Uptake-Resistant Tetrazolium Dyes

by Markus Krummenacker ( <kr "at" ai.sri.com> )

Biolog Phenotype MicroArrays assay cell growth by letting active cell respiration reduce a redox-sensitive tetrazolium dye. In the summer of 2004, I heard that some bacteria, like the oligotrophic Caulobacter crescentus, are growth-inhibited by the presence of this dye. I am postulating that this dye is taken up by the cells, where it might interfere with redox processes. And so, quite possibly the growth-inhibition problem could be fixed by preventing the accidental uptake of the dye by the cells.

The most obvious way of preventing the uptake of a smallish molecule is to attach it to a solid support matrix, or some other fairly large molecular object. Possible candidates could be Starburst Dendrimers, PEG polymers, or Cyclodextrins, which generally will remain soluble and are otherwise chemically fairly inert. It should be fairly easy to covalently attach tetrazolium dyes to such inert and bulky carriers.

It might also be beneficial to prevent insoluble precipitates of the resulting formazan dyes by using highly water soluble variants, as described e.g. in the Dojindo Cell Counting Kit Description.

In summary, preventing cells from uptaking redox active dyes by attaching bulky "anchors" to those dyes could quite likely let the cells grow uninhibited and thus make these cell-based growth assays available to a wider range of sensitive bacteria and other interesting cell types.

Markus Krummenacker <kr "at" n-a-n-o.com> Jul 21 2004