Scaling laws in functional genome content across prokaryotic clades and lifestyles

For high-level functional categories that are represented in almost all prokaryotic genomes, the numbers of genes in these categories scale as power-laws in the total number of genes. We present a comprehensive analysis of the variation in these scaling laws across prokaryotic clades and lifestyles. For the large majority of functional categories, including transcription regulators, the inferred scaling laws are statistically indistinguishable across clades and lifestyles, supporting the simple hypothesis that these scaling laws are universally shared by all prokaryotes.