The note from Alexander Groisman above suggests a certain level of irritation that their 2005 paper was not cited in our MS ('This paper, which is for some reason not cited here...'). We were of course aware of the work by Groisman et al, but since our paper was a primary research paper and not a literature review per se, we restricted our citations to those papers with direct precedent for our own work and results. Of course we did not mean to detract from the significance of the work by Groisman et al. However, with respect to direct relevance, the main point of the paper you
mention is "to perform experiments with non-adherent cells growing to high cell densities in chemostatic conditions" (see introduction). Attention is not focused on single cell measurements. Indeed, no experiment in this paper reports
the measurement of any cell variable (size, timings) or readout (transcriptional
reporter, protein localization) associated to single cells: the reported fluorescence
measurements are limited to the whole area of the microchamber where the cells are grown. To us, "single cell resolution" means that one can plot properties of single cells and not only cell population averages This capability was not demonstrated in that paper, and we believe would be difficult to accomplish given the lack of vertical
confinement. In contrast, our entire paper consisted of carefully quantitated single-cell measurements. We did cite the paper of Paliwal etal Nature 2007, which used a
related flow cell to explore the response of single yeast cells to a pherormone gradient.

Thus the focus of our paper was somewhat related microfluidic methods to study single cell responses, at low cell density comparable to those almost invariably used
in cell cycle experiments already in the literature to allow ready comparison. This focus is essentially the opposite of that stated and employed by Groisman et al, where cells were maintained at very high density and population average measurements were exclusively reported.
For these reasons, we felt that although of course this is an
interesting approach, it was not one that we needed to cite. We do not claim the use of microfluidic methods per se for feeding cells medium and inducer to be novel, since this has indeed been done a number of times including the Groisman et al paper. The novelty was in the accuracy of quantitative analysis of single cells under unperturbed exponential growth conditions, and we think this is indeed novel considering the literature overall at the time we published our paper. We also would like to point out that our paper was not a pure methods paper, since we established some interesting dynamic aspects of single-cell responses to promoter activation as well as information
about dynamics of cell cycle control from a novel perspective - we are continuing along the latter lines with results that we think are quite interesting.

However, since we have no wish to cause offense or to give a misleading impression, we have added an annotation and a citation on the website's main text introduction in order to mention the 2005 Groisman et al. Nature Methods paper.

Gilles Charvin, Fred Cross, Eric Siggia.