Gene number of bacterial genomes versus number of encoded signal transduction genes.

<p>The plot depicts the total number of annotated signal transduction genes in particular bacterial genomes versus the total number of genes of the respective genomes. Data on <i>Archaea</i> are not shown, and multiple genomes per species or species-like taxa were excluded. Strain <i>P. necessarius</i> QLW-P1DMWA-1 is highlighted as a yellow dot. (A) Entire data set consisting of 904 analyzed bacterial genomes. Red dots indicate bacteria obligately associated as symbionts or pathogens with a host; blue dots indicate free-living or facultative host-associated bacteria. (B) Plot of genomes of bacteria classified as free-living or facultative host-associated (shown in (A) as blue dots) with ≤100 signal transduction genes. All blue dots represent bacteria either facultatively associated with hosts (e.g., dwelling in the oral cavity or in the intestinal tract) or dwelling as free-living organisms in extreme environments (permanently anoxic, low or high temperature, low pH). The yellow (strain QLW-P1DMWA-1) and the green dots represent the only exclusively free-living taxa inhabiting non-extreme systems. Almost all of them are phototrophic (<i>Synechococcus</i> and <i>Prochlorococcus</i>) or predominantly heterotrophic taxa (<i>Pelagibacter</i> and <i>Puniceispirillum</i>) dwelling as planktonic bacteria in marine systems. The signal transduction gene data were obtained from the database MIST2 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032772#pone.0032772-Ulrich1" target="_blank">[69]</a>.