadn’t.  At least I don’t think we have.  The PTS and fructose studies were done by a very competent PhD student about 15 years ago, and I’m pretty sure I would have remembered the result of this experiment, since it would either have nicely confirmed our hypothesis or disproved it.  I’ll check her thesis when I get back (I ‘m writing this in the East Lansing airport).

Assuming she didn’t do this, I’ll do it right away.  Two experiments really, a time course of competence development in rich medium and induction by transfer to MIV starvation medium.  I’ll grow wildtype cells in regular sBHI, and at OD =0 0.2 (log phase) I’ll collect them and resuspend them in either MIV or fresh sBHI containing either fructose or glucose (as control).  What sugar concentration should I use - is 0.5% standard?

Hmm, I just remembered some old experiments I did (20 years ago?) testing the effect of adding glucose to MIV  I vaguely remember that the cells became very unhappy  - did they die from unbalanced nutrients???  I know that glycerol added to MIV doesn’t have any effect on competence (very old publication confirmed by me).  I could use a different sugar (ribose? xylose?  one that we know H. influenzae can use).