Assessment of the bimodality in the distribution of bacterial genome sizes.

Bacterial genome sizes have previously been shown to exhibit a bimodal distribution. This phenomenon has prompted discussion regarding the evolutionary forces driving genome size in bacteria and its ecological significance. We investigated the level of inherent redundancy in the public database and the effect it has on the shape of the apparent bimodal distribution. Our study reveals that there is a significant bias in the genome sequencing efforts towards a certain group of species, and that correcting the bias using species nomenclature and clustering of the 16S rRNA gene, results in a unimodal rather than the previously published bimodal distribution. The true genome size distribution and its wider ecological implications will soon emerge as we are currently witnessing rapid growth in the number of sequenced genomes from diverse environmental niches across a range of habitats at an unprecedented rate.