Cultures become modestly competent in colonies on sBHI agar plates and when liquid sBHI cultures approach stationary phase. With the exception of ssb, all genes in the CRE regulon were also modestly induced (4–20 times) as stationary phase approached during growth in rich medium (data not shown). This suggests that the low level of competence seen at this stage is not due to failure of a particular competence function, but to a general low induction of all components. This is supported by the modest increases in expression of sxy and of the CRP-regulon genes induced in MIV.
The paper reports that all genes in the competence regulon were induced 4 to 20 fold in rich media. But is this true? Josh wrote an R script that made a rough plot of what the microarray says about the competence regulon. Red is MIV and blue is sBHI. He took the gene expression value from each timepoint and divided it by the expression value from the first timepoint (as a rough normalization). Therefore, the y-axis corresponds to gene expression level relative to the value from t=-70 (which is why all the t=-70 values are 1). It looks like the y-axis is on a log-scale according to the R script.
This plot is a little rough but that is the consequence of using the R base package for plotting. As a testament to the superiority of ggplot2 to the R base package, I have some new plots that are hopefully more informative. Note that these are not on a log-scale.
I've done a similar plot for the RNAseq data, except using count values instead of the intensity measurements taken by the microarray:
This only shows data from one replicate (A) but I the other two are very similar. Here we see that many genes appear to be slightly downregulated, but a handful are upregulated up to 2 fold.
As it is currently plotted, these two graphs cannot be compared directly since their x-axis differ. To correct for this, I estimated what the OD600 of the microarray data would be assuming that the OD600 at t=0 was 0.2 (when cells were transferred into MIV) and a doubling time of ~32 minutes. Here's what I get when combining both plots:
Overall, I would like to know why the paper claimed that these genes are induced 4-20 fold when in fact they appear to be induced 0-10 fold. Keep in mind though, that this normalization was very rough and the OD values are estimated. But overall, this result makes me a little bit more comfortable with the RNAseq data. I would still like to see in vivo transformation frequencies for the culture used in the RNAseq data.