The percentage of RNA-free outliers (at the nucleotide level) varies from 1.3 to 13% as a function of species (threshold 99%, Table 1 ). B.subtilis shows the highest percentage of atypical regions, whereas Pyrococcus abyssi has the lowest. Percentages among species are found correlated with the cut-off distance: the higher the cut-off distance, the lower the percentage of outliers (P = 0.007). In fact, a high cutoff distance takes place in species that display a high intragenomic variability, also expressed by a high mean distance to the host (Table 1) . Whether the actual percentage of atypical DNA is an intrinsic property of the species or a mere consequence of the resolution power of nucleotide biases-based methods remains consequently an open question. In addition, as already observed (13, 14) , the percentage of outliers is significantly higher for longer genomes (P = 0.004), whereas the cut-off distance is not related to the length of the genome (P = 0.69).