Histograms of pI values at 0.1 unit intervals (left panel) and relationship between length of proteins (log L) and their pI (right panel) for selected prokaryotic proteomes with the different pI bias (b): (A) Natronomonas pharaonis DSM 2160, b = -87%. (B) Silicibacter pomeroyi DSS-3, b = -44%; (C) Ehrlichia ruminantium str. Gardel, b = 0%; (D) Mycoplasma pneumoniae M129, b = 43%; (E) Wigglesworthia glossinidia, b = 86%. Black points represent the set of acidic proteins while grey ones – the set of basic proteins. Diagrams for all analysed proteomes are available in additional data files 2, 3 and 4.